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TABLE OF CONTENTS

Number
0013
0021
0027
0030
0032

Revision
6
8
9
4
0

Title
Guidelines for Loadouts
Guidelines for the approval of towing vessels
Marine lifting operations
Guidelines for marine transportations
Guidelines for moorings

TECHNICAL POLICY BOARD

GUIDELINES FOR LOADOUTS

0013/ND

Once downloaded this document becomes UNCONTROLLED.
Please check the website below for the current version.

6 Dec 10

6

GPB

Technical Policy Board

31 Mar 10

5

GPB

Technical Policy Board

19 Jan 09

4

GPB

Technical Policy Board

01 Dec 04

3

JR

Technical Policy Board

01 Apr 02

2

JR

Technical Policy Board

07 Jul 93

1

JR

Technical Policy Board

16 Oct 86

0

JR

Technical Policy Board

Date

Revision

Prepared by

Authorised by

www.gl-nobledenton.com

GUIDELINES FOR LOADOUTS

PREFACE
This document has been drawn with care to address what are likely to be the main concerns based on the
experience of the GL Noble Denton organisation. This should not, however, be taken to mean that this document
deals comprehensively with all of the concerns which will need to be addressed or even, where a particular matter is
addressed, that this document sets out the definitive view of the organisation for all situations. In using this
document, it should be treated as giving guidelines for sound and prudent practice on which our advice should be
based, but guidelines should be reviewed in each particular case by the responsible person in each project to ensure
that the particular circumstances of that project are addressed in a way which is adequate and appropriate to ensure
that the overall advice given is sound and comprehensive.
Whilst great care and reasonable precaution has been taken in the preparation of this document to ensure that the
content is correct and error free, no responsibility or liability can be accepted by GL Noble Denton for any damage or
loss incurred resulting from the use of the information contained herein.

© 2010 Noble Denton Group Limited, who will allow:
 the document to be freely reproduced,
 the smallest extract to be a complete page including headers and footers but smaller extracts may be
reproduced in technical reports and papers, provided their origin is clearly referenced.

0013/ND REV 6

Page 2

GUIDELINES FOR LOADOUTS

CONTENTS
SECTION

PAGE NO.

SUMMARY
INTRODUCTION
2.1
Scope
2.2
Revisions
2.3
Downloads
3
DEFINITIONS
4
THE APPROVAL PROCESS
4.1
General
4.2
GL Noble Denton Approval
4.3
Certificate of Approval
4.4
Scope of Work Leading to an Approval
4.5
Limitation of Approval
4.6
Safety During Loadout
5
CLASSES OF LOADOUT
6
STRUCTURE TO BE LOADED
6.1
Design
6.2
Weight Control
7
SITE AND QUAY
7.1
Site Capacity
7.2
Marine Aspects
7.3
Loadout Path
8
BARGE
8.1
Class
8.2
Stability
8.3
Barge Freeboard
9
LINK BEAMS, SKIDWAYS AND SKIDSHOES
10
MOORINGS
11
GROUNDED LOADOUTS
12
PUMPING AND BALLASTING
13
LOADOUTS BY TRAILERS, SPMTS OR HYDRAULIC SKID-SHOES
13.1
Structural Capacity
13.2
Load Equalisation & Stability
13.3
Vertical Alignment
13.4
Skidshoes
14
PROPULSION SYSTEM DESIGN, REDUNDANCY AND BACK-UP
15
LIFTED LOADOUTS
16
TRANSVERSE LOADOUTS
17
BARGE REINSTATEMENT AND SEAFASTENINGS
18
TUGS
19
MANAGEMENT AND ORGANISATION
REFERENCES
APPENDIX A - CHECK LIST OF INFORMATION REQUIRED FOR APPROVAL

5
6
6
6
8
9
12
12
12
12
12
12
13
14
15
15
16
17
17
17
17
18
18
18
18
19
20
21
22
24
24
24
24
24
25
28
29
30
31
32
33
34

TABLES
Table 5-1
Table 6-1
Table 10-1
Table 12-1

14
15
20
22

1
2

Loadout Classes
Load Factors
Seastate Reduction Factor
Required Pump Capacity

0013/ND REV 6

Page 3

GUIDELINES FOR LOADOUTS
Table 12-2
Table 14-1
Table 14-2

Example of required pumping capacity calculation
Propulsion System Design
Typical Friction Coefficients

0013/ND REV 6

23
26
27

Page 4

GUIDELINES FOR LOADOUTS

1

SUMMARY

1.1

These Guidelines have been developed for the loadout of items including offshore jackets, SPAR
sections, modules, bridges and components from the shore onto floating or grounded barges and
ships.
The principles of these Guidelines can also be applied to the load-in of structures onto the shore from
a floating vessel/barge.
This document supersedes the previous revision, document no 0013/ND Rev 5 dated 31 March 2010.
The only significant changes are in the Mooring Sections 10.2 to 10.8 and the inclusion of Section 8.3.
These Guidelines are intended to lead to an approval by GL Noble Denton, which may be sought
where an operation is the subject of an insurance warranty, or where an independent third party review
is required.
A description of the Approval Process is included, for those projects which are the subject of an
insurance warranty.
This document includes the requirements for consideration, intended to represent sound practice, for
the structure to be loaded, loadout site, link beams and skidways, trailers, pumping and ballasting,
jacking systems and winches, grounded loadouts, transverse loadouts, moorings, seafastenings, tugs
and weather forecasts.
Methods for lifted loadouts are derived from GL Noble Denton’s 0027/ND “Guidelines for Marine Lifting
Operations”, Ref. [1].
Check lists are appended, to act as a guide to information required.

1.2
1.3
1.4

1.5
1.6

1.7
1.8

0013/ND REV 6

Page 5

6

GUIDELINES FOR LOADOUTS

2

INTRODUCTION

2.1

SCOPE

2.1.1

This document refers to the transfer of a cargo onto a barge or vessel by horizontal movement or by
lifting, including structures such as jackets, SPAR sections, modules, topside components and bridges.
It contains general recommendations and checklists of information required to allow approval of such
operations by GL Noble Denton.
The guidelines and calculation methods set out in this document represent the views of GL Noble
Denton and are considered sound and in accordance with offshore industry practice. Operators should
also consider national and local regulations, which may be more stringent.
Due to the wide range of loadout and loadin methods, this document cannot cover all aspects of every
loadout or loadin scheme. Alternative proposals and methods will be considered on their own merits,
and can be approved if they are shown to be in accordance with safe practice.
This document applies particularly to skidded and trailer transported floating loadouts, in tidal waters.
The varying requirements for grounded loadouts, or loadouts accomplished by lifting are also included.
Reference to a 'barge' includes a 'ship' or a 'vessel' as applicable.
For lifted loadouts, the factors to be applied to rigging arrangements, lift points and structure may be
derived from the latest revision of GL Noble Denton 0027/ND “Guidelines for Marine Lifting
Operations”, Ref. [1]. It should be noted that Ref. [1], although aimed primarily at offshore lifting
operations, also includes methods and factors for lifts by floating cranes inshore, and for loadouts by
shore-mounted cranes.
These guidelines are intended to lead to an approval by GL Noble Denton. Such approval does not
imply that approval by designers, regulatory bodies and/or any other party would be given.

2.1.2

2.1.3

2.1.4

2.1.5

2.1.6

2.2

REVISIONS

2.2.1

Revision 2 dated 1 April 2002 superseded and replaced the previous Revision 1 dated 7 July 1993.
Changes introduced in Revision 2 included:

The inclusion of a Definitions Section

Expansion of the Section on Limitation of Approval

The introduction of the concept of classes of loadout, depending primarily on the tidal conditions

Reference to the Draft ISO Standard on Weight Control

Relaxation of under-keel clearance requirements.

Expansion of the Section on Moorings

Relationship of pumping requirements to the loadout class

Relationship of propulsion, braking and pull-back system requirements to the loadout class

Limited allowance of friction for temporary seafastenings

Reformatting and Section renumbering as necessary.

0013/ND REV 6

Page 6

GUIDELINES FOR LOADOUTS
2.2.2

Revision 3 superseded and replaced Revision 2. Changes included:

Classes of loadout reduced from 6 classes to 5 (Sections 5, 12 and 14.7)

Reference to the ISO weight control standard, to reflect the change from a Draft to a published
Standard (Section 6.2)

Introduction of stability considerations for floating barges (Section 8.2)

Reference to GL Noble Denton’s transportation guideline, for post-loadout stability (Section
8.2.2)

Consideration of stability of hydraulic trailer systems (Section 13.2.2)

Introduction of a new section on transverse loadouts (Section 16)

Modifications to the loading definition and stress levels for barge movements following loadout
(Sections 17.2 and 17.4)

Minor changes to the checklist of information required for approval (Appendix A)

Deletion of the previous flow chart for lifted loadouts (previous Appendix B), which can be
obtained from GL Noble Denton’s 0027/ND Lifting guideline, Ref. [1]

2.2.3

Revision 4 superseded and replaced Revision 3. Changes included:

Addition of Sections 1.2, 4.5.5, 4.6, 6.2.6 to 6.2.8, 10.9, 11.10 to 11.12, 13.1.4, 13.3, 14.11,
15.5, 16.6 and 16.7.

Additions and revision to some Definitions.

Minor text revisions (Sections 4.3.4, 6.1.2, 6.2.4, 7.1.1, 7.2.1, 8.2, 10.1, 10.6, 10.7, 13.2.3, 14.7
and 17.3).

Change in the one third overload allowance in Sections 6.1.7 to 6.1.10.

Addition of requirements for site moves and trailer path grading (Section 7.3).

Skidway line and level documentation (Section 9.7) and Sections 9.8 and 9.9 added.

Additional safety factor included for single line failure mooring cases (Sections 10.4 and 10.5).

Additional requirements for lifted loadouts (Sections 15.2, 15.3, and 15.4).

Addition of tug inspection (Section 18.3).

Removal of Section 12.9 and the addition of an example for pumping system requirements in
Section 12.9.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS
2.2.4

Revision 5 superseded and replaced Revision 4. Significant changes included:

Text in Sections 2.1.1 and 2.1.2 amended

Definitions (Barge, Insurance Warranty, IACS, Loadout, NDT, Survey, Surveyor, Vessel,
Weather Restricted Operation, and Weather Un-restricted Operations) in Section 3 revised.

Text in Section 4.3.2 revised to state loadout.

Link beam adequacy in Section 4.5.3.included.

Skidway tolerances included in Section 6.1.5.

1% load cell accuracy deleted from Section 6.2.5.

Class reinstatement added in Section 8.1.4 and Section 17.7 included.

Grounding pad area and depth added to Section 11.1.

Text added to Section 13.2.2 for stability of 3-point support.

Text in Section 14.3 and Table 14-1 for Class 2 skidded loadout pull-back and braking,
requirements changed from “Required” to “Recommended”. Slope changed to gradient.

Weight and CoG tolerances included in Section 16.7.

Requirements for weight reports and weighing enhanced in Section A.1.2 below.

Link beam construction reports added in Section A.2.8.

Reference to IACS for rigging added in Section A.8.4 and Section A.9.4.

2.2.5

This Revision 6 supersedes and replaces Revision 5. The only significant changes (indicated by a line
in the right hand margin is in the Mooring Sections 10.2 to 10.8 which includes the new 0032/ND
“Guidelines for Moorings”, Ref. [3] and the inclusion of a new Section 8.3 on barge freeboard.

2.3

DOWNLOADS

2.3.1

All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com.

0013/ND REV 6

Page 8

6

GUIDELINES FOR LOADOUTS

3

DEFINITIONS

3.1

Referenced definitions are underlined.
Term or Acronym

Definition

Approval

The act, by the designated GL Noble Denton representative, of issuing a
Certificate of Approval.

Barge

A non-propelled vessel commonly used to carry cargo or equipment.
(For the purposes of this document, the term Barge can be considered to
include Vessel or Ship where appropriate).

Certificate of Approval

A formal document issued by GL Noble Denton stating that, in its
judgement and opinion, all reasonable checks, preparations and
precautions have been taken to keep risks within acceptable limits, and
an operation may proceed.

GL Noble Denton

Any company within the GL Noble Denton Group including any
associated company which carries out the scope of work and issues a
Certificate of Approval, or provides advice, recommendations or designs
as a consultancy service.

Gradient

The maximum angle over the distance between supports that the loadout
skidway, barge deck and/or trailer loadout path makes with the horizontal
plane.

IACS

International Association of Classification Societies

Insurance Warranty

A clause in the insurance policy for a particular venture, requiring the
assured to seek approval of a marine operation by a specified
independent survey house.

Link beam/ linkspan

The connecting beam between the quay and the barge or vessel. It may
provide a structural connection, or be intended solely to provide a smooth
path for skidshoes or trailers /SPMTs.

Loadin

The transfer of a structure from a barge or vessel onto land by horizontal
movement or by lifting.

Loadout

The transfer of a structure onto a barge or vessel by horizontal movement
or by lifting.

Loadout, floating

A Loadout onto a floating barge or vessel.

Loadout Frame

A structural frame that supports the structure during fabrication and
loadout and may support the structure on a barge/vessel to the site. May
also be called a Module Support Frame (MSF).

Loadout, grounded

A Loadout onto a grounded barge or vessel.

Loadout, lifted

A Loadout performed by crane.

Loadout, skidded

A Loadout where the Structure is skidded, using a combination of
skidways, skidshoes or runners, propelled by jacks or winches.

Loadout, trailer

A Loadout where the Structure is wheeled onto the barge or vessel using
Trailers or SPMTs.

LRFD

Load Resistance Factor Design.

MHWS

Mean High Water on Spring Tides.

MLWS

Mean Low Water on Spring Tides.

0013/ND REV 6

Page 9

GUIDELINES FOR LOADOUTS
Term or Acronym

Definition

MSF

Module Support Frame

NDT

Non Destructive Testing

Operational reference
period

The planned duration of the operation, including a contingency period.

Seafastenings

The means of restraining movement of the loaded structure on or within
the barge or vessel

Site Move

An operation to move a structure or partially assembled structure in the
yard from one location to another. The site move may precede a loadout
if carried out as a separate operation or may form part of a loadout. The
site move may be subject to approval if so desired.

Skidshoe

A bearing pad attached to the Structure which engages in the Skidway
and carries a share of the vertical load.

Skidway

The lower continuous rails, either on the quay or on the barge, on which
the Structure is loaded out, via the Skidshoes.

SLS

A design condition defined as a normal Serviceability Limit State / normal
operating case.

SPMT

Self-Propelled Modular Transporter – a trailer system having its own
integral propulsion, steering, jacking, control and power systems.

Structure

The object to be loaded out

Surge

A change in water level caused by meteorological conditions

Survey

Attendance and inspection by a GL Noble Denton representative.
Other surveys which may be required for a marine operation, including
suitability, dimensional, structural, navigational, and Class surveys.

Surveyor

The GL Noble Denton representative carrying out a survey.
An employee of a contractor or Classification Society performing, for
instance, a suitability, dimensional, structural, navigational, or Class
survey.

Tidal Range

Where practicable, the tidal range referred to in this document is the
predicted tidal range corrected by location-specific tide readings obtained
for a period of not less than one lunar cycle before the operation.

Trailer

A system of steerable wheels, connected to a central spine beam by
hydraulic suspension which can be raised or lowered. Trailer modules
can be connected together and controlled as a single unit. Trailers
generally have no integral propulsion system, and are propelled by
tractors or winches. See also SPMT.

ULS

A design condition defined as Ultimate Limit State / survival storm case.

Vessel

A marine craft designed for the purpose of transportation by sea.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS
Term or Acronym

Definition

Weather restricted
operation

A marine operation which can be completed within the limits of an
operational reference period with a favourable weather forecast
(generally less than 72 hours), taking contingencies into account. The
design environmental condition need not reflect the statistical extremes
for the area and season. A suitable factor should be applied between the
design weather conditions and the operational weather limits.

Weather un-restricted
operation

An operation with an operational reference period generally greater than
72 hours. The design weather conditions for such an operation shall be
set in accordance with extreme statistical data for the area and season.

0013/ND REV 6

Page 11

GUIDELINES FOR LOADOUTS

4

THE APPROVAL PROCESS

4.1

GENERAL

4.1.1

GL Noble Denton may act as a Warranty Surveyor, giving Approval to a particular operation, or as a
Consultant, providing advice, recommendations, calculations and/or designs as part of the Scope of
Work. These functions are not necessarily mutually exclusive.

4.2

GL NOBLE DENTON APPROVAL

4.2.1

GL Noble Denton means any company within the GL Noble Denton Group including any associated
company which carries out the scope of work and issues a Certificate of Approval.
GL Noble Denton approval may be sought where an operation is the subject of an Insurance Warranty,
or where an independent third party review is required.
An Insurance Warranty is a clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent survey house. The requirement is normally
satisfied by the issue of a Certificate of Approval. Responsibility for interpreting the terms of the
Warranty so that an appropriate Scope of Work can be defined rests with the Assured.

4.2.2
4.2.3

4.3

CERTIFICATE OF APPROVAL

4.3.1
4.3.2

The deliverable of the approval process will generally be a Certificate of Approval.
The Certificate of Approval is the formal document issued by GL Noble Denton when, in its judgement
and opinion, all reasonable checks, preparations and precautions have been taken to keep risks within
acceptable limits, and an operation may proceed.
The Certificate confirming adequate preparation for an operation will normally be issued immediately
prior to the start of the operation, by the attending surveyor.

4.3.3

4.4

SCOPE OF WORK LEADING TO AN APPROVAL

4.4.1

In order to issue a Certificate of Approval for a loadout, GL Noble Denton will typically consider, as
applicable, the topics and information listed in Appendix A.
Technical studies leading to the issue of a Certificate of Approval may consist of:
a.
Reviews and audits of procedures and calculations submitted by the client or his contractors, or
b.
Independent analyses carried out by GL Noble Denton to verify the feasibility of the proposals,
or
c.
A combination of third party reviews and independent analyses.

4.4.2

4.4.3

Surveys required typically include preliminary surveys of the barge, structure and site; attendance at
loadout meetings; surveys of readiness to start loadout and witnessing of loadout operation.

4.5

LIMITATION OF APPROVAL

4.5.1
4.5.2

A Certificate of Approval is issued for a particular loadout only.
A Certificate of Approval is issued based on external conditions observed by the attending surveyor of
hull(s), machinery and equipment, without removal, exposure or testing of parts.
Fatigue damage is excluded from any GL Noble Denton approval, unless specific instructions are
received from the client to include it in the scope of work.
A Certificate of Approval for a loadout covers the marine operations involved in the loadout only.
Loadout is normally deemed to start at the time when the structure is either moved from its
construction support(s) or the structure first crosses the edge of the quay or linkbeam. It is normally
deemed to be completed at the end of the marine operations forming part of the loadout, including set
down on the barge, completion of required initial seafastening to turn the barge, and turning the barge
back to the quay if carried out on the same tide as loadout.

4.5.3
4.5.4

0013/ND REV 6

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GUIDELINES FOR LOADOUTS
4.5.5

4.5.6

4.5.7

A Certificate of Approval for a loadin covers the marine operations involved in the loadin only. Loadin
is normally deemed to start at the time when the structure is moved from its barge grillage support(s),
and all barge ballasting and mooring activities are complete. It is normally deemed to be completed at
the end of the operations forming part of the loadin procedure, including set down on the shore
supports.
Unless specifically included, a Certificate of Approval for loadout does not include any moorings of the
barge or vessel following completion of loadout or loadin. If approval of moorings is required, other
than for the loadout or loadin operation itself, then specific approval should be requested.
Any alterations to the surveyed items or agreed procedures after issue of the Certificate of Approval
may render the Certificate invalid unless the changes are approved by GL Noble Denton in writing.

4.6

SAFETY DURING LOADOUT

4.6.1

During the loadout there will be a number of construction activities ongoing and hazards present for
operations that will be carried out in a relatively short period of time. The Surveyor, and all others
involved in loadout operations, should be aware of these hazards and participate in the fabrication yard
safety culture that prevails. Some hazards are, but not limited to those listed below:

Wires under tension

Trip hazards, grease on decks and hydraulic oil leaks

Openings in the barge deck

High pressure hoses/equipment

Temporary access bridges /scaffolding /wire hand railing

Hot works

Overside working

Other shipping operations in the vicinity.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

5

CLASSES OF LOADOUT
The loadout operation will be classed according to the tidal conditions. Requirements for design,
reserves and redundancy of mechanical systems will vary according to the class of loadout.
Table 5-1
Class

0013/ND REV 6

Loadout Classes

Tidal limitations

1

The tidal range is such that regardless of the pumping capacity provided, it is not
possible to maintain the barge level with the quay throughout the full tidal cycle, and the
loadout must be completed within a defined tidal window, generally on a rising tide.

2

The tidal range is such that whilst significant pumping capacity is required, it is possible
to maintain the barge level with the quay during the full spring tidal cycle, and for at
least 24 hours thereafter.

3

Tidal range is negligible or zero, and there are no tidal constraints on loadout. Pumping
is required only to compensate for weight changes as the loadout proceeds.

4

Grounded loadout, with tidal range requiring pumping to maintain ground reaction
and/or barge loading within acceptable limits.

5

Grounded loadout requiring no pumping to maintain ground reaction and/or barge
loading within acceptable limits.

Page 14

GUIDELINES FOR LOADOUTS

6

STRUCTURE TO BE LOADED

6.1

DESIGN

6.1.1

The item to be loaded, hereafter called the 'structure', shall be designed taking into account static and
dynamic loads, support conditions, environmental loads and loads due to misalignment of the barge
and shore skidways or uneven ballasting.
For skidded loadouts, analyses which account for the structure and skidway should be presented
which consider the elasticity, alignment and as-built dimensions of the shore and barge skidways for
each stage of loadout. In the absence of detailed information, a 75/25 percent distribution of load
across either diagonal may be considered as appropriate.
For trailer or SPMT loadouts, the reactions imposed by the trailer configuration shall be considered.
For lifted loadouts, the structure, including the padeyes, shall be analysed for the loads and reactions
imposed during the lift, as set out in 0027/ND, Ref. [1]
The structure and supports shall be demonstrated as being capable of withstanding the subsidence of
any single support with respect to the others by at least 25mm.
Consideration shall also be given to lifting off construction supports or onto seafastening supports
where these operations form an integral part of the loadout operation.
The primary structure shall be of high quality structural steelwork with full material certification and
NDT inspection certificates showing appropriate levels of inspection. It shall be assessed using the
methodology of a recognised and applicable offshore code including the associated load and
resistance factors for LRFD codes or safety factors for ASD/WSD codes.
Traditionally AISC has also been considered a reference code - see Section 6.1.9 below regarding its
applicability. If the AISC 13th edition is used, the allowables shall be compared against member
stresses determined using a load factor on both dead and live loads of no less than those detailed in
the following Table 6-1.

6.1.2

6.1.3
6.1.4
6.1.5
6.1.6
6.1.7

6.1.8

Table 6-1

6.1.9
6.1.10

Load Factors

Type

WSD option

LRFD Option

SLS:

1.00

1.60

ULS:

0.75

1.20

Except as allowed by Section 17.4, all load cases shall be treated as a normal serviceability limit state
(SLS) / Normal operating case.
The infrequent load cases covered by Section 17.4 may be treated as ultimate limit state (ULS) /
Survival storm cases. This does not apply to:

Steelwork subject to deterioration and/or limited initial NDT unless the condition of the entire
loadpath has been verified, for example the underdeck members of a barge or ship.


Steelwork subject to NDT prior to elapse of the recommended cooling and waiting time as
defined by the Welding Procedure Specification (WPS) and NDT procedures. In cases where
this cannot be avoided by means of a suitable WPS, it may be necessary to impose a reduction
on the design/permissible seastate.



Steelwork supporting sacrificial bumpers and guides.



Spreader bars, lift points and primary steelwork of lifted items.



Structures during a load-out.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS
6.2

WEIGHT CONTROL

6.2.1

Weight control shall be performed by means of a well defined, documented system, in accordance with
current good practice, such as International Standard ISO 19901-5 – Petroleum and natural gas
industries – specific requirements for offshore structures – Part 5: Weight control during engineering
and construction, Ref. [4]
Ref. [4] states (inter alia) that:

“Class A (weight control) will apply if the project is weight- or CoG- sensitive for lifting and
marine operations or during operation (with the addition of temporaries), or has many
contractors with which to interface. Projects may also require this high definition if risk gives
cause for concern”.

“Class B (weight control) shall apply to projects where the focus on weight and CoG is less
critical for lifting and marine operations than for projects where Class A is applicable”.

“Class C (weight control) shall apply to projects where the requirements for weight and CoG
data are not critical”.

6.2.2

6.2.3

6.2.4
6.2.5
6.2.6
6.2.7
6.2.8

Unless it can be shown that a particular structure and specific loadout operation is not weight or CoG
sensitive, then Class A weight control definition will be needed, as shown in Ref. [4], Section 4.2. If the
50/50 weight estimate as defined in Ref. [4] is derived, then a reserve of not less than 5% shall be
applied. The extremes of the CoG envelope shall be used.
A reserve of not less than 3% shall be applied to the final weighed weight.
If weighing takes place shortly before loadout, the effect on the loadout procedures of any weight
changes shall be assessed, and the procedures modified if necessary.
Prior to any structure being weighed, a predicted weight and CoG report shall be issued, so that the
weighed weight and CoG can immediately be compared with the predicted results.
Any items added after weighing shall be carefully monitored for weight and position to facilitate
accurate calculation of a final loadout weight and centre of gravity.
A responsible engineer shall provide a statement verifying the adequacy of existing calculations and
analyses following reconciliation with the weight and CoG values used in those analyses and the final
derived weight values following weighing.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

7

SITE AND QUAY

7.1

SITE CAPACITY

7.1.1

A statement shall be submitted showing the adequacy for the loadout of the quay, quay approaches,
wall and foundations. This can be in the form of historical data.
A statement shall be submitted showing the capacity of all mooring bollards, winches and other
attachments to be used for the loadout.
Compatibility between quay strength and elasticity, and the support conditions used for analysis of the
structure, shall be demonstrated where appropriate.

7.1.2
7.1.3

7.2

MARINE ASPECTS

7.2.1

Bathymetric information for the area covered or crossed by the barge during loadout, post-loadout
operations and sailaway shall be supplied. Underkeel clearance shall not normally be less than 1.0 m
during the period for which the barge is in position for loadout. This may be relaxed to 0.5 m, subject
to confidence in the lowest predicted water levels, and provided a check of the loadout area has been
made by bar sweep, divers’ inspection or side-scan survey sufficiently recently to represent actual
conditions at the time of loadout. Where there is a risk of debris reducing underkeel clearance, a
sweep shall be made immediately prior to the barge berthing to ensure that no debris exists that could
damage the barge keel plating. The results of the sweep shall be confirmed by further soundings
check around the barge perimeter after barge berthing.
For tidal loadouts, an easily readable tide gauge shall be provided adjacent to the loadout quay in such
a location that it will not be obscured during any stage of the loadout operation. Where the tide level is
critical, the correct datum should be established.
Port authority approval for the operation should be obtained, and control of marine traffic instituted, as
required.

7.2.2

7.2.3

7.3

LOADOUT PATH

7.3.1

The loadout path shall be freshly graded prior to loadout, pot holes filled and compacted, debris
removed and obstructions to the loadout path identified and removed.
Where a structure cannot be loaded out directly onto a barge or vessel without turning, turning radii
shall be maximised where possible. For small turning radii, lateral supports /restraints shall be
installed between the trailer and the structure /loadout frame /cribbage. It is possible that a site move
may be part of the loadout operation.

7.3.2

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

8

BARGE

8.1

CLASS

8.1.1

The barge shall be classed by a recognised IACS Member. Alternatively, structural drawings and
results of structural analyses shall be supplied to GL Noble Denton for review. Additional surveys may
be required by GL Noble Denton.
The loads induced during loadout, including longitudinal bending, loads on internal structure and local
loads, shall be checked to be within the approved design capabilities.
Mooring attachments and all attachments for jacking or winching shall be demonstrated to be adequate
for the loads anticipated during or after loadout. See also Section 10.
Some loadout operations may temporarily invalidate the class or loadline certificate, and it will be
necessary for any items temporarily removed for loadout be reinstated after loadout. This may apply if,
for instance, holes have been cut in the deck for ballasting, if towing connections have been removed
or, in some instances, after grounding on a pad. In such cases the vessel must be brought back into
class prior to sailaway.

8.1.2
8.1.3
8.1.4

8.2

STABILITY

8.2.1

Barge stability shall be shown to be adequate throughout the loadout operation. Particular attention
should be paid to:

A loadout onto a barge with a small metacentric height, where an offset centre of gravity may
induce a heel or trim as the structure transfer is completed – i.e. when any transverse moment
ceases to be restrained by the shore skidways or trailers.

A loadout where there is a significant friction force between the barge and the quay wall,
contributed to by the reaction from the pull on system and the moorings. The friction may cause
“hang-up” by resisting the heel or trim, until the pull-on reaction is released, or the friction force
is overcome, whereupon a sudden change of heel or trim may result. (See also Section 14.5).

Cases where a change of wind velocity may cause a significant change of heel or trim during
the operation.

8.2.2

After the structure is fully on the barge, then stability should comply with the requirements of 0030/ND
“Guidelines for Marine Transportations”, Ref. [2] and those of the flag state.

8.3

BARGE FREEBOARD

8.3.1

The minimum barge freeboard during loadout shall be 0.5 m plus 50% of the maximum wave height
expected during the loadout operation. The bunding of openings in the barge deck shall also be
considered for low freeboards.

0013/ND REV 6

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6

GUIDELINES FOR LOADOUTS

9

LINK BEAMS, SKIDWAYS AND SKIDSHOES

9.1

Documentation including a statement showing the strength of the skidways, link beams and skid shoes
shall be submitted, demonstrating compatibility with the statements made and assumptions used for
the structural analysis.
Link beams shall be checked for loads induced by barge moorings, barge movements and pull on/pull
back forces.

9.2
9.3
9.4

9.5
9.6
9.7

Tolerances on link beam movement shall be shown to be suitable for anticipated movements of the
barge during the operation.
Where a barge, because of tidal limitations, has to be turned within the loadout tidal window the design
of the link beams shall be such that when the loaded unit is in its final position they are not trapped, i.e.
they are free for removal.
Suitable lateral guides shall be provided along the full length of skidways.
Sufficient articulation or flexibility of skid shoes shall be provided to compensate for level and slope
changes when crossing from shore to barge.
The line and level of the skidways and skidshoes shall be documented by dimensional control surveys
and reports. The line and level shall be within the tolerances defined for the loadout operation and
skidway/skidshoe design.

9.8

For floating loadouts care shall be taken to ensure that minimum friction exists between the barge and
quay face. Where the quay has a rendered face, steel plates shall be installed in way of the barge
fendering system.

9.9

The interface between the barge and barge fendering shall be liberally lubricated with a grease or
other substitute which complies with local environmental rules.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

10

MOORINGS

10.1

A loadout may normally be considered a weather restricted operation. Limiting weather conditions for
the loadout operation shall be defined, taking into account:

the forecast reliability for the area

the duration of the operation including a suitable contingency period

the exposure of the site

the time required for any operations before or after the loadout operation including barge
movements and moorings, ballasting, system testing, final positioning and initial seafastening

currents during and following the operation, including blockage effects if applicable

the wind area of the cargo and the barge/vessel.

10.2

Unless agreed otherwise with GL Noble Denton, for loadout operations with an operational duration of
no more than 24 hours the maximum forecast seastate shall not exceed the design seastate multiplied
by the applicable factor from Table 10-1 below. For operations with other durations alternative factors
apply and should be agreed with GL Noble Denton. The forecast wind and current shall be similarly
considered when their effects on the operation or structure are significant.
Table 10-1

Seastate Reduction Factor

Weather Forecast Provision

10.3
10.4

10.5
10.6

10.7

10.8

10.9

Reduction Factor

No project-specific forecast (in emergencies only)

0.50

One project-specific forecast source

0.65

One project-specific forecast source plus local wave monitoring (wave
rider buoy)

0.70

One project-specific forecast source plus local wave monitoring and local
meteorologist

0.75

Moorings for the loadout operation shall be designed for the limiting weather as defined in Sections
10.1 and 10.2 above.
The analysis of environmental forces for the barge/vessel mooring arrangement, and the resulting
design of the mooring system shall be carried out in accordance with 0032/ND “Guidelines for
Moorings”, Ref [3].
New synthetic lines/ropes, if used, should be pre-stretched.
If the mooring load is to be held on the winch brake, then the winch brake capacity, with the outer wrap
on the drum, should exceed the maximum mooring design load (intact or damaged) times by a
minimum factor of 1.2. Where winches are used, tension monitoring devices/meters shall be used.
In cases where existing yard loadout mooring equipment is being used, wires and winches may
sometimes be offered which have a breaking load greater than the barge equipment to which they are
connected. Great care is needed in such situations, and the wire loadings should be controlled and
monitored.
Mooring prior to and after loadout shall normally be considered an unrestricted operation. If approval
is required for such moorings, they shall normally be designed to the 10 year return period storm for
the area and season and in accordance with 0032/ND, Ref [3].
Safety factors in mooring design may be reduced on a case by case basis on the submission of risk
mitigation measures, provision of standby tugs, restricted operations or rigorous mooring design
calculations.

0013/ND REV 6

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6

GUIDELINES FOR LOADOUTS

11

GROUNDED LOADOUTS

11.1

The plan area of the grounding pad with respect to the barge keel shall be of sufficient extent to ensure
stability of the edges of the grounding pad. Geotechnical site investigation data shall be submitted
together with geotechnical calculations demonstrating the capacity of the grounding pad.
A survey of levels over an area including the grounding pad shall be submitted, showing suitable
support conditions for the barge.
A bar sweep or side-scan survey, supported by divers’ inspection if appropriate, shall be made just
before positioning the barge, to ensure that no debris exists which could damage the barge bottom
plating.
If even support over the barge bottom plating cannot be achieved, then calculations shall be submitted
showing that no overstress will occur.
The barge shall be ballasted to provide sufficient ground reaction to withstand the 10 year return period
storm loadings, in both pre and post-loadout conditions, at mean high water spring tide and 10 year
storm surge condition.
The barge should be positioned and ballasted onto the pad several tides before the loadout operation,
to allow for consolidation and settlement. Barge levels should be monitored during this time.
Final skidway levels shall be compatible with assumptions used for structural analysis as in Sections
6.1.1 and 6.1.2.
The ballast shall be adjusted during loadout, if required, to avoid barge settlement or overstress.
A plan shall be prepared for the initial seafastening and float-off operation following completion of
loadout.
Even when the barge is on the grounding pad, mooring lines between the barge and quayside shall be
maintained.
Between loadout and sailaway, the barge keel shall be inspected, either by diver survey or internal
tank inspection, in order to maintain the barge in class. Class surveyor attendance will be required.
The grounding pad elevation shall be defined based on the actual depth of the barge and not the
moulded barge depth.

11.2
11.3

11.4
11.5

11.6
11.7
11.8
11.9
11.10
11.11
11.12

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

12

PUMPING AND BALLASTING

12.1

Pumping capacity shall be provided as follows, depending on the Class of loadout as defined in
Section 5, and to satisfy each Condition as defined below:
Condition A:
The nominal maximum pump capacity computed for the loadout as planned, to
compensate for tidal changes and weight transfer, with no contingencies.
Condition B:
The computed capacity required, as a contingency, to hold the barge level with
the quay, at the maximum rate of a rising or falling tide, assuming horizontal
movement of the structure is halted.
Condition C:
The computed capacity required, as a contingency, to provide the requirements
of either Condition A or Condition B, whichever is the greater, in the event of the
failure of any one pump, component or pumping system. Where two or more
pumps are supplied from a common power source, this shall count as a single
system.
Table 12-1
Condition

Pump capacity required, as a percentage of
computed capacity

A

150%

B

150%

C

120%

2

A

150%

(Constant deck level
>24hrs)

B

120%

C

100%

A

100%

B

No requirements

C

75%

A

120%

B

120%

C

100%

All

No requirements

Loadout Class

1
(Tidal window)

3
(Little tide)
4
(Grounded + pumping)
5 (Grounded)
12.2
12.3

12.4

12.5

Required Pump Capacity

Pump capacity shall be based on the published pump performance curves, taking account of the
maximum head for the operation, and pipeline losses.
If the barge pumping system is used as part of the main or back-up pump capacity, then a barge
engineer familiar with the system shall be in attendance throughout the operation. The loadout
communication system should include the pumproom.
All pumps and systems shall be tested and shown to be operational within 24 hours of the start of
loadout. At the discretion of the GL Noble Denton surveyor, a verification of pump capacity may be
required.
Pumps which require to be reversed in order to be considered as part of the back-up capacity shall be
capable of such reversal within 10 minutes, and adequate resources shall be available to perform this
operation.

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GUIDELINES FOR LOADOUTS
12.6

12.7
12.8

12.9

Pumps which require to be moved around the barge in order to be considered as part of the back-up
capacity, shall be easily transportable, and may only be so considered if free access is provided at all
stages of loadout between the stations at which they may be required. Adequate resources shall be
available to perform this operation.
Ballast and barge levels shall be monitored during loadout, and shown to be within the limits of
movements of any link beams and the structural limitations of the barge and structure.
Where a barge, vessel or ship has a compressed air ballast/de-ballast system the time lag needed to
pressurise or de-pressurise a tank should be taken into account, as should any limitations on
differential pressure across a bulkhead.
The following table gives an example for a Class 2 Loadout that assumes that the worst single system
failure reduces the pumping capacity to 80% of the full capacity (with any consistent units).
Table 12-2
Condition

Nominal capacity

Factor

Required capacity

A

1,000

150%

1,500

B

1,100

120%

1,320

C

1,100 (Condition B) / 80% = 1,375

100%

1,375

Required

0013/ND REV 6

Example of required pumping capacity calculation

1,500 (Condition A)

Page 23

GUIDELINES FOR LOADOUTS

13

LOADOUTS BY TRAILERS, SPMTS OR HYDRAULIC SKID-SHOES

13.1

STRUCTURAL CAPACITY

13.1.1
13.1.2

Maximum axle loading shall be shown to be within the trailer manufacturer's recommended limits.
"Footprint" pressure on the quayside, linkbeam and barge deck shall be shown to be within the
allowable values.
Shear force and bending moment curves shall be prepared for the trailer spine structure, and
maximum values shall be shown to be within the manufacturer's allowable figures.
Linkspan bridge capacity shall be demonstrated by calculation and these calculations shall form part of
the loadout procedure.

13.1.3
13.1.4

13.2

LOAD EQUALISATION & STABILITY

13.2.1

In general, hydraulic systems should be linked or balanced as a three point hydraulically linked system
to provide a statically determinate support system thus minimising torsion on the structure. In any
event the arrangement shall be compatible with the support assumptions considered for structural
analysis of the structure being loaded out. A contingency plan shall be presented to cover potential
hydraulic leakage or power pack failure.
Stability of the hydraulic system to resist overturning shall be shown to be adequate, particularly when
a 3-point hydraulic linkage system is proposed. The centre of action of the structure CoG shall remain
within the middle quarter of the trailer support base, taking into account any uncertainty in:

the horizontal and vertical centre of gravity,

the design wind,

any inclination of the structure/trailer assembly on shore,

the predicted inclination of the barge under the design wind,

possible change of heel or trim due to release of hang-up between the barge and the quay, and

any free surface liquids within the structure.
Note: Whilst a 3-point linkage system results in a determinate support system, a 3-point support
system is generally less stable than a 4-point support system. Stability for both 3 point and 4
point support systems shall be documented.
Loadouts with high slender structures on narrow support bases, or offset from the barge centreline,
shall be subject to special attention in terms of the effects of uncertainties in ballasting and deballasting.

13.2.2

13.2.3

13.3

VERTICAL ALIGNMENT

13.3.1

Vertical alignment of barge, linkbeam and quay, including the effects of any change of slope and any
movement of the barge due to wave or swell action, should generally be within approximately one third
of the maximum travel of the axles relative to the trailer spine.

13.4

SKIDSHOES

13.4.1

As appropriate, the requirements for trailers and SPMTs shall also apply to hydraulically operated
skidshoes. The stability of hydraulic skidshoes transverse to their line of action shall be demonstrated
to be adequate. Attention should be paid to the effects listed in Section 13.2.2.

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

14

PROPULSION SYSTEM DESIGN, REDUNDANCY AND BACK-UP

14.1

The propulsion system, including back-up and contingency systems shall be designed according to the
Class of loadout as defined in Table 5-1, and as shown in Table 14-1 . Requirements for skidded
loadouts include propulsion by wire and winch, hydraulic jacks or stand jacks. Requirements for nonpropelled trailer loadouts include propulsion by wire and winch or tractors.
“System redundancy” means that adequate back-up systems shall be provided such that the loadout
can still proceed in the event of failure of any one mechanical component, hydraulic system, control
system, prime mover or power source.
Where Table 14-1 states that a requirement is “recommended” and it is not planned to provide that
requirement, a risk assessment shall be carried out, and the risks shown to be acceptable to the
approving office. “Recommended” shall be taken to read “required” if a foreseeable failure could
extend the operation outside the planned window.
Where a requirement is assumed to be “built-in”, including reversibility of motion, it shall be
demonstrated that this is indeed the case.
Where the propulsion method induces a reaction between the barge and the quay, then the possible
effects of this reaction shall be considered, including “hang-up” and sudden release. (See also
Sections 8.2.1 and 13.2.2). Mooring line tensions may also contribute to the reaction.
Where a pull back system is required, and is achieved by de-rigging and re-rigging the pull on system,
then the time taken to achieve this shall be defined, taking into account the Class of loadout.

14.2

14.3

14.4
14.5

14.6

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GUIDELINES FOR LOADOUTS
14.7

Propulsion system design shall be in accordance with the following table:
Table 14-1

Propulsion System Design

Class

Propulsion System
Design Requirement

Skidded loadouts

1

Propulsion capacity

2

3

4

5

Trailer loadouts

Non-propelled

SPMT

Actual Gradient
+3%

Actual Gradient
+3%

Actual Gradient
+3%

System redundancy

Required

Required

Required

Braking system

Required

Built-in

Built-in

Pull back system

Required

Required

Built-in

Propulsion capacity

Actual Gradient
+2%

Actual Gradient
+2%

Actual Gradient
+2%

System redundancy

Recommended

Recommended

Recommended

Braking system

Required

Built-in

Built-in

Pull back system

Recommended

Built in

Built-in

Propulsion capacity

Actual Gradient
+1%

Actual Gradient
+1%

Actual Gradient
+1%

System redundancy

Not required

Not required

Not required

Braking system

Required

Built-in

Built-in

Pull back system

Not required

Not required

Built-in

Propulsion capacity

Actual Gradient

Actual Gradient

Actual Gradient

System redundancy

Not required

Not required

Not required

Braking system

Not required

Built-in

Built-in

Pull back system

Not required

Not required

Built-in

Propulsion capacity

Actual Gradient

Actual Gradient

Actual Gradient

System redundancy

Not required

Not required

Not required

Braking system

Not required

Built-in

Built-in

Pull back system

Not required

Not required

Built-in

Note:
Where “recommended” is stated, and it is not planned to provide that requirement, a risk
assessment shall be carried out, and the risks shown to be acceptable to the approving office.
“Recommended” shall be taken to read “required” if a foreseeable failure could extend the operation
outside the planned window.

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GUIDELINES FOR LOADOUTS
14.8

The coefficients of friction used for design of propulsion systems shall not be less than the “maximum”
values shown in the following table, unless justification can be provided for a lower value. The “typical”
values shown are for information only, and should be justified if used.
Table 14-2
Level surfaces

Typical Friction Coefficients
Static

Typical

Moving
Maximum

Typical

Maximum

Sliding

Steel /steel

0.15

0.30

0.12

0.20

Steel /Teflon

0.12

0.25

0.05

0.10

Stainless steel /Teflon

0.10

0.20

0.05

0.07

Teflon /wood

0.14

0.25

0.06

0.08

Steel /waxed wood

0.10

0.20

0.06

0.12

Steel wheels /steel

0.01

0.02

0.01

0.02

Rubber tyres /steel

-

0.02

-

0.02

Rubber tyres /asphalt

-

0.03

-

0.03

Rubber tyres /gravel

0.03

0.04

0.03

0.04

Rolling

14.9

14.10

14.11

The nominal computed load on winching systems shall not exceed the certified safe working load
(SWL), after taking into account the requirements of Sections 14.7 and 14.8 and after allowance for
splices, bending, sheave losses, wear and corrosion. If no certified SWL is available, the nominal
computed load shall not exceed one third of the breaking load of any part of the system.
The winching system should normally be capable of moving the structure from fully on the shore to
fully on the barge without re-rigging. If re-rigging cannot be avoided, then this should be included in
the operational procedures, and adequate resources should be available.
For skidded loadouts the structure may be moved closer to the quay edge prior to the commencement
of loadout.

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GUIDELINES FOR LOADOUTS

15

LIFTED LOADOUTS

15.1

Where the structure is lifted onto the barge by shore-based or floating crane, the requirements of
0027/ND “Guidelines for Marine Lifting Operations”, Ref. [1] shall apply, as appropriate.
Loads imposed by shore-based mobile cranes on the quay shall be shown to be within allowable
values, either by calculation or historical data.
Floating cranes shall be moored as required by Section 10. Thruster assistance may be used if
available to augment the mooring arrangement following successful DP tests carried out immediately
prior to loadout.
Where the offshore lifting padeyes are used for loadout, then a programme for inspection of the lift
points after loadout shall be presented. As a minimum, inspection of the padeyes and their connection
into the structure shall be carried out by a qualified NDT inspector in accordance with the original
fabrication drawings. Access for this (including the possible de-rigging of the lift point) shall be
provided as required. At the discretion of the attending surveyor, additional NDT inspections may be
required.
If the offshore lift rigging is used for loadout then the rigging shall be inspected by a competent person
prior to departure of the structure.

15.2
15.3

15.4

15.5

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

16

TRANSVERSE LOADOUTS

16.1

Loadouts where the Structure is moved transversely onto the barge require special consideration and
care, for various, but not limited to, the following reasons:

In nearly all cases the ballast plan must take account of additional parameters. Structure
weight transfer, transverse heel, longitudinal trim and tidal level must all be considered.

Friction between the side of the barge and the quay may be more critical than for an end-on
loadout, as there may be a smaller righting moment available in heel than in trim to overcome
this force. Snagging or hang-up can lead to the ballast operator getting out of synchronisation
with the structure travel. Release of the snagging load has led to instability and failures.

Stability may be more critical than for an end-on loadout and changes of heel may be
significant. The moment to change the barge heel 1 degree should be computed and
understood for all stages of loadout.

16.2

A risk assessment should be made of the effects of potential errors in ballasting, and of friction
between the barge and the quay.
Calculations should be carried out for the full range of probable GM values, module weight and centre
of gravity predicted during loadout.
Ideally, discrete ballast programmes should be prepared for tidal level, weight on barge, trim and heel
corrections.
Where a winch or strand jack system is used to pull the structure onto the barge, the effects of the
pulling force on the friction on the fenders should be considered.
For sliding surfaces between the barge and the quay, particular attention should be paid to lubrication
and use of low friction or rolling fenders.
Ballasting calculations for transverse loadouts shall be based on the weighed weight and CoG and
include load combinations addressing weight and CoG contingencies.

16.3
16.4
16.5
16.6
16.7

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GUIDELINES FOR LOADOUTS

17

BARGE REINSTATEMENT AND SEAFASTENINGS

17.1
17.2

Seafastening work shall be started as soon as possible after positioning the structure on the barge.
No movement of the barge shall take place until sufficient seafastening is completed to withstand the
greatest of:
a.
an inclination equivalent to a horizontal force of 0.1 x structure weight, or
b.
the inclination caused by damage to any one compartment of the barge, or
c.
the direct wind loading, and inclination due to the design wind.
Inclination loadings shall be applied at the structure centre of gravity; direct wind load shall be applied
at the structure centre of area.
In specific circumstances where very limited barge movements may be required, e.g. turning from endon to alongside the quay before it is practical to install seafastenings fully in accordance with
Section 17.2, then friction may be allowed to contribute to the seafastenings, provided that it forms part
of a design loadcase. Design and condition of the actual supporting structure, and potential sliding
surfaces, at the time of movement, must be taken into account. The possibility of contaminants such
as grease, water or sand, which may reduce the friction between the sliding surfaces, should be
assessed.
The greatest of the loadings shown in Section 17.2 may be considered to be an extreme loading, and
the seafastening strength assessed as an ultimate limit state ULS / Survival storm case, as described
in Sections 6.1.7 to 6.1.10.
Approval of barge movements in any case shall be subject to the specific approval of the attending
surveyor, after consideration of the procedures for moving the barge, the state of completion of the
seafastenings and the weather and tidal conditions for the movement.
All manhole covers shall be replaced as soon as practical after loadout.
Any holes cut for ballasting purposes shall be closed as soon as practical and the barge certification
and class reinstated before sailaway.
Final seafastening connections should be made with the barge ballast condition as close as practical to
the transport condition.

17.3

17.4

17.5

17.6
17.7
17.8

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GUIDELINES FOR LOADOUTS

18

TUGS

18.1

Approved tugs shall be available or in attendance as required, for barge movements, removal of the
barge from the loadout berth in the event of deteriorating weather, or tug back-up to the moorings.
Towing operations following loadout should generally be in accordance with GL Noble Denton
document 0030/ND – “Guidelines for Marine Transportations” Ref. [2].
If tugs are used as part of the loadout, inspections shall be carried out as part of the approval, i.e. for
communications and adequacy. Tug inspections shall be carried out at least 12 hours prior to the start
of operations.

18.2
18.3

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

19

MANAGEMENT AND ORGANISATION

19.1

Sufficient management and resources shall be provided to carry out the operation efficiently and
safely.
Quality, safety and environmental hazards shall be managed by a formal Quality Management System.
The management structure, including reporting and communication systems, and links to safety and
emergency services should be demonstrated.
Shift changes shall be avoided at critical stages of loadout.
A readiness meeting should be held shortly before the start of loadout, attended by all involved parties.
A weather forecast from an approved source, predicting that conditions will be within the prescribed
limits, shall be received not less that 48 hours prior to the start of the operation, and at 12 hourly
intervals thereafter, or more frequently if appropriate, until the barge is moored in accordance with
Section 10.8 and the seafastening is completed in accordance with Section 17.2.
Fit-for-purpose safety procedures shall be in effect.

19.2
19.3
19.4
19.5
19.6

19.7

0013/ND REV 6

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GUIDELINES FOR LOADOUTS

REFERENCES
[1]
[2]
[3]
[4]

GL Noble Denton 0027/ND – Guidelines for Marine Lifting Operations.
GL Noble Denton 0030/ND – Guidelines for Marine Transportations.
GL Noble Denton 0032/ND - Guidelines for Moorings
ISO International Standard ISO 19901-5 – Petroleum and natural gas industries – specific requirements for
offshore structures – Part 5: Weight control during engineering and construction.

All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com

0013/ND REV 6

Page 33

6

GUIDELINES FOR LOADOUTS

APPENDIX A - CHECK LIST OF INFORMATION REQUIRED FOR APPROVAL
A.1

STRUCTURE

A.1.1

Structural analysis report, including:

Structural drawings including any additional loadout steelwork

Description of analyses programs used

Structural model

Description of support conditions

Loadcases including derivation of weights and contingencies

Unity checks greater than 0.8 for members and joints

Justification of over-stressed members

Detailed checks on structure support points, padeyes, winch connection points

Proposals for reinforcements if required.

A.1.2

Weight report for structure (including results of weighing operation and load cell calibration
certificates).

A.2

SITE

A.2.1

Site plan, showing loadout quay, position of structure, route to quay edge if applicable, position of all
mooring bollards and winches and any reinforced areas with allowable bearing capacities.
Section through quay wall.
Drawing showing heights above datum of quay approaches, structure support points, barge,
linkbeams, pad (if applicable) and water levels. The differential between civil and bathymetric datums
shall be clearly shown.
Statement of maximum allowable loadings on quay, quay approaches, wall, grounding pads and
foundations.
Specification and capacity of all mooring bollards and other attachment points proposed.
Bathymetric survey report of area adjacent to the quay and passage to deep water, related to same
datum as item A.2.3.
Bathymetric survey of pad, for grounded loadouts, related to the same datum as item A.2.3.
Structural drawings of skidways and link beams, with statement of structural capacity, construction
(material and NDT reports) and supporting calculations.
Method of fendering between barge and quay, showing any sliding or rolling surfaces and their
lubrication.

A.2.2
A.2.3

A.2.4
A.2.5
A.2.6
A.2.7
A.2.8
A.2.9

A.3

BARGE

A.3.1
A.3.2
A.3.3
A.3.4
A.3.5
A.3.6
A.3.7

General arrangement and compartmentation drawings.
Hydrostatic tables and tank tables.
Details of class.
Static stability at all stages of loadout.
Allowable deck loadings and skidway loadings if applicable.
Specification and capacity of all mooring bollards.
Details of any additional steelwork such as grillages or winch attachments.

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GUIDELINES FOR LOADOUTS
A.3.8

Details of barge pumping system.

A.4

TRAILERS

A.4.1
A.4.2
A.4.3
A.4.4
A.4.5
A.4.6
A.4.7
A.4.8

Trailer specification and configuration.
Details of any additional supporting steelwork, including linkspan bridges and attachments.
Allowable and actual axle loadings.
Allowable and actual spine bending moments and shear forces.
Schematic of hydraulic interconnections.
Statement of hydraulic stability of trailer or SPMT system, with supporting calculations.
For SPMTs, details of propulsion axles and justification of propulsion capacity.
Specifications of tractors if used.

A.5

PUMPS

A.5.1
A.5.2
A.5.3

Specification and layout of all pumps, including back-up pumps.
Pipe schematic, and details of manifolds and valves where applicable.
Pump performance curves.

A.6

JACKING AND/OR WINCHING

A.6.1
A.6.2
A.6.3
A.6.4
A.6.5
A.6.6

Jack/winch specification.
Layout of pull-on system.
Layout of pull-back and braking systems.
Details of power sources and back-up equipment.
Calculations showing friction coefficient, allowances for bending and sheaves, loads on attachment
points and safety factors.
Reactions induced between barge and quay.

A.7

BALLAST CALCULATIONS

A.7.1
A.7.2

Planned date, time and duration of loadout, with alternative dates, tidal limitations and windows.
Ballast calculations for each stage showing:

Time

Tidal level

Structure position

Weight on quay, linkbeam and barge

Ballast distribution

Barge draft, trim and heel

Pumps in use, and pump rates required

Moment to change heel and trim.

A.7.3

Stages to be considered should include as a minimum:

Start condition with structure entirely on shore

A suitable number of intermediate steps, e.g. 25%, 50% and 75% of travel, steps of 5 axles, or
half jacket node spacing, whichever is appropriate

100% of weight on barge

Any subsequent movements on barge up to the final position.
Any stages requiring movement or reconnection of pumps shall be defined.

A.7.4

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GUIDELINES FOR LOADOUTS

A.8

LIFTED LOADOUTS

A.8.1
A.8.2
A.8.3
A.8.4

A.8.6
A.8.7
A.8.8
A.8.9

Crane specification, including load-radius curve.
Copy of crane certification.
Slinging arrangement.
Copy of certificates of slings, shackles and other equipment. These certificates shall be issued or
endorsed by bodies approved by an IACS member or other recognised certification body accepted by
GL Noble Denton.
For mobile cranes, position of crane at pick-up and set-down, travel route if applicable, actual and
allowable ground bearing pressures at all locations.
Non-destructive testing report of lifting attachments and connection into structure.
Mooring arrangements and thruster specification for floating cranes.
If the lift points and offshore lift rigging will be re-used offshore, proposals for inspection after loadout.
Rigging calculations.

A.9

MOORINGS

A.9.1
A.9.2
A.9.3

A.9.5
A.9.6

Limiting design and operational weather conditions for loadout.
Mooring arrangements for loadout operation and post-loadout condition.
Mooring design calculations showing environmental loads, line tensions and attachment point loads for
limiting weather condition for loadout, and for post-loadout moorings if applicable.
Specification and certificates of all wires, ropes, shackles, fittings and chains. This certificate shall be
issued or endorsed by a body approved by an IACS member or other recognised certification body
accepted by GL Noble Denton.
Specification for winches, details and design of winch foundation/securing arrangements.
Details of fendering including lubrication arrangements as appropriate.

A.10

TUGS

A.10.1

Details of any supporting tugs including bollard pull and towing equipment.

A.11

MANAGEMENT

A.11.1
A.11.2
A.11.3
A.11.4
A.11.5
A.11.6
A.11.7
A.11.8

Organogram showing management structure and responsibilities.
Location of key personnel.
Details of manning levels, showing adequate coverage for all operations and emergency procedures.
Times of shift changes, if applicable.
Weather forecast arrangements.
Communications.
Adequate lighting for all critical areas.
Operation bar-chart showing time and duration of all critical activities including:

Mobilisation of equipment

Testing of pumps and winches

Testing of pull-on and pull-back systems

Barge movements

Initial ballasting

Structure movements

Loadout operation

Trailer removal

A.8.5

A.9.4

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GUIDELINES FOR LOADOUTS



A.11.9

Seafastening
Re-mooring
Decision points.

A.11.11
A.11.12
A.11.13

Methods of monitoring barge level and trim, and ballast quantities, including consideration of hang-up
between barge and quay.
If a computerised ballast control system is to be used, a description of the system, with back-up
arrangements, should be supplied.
Time and place for progress and decision meetings.
Safety procedures.
HAZOPs, HAZIDs and Risk Assessments,

A.12

CONTINGENCIES

A.12.1

Contingency plans shall be presented for all eventualities, including as appropriate:

Pump failure

Mains power supply failure

Jack-winch failure

Trailer/skidshoe power pack failure

Trailer/skidshoe hydraulics failure

Trailer tyre failure

Tractor failure

Failure of any computerised control or monitoring system

Mooring system failure

Structural failure

Deteriorating weather.

A.11.10

0013/ND REV 6

Page 37

TECHNICAL POLICY BOARD
GUIDELINES FOR THE APPROVAL OF
TOWING VESSELS

0021/ND

Once downloaded this document becomes UNCONTROLLED.
Please check the website below for the current version.

31 Mar 10

8

RLJ

Technical Policy Board

17 Nov 08

7

RLJ

Technical Policy Board

4 Oct 06

6

PJD

Technical Policy Board

1 Apr 02

5

JMRL

Technical Policy Board

1 Dec 01

4

JMRL

Technical Policy Board

1 Apr 01

3

JMRL /JR

For use in TVAS

2 Apr 96

2

JMRL

For use in TVAS

28 Dec 89

1

PAC

Technical Policy Board

DATE

REVISION

PREPARED BY

AUTHORISED BY

www.gl-nobledenton.com

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

PREFACE
This document has been drawn with care to address what are likely to be the main concerns based on the
experience of the GL Noble Denton organisation. This should not, however, be taken to mean that this document
deals comprehensively with all of the concerns which will need to be addressed or even, where a particular matter is
addressed, that this document sets out the definitive view of the organisation for all situations. In using this
document, it should be treated as giving guidelines for sound and prudent practice on which our advice should be
based, but guidelines should be reviewed in each particular case by the responsible person in each project to ensure
that the particular circumstances of that project are addressed in a way which is adequate and appropriate to ensure
that the overall advice given is sound and comprehensive.
Whilst great care and reasonable precaution has been taken in the preparation of this document to ensure that the
content is correct and error free, no responsibility or liability can be accepted by GL Noble Denton for any damage or
loss incurred resulting from the use of the information contained herein.

© 2010 Noble Denton Group Limited, who will allow:



the document to be freely reproduced,
the smallest extract to be a complete page including headers and footers but smaller extracts may be
reproduced in technical reports and papers, provided their origin is clearly referenced.

0021/ND REV 8

Page 2

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

CONTENTS
SECTION
1
2

3
4

5

6

7
8

9
10
11
12

PAGE NO.

SUMMARY
INTRODUCTION
2.1
BACKGROUND
2.2
TOWING VESSEL APPROVABILITY SCHEME (TVAS)
2.3
SUMMARY OF REQUIREMENTS
2.4
OTHER GL NOBLE DENTON GUIDELINES
2.5
BOLLARD PULL AND EQUIPMENT TESTS
DEFINITIONS
TOWING VESSEL CATEGORIES
4.1
OCEAN-GOING SALVAGE TUG (ST)
4.2
UNRESTRICTED TOWAGES (U)
4.3
COASTAL TOWAGES (C)
4.4
RESTRICTED TOWAGES (R1)
4.5
BENIGN AREA TOWAGES (R2)
4.6
RESTRICTED BENIGN AREA TOWAGES (R3)
4.7
LIMITED DURATION AND SHORT DISTANCE TOWAGES
DOCUMENTATION
5.1
GENERAL SPECIFICATION
5.2
GENERAL ARRANGEMENT PLANS
5.3
TOWING/ANCHOR-HANDLING WINCHES
5.4
TOWING EQUIPMENT
5.5
CERTIFICATES
5.6
SALVAGE EQUIPMENT
TOWING EQUIPMENT
6.1
OCEAN-GOING SALVAGE TUGS (ST)
6.2
UNRESTRICTED (U) OR COASTAL (C) CATEGORIES
6.3
RESTRICTED CATEGORIES (RI)
6.4
BENIGN AREA CATEGORIES (R2)
6.5
RESTRICTED BENIGN AREA CATEGORIES (R3)
6.6
ALL ENTERED VESSELS
TOWING WINCH
TOWING WIRE PROTECTION AND CONTROL
8.1
PROTECTORS
8.2
TOW BARS, CARGO PROTECTION RAIL, BULWARKS, STERN RAIL, TAILGATE AND STERN
ROLLER
8.3
ADJUSTABLE GOGWIRE SYSTEM
8.4
FIXED GOGWIRE SYSTEM
8.5
TOWING POD
STABILITY
MANNING AND ACCOMMODATION
SEAKEEPING
ADDITIONAL EQUIPMENT FOR SALVAGE TUGS (ST)

5
6
6
6
6
7
7
8
10
10
10
11
11
11
12
12
13
13
13
13
13
14
14
15
15
16
16
17
17
17
19
20
20
20
20
20
20
21
22
23
24

REFERENCES

25

APPENDIX A - SUMMARY OF REQUIREMENTS

26

APPENDIX B - BOLLARD PULL TESTS

27

APPENDIX C - TOWING EQUIPMENT TESTS

29

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
TABLES
Table 6-1
Table 6-2
Table 6-3
Table 6-4

Towline Minimum Breaking Loads for Salvage Tugs
Towline Minimum Breaking Loads for Unrestricted Towages
Towline Minimum Breaking Loads for Restricted Towages
Default Shackle SWL

0021/ND REV 8

15
16
16
18

Page 4

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

1

SUMMARY

1.1

These Guidelines are intended to lead to an approval by GL: Noble Denton for entry into the Towing
Vessel Approvability Scheme. They also provide guidance for the approval of towing vessels for
specific tows, and bollard pull tests. They do not cover the towage of specific vessels or barges,
guidance for which may be found in 0030/ND.

1.2

This revision 8 supersedes revision 7 dated 17th Nov 2008. Changes are described in Section 2.1.5.

1.3

This report refers to, and should be read in conjunction with other GL Noble Denton Guideline
documents, in particular Reference [1] - GL Noble Denton report 0030/ND - “Guidelines for Marine
Transportations”.

1.4

A definitions section is included.

1.5

A description of the approval process is included.

1.6

There are Sections on:


Towing Vessel Categories (Section 4)



Documentation (Section 5)



Towing Equipment (Section 6)



Towing Winch (Section 7)



Towing Wire Protection and Control (Section 8)



Stability (Section 9)



Manning and Accommodation (Section 10)



Seakeeping (Section 11)



Additional Equipment for Salvage Tugs (ST - Section 12)

0021/ND REV 8

Page 5

8

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

2

INTRODUCTION

2.1

BACKGROUND

2.1.1

These guidelines are the basis for the approval of towing vessels for specific towages.

2.1.2

The guidelines are also the standard for owners, charterers, managers or builders of towing vessels
when they seek entry of a vessel into the GL Noble Denton Towing Vessel Approvability Scheme
(TVAS).

2.1.3

Revision 6 superseded Revision 5 dated 1st April 2002. Major changes were:

2.1.4

2.1.5



Updating to reflect changes to 0030/ND



Modified definition of Approved Bollard Pull



Recommendations for carrying a towing wire history for categories U and R1.

Revision 7 superseded Revision 6 dated 4 October 2006. Major changes were:


Introduction of a new category, Coastal Towages (C), in Section 4.3 for smaller tugs for vessels
with an overall length of less than 40 metres unless they have very good seakeeping qualities
including good propeller immersion in bad weather and a displacement greater than 1,000
tonnes.



(For vessels with only one towing winch drum). Introduction in Section 7.10 of a maximum time
requirement for safely transferring a spare towline to the towing winch after a towline break in
bad weather.



Introduction in Section 9 of stability requirements that allow for the effect of the towline force.



Removal of the draught /length ratios in Section 11.4.



Introduction in Section 11.5 of a requirement for the height of raised forecastles to be at least 2
metres above the freeboard deck for all categories except for in benign weather areas.

This revision 8 supersedes Revision 7 dated 17 November 2008. Changes include:


the change from Noble Denton to GL Noble Denton



certificate requirements in Section 5.5



reduction in the maximum ULC of bridles for Category ST in Section 6.1.6.



bollard pull test requirements in Section B.4.4.

8

2.2

TOWING VESSEL APPROVABILITY SCHEME (TVAS)

2.2.1

The GL Noble Denton entity in London operates the GL Noble Denton Towing Vessel Approvability
Scheme on behalf of the GL Noble Denton Group.

2.2.2

These guidelines provide a standard against which a towing vessel will be assessed for the issue of a
Towing Vessel Approvability Certificate and entry into the TVAS database.

2.2.3

Such approval does not imply that approval by designers, regulatory bodies, harbour authorities and/or
any other parties would be given. Nor does it imply approval of a vessel for any specific towage or
operation for which further consideration of the suitability of the vessel for the towage or operation
would be required.

2.3

SUMMARY OF REQUIREMENTS
A summary of the requirements for each towing vessel category is appended to this document as
Appendix A.

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
2.4

OTHER GL NOBLE DENTON GUIDELINES
This document shall be read in conjunction with other GL Noble Denton current guideline documents.
In the event of conflict between two or more GL Noble Denton Guideline Documents, the last dated
shall apply unless specifically agreed otherwise.

2.5

BOLLARD PULL AND EQUIPMENT TESTS
Guidance notes for carrying out bollard pull and towing equipment tests are appended to this
document as Appendices B and C.

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

3

DEFINITIONS

3.1

Referenced definitions are underlined.
Term or Acronym

Definition

Approved Bollard Pull

The Approved Bollard Pull is the continuous static bollard pull which GL
Noble Denton is prepared to accept for towing service.
Continuous static bollard pull is that obtained by a test at 100% of the
Maximum Continuous Rating (MCR) of main engines, averaged over a
period of 10 minutes.
Where a certificate of Continuous Static Bollard Pull less than 10 years old
can be produced, then this will normally be used as the Approved Bollard
Pull.
Approved Bollard Pull for tugs under 10 years old without a bollard pull
certificate may be estimated as 1 tonne /100 (Certified) BHP of the main
engines.
Approved Bollard Pull for tugs over 10 years old, without a bollard pull
certificate less than 10 years old, may be the greater of:
 the certified value reduced by 1% per year of age since the BP test, or
 1 tonne/100 (Certified) BHP reduced by 1% per year of age greater
than 10.

Benign area

An area which is free of tropical revolving storms and travelling
depressions, (but excluding the North Indian Ocean during the southwest
monsoon season and the South China Sea during the northeast monsoon
season). The specific extent and seasonal limitations of a benign area
should be agreed with the GL Noble Denton office concerned.

BHP /
Brake Horse Power

The measure of horsepower at continuous engine output after the
combustion stage.

CBP /
Continuous Bollard Pull

See Approved Bollard Pull (above)

GL Noble Denton

Any company within the GL Noble Denton Group including any associated
company which carries out (part of) the scope of work and issues a
Certificate of Approval.

GL Noble Denton
Consultants Ltd.

The company in London within the GL Noble Denton Group operating the
Towing Vessel Approvability Scheme.

IACS

International Association of Classification Societies

MBL /
Minimum Breaking
Load (MBL)

Certified Minimum Breaking Load of wire rope, chain, stretcher or shackle
in tonnes.

MBP /
Maximum Bollard Pull

The bollard pull obtained by a test, typically at 110% of the Maximum
Continuous Rating (MCR) of main engines, over a period of 5 minutes.

MCR /
Maximum Continuous
Rating

Manufacturer’s recommended Maximum Continuous Rating of the main
engines.

Register

The list published from time to time of towing vessels, including all towing
vessels entered into the Towing Vessel Approvability Scheme.

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
Term or Acronym

Definition

Survey

Attendance and inspection by a GL Noble Denton representative. Other
surveys which may be required for a marine operation, including suitability,
dimensional, structural, navigational, and Class surveys.

Surveyor

The GL Noble Denton representative carrying out a ‘Survey’.
An employee of a contractor or Classification Society performing, for
instance, a suitability, dimensional, structural, navigational or Class survey.

SWL

Safe Working Load in tonnes. (See also Working Load Limit)

Tonnes

Metric tonnes of 1,000 kg (approximately 2,204.6 lbs) are used throughout
this document. The necessary conversions must be made for equipment
rated in long tons (2,240 lbs, approximately 1,016 kg) or short tons (2,000
lbs, approximately 907 kg).

Towing Vessel
Approvability Scheme
(the Scheme)

The scheme whereby owners of vessels may apply to have their vessels
surveyed and entered into the Scheme and the Register. The Scheme is
administered by Rules, a copy of which may be obtained from NDC.

Towing Vessel Report

The surveyor’s report on which the issue of a TVAC is based.

TVAC /
Towing Vessel
Approvability Certificate

The document issued by NDC stating that a vessel complied with these
guidelines at the time of survey, or was reportedly unchanged at the time
of revalidation, in terms of design, construction, equipment and condition,
and is considered suitable for use in towing service within the limitations of
its Category, bollard pull and any geographical limitations which may be
imposed.

ULC /
Ultimate Load Capacity

Ultimate load capacity of a wire rope, chain or shackle or similar is the
certified minimum breaking load, in tonnes. The load factors allow for
good quality splices in wire rope.
Ultimate load capacity of a padeye, clench plate, delta plate or similar
structure, is defined as the load, in tonnes, which will cause general failure
of the structure or its connection into the barge or other structure.

WLL /
Working Load Limit

0021/ND REV 8

The maximum static load that the wire, cable or shackle is designed to
withstand.

Page 9

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

4

TOWING VESSEL CATEGORIES
Vessels that are entered into the Scheme or proposed for towing duties will be designated one of six
(6) categories. The requirements for each category are stated below, and summarised in Appendix A.

4.1

OCEAN-GOING SALVAGE TUG (ST)

4.1.1

Vessels within this category are approvable for all towages within the limits of their bollard pull in all
geographical areas subject to the vessel’s Ice Classification.

4.1.2

Vessels shall be equipped with two (2) main towing wires and a spare towing wire, all of which shall
comply with the strength and length requirements of Section 6.1.

4.1.3

Vessels shall be adequately manned for towing operations in all geographical areas. Each vessel shall
have a minimum complement of officers and crew as required in the safe manning certificates and also
have the capability of accommodating increased manning levels where it is deemed necessary for a
specific towage. Refer to Section 10 and Appendix A.

4.1.4

Vessels shall be of such a design that they are capable of undertaking towages in all geographical
areas subject to their Ice Classification (see Section 11). They must have very good seakeeping
qualities including good propeller immersion in bad weather. These qualities are unlikely to be
satisfied with a Length Over All (LOA) less than 40 metres and a displacement of less than 1,000
tonnes.

4.1.5

Vessels shall have a minimum bunker capacity of at least 35 days consumption at 80% MCR.

4.1.6

Vessels shall be equipped with a workboat with sufficient power and capacity to carry four (4) persons
plus material/equipment to the casualty/tow.

4.1.7

Vessels shall be equipped with the additional equipment listed in Section 12.

4.2

UNRESTRICTED TOWAGES (U)

4.2.1

Vessels within this category are approvable for all towages within the limits of their bollard pull in all
geographical areas subject to the vessels’ Ice Classification.

4.2.2

Vessels shall be equipped with a main towing wire and a spare towing wire, both of which shall comply
with the strength and length requirements of Section 6.2.

4.2.3

Vessels shall be adequately manned for towing operations in all geographical areas. Each vessel shall
have a minimum complement of officers and crew as required in the safe manning certificates and also
have the capability of accommodating increased manning levels where it is deemed necessary for a
specific towage. Refer to Section 10 and Appendix A.

4.2.4

Vessels shall be of such a design that they are capable of undertaking towages in all geographical
areas subject to their Ice Classification and Section 11. They must have very good seakeeping
qualities including good propeller immersion in bad weather. These qualities are unlikely to be
satisfied with a Length Over All (LOA) less than 40 metres and a displacement of less than 1,000
tonnes.

4.2.5

Vessels shall be equipped with a workboat with sufficient power and capacity to carry four (4) persons
plus material/equipment to the tow. The man overboard boat may be considered as a workboat
provided there is sufficient space to carry out a workboat function and the appropriate flag state is in
agreement that it will not only be used for man overboard duties.

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
4.3

COASTAL TOWAGES (C)

4.3.1

Vessels within this category are approvable for all coastal towages within the limits of their bollard pull
in all geographical areas subject to the vessels’ Ice Classification. Coastal towages are defined as
routes for which a tow can safely reach a place of safety within the period of a reliable weather
forecast, or are in benign weather areas.

4.3.2

Vessels shall be equipped with a main towing wire and a spare towing wire, both of which shall comply
with the strength and length requirements of Section 6.2.

4.3.3

Vessels shall be adequately manned for towing operations in all relevant geographical areas. Each
vessel shall have a minimum complement of officers and crew as required in the safe manning
certificates and also have the capability of accommodating increased manning levels where it is
deemed necessary for a specific towage. Refer to Section 10 and Appendix A.

4.3.4

Vessels shall be of such a design that they are capable of undertaking towages in all relevant
geographical areas subject to their Ice Classification and Section 11.

4.3.5

Vessels shall be equipped with a workboat with sufficient power and capacity to carry four (4) persons
plus material/equipment to the tow. The man overboard boat may be considered as a workboat
provided there is sufficient space to carry out a workboat function and the appropriate flag state is in
agreement that it will not only be used for man overboard duties.

4.4

RESTRICTED TOWAGES (R1)

4.4.1

Vessels within this category are approvable for assisting with towages within the limits of their bollard
pull in all geographical areas subject to the vessels’ Ice Classification.

4.4.2

Vessels shall be equipped with a minimum of one main towing wire which shall comply with the
strength and length requirements of Section 6.3.

4.4.3

Vessels in this category shall comply with the requirements for manning and seakeeping as outlined in
Sections 4.2.3, 4.2.4, 10 and 11.

4.4.4

If proposed as the lead or only tug for a particular towage, as may be allowed in Section 4.7, vessels
shall be equipped with a workboat with sufficient power and capacity to carry four (4) persons plus
material/equipment to the tow. The man overboard boat may be considered as a workboat provided
there is sufficient space to carry out a workboat function and the appropriate flag state is in agreement
that it will not only be used for man overboard duties.

4.5

BENIGN AREA TOWAGES (R2)

4.5.1

Vessels within this category are approvable for towages within the limits of their bollard pull and the
defined geographical limits of Benign Areas.

4.5.2

Vessels shall be equipped with a main towing wire and a spare towing wire, both of which shall comply
with the strength and length requirements of Section 6.4.

4.5.3

Vessels shall be adequately manned for towage operations within the geographical limits of Benign
Areas. These vessels shall have the capability of accommodating increased manning levels where it is
deemed necessary for a specific towage. Refer to Section 10.

4.5.4

Vessels shall be of such a design that they are capable of undertaking towages within the geographical
limits of Benign Areas. Refer to Section 11.

4.5.5

If proposed as the lead or only tug for a particular towage, vessels shall be equipped with a workboat
with sufficient power and capacity to carry three (3) persons plus material/equipment to the tow. The
man overboard boat may be considered as a workboat provided there is sufficient space to carry out a
workboat function and the appropriate flag state is in agreement that it will not only be used for man
overboard duties.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
4.6

RESTRICTED BENIGN AREA TOWAGES (R3)

4.6.1

Vessels in this category are approvable for assisting with towages within the limits of their bollard pull
and the defined geographical limits of Benign Areas.

4.6.2

Vessels shall be equipped with a minimum of one main towing wire which shall comply with the
strength and length requirements of Section 6.5.

4.6.3

Vessels shall comply with the requirements for manning and seakeeping as outlined in Sections 4.5.3,
4.5.4, 10 and 11.

4.7

LIMITED DURATION AND SHORT DISTANCE TOWAGES

4.7.1

GL Noble Denton will not in normal circumstances approve single tug towages where the tug is
equipped with only one tow wire. However, vessels in category R1 may in certain circumstances be
approved for single tug towages where the towage is in sheltered waters or within the limits of a
reliable weather forecast. Approval of a vessel for this type of towage will be subject to a specific
assessment.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

5

DOCUMENTATION
Prior to a survey of the vessel being carried out for entry into the Scheme, and in order to assess the
likelihood of successful entry, copies of the following documents should be submitted to NDC for
review.

5.1

GENERAL SPECIFICATION
This should include, but is not limited to, general details of:

5.2



Overall dimensions and tonnages



Classification



Propulsion equipment



Speed, consumption and bunker capacity



Towing and anchor-handling equipment



Anchoring system



Accommodation capacity and layout

GENERAL ARRANGEMENT PLANS
These should show the overall arrangement of the vessel, and should be sufficiently detailed to show
the deck area including the towing, anchor handling and mooring equipment.

5.3

TOWING/ANCHOR-HANDLING WINCHES
Specifications of the towing/anchor-handling winch and its foundation.

5.4

TOWING EQUIPMENT
Specifications of all towing equipment carried including bridles, chains, towing wires, pennant wires,
stretchers, towing shackles and connecting links.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
5.5

CERTIFICATES
Copies of the following valid documents (unless not legally required, typically for some vessels less
than 500 gt) shall be submitted to NDC, or made available to the surveyor at time of survey:

5.6



Certificate of registry



International load line certificate



Certificates of class for hull and machinery



Cargo ship safety equipment certificate



Cargo ship safety radio certificate



Safety Construction Certificate



Certificate of safe manning



International Oil Pollution Prevention Certificate



Safety Management Certificate



International Ship Security Certificate



Ballast Water Exchange Certificate (if required)



Certificates for all required bridles, chains, tow wires, pennants, stretchers, and shackles and
connecting links. These certificates shall be issued or endorsed by bodies approved by an
IACS member or other recognised certification body accepted by GL Noble Denton.



Bollard Pull Certificate (by a recognised authority or body)



Approved Stability Booklet.

SALVAGE EQUIPMENT
For the entry of Ocean-Going Salvage Tugs (ST) details of the salvage equipment should be
submitted. A list of the minimum requirements appears in Section 12.

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8

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

6

TOWING EQUIPMENT

6.1

OCEAN-GOING SALVAGE TUGS (ST)

6.1.1

Vessels shall be equipped with two (2) main towing wires on separate winch drums, and one spare
towing wire, each of adequate strength to satisfy the requirements of Minimum Breaking Load (MBL)
as follows:
Table 6-1

Towline Minimum Breaking Loads for Salvage Tugs

Bollard Pull (BP)

6.1.2

Minimum Breaking Load (MBL)

Up to 90 tonnes

(3.8 - BP/50) x BP

Over 90 tonnes

2.0 x BP

The minimum length (L) of both main wires and the spare towing wire shall be determined from the
formula:
L = (BP/MBL) x 2,000 METRES

6.1.3

except that in no case shall the length be less than 800 metres (see also Section 6.6.4).
A towing log indicating service history, maintenance and inspections shall be kept for each tow wire
and each synthetic stretcher held on board the vessel.

6.1.4

Vessels shall be equipped with at least four (4) towing pennants of not less than the required MBL of
the towing wire, and of the same lay.

6.1.5

If a surge chain is supplied then the MBL shall not be less than that of the main towing wire. The surge
chain shall be a continuous length of welded studlink chain with an enlarged open link at each end.

6.1.6

Vessels shall be provided with the components for one towing bridle, which may be either all chain, or
a combination of chain and wire. The ultimate load capacity (ULC), in tonnes, of each bridle leg shall
be not less than:

6.1.7

8

ULC = 1.25 x MBL

(for MBL < 160 tonnes) or

ULC = MBL + 40

(for MBL >160 tonnes) with a maximum of ULC of 400 tonnes (considered
to be the maximum able to be handled at sea without a crane)

Vessels shall be equipped with at least twelve (12) towing shackles in accordance with the
requirements of Sections 6.6.13 and 6.6.14.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
6.2

UNRESTRICTED (U) OR COASTAL (C) CATEGORIES

6.2.1

Vessels shall be equipped with both a main and a spare towing wire, each of adequate strength to
satisfy the requirements of minimum breaking load (MBL) as follows:
Table 6-2

Towline Minimum Breaking Loads for Unrestricted Towages

Bollard Pull (BP)

Minimum Breaking Load (MBL)

Less than 40 tonnes

6.2.2

3.0 x BP

40 to 90 tonnes

(3.8 - BP/50) x BP

Over 90 tonnes

2.0 x BP

The minimum length (L) of both the main and spare towing wires shall be determined from the formula:
L = (BP/MBL) x 1,800 METRES
except that in no case shall the length be less than 650 metres for Unrestricted categories or 500
metres for Coastal (see also Section 6.6.4).

6.2.3

A towing log indicating service history, maintenance and inspections is recommended to be kept for
each tow wire and each synthetic stretcher held on board the vessel.

6.3

RESTRICTED CATEGORIES (RI)

6.3.1

Vessels shall be equipped with one main towing wire of adequate strength to satisfy the requirements
of minimum MBL as follows.
Table 6-3

Towline Minimum Breaking Loads for Restricted Towages

Bollard Pull (BP)

Minimum Breaking Load (MBL)

Less than 40 tonnes

6.3.2

3.0 x BP

40 to 90 tonnes

(3.8 - BP/50) x BP

Over 90 tonnes

2.0 x BP

The minimum length (L) of the towing wire shall be determined from the formula:
L = (BP/MBL) x 1,800 METRES
except that in no case shall the length be less than 650 metres (see also Section 6.6.4).

6.3.3

It is good practice to keep a towing log, indicating service history, maintenance and inspections, for
each tow wire and each synthetic stretcher held on board the vessel.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
6.4

BENIGN AREA CATEGORIES (R2)

6.4.1

Vessels shall be equipped with both a main and spare towing wire each of adequate strength to satisfy
the requirements of Minimum BL as follows:
MBL = 2.0 x BP

6.4.2

The minimum length (L) of both the main and spare towing wires shall be determined from the formula:
L = (BP/MBL) x 1,200 METRES
except that in no case shall the length be less than 500 metres (see also Section 6.6.4).

6.5

RESTRICTED BENIGN AREA CATEGORIES (R3)

6.5.1

Vessels shall be equipped with a towing wire of adequate strength to satisfy the requirements of MBL
as follows:
MBL = 2.0 x BP

6.5.2

The minimum length (L) of the towing wire shall be determined from the formula:
L = (BP/MBL) x 1,200 METRES
except that in no case shall the length be less than 500 metres (see also Section 6.6.4).

6.6

ALL ENTERED VESSELS

6.6.1

All towing wires shall have hard eyes formed by a heavy-duty gusseted thimble, “pee-wee” or a closed
spelter socket fitted at the outer end.

6.6.2

The main towing wire(s) should be spooled onto the towing winch drum(s) using adequate tension.
The end of the wire must be adequately secured to the winch drum.

6.6.3

Where a spare towing wire is carried, it shall be stowed on a winch drum, or reverse stowed on a reel.
Where the spare wire is stowed on a reel, it shall be accessible even in heavy weather, and be in such
a position as to ensure that transfer to the main towing drum can be achieved safely and efficiently.

6.6.4

Where a reduced towline length demands a higher Minimum Breaking Load (MBL) in order to satisfy
the towline length formula, then this increased MBL shall be the required MBL when determining the
strength of the other components in the towing arrangement.

6.6.5

Vessels shall be equipped with at least 2 (4 for category ST) towing pennants of not less than the
required breaking load of the main towing wire.

6.6.6

Pennants shall be of the same lay as the towing wire.

6.6.7

Pennants shall have hard eyes formed by a heavy-duty gusseted thimble, “pee-wee” or a spelter
socket at each end.

6.6.8

If a soft-eyed pennant is carried, then such pennant shall be additional to the other requirements of this
Section.

6.6.9

The towing pennants shall have a length appropriate to their intended service. Typically these will be
in the range of 10 to 50 metres long but at least 2 should be suitable for making up a towing bridle.

6.6.10

If synthetic stretchers are used, at least 2 shall be carried. For Benign Areas, one (1) synthetic
stretcher may be acceptable.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
6.6.11

If synthetic stretchers are used, the pennants should be in a sound condition and the Minimum
Breaking Load should not be less than:


2.0 times the required towline MBL, for tugs with bollard pull less than 40 tonnes.



1.5 times the required towline MBL, for tugs with bollard pull greater than 90 tonnes.



linearly interpolated between 1.5 and 2.0 times the required towline MBL for tugs with bollard
pull between 40 tonnes and 90 tonnes.

When determining the required minimum towline break load the comments in Section 6.6.4 shall be
taken into account.
6.6.12

The synthetic stretchers shall have a heavy-duty gusseted thimble at each end and be adequately
protected against chafe.

6.6.13

Vessels shall be equipped with at least 6 (12 for category ST) towing shackles or approved connecting
links.

6.6.14

The required capacity of towing shackles or connecting links shall be determined from the Certified
Minimum Breaking Load (MBL), Certified Safe Working Load (SWL) or Certified Working Load Limit
(WLL). If the MBL of a shackle is known, then the MBL shall not be less than 110% of the required
MBL of the towing wire.

6.6.15

If the Minimum Breaking load of the shackle cannot be identified then the minimum Safe Working Load
may be related to the continuous static bollard pull (BP) of the largest tug proposed, as follows:
Table 6-4

Default Shackle SWL

Bollard Pull (BP)
(tonnes)

Safe Working Load (SWL) or Working Load Limit (WLL)
(tonnes)

Less than 40

1.0 x BP

40 or more

(0.5 x BP) + 20

except that the comments contained in Section 6.6.4 shall be taken into account as appropriate, and
the shackle SWL be increased in proportion.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

7

TOWING WINCH

7.1

Vessels in all categories shall be provided with at least one towing winch, (two towing winch drums for
category ST).

7.2

The towing winch and its connection to the vessel shall be strong enough to withstand a force equal to
the breaking load of the tow wire acting at its maximum height above deck, without over-stressing
either the winch or the deck connections

7.3

If the power for the towing winch is supplied via a main engine shaft generator during normal operating
conditions, then another generator shall be available to provide power for the towing winch in case of
main engine or generator failure.

7.4

If a multi-drum winch is used, then each winch drum shall be capable of independent operation.

7.5

The towing winch drum(s) shall have sufficient capacity to stow the required minimum length of the tow
wire(s).

7.6

A spooling device shall be provided such that the tow wire(s) is effectively spooled on to the winch
drum(s).

7.7

The towing winch brake shall be capable of preventing the towing wire from paying out when the
vessel is towing at its maximum continuous static bollard pull and shall not release automatically in
case of a power failure.

7.8

The winch shall be fitted with a mechanism for emergency release of the tow wire.

7.9

There shall be an adequate means of communication between the winch control station(s) and the
engine control station(s) and the bridge.

7.10

If there is only one towing winch then the crew must be able to demonstrate that a spare tow wire can
be safely run onto the towing winch within 6 hours of a towline break in bad weather.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

8

TOWING WIRE PROTECTION AND CONTROL

8.1

PROTECTORS

8.1.1

Sufficient towing wire protectors shall be provided to prevent the towing wire from being damaged by
abrasion and chafe against tow bars, cargo protection rails, bulwarks, stern rail, tail gate or stern roller.

8.1.2

If a “fixed” gogwire system or towing pod is used, then whenever possible, towing wire protectors
should also be provided for the towing wire at the gogwire shackle or towing pod.

8.2

TOW BARS, CARGO PROTECTION RAIL, BULWARKS, STERN RAIL, TAILGATE AND
STERN ROLLER

8.2.1

The top of the tow bars, cargo protection rail, bulwarks, stern rail, tail gate and stern roller shall be free
of sharp edges, corners or obstructions which could damage the towing wire or prevent it from free
lateral movement.

8.2.2

Where, during normal towing conditions, the towing wire bears on tow bars, cargo protection rail,
bulwarks, stern rail or tailgate, the radius of bend shall be at least ten (10) times the diameter of the
towing wire.

8.3

ADJUSTABLE GOGWIRE SYSTEM

8.3.1

Preference shall be given to the use of an adjustable gogwire system.

8.3.2

The winch or capstan used to adjust the gogwire system shall be controlled from a safe location.

8.4

FIXED GOGWIRE SYSTEM

8.4.1

If a single wire or single chain gogwire system is used, then the connection point on the aft deck shall
be on the centreline of the vessel.

8.4.2

The length of the single wire or single chain of the gogwire system shall not exceed half the distance
between the cargo protection rails or bulwarks, whichever is less.

8.4.3

Either a “wide body” sling shackle, having an enlarged bearing surface at the bow, or a purposedesigned sheave, shall be used to connect the gogwire system to the towing wire.

8.5

TOWING POD

8.5.1

The centre line of the towing pod shall be in line with the centre line of the towing wire winch drum.

8.5.2

The towing pod shall be well faired and have a bend radius of at least ten (10) times the diameter of
the towing wire.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

9

STABILITY

9.1

The stability of the vessel shall never be less than that required by the ”Guidelines for the Design and
Construction of Offshore Supply Vessels” (Resolution A.469 [XII] adopted by the International Maritime
Organisation 1981) and the Merchant Shipping (Load Line) Rules 1966, S.I. 1053.

9.2

In addition, if the vessel has an IACS class notation of "Tug" or “Towing Vessel” then the stability
booklet should contain an example loading condition that fulfils the Classification Society's Notation.
The vessel’s Master should show to the attending surveyor how the example loading condition relates
to that for the voyage(s), including whether any roll reduction tanks may be in use.

9.3

If the example loading condition varies, the Master should prove adequate stability, including the arrival
fuel loads. The relevant print out(s) from the onboard calculations (e.g.“Loadmaster”) should be given
to the surveyor.

9.4

If the vessel cannot show that it satisfies an IACS class “Tug" or “Towing Vessel” notation as described
above, then the heeling lever (defined below) must not exceed 0.5 times the maximum GZ for the most
critical loading condition.

9.5

Heeling Lever =

9.6

The height of the hawser should be measured at:

9.7

[0.6 x Max. Bollard Pull x Vertical Distance between Hawser and Centre of the
Propeller(s)] /Displacement



the fixed gog, or the side rails if higher, if a fixed gog is always used, or



the top of the winch drum (with no towline deployed), or the side rails if higher, if a fixed gog is not
always used.

If the maximum GZ occurs at an angle greater than 30 degrees of heel then the GZ value for 30
degrees of heel should be used instead of the angle of maximum GZ.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

10

MANNING AND ACCOMMODATION

10.1

Vessels in all categories shall be manned to meet the minimum requirements laid down by Statutory
Regulations.

10.2

Manning levels for vessels in all categories will be subject to the requirements of a specific towage.

10.3

Where vessels are required to undertake long duration towages, difficult towages or where the tow is
unmanned, they shall have adequate certified accommodation to enable manning levels to be
increased. Any increase in manning levels will be subject to the limitations of the regulations relating
to life-saving appliances.

10.4

Category ST. In general, to satisfy category ST, certified accommodation and life-saving appliances
shall be provided for a minimum of twelve (12) persons.

10.5

Vessels in category ST shall, when engaged in towing operations, carry a minimum of five (5)
certificated officers. These would normally be the Master, two (2) Deck Officers and two (2) Engineer
Officers.

10.6

Categories U, C and R1. In general, to satisfy categories U, C and R1, certified accommodation and
life-saving appliances shall be provided for a minimum of eight (8) persons.

10.7

Vessels in categories U, C and R1 shall, when engaged in towing operations, carry a minimum of four
(4) certificated officers. These would normally be the Master, one (1) Deck Officer and two (2)
Engineer Officers.

10.8

Vessels in Categories R2 and R3 shall, when engaged in towing operations, carry a minimum of
three (3) certificated officers. These would normally be the Master, one (1) Deck Officer and one (1)
Engineer Officer.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

11

SEAKEEPING

11.1

Vessels in all categories shall be of such a design to allow them to operate safely and effectively in
their designated areas.

11.2

Vessels in all categories must be purpose-built for towing operations or be of a multi-purpose design
having towing capability.

11.3

Vessels must be assigned an appropriate Classification by a recognised Classification Society.

11.4

The length and normal operating draught of the vessel shall be adequate to maintain propeller
effectiveness and reduce slamming in heavy weather conditions.

11.5

Vessels in category ST, U, C and R1 shall have a raised forecastle with a height of at least 2 metres
above the freeboard deck. The forecastle shall be of such a design to ensure minimum water
retention.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

12

ADDITIONAL EQUIPMENT FOR SALVAGE TUGS (ST)
All vessels in category ST shall carry the following equipment:

12.1

Lifting Equipment
A deck crane or derrick with a minimum capacity of two (2) tonnes for transferring equipment.

12.2

Pumps
Portable salvage pumps with an ample supply of suitable hoses.

12.3

Generators
Portable generator or facilities and cabling to allow power to be distributed to the casualty /tow from the
tug.

12.4

Air Compressor
Portable air compressor suitable for salvage purposes with ample supply of hoses or facility to allow
compressed air to be distributed to the casualty /tow.

12.5

Welding/Cutting
Portable welding and cutting equipment with ample supply of extension cables, hoses and
consumables.

12.6

Damage Control
Assorted steel plate, timber, canvas, cement, sand, tools, etc. for damage control purposes.

12.7

Spare Parts
A comprehensive inventory of spare parts should be carried, for the vessel to allow repairs to be
carried out during long voyages.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

REFERENCES
[1]

GL Noble Denton report 0030/ND - Guidelines for Marine Transportations

[2]

International Maritime Organization (IMO), Guidelines for Safe Ocean Towing, Ref T1/3.02
All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

APPENDIX A - SUMMARY OF REQUIREMENTS
The following table provides a summary of the requirements contained in this Guideline for each Category of vessel.
Use of the table should be made together with reference to the appropriate text in the Guideline.
Category
General design and range
Adequate displac (LOA > 40m)
Raised fo’csle
Bunker capacity at 80% power
Certificates/documentation
Registry
Loadline
Class, hull for this category
Safe manning
Safety equipment
Safety radio
All towing equipment
Bollard Pull
Towing wire log
Towage and salvage equipment
Towing winch
Number of winch drums
Number of main tow wires
Number of spare tow wires
Towline MBL, tonnes (BP> 90t)
Towline MBL, tonnes (40<BP< 90t)
Towline MBL, tonnes (BP<40t)
Towline length, metres
(European formula)
Minimum towline length (m)
Towing pennants
Shackles /Connecting Links
Surge chain
Towing bridle (see Section 6.1.6)
Salvage equipment
Work boat
Crane/derrick
Pumps
Compressor
Welding equipment
Damage control
Spares
Manning and accommodation
Accommodation
LSA
Number of certificated officers

ST
Salvage
Tug

U
Unrestrict
ed

C

R1
Assist

R2
Benign
area

R3
Assist /
Benign

Coastal

Yes
Yes
35 days

Yes
Yes
-

Yes
-

Yes
-

-

-

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
-

Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
-

Yes
2
2
1
2.0 x BP
(3.8-BP/50)
x BP
(3.8-BP/50)
x BP
(BP/MBL) x
2,000
800
4
12
Optional
1
Yes
Yes
2 tonnes
Yes
Yes
Yes
Yes
Yes

Yes
1
1
1
2.0 x BP
(3.8-BP/50)
x BP
3.0 x BP

Yes
1
1
1
2.0 x BP
(3.8-BP/50)
x BP
3.0 x BP

Yes
1
1
2.0 x BP
(3.8-BP/50)
x BP
3.0 x BP

Yes
1
1
1
2.0 x BP
2.0 x BP

Yes
1
1
2.0 x BP
2.0 x BP

2.0 x BP

2.0 x BP

(BP/MBL) x
1,800
650
2
6
Yes
-

(BP/MBL) x
1,800
500
2
6
Yes
-

(BP/MBL) x
1,800
650
2
6
Yes*
-

(BP/MBL) x
1,200
500
2
6
Yes*
-

(BP/MBL) x
1,200
500
2
6
-

12
12
5

8
8
4

8
8
4

8
8
4

3

3

* A workboat is required for Categories R1 and R2 if the vessel is proposed as the lead tug or only tug for a
particular towage.

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

APPENDIX B - BOLLARD PULL TESTS
B.1

GENERAL

B.1.1

The following guidance notes apply to the bollard pull test of any towing vessel which GL Noble Denton
is requested to approve or attend.

B.1.2

The safe working load of the test equipment, fittings and any connection points ashore shall be at least
10% in excess of the designed maximum continuous static bollard pull of the vessel.

B.2

LOCATION

B.2.1

The water depth at the test location shall be at least 20 metres within a radius of 100 metres of the
vessel.

B.2.2

If a water depth of 20 metres cannot be obtained at the test location, then a minimum water depth
which is equal to twice the maximum draught of the vessel may be accepted. The owner of the vessel
must be advised that the reduced water depth may adversely affect the test results.

B.2.3

The test location shall be clear of navigational hazards and underwater obstructions within a radius of
300 metres of the vessel.

B.2.4

The current shall be less than 0.5 metres/second from any direction.

B.2.5

The wind speed shall be less than 5 metres/second from any direction.

B.2.6

The condition of the sea at the test location shall be calm, without swell or waves.

B.3

VESSEL

B.3.1

The draught and trim of the vessel shall be as near as possible to the draught and trim under normal
operating conditions.

B.3.2

The propellers and fuel used during the tests shall be the same as the propellers and fuel used under
normal operating conditions.

B.3.3

All auxiliary equipment such as pumps, generators and other equipment which are driven from the
main engine(s) or propeller shaft(s) during normal operation of the vessel shall be connected during
the test.

B.4

TEST

B.4.1

The distance between the stern of the vessel and the shore shall be at least 300 metres.

B.4.2

If it is not possible to maintain a distance of 300 metres between the stern of the vessel and the shore,
then a minimum distance which is equal to twice the waterline length of the vessel may be accepted.
The owner of the vessel must be advised that the reduced distance between the vessel’s stern and the
shore may adversely affect the test results.

B.4.3

Adequate communications shall be established between the vessel and instrument recording station.

0021/ND REV 8

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GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
B.4.4

The Continuous Bollard Pull (CBP) test shall be carried out at the manufacturer’s recommended
maximum continuous rating of the main engines (100% MCR), for a period of 10 minutes (see IMO
requirements in Ref [2]) with the vessel on a steady heading.

B.4.5

Whenever possible a maximum (MBP) test shall be carried out at the manufacturer’s maximum rating
of the main engines (typically 110% MCR), for a period of 5 minutes.

B.4.6

When requested, continuous bollard pull may also be verified at different RPM and/or propeller pitch
settings or with fewer propellers or engines in use.

B.4.7

The load cell used for measuring the bollard pull shall have an accuracy of 2% for the average
temperature observed during the test and shall have been calibrated not more than six (6) months prior
to the test date. The calibration certificate shall be available.

B.4.8

An autographic recording instrument giving a continuous read-out of the bollard pull shall be connected
to the load cell.

B.4.9

If no continuous record of the test is printed, then the bollard pull shall be the mean of consecutive
readings recorded at 20 second intervals over the test period.

B.5

BOLLARD PULL TESTS ACCEPTANCE

B.5.1

Bollard pull test certificates issued by Classification Societies are acceptable, or by another recognised
body provided that acceptable procedures for the tests are produced.

0021/ND REV 8

Page 28

8

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS

APPENDIX C - TOWING EQUIPMENT TESTS
C.1

GENERAL

C.1.1

The following guidance notes apply to the towing equipment tests of any vessel which GL Noble
Denton is requested to approve or attend.

C.1.2

Before carrying out any tests, it shall be ascertained that the equipment to be tested has been installed
according to the manufacturer’s recommendations and can be operated safely.

C.1.3

The wire used during the winch tests shall be equal to the towing wire in breaking load, diameter and
construction and shall be spooled onto the towing winch drum with a tension of 25% of the vessel’s
CBP or 40 tonnes, whichever is less.

C.1.4

During stalling, brake and quick release tests, the wire shall be kept as near as possible to the centre
line of the vessel.

C.1.5

The safe working load of the test equipment, fittings and any connection points ashore shall be at least
ten (10) percent in excess of the designed maximum static bollard pull of the vessel.

C.2

WINCH TESTS

C.2.1

Stalling Test
First Test:

To be carried out with a full drum.

Second Test:

To be carried out with an effective drum diameter which is estimated to stall the
winch at CBP.

The winch shall be heaving in wire while the engine revolution or propeller pitch is gradually increased.
When the winch stalls, the following shall be recorded:
a.
Bollard Pull
b.
C.2.2

Effective Drum Diameter

Brake Test
The test shall be carried out with a full drum of wire.
A wire of approximately 300 metres shall be connected to the winch wire if required.
The brake shall be applied at maximum holding capacity.
The engine revolutions or propeller pitch shall be gradually increased until CBP is achieved.
The following shall be recorded:
a.
Bollard Pull
b.

0021/ND REV 8

Brake Pressure

Page 29

GUIDELINES FOR THE APPROVAL OF TOWING VESSELS
C.2.3

Quick Release Test
The quick release tests shall be carried out when the vessel is towing at approximately 30% of its CBP.

C.2.4

First Test:

When heaving in the test wire.

Second Test:

When the brake is engaged.

Spooling Gear Test (if fitted)
The spooling gear shall be engaged when tested.
The engine power or propeller pitch shall be gradually increased to CBP.
The test wire shall be at an angle of approximately 60° to the centreline, on each side of the vessel.
The duration of the test shall be not less than one (1) minute.

C.3

FIXED GOGWIRE SYSTEM, TOWING POD, LINE STOPS AND GUIDE PINS
TESTS

C.3.1

The spooling gear, if fitted, shall be disengaged during the “fixed” gogwire system, towing pod, line
stops and guide pin tests.

C.3.2

The engine power or propeller pitch shall be gradually increased to the CBP.

C.3.3

The test wire shall be at an angle of approximately 60° to the centreline, on each side of the vessel.

C.3.4

The duration of each test shall not be less than one (1) minute.

0021/ND REV 8

Page 30

TECHNICAL POLICY BOARD
GUIDELINES FOR MARINE LIFTING OPERATIONS

0027/ND

Once downloaded this document becomes UNCONTROLLED.
Please check the website below for the current version.

31 Mar 10

9

GPB

Technical Policy Board

23 Jun 09

8

GPB

Technical Policy Board

15 Apr 09

7

GPB

Technical Policy Board

19 Jan 09

6

GPB

Technical Policy Board

17 Feb 06

5

RLJ

Technical Policy Board

30 Nov 05

4

JR

Technical Policy Board

15 Oct 02

3

JR

Technical Policy Board

01 May 02

2

JR

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11 Aug 93

1

JR

Technical Policy Board

31 Oct 90

0

JR

Technical Policy Board

DATE

REVISION

PREPARED

AUTHORISED BY

www.gl-nobledenton.com

GUIDELINES FOR MARINE LIFTING OPERATIONS

PREFACE
This document has been drawn with care to address what are likely to be the main concerns based on the
experience of the GL Noble Denton organisation. This should not, however, be taken to mean that this document
deals comprehensively with all of the concerns which will need to be addressed or even, where a particular matter is
addressed, that this document sets out the definitive view of the organisation for all situations. In using this
document, it should be treated as giving guidelines for sound and prudent practice on which our advice should be
based, but guidelines should be reviewed in each particular case by the responsible person in each project to ensure
that the particular circumstances of that project are addressed in a way which is adequate and appropriate to ensure
that the overall advice given is sound and comprehensive.
Whilst great care and reasonable precaution has been taken in the preparation of this document to ensure that the
content is correct and error free, no responsibility or liability can be accepted by GL Noble Denton for any damage or
loss incurred resulting from the use of the information contained herein.

© 2010 Noble Denton Group Limited, who will allow:
 the document to be freely reproduced,
 the smallest extract to be a complete page including headers and footers but smaller extracts may be
reproduced in technical reports and papers, provided their origin is clearly referenced.

0027/ND REV 9

Page 2

GUIDELINES FOR MARINE LIFTING OPERATIONS

CONTENTS
SECTION
1
2
3
4

5

6

7

8

9

SUMMARY
INTRODUCTION
DEFINITIONS
THE APPROVAL PROCESS
4.1
GL NOBLE DENTON APPROVAL
4.2
CERTIFICATE OF APPROVAL
4.3
SCOPE OF WORK LEADING TO AN APPROVAL
4.4
APPROVAL OF MOORINGS
4.5
LIMITATION OF APPROVAL
LOAD AND SAFETY FACTORS
5.1
INTRODUCTION
5.2
WEIGHT CONTINGENCY FACTORS
5.3
HOOK LOADS
5.4
RIGGING GEOMETRY
5.5
LIFT POINT AND SLING LOADS
5.6
DYNAMIC AMPLIFICATION FACTORS
5.7
SKEW LOAD FACTOR (SKL)
5.8
2-HOOK LIFT FACTORS
5.9
LATERAL LIFT POINT LOAD
5.10
2-PART SLING FACTOR
5.11
TERMINATION EFFICIENCY FACTOR
5.12
BENDING EFFICIENCY FACTOR
5.13
SLING OR GROMMET SAFETY FACTORS
5.14
SHACKLE SAFETY FACTORS
5.15
GROMMETS
5.16
CONSEQUENCE FACTORS
THE CRANE AND CRANE VESSEL
6.1
HOOK LOAD
6.2
DOCUMENTATION
STRUCTURAL CALCULATIONS
7.1
LOAD CASES AND STRUCTURAL MODELLING
7.2
STRUCTURE
7.3
LIFT POINTS
7.4
SPREADER BARS OR FRAMES
7.5
ALLOWABLE STRESSES
LIFT POINT DESIGN
8.1
INTRODUCTION
8.2
SLING OVALISATION
8.3
PLATE ROLLING AND LOADING DIRECTION
8.4
PIN HOLES
8.5
CAST PADEARS AND WELDED TRUNNIONS
8.6
NON-DESTRUCTIVE TESTING
8.7
CHEEK PLATES
CLEARANCES
9.1
INTRODUCTION
9.2
CLEARANCES AROUND LIFTED OBJECT
9.3
CLEARANCES AROUND CRANE VESSEL
9.4
CLEARANCES AROUND MOORING LINES AND ANCHORS

0027/ND REV 9

PAGE NO.
5
6
9
13
13
13
14
14
15
16
16
18
18
18
19
19
20
21
21
21
22
22
22
23
23
23
24
24
24
25
25
25
25
25
25
27
27
27
27
27
27
27
28
29
29
29
29
30

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GUIDELINES FOR MARINE LIFTING OPERATIONS
10

11
12

BUMPERS AND GUIDES
10.1
INTRODUCTION
10.2
MODULE MOVEMENT
10.3
POSITION OF BUMPERS AND GUIDES
10.4
BUMPER AND GUIDE FORCES
10.5
DESIGN CONSIDERATIONS
PRACTICAL CONSIDERATIONS
INFORMATION REQUIRED FOR APPROVAL
12.1
GENERAL INFORMATION REQUIRED
12.2
THE STRUCTURE TO BE LIFTED
12.3
INDEPENDENT ANALYSIS
12.4
CODES AND SPECIFICATIONS
12.5
EVIDENCE OF SATISFACTORY CONSTRUCTION
12.6
RIGGING ARRANGEMENTS
12.7
THE CRANE VESSEL
12.8
PROCEDURES AND MANAGEMENT
12.9
SURVEYS

32
32
32
32
33
33
35
37
37
37
37
38
38
38
39
40
41

REFERENCES

42

FIGURES
Figure 5.1

Lift Calculation Flowchart

17

TABLES
Table 5-1
Table 5-2
Table 5-3
Table 5-4
Table 12-1

In Air Dynamic Amplification Factors (DAF)
Seastate Reduction Factor
Bending Efficiency Factors
Consequence Factors
Typically Required Surveys

19
20
22
23
41

0027/ND REV 9

Page 4

GUIDELINES FOR MARINE LIFTING OPERATIONS

1

SUMMARY

1.1

These guidelines have been developed for the design and approval of marine lifting operations.

1.2

This document supersedes the previous revision, document No. 0027/NDI Rev 8 dated 23 Jun 09.
The changes are described in Section 2.12.

1.3

These guidelines cover lifting operations by floating crane vessels, including crane barges, crane
ships, semi-submersible crane vessels and jack-up crane vessels. They may also be applied to lifting
operations by land-based cranes for the purpose of loadout. They are intended to lead to an approval
by GL Noble Denton, which may be required where an operation is the subject of an insurance
warranty, or where an independent third party review is required.

1.4

A description of the approval process is given for those projects which are the subject of an insurance
warranty.

1.5

The report includes guidelines for the load and safety factors to be applied at the design stage.

1.6

Comments on the practical aspects of the management of the operation are also offered.

0027/ND REV 9

Page 5

9

GUIDELINES FOR MARINE LIFTING OPERATIONS

2

INTRODUCTION

2.1

This document provides guidelines on which the design and approval of marine lifting operations may
be based.

2.2

It covers lifting operations by floating crane vessels, including crane barges, crane ships, semisubmersible crane vessels and jack-up crane vessels. It refers to lifting operations inshore and
offshore. Reference is also made to lifting operations by land-based cranes for the purpose of loadout
onto a barge or other transportation vessel.

2.3

The guidelines and calculation methods set out in this report represent the views of GL Noble Denton
and are considered to be sound and in accordance with offshore industry practice. Operators should
also consider national and local regulations, which may be more stringent.

2.4

The Report includes guidelines for the safety factors to be applied, comments on safe rigging practice
and the information and documentation to be produced by others in order to obtain GL Noble Denton
approval.

2.5

Revision 2 superseded and replaced the previous version, Revision 1, dated 11th August 1993.
Principal changes in Revision 2 included:


Reference to the ISO Draft Standard on weight control



Reserves specified on weights as calculated or measured according to the ISO/DIS



Limitations of GL Noble Denton Approval clarified



Changes to the required clearances on pipelines and other subsea assets



Addition to a section on heave-compensated lifts



Addition of a section on lifts using Dynamic Positioning.

2.6

Revision 3 superseded and replaced Revision 2, and includes additional clarification on safety factors
for shackles, and testing and certification requirements.

2.7

Revision 4 superseded and replaced Revision 3, and includes:

2.8



Changes to referenced documents (Sections 2.8 and References)



Some changes to definitions (Section 3)



Changes to Dynamic Amplification Factors, to eliminate discontinuities (Section 5.6)



Elimination of an anomaly in the definition of Hook Load (Section 5.3)



Inclusion of consideration of fibre slings (Sections 5.10, 5.15 and 12)



Elimination of an anomaly in the treatment of spreader bars and frames (Sections 5.16 and 7.4)



Modification of the flow chart (old Section 5.16)



Changes to the derivation of bumper and guide design forces (Section 10.3).

Revision 5 superseded and replaced Revision 4, and corrected typographical errors in Table 5-1.

0027/ND REV 9

Page 6

GUIDELINES FOR MARINE LIFTING OPERATIONS
2.9

Revision 6 superseded and replaces Revision 5, and made the following principal revisions,
highlighted by a line in the right hand margin:


The Guideline refers as appropriate to other standards, including

-

ISO International Standard ISO2408 - Steel wire ropes for General Purposes Characteristics [Ref. 4]
ISO International Standard ISO 7531 - Wire Rope slings for General Purposes Characteristics and Specifications [Ref.5].



Definitions in Section 3 were generally revised and expanded.



Section 4.1.2 added for the Certificate of Approval



Section 5 was re-ordered, Figure 5.1 revised, DAF's expanded to include submerged lifts,
guidelines for 1 crane-2 hook lifts added, yaw factor for inshore lifts deleted, use of alternative
codes added, minimum sling angles included



Old Section 11 (Underwater Lifting) moved into Section 5.6.6



Section 5.6.8 added for inshore lifts made by jack-up crane vessels.



Section 5.6.9 expanded to include weather forecast levels.



Section 5.7.6 added: SKL for multi hook lifts.



Table 5-4: consequence factors revised.



Section 5.12.6 added: sling eye design.



Sections 6.1.5 and 8.7 added.



Old Section 12 (Heave compensated lifts) moved to Section 6.1.5



Section 8.5 expanded to include trunnions and sling retainers.



Clearances in Section 9.3 generally updated and expanded.



Dimensional control requirements added to 10.3 and design requirements in Section 10.5.4.



Sections 9.2.6 - 9.2.8 added: bumper and guide clearances and dropped objects.



Limitation on number of chained shackles and shackle orientation added in Section 11.11.



Section 12 updated, showing requirements for sling certificates, doubled sling restrictions and
requirements for wire/sling type.



Old Section 13 (Lifts using DP) moved to Sections 12.7.1 and 12.8.9.



Sections 12.8.7 and 12.8.8 amended for in field environmental condition monitoring.



Section 12.8.10 added for risk assessments and HAZOPs



General text changes and revisions made.

2.10

Revision 7 superseded and replaced Revision 6. The changes are the removal of “by Floating Crane
Vessels” in the document title and a correction in Section 5.14.1.

2.11

Revision 8 superseded and replaced Revision 7. The change is a correction in Section 5.12.5.

0027/ND REV 9

Page 7

GUIDELINES FOR MARINE LIFTING OPERATIONS
2.12

2.13

This Revision 9 supersedes and replaces Revision 8. The changes are:


Definitions (Barge, IACS, Insurance Warranty, NDT, Survey, Vessel, Surveyor, Weather
Restricted Operation, and Weather Un-restricted Operations) in Section 3 revised.



Text modified in Section 4.1.4.



Weather forecast needs modified in Section 4.4.1.



Weight and CoG factor for piles added in Section 5.2.6.



CoG factor included for lifts not using a CoG envelope in Section 5.5.3.



DAF for lifts 100t to 1000t revised in Table 5-1.



Text added in Section 5.7.7 for 4 unequal slings in a single hook lift.



Factor for fibre rope sling splices included in Section 5.11.1.



Radius changed to diameter in Section 5.12.5.



Shackle MBL used instead of sling MBL in Section 5.14.2



Text amended in Sections 6.1.4, 8.4.1 and 11.7.h.



Clause added for tuggers attached to lift points in Section 7.3.3.



Clearances clarified in Sections 8.7.2 , 9.2.1.



Bumper force increased in Section 10.4.1.d.



Secondary bumper and guide forces added in Section 10.4.4.



Set down loads added in Section 10.4.3.



IACS member certification added in Sections 12.1.1 and 12.6.1.



Sling certificate validity added in Section 12.6.3.



Spreader bar/frame certification added in Sections 12.6.6 and 12.6.7.



Reference 6 added.



Mooring analysis requirements added to Sections 12.1.1 and 12.7.3 to 12.7.7.



Reference [7] added.

9

All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com.

0027/ND REV 9

Page 8

GUIDELINES FOR MARINE LIFTING OPERATIONS

3

DEFINITIONS

3.1

Referenced definitions are underlined.
Term or Acronym

Definition

Approval

The act, by the designated GL Noble Denton representative, of issuing
a Certificate of Approval

Barge

A non-propelled vessel commonly used to carry cargo or equipment.
(For the purposes of this document, the term Barge can be considered
to include Vessel or Ship where appropriate).

Cable-laid sling

A cable made up of 6 ropes laid up over a core rope, as shown in Ref.
[3], with terminations at each end.

Certificate of Approval

The formal document issued by GL Noble Denton when, in its
judgement and opinion, all reasonable checks, preparations and
precautions have been taken, and an operation may proceed.

CGBL /
Calculated Grommet
Breaking Load

The load at which a grommet will break, calculated in accordance with
one of the methods shown in Ref. [3].

Consequence Factor

A factor to ensure that main structural members, lift points and
spreader bars /frames have an increased factor of safety (including
lateral loads) related to the consequence of their failure.

Crane vessel

The vessel, ship or barge on which lifting equipment is mounted. For
the purposes of this report it is considered to include: crane barge,
crane ship, derrick barge, floating shear-leg, heavy lift vessel, semisubmersible crane vessel (SSCV) and jack-up crane vessel.

CRBL /
Calculated Rope
Breaking Load

The load at which a cable laid rope will break, calculated in accordance
with one of the methods shown in Ref. [3].

CSBL /
Calculated Sling
Breaking Load

The load at which a sling will break, calculated in accordance with one
of the methods shown in Ref. [3]. The breaking load for a sling takes
into account the ‘Termination Efficiency Factor’

DAF /
Dynamic Amplification
Factor

The factor by which the ‘gross weight’ is multiplied, to account for
accelerations and impacts during the lifting operation

Determinate lift

A lift where the slinging arrangement is such that the sling loads are
statically determinate, and are not significantly affected by minor
differences in sling length or elasticity

DP

Dynamic Positioning

EB /
Bending reduction factor

The reduction factor applied to the breaking load of a rope or cable to
take account of the reduction in strength caused by bending round a
shackle, trunnion or crane hook.

ET /
Termination efficiency
factor

The factor by which the breaking load of a wire or cable is multiplied to
take account of the reduction of breaking load caused by a splice or
mechanical termination.

FMEA

Failure Modes and Effects Analysis

0027/ND REV 9

Page 9

GUIDELINES FOR MARINE LIFTING OPERATIONS
Term or Acronym

Definition

GL Noble Denton

Any company within the GL Noble Denton Group including any
associated company which carries out the scope of work and issues a
‘Certificate of Approval’

Grommet

A grommet is comprised of a single length of unit rope laid up 6 times
over a core, as shown in Ref. [3] to form an endless loop

Gross weight

The calculated or weighed weight of the structure to be lifted including
a weight contingency factor and excluding lift rigging. See also NTE
weight.

Hook load

The hook load is the ‘gross weight’ or NTE weight plus the ‘rigging
weight’

IACS

International Association of Classification Societies

Indeterminate lift

Any lift where the sling loads are not statically determinate

Insurance Warranty

A clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent survey
house.

LAT

Lowest Astronomical Tide

Lift point

The connection between the ‘rigging’ and the ‘structure’ to be lifted.
May include ‘padear’, ‘padeye’ or ‘trunnion’

Loadin

The transfer of a major assembly or a module from a barge onto land
by horizontal movement or by lifting

Loadout

The transfer of a major assembly or a module from land onto a barge
by horizontal movement or by lifting

Matched pair of slings

A matched pair of slings are fabricated or designed so that the
difference does not exceed 0.5d, where d is the nominal diameter of
the sling or grommet, Ref [3]

MBL /
Minimum Breaking Load

The minimum allowable value of ‘breaking load’ for a particular sling or
grommet.

Mechanical Termination

A sling eye termination formed by use of a ferrule that is mechanically
swaged onto the rope, Ref. [4] and [5].

NDT

Non Destructive Testing

Nett weight

The calculated or weighed weight of a structure, with no contingency or
weighing allowance

NTE Weight

A Not To Exceed weight, sometimes used in projects to define the
maximum possible weight of a particular structure.

Operational reference
period

The planned duration of the operation, including a contingency period

Padear

A lift point consisting of a central member, which may be of tubular or
flat plate form, with horizontal trunnions round which a sling or grommet
may be passed

Padeye

A lift point consisting essentially of a plate, reinforced by cheek plates if
necessary, with a hole through which a shackle may be connected

Rigging

The slings, shackles and other devices including spreaders used to
connect the structure to be lifted to the crane

Rigging weight

The total weight of rigging, including slings, shackles and spreaders,
including contingency.

0027/ND REV 9

Page 10

GUIDELINES FOR MARINE LIFTING OPERATIONS
Term or Acronym

Definition

Rope

The unit rope from which a cable laid sling or grommet may be
constructed, made from either 6 or 8 strands around a steel core, as
indicated in Ref [3], [4] and [5]

Seafastenings

The system used to attach a structure to a barge or vessel for
transportation

Sling eye

A loop at each end of a sling, either formed by a splice or mechanical
termination

Single Laid Sling

A cable made up of 6 ropes laid up over a core rope, as shown in Ref.
[4] and [5], with terminations each end.

Sling breaking load

The breaking load of a ‘sling’, being the calculated breaking load
reduced by termination efficiency factor or bending reduction factor as
appropriate.

SLS

A design condition defined as a normal Serviceability Limit State /
normal operating case.

SKL /
Skew Load Factor

The factor by which the load on any lift point or pair of lift points and
rigging is multiplied to account for sling length mis-match in a statically
indeterminate lift

Splice

That length of sling where the rope is connected back into itself by
tucking the tails of the unit ropes back through the main body of the
rope, after forming the sling eye

Spreader bar (frame)

A spreader bar or frame is a structure designed to resist the
compression forces induced by angled slings, by altering the line of
action of the force on a lift point into a vertical plane. The structure
shall also resist bending moments due to geometry and tolerances.

Structure

The object to be lifted

Survey

Attendance and inspection by a GL Noble Denton representative.

Surveyor

The GL Noble Denton representative carrying out a ‘Survey’.
An employee of the fabrication or loadout contractor or Classification
Society performing, for instance, a dimensional, structural or Class
survey.

SWL /
Safe Working Load

See Working Load Limit (WLL).

Trunnion

A lift point consisting of a horizontal tubular cantilever, round which a
sling or grommet may be passed. An upending trunnion is used to
rotate a structure from horizontal to vertical, or vice versa, and the
trunnion forms a bearing round which the sling, grommet or another
structure will rotate.

ULS

A design condition defined as Ultimate Limit State / survival storm case.

Vessel

A marine craft designed for the purpose of transportation by sea.

Weather restricted
operation

A marine operation which can be completed within the limits of an
operational reference period with a favourable weather forecast
(generally less than 72 hours), taking contingencies into account. The
design environmental condition need not reflect the statistical extremes
for the area and season. A suitable factor should be applied between
the design weather conditions and the operational weather limits

0027/ND REV 9

Page 11

GUIDELINES FOR MARINE LIFTING OPERATIONS
Term or Acronym

Definition

Weather un-restricted
operation

An operation with an operational reference period generally greater
than 72 hours. The design environmental condition for such an
operation shall be set in accordance with extreme statistical data.

WLL /
Working Load Limit

The maximum load that rigging equipment is certified to raise, lower or
suspend

9-Part sling

A sling made from a single laid sling braided nine times with the single
laid sling eyes forming each eye of the 9-part sling.

50/50 weight estimate

The value representing the median value in the probability distribution
of weight

0027/ND REV 9

Page 12

GUIDELINES FOR MARINE LIFTING OPERATIONS

4

THE APPROVAL PROCESS

4.1

GL NOBLE DENTON APPROVAL

4.1.1

GL Noble Denton approval may be sought where the lift forms part of a marine operation covered by
an insurance warranty, or where an independent third party review is required.
The Certificate of Approval is the formal document issued by GL Noble Denton when, in its judgement
and opinion, all reasonable checks, preparations and precautions have been taken, and an operation
may proceed.
An Insurance Warranty is a clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent surveyor. The requirement is normally
satisfied by the issue of a Certificate of Approval. Responsibility for interpreting the terms of the
Warranty so that an appropriate scope of work can be defined rests with the client.
Approval may be given for such operations as:

Installation of liftable jackets

4.1.2

4.1.3

4.1.4

4.1.5

4.1.6



Hook-assisted installation of launched or lifted jackets



Installation of templates and other sub-sea equipment



Handling of piles



Installation of decks, topsides modules, bridges and flare towers/booms



Loadouts and Loadins.



Transfer of items between a transport barge and the deck of a crane vessel.

9

Lifts may be by a variety of crane configurations, including single cranes, two cranes on a single
vessel, two or more cranes on separate vessels, single crane multi-hook sheerleg vessels, cranes
mounted on jack-up vessels, or by one or more land based cranes.
GL Noble Denton approval may be given for the operation, including reviews of marine and
engineering calculations and procedures, and consideration of:

The actual and forecast weather conditions


The suitability and readiness of all equipment



The behaviour of the lifting vessel



Any site changes in procedures



The general conduct of the preparations for the operation.

4.2

CERTIFICATE OF APPROVAL

4.2.1

The deliverable of the approval process will generally be a Certificate of Approval. This will be issued
on site, immediately prior to the lift taking place.
For an offshore lift, the Certificate will normally be issued after lift rigging and tuggers have been
connected / inspected and prior to cutting the seafastenings on the transport barge or vessel.
Consideration shall be given where a partial seafastening removal is proposed to be carried out in
parallel with rigging up operations. The lifting operation will be deemed to have commenced when
seafastening cutting starts. The lift will be deemed to be completed when the load is landed in its final
position, and the crane(s) has been disconnected.
The Certificate confirming adequate preparation for an operation will normally be issued immediately
prior to the start of the operation, by the attending surveyor.

4.2.2

4.2.3

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS
4.3

SCOPE OF WORK LEADING TO AN APPROVAL

4.3.1

In order to issue a Certificate of Approval, GL Noble Denton will require to consider the following
topics:

The strength of the structure to be lifted, including the strength of the lift points.


The capacity of the crane, taking into account the radius at which the lift will take place, whether
the crane will be fixed or revolving and whether any down-rating is required for operations in a
specified design and operational seastate.



The capacity of the crane in the event that multiple hooks are used to suspend /upend a load.



The rigging arrangement, including slings, shackles and any spreader frames or beams, and
the certification of the rigging components.



The mooring arrangements for the crane vessel, as outlined in Section 4.4.



The limiting weather conditions proposed, and the anticipated behaviour of the crane vessel in
those conditions.



The arrangements for handling and mooring the transport barge or vessel alongside the crane
vessel.



The arrangements for cutting seafastenings prior to lifting.



The management structure for the operations and Management of Change procedures.



Risk assessments, HAZOP /HAZID studies carried out by Contractor involving all parties.



Simultaneous Marine Operations (SIMOPS).

4.3.2

The information required in order to issue a Certificate of Approval is discussed in more detail in
Section 12.

4.4

APPROVAL OF MOORINGS

4.4.1

A lift may normally be considered a weather restricted operation. Limiting weather conditions for the lift
operation shall be defined, taking into account:

the weather forecast reliability and frequency for the area


the duration of the operation, including a suitability contingency period



the exposure of the site



the time required for any operations before or after the lift operation, including crane vessel and
transport barge movements.



currents on the lifting vessel/transport barge during the lift.



currents on the lifted structure during lowering through the water column.

0027/ND REV 9

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9

GUIDELINES FOR MARINE LIFTING OPERATIONS
4.4.2

4.4.3

4.4.4

An approval of a lift will normally include the approval of the crane vessel and transport barge
moorings in the limiting weather conditions specified for the lifting operation. When operating
alongside an offshore installation, procedures should be submitted which show that the crane vessel
and transport barge can and will be removed to a safe distance when the weather conditions exceed a
specified level. An approval of a lift does not include approval of the vessel moorings in extreme
weather conditions).
Similarly, an approval of a lifted loadout will include the approval of the crane vessel and transport
barge moorings at the loadout quay in the limiting weather conditions specified for loadout. It does not
necessarily include approval of either moorings in extreme weather conditions. Note that for approval
of loadouts, reference should also be made to GL Noble Denton Report 0013/ND - Guidelines for
Loadouts Ref. [1].
Additionally, and if specifically requested, GL Noble Denton will study and issue an approval of the
moorings of the crane vessel or the transport barge, for a more extended period.

4.5

LIMITATION OF APPROVAL

4.5.1
4.5.2

A Certificate of Approval is issued for a particular lift only.
A Certificate of Approval is issued based on external conditions observed by the attending surveyor of
hull(s) machinery and equipment, without removal, exposure or testing of parts.
A Certificate of Approval for a lift covers the marine operations involved in the lift only. A lift is normally
deemed to start offshore when cutting of seafastenings starts, and after the crane is connected and
slings tensioned. It is normally deemed to be completed when the lifted object is set down in its
intended position. For completion of lifted loadouts see Ref. [1].
Unless specifically included, a Certificate of Approval for a lift excludes moorings of the crane vessel
and transport barge outside the period of the immediate lift, as defined in Section 4.4.2.
Any alterations to the surveyed items or agreed procedures after issue of the Certificate of Approval
may render the Certificate invalid unless the changes are approved in writing by GL Noble Denton.

4.5.3

4.5.4
4.5.5

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS

5

LOAD AND SAFETY FACTORS

5.1

INTRODUCTION

5.1.1

For any lift, the calculations carried out shall include allowances, safety factors, loads and load effects
as described in these guidelines.
The various factors and their application are illustrated in Figure 5.1. This flowchart is for guidance
only, and is not intended to cover every case. In case of any conflict between the flowchart and the
text, the text shall govern. Figures in parentheses relate to sections in these guidelines.
Use of other recognised offshore codes of practice relating to lift engineering can also be considered,
but care should be taken since not all other codes are exhaustive in determining the actual behaviour
of lifting systems.

5.1.2

5.1.3

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS
Figure 5.1








Lift Calculation Flowchart

OBTAIN
Crane data
Lift arrangement
Number of cranes & hooks
Structure gross weight
Lift point geometry
In air or submerged lift
Barge ballast data

Apply weight contingency factor [5.2]
Calculate lift point and sling loads [5.5]








DETERMINE LIFT FACTORS
DAF [5.6]
SKL factor [5.7]
Tilt factor (2-hook lift) [5.8]
Yaw factor (2-hook lift) [5.8]
CoG shift factor (2 hook lift) [5.8]
Minimum Sling angle [5.4]

CHECK HOOK LOAD
WITH CRANE
CAPACITY (STATIC &
DYNAMIC) AT THE
GIVEN RADIUS [6.1]

CALCULATE STATIC AND DYNAMIC
HOOK LOADS [5.3]

APPLY CONSEQUENCE
FACTORS FOR SPREADER
BAR & LIFT POINT DESIGN
CHECKS [5.16]

VERIFY GLOBAL
STRUCTURAL DESIGN OF
THE LIFTED STRUCTURE
[7]

VERIFY LIFT POINT AND
SPREADER BAR DESIGN
[7]

LIFT POINT &
SPREADER BAR OK

0027/ND REV 9

DETERMINE LATERAL
LIFT POINT LOAD [5.9]

REVIEW
 Installation clearances above &
below waterline [9]
 Bumper & guide design &
geometry [10]

DEFINE SLING / GROMMET
CRBL OR CGBL & SHACKLE
WLL REQUIRED [5.10 to 5.15]

IDENTIFY / REPORT
RIGGING UTILISATION
FACTORS & RIGGING
GEOMETRY

RIGGING OK

CRANE OK

Page 17

GUIDELINES FOR MARINE LIFTING OPERATIONS
5.2

WEIGHT CONTINGENCY FACTORS

5.2.1

Weight control shall be performed by means of a well defined, documented system, in accordance with
current good practice, such as ISO International Standard ISO 19901-5:2003 – Petroleum and natural
gas industries – specific requirements for offshore structures – Part 5: Weight control during
engineering and construction Ref. [2], in order to derive correct loads for the design of rigging and lift
points.
In relation to weight control classes, Reference [2] states (inter alia) that:

“Class A shall apply if the project is weight or CoG-sensitive for lifting and marine operations or
during operation (with the addition of temporaries) or has many contractors with which to
interface. Project may also require this high definition if risk gives cause for concern”.

5.2.2

5.2.3

5.2.4
5.2.5

5.2.6



“Class B weight control definition shall apply to projects where the focus on weight and CoG is
less critical for lifting and marine operations”.



“Class C weight control definition shall apply to projects where the requirement for weight and
CoG data are not critical”.

Unless it can be shown that a particular structure and specific lift operation are not weight or CoG
sensitive, then Class A weight control definition will be needed, as shown in Ref [2], Section 4.2. If the
50/50 weight estimate as defined in Ref. [2] is derived, then an appropriate weight contingency factor,
which shall be not less than 1.05, shall be applied to the Nett Weight. The extremes of the CoG
envelope (if used) shall be used.
For Class B and C structure lifts, the minimum weight contingency factor shall be 1.10 applied to the
Nett Weight for rigging and lift point design.
Except for piles, a weight contingency factor of not less than 1.03 shall generally be applied to the final
weighed weight. This may be reduced if a Certificate is produced from a Competent Body stating, for
the specific case in question, that the weighing accuracy is better than 3%.
The weight and CoG contingency factors for piles shall be determined considering the pile length and
plate thickness tolerances.

5.3

HOOK LOADS

5.3.1

In general, when considering the loading on a lift point or the structure, the hook load including
contingency should be used. Loads in lift points and slings, and the total loading on the crane should
be based on hook loads, where:
Static Hook load
= (gross weight or NTE weight) + (rigging weight)
Dynamic Hook load = Static Hook load x DAF

5.3.2
5.3.3

Rigging weight includes all items between the lift points and the crane hook, including slings, shackles
and spreaders as appropriate.
For twin hook lifts whether cranes are on the same vessel, or multiple vessels, or the structure is
suspended from two hooks on the same crane on the same vessel, the factors as described in Section
5.8 shall be used to derive individual hook loads.

5.4

RIGGING GEOMETRY

5.4.1

The rigging geometry shall normally be configured so that the maximum tilt of the structure does not
exceed 2 degrees.
In special circumstances (e.g. flare booms, flare towers and cantilevered modules) the design angle of
tilt may require to be greater than 2 degrees to permit the effective use of installation aids. These
structures shall be reviewed as special cases.

5.4.2

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GUIDELINES FOR MARINE LIFTING OPERATIONS
5.5

LIFT POINT AND SLING LOADS

5.5.1

5.5.6

The basic vertical lift point load is the load at a lift point, taking into account the structure gross weight
proportioned by the geometric distance of the centre of gravity from each of the lift points. The basic
lift point load is further increased by the factors as listed in Figure 5.1 as appropriate for the lifting
arrangement under consideration.
Where the allowable centre of gravity position is specified as a cruciform or other geometric envelope,
then the most conservative centre of gravity position within the envelope should be taken. Where a
CoG envelope is used, an additional factor of 1.03 should be added, to account for errors in the final
CoG location.
If a CoG envelope is not used then a CoG inaccuracy factor of 1.10 shall be applied to the weight.
The sling load is the vertical lift point load resolved by the sling angle to determine the direct (axial)
load in the sling and lift point using the minimum possible sling angle.
A minimum sling angle of sixty degrees is recommended, but a lower sling angle is possible, taking
due account of the forces on the lift points, the structure and the crane hook(s).
For lift point design, the rigging weight shall not form part of the lift point load.

5.6

DYNAMIC AMPLIFICATION FACTORS

5.6.1

Unless operation-specific calculations show otherwise, for lifts by a single crane in air, the DAF shall
be derived from the following Table.

5.5.2

5.5.3
5.5.4
5.5.5

Table 5-1
Gross weight, W
(tonnes)

5.6.2

5.6.3
5.6.4

5.6.5

9

In Air Dynamic Amplification Factors (DAF)
DAF
Offshore

Onshore

Floating
Inshore

Moving

Static

W ≤100

1.30

1.15

1.00

100 < W < 500

1.25

1.10

1.00

500 < W < 1,000

1.20

1.10

1.00

1,000 < W ≤ 2,500

1.15

1.05

1.00

2,500 < W < 10,000

1.10

1.05

1.00

9

The DAF as indicated in Table 5-1 above shall also apply to the following lift combinations of vessels,
cranes and locations:

For lifts by 2 cranes on the same vessel


For inshore lifts, in totally sheltered waters, by 2 or more vessels



For onshore lifts by 2 or more cranes



For offshore lifts by 2 or more hooks on the same crane boom

For offshore lifts by 2 or more vessels, the DAF shall be found by dynamic analysis.
For offshore lifts by 2 or more hooks on the same crane boom, total load on the crane boom structure
shall be documented, based on Table 5-1 DAF’s increased by 1.10 unless certified crane curves for
this specific application can be provided.
For onshore lifts, where the crane(s) may move horizontally, the “Moving” column of Table 5-1 shall
apply. The “Static” column shall only apply if there is no crane movement other than lifting or lowering.

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS
5.6.6

5.6.7

5.6.8
5.6.9

If any part of the lifting operation includes lifting or lowering through water, analyses shall be submitted,
which either:

Show how the total in-water lifting loads are derived, taking into account weight, buoyancy,
entrained mass, boom-tip velocities and accelerations, inertia and drag forces, or;


Calculate the dynamic sling and hook loads to document that slack slings do not occur and
provide limiting seastate data for the offshore operation.



Calculate slamming loads on the structure being lifted.



The dynamic analysis results for a submerged or partially submerged lift may restrict the
operability of an operation that is subject to the issue of a Certificate of Approval, depending on
the DAF used for rigging and structure design.

As an alternative to the DAF’s in Table 5-1, the DAF may be derived from a suitable calculation or
model test. Where the lift is from or onto a barge or vessel alongside the crane vessel, then the barge
or vessel motions must be taken into account as well as the crane boom-tip motions.
For lifts from floating barges/vessels made by Jack-up crane vessels at an inshore location the DAF as
indicated in Table 5-1 Inshore column shall apply.
Where a DAF is derived by calculation or model tests, the limiting operational seastate from this
analysis shall recognise the uncertainties in weather forecasts when determining critical operational
durations. Weather forecasting uncertainties can be mitigated by in-field wave monitoring and/or infield meteorologists. The limiting design seastate shall be reduced based on Table 5-2 below for
marine operations with an operational duration of 24 hours.
Table 5-2

Seastate Reduction Factor

Weather Forecast Provision

Reduction Factor

No specific forecast

0.50

One forecast

0.65

One forecast plus in-field wave monitoring (wave rider buoy)

0.70

One forecast plus in-field wave monitoring and offshore meteorologist

0.75

5.6.10

For marine operations with an operational duration less than 24 hours, special consideration (DAF
analysis results, water depth, lift vessel type/class, object form, rigging system, weather forecast
provision, exposure period, lowering procedure) shall be given to the reduction factors in Table 5-2.

5.7

SKEW LOAD FACTOR (SKL)

5.7.1

Skew load is a load distribution factor based on sling length manufacturing tolerances, rigging
arrangement and geometry, fabrication tolerances for lift points, sling elongation, and should be
considered for any rigging arrangement and structure (Section 7.1) that is not 100% determinate. A
significantly higher SKL factor may be required for new slings used together with existing slings as one
sling may exhibit more elongation than the others.
For indeterminate 4-sling lifts using matched pairs of slings, a Skew Load Factor (SKL) of 1.25 shall be
applied to each diagonally opposite pair of lift points in turn.
For determinate lifts the SKL may be taken to be 1.0, provided it can be demonstrated that sling length
errors do not significantly affect the load attitude or lift system geometry. The permitted length
tolerance on matched pairs of slings is defined according to Ref. [3].
For a lift system incorporating spreader bars using matched pairs of slings a SKL of 1.10 is applicable.
For a lift system incorporating a single spreader bar using matched pairs of slings a SKL of 1.05 is
applicable.

5.7.2
5.7.3

5.7.4
5.7.5

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS
5.7.6

5.7.7

For multi hook lifts where the hook elevation can be shown to be individually controlled, a lower skew
load factor than stated above may be applicable, subject to evaluation of sling length tolerances,
rigging arrangement and crane operating procedures.
For a single hook lift where four slings of un-equal length are used (i.e. not Matched Pairs), the skew
load factor shall be calculated by the designer (considering sling length tolerances and measured
lengths) and applied to the structure and lift system design accordingly. Where the calculated SKL is
less 1.25 (as required in Section 5.7.2), an SKL of 1.25 shall be applied.

5.8

2-HOOK LIFT FACTORS

5.8.1

For a 2-hook lift (hooks on the same vessel) the individual gross weight at each hook shall be
multiplied by the following factors, to account for increased loads due to the tolerances of the elevation
in the crane hooks:
Centre of gravity shift factor = 1.03
Tilt factor

= 1.03

Reduced factors to those defined above may be used, subject to supporting analyses, limiting seastate
criteria and installation procedure steps/controls.
5.8.2

For a 2-hook lift, with 2 slings to each hook, the load to each lift point shall be multiplied by a yaw
factor, to account for tolerances in lift radii of the 2 hooks:
Yaw factor
= 1.05
Yaw factors for 2-hook lifts with other rigging arrangements will require special consideration.

5.8.3
5.8.4

For 2 hook lifts where the crane hooks are located on separate vessels the factors in Sections 5.8.1
and 5.8.2 shall be applied for inshore lifts, and be subject to calculation for offshore lifts.
For 2 hook lifts where the hooks are on the same crane, the factors in Sections 5.8.1 and 5.8.2 shall
be applied.

5.9

LATERAL LIFT POINT LOAD

5.9.1

Provided the lift-point is correctly orientated with the sling direction, then a horizontal force equal to 5%
of the resolved lift point load shall be applied, acting through the centreline and along the axis of the
padeye pin-hole or trunnion /padear geometric centre.
If the lift point is not correctly orientated with the sling direction, then the computed forces acting
transverse to the major lift point axis of the pin-hole or trunnion /padear geometric centre shall be
added to the lateral lift point load as defined in Section 5.9.1 above.

5.9.2

5.10

2-PART SLING FACTOR

5.10.1

Where a 2-part sling or grommet passes over, round or through a shackle, trunnion, padear or crane
hook, other than at a termination, the total sling force shall be distributed into each part in the ratio
45:55 to account for frictional losses over the bend.
Where a 2-part sling or grommet passes over a rotating greased sheave on a trunnion the total sling
force shall be distributed into each part in the ratio 49:51 to account for the frictional losses over the
rotating sheave on the trunnion.

5.10.2

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GUIDELINES FOR MARINE LIFTING OPERATIONS
5.11

TERMINATION EFFICIENCY FACTOR

5.11.1

The breaking load of a sling ending in a termination shall be the calculated rope breaking load
multiplied by a factor as follows:

For hand splices, including fibre slings: 0.75


For resin sockets: 1.00



Swage fittings, e.g. “Superloop or Flemish Eye”: 1.00



Steel ferrules (mechanical termination): 0.80



Fibre rope sling splices: 0.90

9

Other methods of termination (i.e. 9-part slings) will require special consideration.

5.12

BENDING EFFICIENCY FACTOR

5.12.1

Where any wire rope sling or grommet is bent round a shackle, trunnion, padear or crane hook, the
breaking load shall be assumed to be the calculated breaking load multiplied by a bending efficiency
factor in accordance with Ref. [3]:
Bending efficiency factor = 1 - 0.5/( D/d),
where:

5.12.2

d

=

the sling or cable laid rope diameter

D

=

the minimum diameter over which the sling body, sling eye, or grommet is
bent.

For wire rope slings and grommets, this results in the bending efficiency factors detailed in the
following Table 5-3.
Table 5-3

5.12.3
5.12.4
5.12.5

5.12.6

Bending Efficiency Factors

D/d

<1.0

1.0

1.5

2.0

3.0

4.0

5.0

6.0

7.0

Factor

Not
Advised

0.50

0.59

0.65

0.71

0.75

0.78

0.80

0.81

For fibre rope slings, the bending efficiency may normally be taken as 1.00, provided the bending
diameter is not less than the minimum specified by the manufacturer.
It should be noted that termination and bending factors should not be applied simultaneously. The one
which results in the lower value of breaking load will govern, and should be used.
Under no circumstances should the sling or grommet body contact any surface where the diameter is
less than 1.0d to maintain the sling in good condition under load. Bending in way of splices shall be
avoided.
In certain circumstances, it will be necessary to check sling eye bending losses around a shackle or
trunnion, where the D/d ratio is less that 4.0.

5.13

SLING OR GROMMET SAFETY FACTORS

5.13.1

The minimum safety factor on sling or grommet breaking load shall be calculated after:

resolution of the load based on centre of gravity position and sling angle, and


5.13.2

consideration of the factors shown in Sections 5.2 to 5.12 as appropriate.

For steel slings and grommets the minimum safety factor shall be not less than 2.25.

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GUIDELINES FOR MARINE LIFTING OPERATIONS
5.13.3
5.13.4

For fibre slings and grommets the minimum safety factor shall be not less than 4.75.
Further safety factors shall be applied to the sling design based on termination and sling bending
efficiency and sling usage.

5.14

SHACKLE SAFETY FACTORS

5.14.1
5.14.2

The shackle WLL should not be less than the static sling load.
In addition to Section 5.14.1 above, the dynamic sling load (static sling load x DAF) shall not exceed
the shackle MBL divided by a safety factor equal to 3.0.
Where the shackle is at the lower end of the rigging, the weight of the rigging components above the
shackle, (including effects of the DAF and taking account of sling angle) may be deducted from the
shackle load.

5.14.3

5.15

GROMMETS

5.15.1

Grommets require special consideration, to ensure that the rope breaking load and bending efficiency
have been correctly taken into account. It is assumed that grommets are constructed and used in
accordance with Ref. [3].
The load in a grommet shall be distributed into each part in the ratio 45:55, as indicated by Section
5.10.
The core of a grommet should be discounted when computing breaking load. The breaking load of a
grommet is determined in accordance with Ref. [3].
The bending efficiency factors at each end of a grommet may differ, and the more severe value should
be taken. Bending efficiency is derived as in Section 5.12 where rope diameter is the single part
grommet diameter.
Bending in way of grommet butt and tuck positions shall be avoided. The location of the butt
connection shall be marked.

5.15.2
5.15.3
5.15.4

5.15.5

5.16

CONSEQUENCE FACTORS

5.16.1

The following consequence factors shall be further applied to the structure including lift points and the
lateral load effects on lift points, and their attachments into the structure:
Table 5-4

5.16.2

Consequence Factors

Lift points including spreader bars and frames

1.30

Attachments of lift points to structure

1.30

Members directly supporting or framing into the lift points

1.15

Other structural members

1.00

The consequence factors shown in Table 5-4 shall be applied based on the calculated lift point loads
after consideration of all the factors shown in Sections 5.2 through 5.10. If a partial load factor design
is used then the consequence factors in Table 5-4 shall also be applied to the partial load factors for
structural design. Consequence factors in Table 5-4 shall also be applied to lift point lateral loads.

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS

6

THE CRANE AND CRANE VESSEL

6.1

HOOK LOAD

6.1.1

The hook load shall be shown not to exceed the allowable crane capacity as taken from the loadradius curves. Crane curves are generally expressed as safe working loads or static capacities.
Information should be obtained to document this.
The allowable load-radius curves as presented may sometimes include a dynamic effect allowance. If
a suitable statement is received to this effect, the hook load may, for comparison with the load-radius
curves, be derived from the dynamic hook load as defined in Section 5.3.
Some crane curves specify different allowable load curves for different seastates. These may similarly
be taken to include dynamic effects. A seastate representing the probable limits for the operation
should be chosen, and the gross weight used.
If the DAF included in the crane curves differs from the operation-specific value derived from Section
5.6, then the allowable load should be adjusted accordingly but shall not exceed the certified crane
(SWL or WLL) load-radius curve.
Where heave compensated lifts are planned, then the following information on the crane or cranes
shall be obtained:

Crane technical description and operating procedures,

6.1.2

6.1.3

6.1.4

6.1.5



Load radius curves in heave compensated mode plus limiting seastates and boom slew angles,



Crane de-rating curves,



FMEA for the crane system,



DAF analysis in heave compensated mode



Verify engine room/deck mechanics maintenance logs

6.2

DOCUMENTATION

6.2.1

Where Approval is required, the documentation as stated in Section 12 shall be submitted.

0027/ND REV 9

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GUIDELINES FOR MARINE LIFTING OPERATIONS

7

STRUCTURAL CALCULATIONS

7.1

LOAD CASES AND STRUCTURAL MODELLING

7.1.1

Structural calculations, based on the load factors discussed above, shall include adequate loadcases
to justify the structure. For example, for an indeterminate, 4-point lift the following loadcases should
normally be considered:
a.
Base case, using gross or NTE weight, resolved to the lift points, but with no skew load factor.
b.

Gross or NTE weight, with skew load factor applied to one diagonal.

c.

Gross or NTE weight, with skew load factor applied to the other diagonal.

7.1.2

In all cases the correct or minimum sling angle and point of action, and any offset or torsional loading
imposed by the slings shall be considered.

7.2

STRUCTURE

7.2.1
7.2.2

The overall structure shall be analysed for the loadings shown in Section 7.1.
The primary supporting members shall be analysed using the most severe loading resulting from
Section 7.1, with a consequence factor applied (see Section 5.16).

7.3

LIFT POINTS

7.3.1

7.3.3

An analysis of the lift points and attachments to the structure shall be performed, using the most
severe load resulting from Section 7.1 and all the factors as appropriate from Section 5.
Where the lift point forms an integral part of the structural node, then the lift point calculations shall
also include the effects of loads imposed by the members framing into the lift point.
Where tugger lines are attached to lift points their effect shall be considered in the lift point design.

7.4

SPREADER BARS OR FRAMES

7.4.1

Spreader bars or frames, if used, should be similarly treated, with loadcases as above. A
consequence factor shall be applied to spreader bars and frames, in accordance with Section 5.16.

7.5

ALLOWABLE STRESSES

7.5.1

The structural strength of high quality structural steelwork with full material certification and NDT
inspection certificates showing appropriate levels of inspection shall be assessed using the
methodology of a recognised and applicable offshore code including the associated load and
resistance factors for LRFD codes or safety factors for ASD/WSD codes. Traditionally AISC and API
RP2A have also been considered a reference code - see Note 1 in Section 7.5.3 regarding its
applicability.
Except for sacrificial bumpers and guides, the loading shall be treated as a normal serviceability limit
state (SLS) / Normal operating case.

7.3.2

7.5.2

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GUIDELINES FOR MARINE LIFTING OPERATIONS
7.5.3

Infrequent load cases on sacrificial bumpers and guides should be treated as an ultimate limit state
(ULS)/Survival storm case. This does not apply to:

Steelwork subject to deterioration and/or limited initial NDT unless the condition of the entire
loadpath has been verified, for example the underdeck members of a barge or ship


Steelwork subject to NDT prior to elapse of the recommended cooling and waiting time as
defined by the Welding Procedure Specification (WPS) and NDT procedures. In cases where
this cannot be avoided by means of a suitable WPS, it may be necessary to impose a reduction
on the design/permissible seastate



Steelwork supporting sacrificial bumpers and guides



Spreader bars, lift points and primary steelwork of lifted items



Structures during a load-out.

Note: If the AISC 13th Edition is used, the allowables shall be compared against member stresses
determined using a load factor on both dead and live loads of no less than:

0027/ND REV 9

WSD Option

LRFD Option

SLS:

1.00

1.60

ULS:

0.75

1.20

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GUIDELINES FOR MARINE LIFTING OPERATIONS

8

LIFT POINT DESIGN

8.1

INTRODUCTION

8.1.1

In addition to the structural requirements shown in Sections 5 and 7, the following should be taken into
account in the lift point design:

8.2

SLING OVALISATION

8.2.1

Adequate clearance is required between cheek plates, shackle pins or inside trunnion keeper plates, to
allow for ovalisation under load. In general, the width available for the sling shall be not less than
(1.25D + 25mm), where D is nominal sling diameter. However, the practical aspects of the rigging and
de-rigging operations may demand a greater clearance than this.
For cast padears the geometry of the padear shall be configured to fully support and maintain the sling
geometry and shape under load.

8.2.2

8.3

PLATE ROLLING AND LOADING DIRECTION

8.3.1
8.3.2

In general, for fabricated lift points, the direction of loading should be in line with the plate rolling
direction. Lift point drawings should show the rolling direction.
Through thickness loading of lift points and their attachments to the structure should be avoided if
possible. If such loading cannot be avoided, the material used shall be documented to be free of
laminations, with a recognised through-thickness designation.

8.4

PIN HOLES

8.4.1

Pin-holes should be bored /reamed, and should be designed to suit the shackle proposed. The pin
hole diameter shall be 2mm or 3% larger than the diameter of the shackle pin, whichever is the
greater, up to a maximum of 6mm.

8.5

CAST PADEARS AND WELDED TRUNNIONS

8.5.1

Cast padears and trunnions shall be designed taking into account the following aspects:

The geometrical considerations as indicated in Section 8.2.


The stress analysis and finite element design process (modelling and load application).



Load paths, trunnion geometry and space and support for slings. And grommets



The manufacturing process and quality control.



Sling keeper plates shall be incorporated into the padear/trunnions design to prevent the loss of
sling or grommets during load application and lifting. These devices shall be proportioned to
allow easy rigging and de-rigging whilst being capable of supporting the weight of the sling
section during transportation.

8.6

NON-DESTRUCTIVE TESTING

8.6.1
8.6.2

The extent of NDT shall be submitted for review.
Where repeated use is to be made of a lift point, a procedure should be presented for re-inspection
after each lift.

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8.7

CHEEK PLATES

8.7.1

Individual cheek plate thicknesses shall not exceed 50% of the main plate thickness to maintain the
primacy of the main plate in load transfer to the structure, and to provide robustness to lateral loads.
Non-load bearing spacer plates may be used to centralise shackle pins, by effectively increasing the
padeye thickness. The diameter of the internal hole in such spacer plates shall be greater than the pin
hole diameter. Spacer plates, if used, shall provide a 20-30mm clearance to the inside width of the
shackle (i.e. 10 to 15mm each side).
Cheek plate welds shall be proportioned and designed with due regard to possible uneven bearing
across the padeye/cheek plate thickness due to combined nominal (5%) and actual lateral loads.

8.7.2

8.7.3

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9

CLEARANCES

9.1

INTRODUCTION

9.1.1

9.1.2

The required clearances will depend on the nature of the lift, the proposed limiting weather conditions,
the arrangement of bumpers and guides and the size and motion characteristics of the crane vessel
and the transport barge.
Subject to the above, for offshore lifts, the following clearances should normally be maintained at each
stage of the operation. Smaller clearances may be acceptable for inshore or onshore lifts. Clearances
are based on a level lift (no tilt) of each structure. Additional clearances may be required for structures
with a prescribed tilt.

9.2

CLEARANCES AROUND LIFTED OBJECT

9.2.1

3 metres between any part of the lifted object (including spreaders and lift points) and crane boom,
when the load is suspended.
3 metres vertical clearance between the underside of the lifted object and any other previously
installed structure, except in the immediate vicinity of the proposed landing area or installation aid
where 1.5m clearance shall be adequate.
5 metres between the lifted object and other structures on the same transport barge unless bumpers
and guides are used for lift-off.
3 metres horizontal clearance between the lifted object and any other previously installed structure,
unless purpose-built guides or bumpers are fitted.
3 metres remaining travel between travelling block and fixed block at maximum load elevation with the
lift vessel at LAT.
Where a structure is securely engaged within a bumper/guide or pin/bucket system, clearance
between the extremities of the structure and the host structure must be demonstrated to be positive,
considering the worst possible combinations of tilt. This may require dimensional control surveys to be
carried out on the host structure and the structure to be installed.
Lift arrangement drawings shall clearly show all clearances as defined above.
Clearances above for lifts by floating crane vessels onto floating structures (e.g. spars, FPSO’s) will
need special consideration. It is expected that these clearances will need to be larger than those
stated above, and is dependent on the transient motion of the floating structure and the lifting vessel.
Consideration should be given when lifting and overboarding structures over or in the vicinity of a
subsea asset to provide sufficient horizontal clearance for dropped objects.

9.2.2

9.2.3
9.2.4
9.2.5
9.2.6

9.2.7
9.2.8

9.2.9

9.3

CLEARANCES AROUND CRANE VESSEL

9.3.1

Where the crane vessel is moored adjacent to an existing fixed platform the following clearances
apply, for an intact mooring system:

3m between any part of the crane vessel/crane and the fixed platform on lifted structure;

9.3.2
9.3.3



5m between any part of the crane vessel hull extremity and the fixed platform or submerged lift;



10 m between any anchor line and the fixed platform.

Where the crane vessel is dynamically positioned in accordance with class 3 DP regulations, a 5m
nominal clearance between any part of the crane vessel and the fixed platform shall be maintained.
3m between crane vessel keel (including thrusters) and seabed, after taking account of tidal
conditions, vessel motions, increased draft and changed heel or trim during the lift.

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9.3.4

Clearances around the crane vessel either moored or dynamically positioned and any floating platform,
drilling rig or submersible, shall be determined as special cases based on the station keeping analysis
of the floating structure and the lifting vessel. Positioning equipment and procedures shall be defined
to maintain minimum clearances for specific operations and minimum durations.

9.4

CLEARANCES AROUND MOORING LINES AND ANCHORS

9.4.1

The clearances stated below are given as guidelines to good practice. The specific requirements and
clearances should be defined for each project and operation, taking into account particular
circumstances such as:

water depth

9.4.2
9.4.3
9.4.4

9.4.5
9.4.6

9.4.7

9.4.8
9.4.9
9.4.10
9.4.11

9.4.12

9.4.13



proximity of subsea assets



survey accuracy



the station keeping ability of the anchor handling vessel



seabed conditions



estimated anchor drag during embedment



single mooring line failure in the vessel stand-off position



the probable weather conditions during anchor installation.

Operators may have their own requirements which may differ from those stated below, and should
govern if more conservative.
Clearances should take into account the possible working and stand-off positions of the crane vessel.
Moorings should never be laid in such a way that they could be in contact with any subsea asset. This
may be relaxed when the subsea asset is a trenched pipeline, provided it can be demonstrated that the
mooring will not cause frictional damage or abrasion to coating systems.
Moorings shall never be run over the top of a subsea completion or wellhead.
Whenever an anchor is run out over a pipeline, flowline or umbilical, the anchor shall be securely
stowed on the deck of the anchor handling vessel. In circumstances where either gravity anchors or
closed stern tugs are used, and anchors cannot be stowed on deck, the anchors shall be double
secured through the additional use of a safety strap or similar.
The vertical clearance between any anchor line and any subsea asset should be not less than 20
metres in water depths exceeding 40 metres, and 50% of water depth in depths of less than 40 metres.
Anchor catenaries shall be presented indicating minimum and maximum tensions in order to
demonstrate that these clearances can be met.
Horizontal clearance between any mooring line and any structure other than a subsea asset should not
be less than 10 metres.
When an anchor is placed on the same side of a subsea asset as the crane vessel, it should not be
placed closer than 100 metres to the subsea asset.
When the subsea asset lies between the anchor and the crane vessel, the final anchor position should
be no less than 200 metres from the subsea asset.
During lifting operations, crossed mooring situations should be avoided wherever practical. Where
crossed moorings cannot be avoided, the separation between active catenaries should be no less than
30 metres in water depths exceeding 100 metres, and 30% of water depth in water depths less than
100 metres.
If any of the clearances specified in Sections 9.4.7 to 9.4.11 are impractical because of the mooring
configuration or seabed layout, a risk assessment shall be carried out and special precautions taken as
necessary.
Temporary lay-down of an anchor wire (but not chain) over a pipeline, umbilical, spool or cable may be
acceptable subject to all of the following being submitted to this office:

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GUIDELINES FOR MARINE LIFTING OPERATIONS
a.

Evidence that there is no other practicable anchor pattern that would avoid the lay-down.

b.

The status of a pipeline or spool (e.g. trenched, live, rock-dumped, on surface) and its contents
(e.g. oil, gas, water) and internal pressure.

c.

Procedures clearly stating the maximum duration that the anchor wire is in contact with the
pipeline, umbilical, spool or cable and the reason for the contact.

d.

Written evidence that the pipeline owner accepts the laying down of the anchor wire over the
pipeline, umbilical, spool or cable.

e.

Evidence that the anchor wire will be completely slack i.e. no variation in tension.

f.

Evidence that the seastate during the lay-down will be restricted to an acceptable value.

g.

Documentation demonstrating that the anchor wire or its weight will not overstress or damage
the coating on the pipeline, umbilical, spool or cable.

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10

BUMPERS AND GUIDES

10.1

INTRODUCTION

10.1.1

For module installation the arrangement and design philosophy for bumpers and guides shall be
submitted, where applicable. In general, bumpers and guides should be designed in accordance with
this Section taking into account of their use, configuration and geometry.

10.2

MODULE MOVEMENT

10.2.1

The maximum module movement during installation should be defined. In general the module motions
should be limited to:

Vertical movement:+ 0.75 m


Horizontal movement: + 1.50 m



Longitudinal tilt: 2 degrees



Transverse tilt: 2 degrees



Plan rotation: 3 degrees.

10.2.2

The plan rotation limit is only applicable prior to engagement on the bumper/guide or pin/bucket
system, and when the module is close to its final position or adjacent to another structure on a cargo
barge.

10.3

POSITION OF BUMPERS AND GUIDES

10.3.1

The position of bumpers and guides shall be determined taking into account acceptable support points
on the module.
Dimensional control reports shall be reviewed of the as-built bumper and guide system to ensure fit up
offshore.
Nominal clearances between bumpers/guides and pins/buckets shall be +/-25mm to account for
fabrication and installation tolerances. These may be reduced based on trial fits and/or a more
stringent dimensional control regime.

10.3.2
10.3.3

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10.4

BUMPER AND GUIDE FORCES

10.4.1

For offshore lifts, bumpers and guides should be designed to the following forces (where W = static
hook load):
a.
Vertical sliding bumpers
Horizontal force in plane of bumper:

0.10 x W

Horizontal (friction) force, out of plane of bumper:

0.05 x W

Vertical (friction) force:

0.01 x W

Forces in all 3 directions will be combined to establish the worst design case.
b.

Pin/bucket guides
Horizontal force on cone/end of pin:

0.05 x W

Vertical force on cone/end of pin:

0.10 x W

Horizontal force in any direction will be combined with the vertical force to establish the
worst design case.
c.

Horizontal “cow-horn” type bumpers with vertical guide
Horizontal force in any direction:

0.10 x W

Vertical (friction) force:

0.01 x W

Horizontal force in any direction will be combined with the vertical force to establish the worst
design case.
d.

10.4.2
10.4.3
10.4.4

Vertical “cow-horn” type guide with horizontal bumper
Horizontal force in any direction:

0.10 x W

Vertical force on inclined guide-face:

0.10 x W

Horizontal force in any direction will be combined with the vertical force to establish the worst design
case.
For inshore lifts under controlled conditions, bumpers and guides may be designed to 50% of the
forces shown in Section 10.4.1.
Bumpers and guides that are deemed to arrest secondary motions may be designed to 50% of the
forces shown in Section 10.4.

10.5

DESIGN CONSIDERATIONS

10.5.1

The connection into the module, and the members framing the bumper or guide location, should be at
least as strong as the bumper or guide.
The stiffness of bumper and guide members should be as low as possible, in order that they may
deflect appreciably without yielding.
Design of bumpers and guides should cater for easy sliding motion of the guide in contact with
bumper. Sloping members should be at an acute angle to the vertical. Ledges and sharp corners
should be avoided on areas of possible contact, and weld beads should be ground flush.

10.5.2
10.5.3

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10.5.4

With reference to Section 7.5.1, the strength of bumpers and guides that are deemed to be “sacrificial”
should be assessed to the ultimate limit state (ULS). The bumper and guide connection to the
supporting structure shall be assessed to the normal serviceability limit state (SLS).

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11

PRACTICAL CONSIDERATIONS

11.1

Adequate and safe access and working platforms should be provided for connection of slings,
particularly where connection or disconnection is required offshore or underwater.

11.2

Seafastening on the transport barge should be designed:


To minimise offshore cutting



To provide restraint after cutting



To allow lift off without fouling.

11.3

All cut lines should be clearly marked. Where a 2-stage lift is planned - e.g. barge to lift vessel, then lift
vessel to final position, involving 2 sets of cut lines, these should preferably be in different colours.

11.4

Adequate equipment must be available on the transport barge, including as appropriate:


Burning sets



Tuggers and lifting gear



Means of securing loose seafastening material



Lighting for night operations



Safety equipment for personnel.



Safe access to and from the transport barge.

11.5

All loose equipment, machinery, pipework and scaffolding shall be secured against movement during
the lift, and the weights and positions allowed for in the gross weight.

11.6

Prior to the start of the lift, a forecast of suitable weather shall be received, of a duration adequate to
complete the operation, with contingencies, and taking into account any subsequent critical marine
operations.

11.7

The sling laydown arrangement shall show that:

11.8

a.

The slinging arrangement is in accordance with acceptable good practice.

b.

Large diameter slings and grommets shall be painted with a white line along the length to
monitor twisting during handling and laydown.

c.

The slings are matched as accurately as possible, unless the rigging arrangement is
deliberately non-symmetrical to take account of centre of gravity offset, in which case matched
pairs of slings should normally be used. Where minor mismatch in sling length exists, the slings
should be arranged to minimise skew loads.

d.

The slings are adequately secured against barge motions, prior to the start of the lift.

e.

The slings will not foul obstructions such as walkways and handrails when lifted, and any
unavoidable obstructions are properly protected.

f.

The slings will not kink when lifted.

g.

After the lift the slings (and spreaders if used) can be safely laid down again, without damage.

h.

In the event that a single sling attached to a single lift point is planned, it should be doubled to
prevent the sling unwinding under load.

Slings with hand spliced terminations must be prevented from rotation.

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GUIDELINES FOR MARINE LIFTING OPERATIONS
11.9

No bending is allowed at or close to a termination.

11.10

It is permissible to shackle slings together end-to-end to increase the length. However, slings of
opposite lay should never be connected together.

11.11

It is permissible to increase the length of a sling by inserting an extra shackle or specifically designed
link plates. Any shackle to shackle connections should be bow-to-bow, not pin-to-pin or pin-to-bow so
that shackles remain centred under load and also the load take-up.

11.12

Crane vessel motions should be monitored in the period prior to the lift, to confirm that the dynamic
behaviour is acceptable, taking into account the weight and size of the lifted object, the clearances for
lifting off the transport barge, the hoisting speed, the clearances for installation and the installation
tolerances.

11.13

Transport barge motions should be similarly monitored prior to the start of the lift. The change in
attitude of the transport barge when the weight is removed should be taken into account.

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12

INFORMATION REQUIRED FOR APPROVAL

12.1

GENERAL INFORMATION REQUIRED

12.1.1

Where approval is required, a package shall be submitted to GL Noble Denton for review, consisting
of:
a.
Justification of weight and centre of gravity, by Weight Control Report or weighing report.
b.

Structural analysis report for structure to be lifted, including lift points and spreaders, as set out
in Section 7.

c.

Rigging arrangement package, showing sling geometry, computed sling loads, required
breaking loads, tabulation of slings and shackles proposed, certificates for slings and shackles.
This certificate shall be issued or endorsed by a body approved by an IACS member or other
recognised certification body accepted by GL Noble Denton. Crane details, including loadradius curve with lift superimposed, and details of vertical and horizontal clearances.

d.

Mooring arrangements, mooring analyses, anchor catenaries and anchor running procedures.

e.

The management structure and marine procedures.

f.

Site survey reports.

12.2

THE STRUCTURE TO BE LIFTED

12.2.1

Calculations shall be presented for the structure to be lifted, demonstrating its capacity to withstand,
without overstress, the loads imposed by the lift operation, with the load and safety factors stated in
Section 5, and the loadcases discussed in Section 7.
The calculation package shall present, as a minimum:
a.
Plans, elevations and sections showing main structural members

12.2.2

12.2.3

b.

The structural model. This should account for the proposed lifting geometry, including any
offset of the lift points

c.

The weight and centre of gravity

d.

The steel grades and properties

e.

The loadcases imposed

f.

The Codes used

g.

A tabulation of member and joint Unity Checks greater than 0.8

h.

Justification or proposal for redesign, for any members with a Unity Check in excess of 1.0.

i.

Copies of existing sling certificates planned to be used (consolidation and dimensional
conformity certificates). This certificate shall be issued or endorsed by a body approved by an
IACS member or other recognised certification body accepted by GL Noble Denton.

12.2.4

An analysis or equivalent justification shall be presented for all lift points, including padeyes, padears
and trunnions, to demonstrate that each lift point, and its attachment into the structure, is adequate for
the loads and factors set out in Sections 5 and 7.
A similar analysis shall be presented for spreader bars, beams and frames.

12.3

INDEPENDENT ANALYSIS

12.3.1

Alternatively, GL Noble Denton will, if instructed, perform an independent analysis of the structure to
be lifted, including the lift points, on receipt of the necessary information.

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12.4

CODES AND SPECIFICATIONS

12.4.1

For analysis of the structure to be lifted and the lift points, an accepted offshore structural design code
shall be used as described in Section 7.5.
Adequate specifications for material properties, construction, welding, casting, inspection and testing
shall be used.

12.4.2

12.5

EVIDENCE OF SATISFACTORY CONSTRUCTION
Confirmation shall be presented, from a Certifying Authority, Classification Society or similar, that the
structure including the lift points and their attachments has been constructed in accordance with the
drawings and specifications.

12.6

RIGGING ARRANGEMENTS

12.6.1

A proposal shall be presented showing:
a.
The proposed rigging geometry showing dimensions of the structure, centre of gravity position,
lift points, crane hook, sling lengths and angles, including shackle dimensions and "lost" length
around hook and trunnions.

12.6.2

12.6.3

12.6.4
12.6.5

b.

A computation of the sling and shackle loads and required breaking loads, taking into account
the factors set out in Section 5.

c.

A list of actual slings and shackles proposed, tabulating:



Sling/shackle identification number



Sling length and diameter



Rigging utilisation factor summaries



CSBL, CRBL for slings or CGBL for grommets,



SWL or WLL for shackles



Construction



Direction of lay



Wire grade and wire type (bright or galvanised).



Copies of inspection/test Certificates for all rigging components. These certificates shall be
Position on structure



issued or endorsed by a body approved by an IACS member for the certification of that type of
equipment.

Slings and grommets should be manufactured and inspected in accordance with the International
Marine Contractors Association Guidance on Cable laid slings and grommets Ref. [3], or similar
acceptable standard. A thorough examination shall be carried out as required by that document for all
rigging components whether new or existing.
Shackles manufactured by an industry-recognised manufacturer, shall be covered by a test certificate
not exceeding 6 months old, and if not new, a report of an inspection by a competent person since the
last lift. The lift shall be executed within the date validity of the sling certificate.
Where 9-part slings are proposed for use in a lifting system, certification of these slings shall be given
special consideration.
Where an existing sling has been used doubled and this sling shows a permanent kink, it shall not be
used in a single configuration.

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12.6.6

12.6.7

Where spreader bars or spreader frames are used in a lifting system, there shall either be a load test
certificate provided indicating the SWL or WLL, tested in accordance with ref [6], or an as-built dossier
provided with data as listed in Section 12.6.7.
Where spreader bars or spreader frames are not load tested an as-built fabrication dossier shall be
provided listing the following minimum information:
a.
Material certificates (3rd party endorsed),
b.

Welding consumables certificates,

c.

Weld procedures,

d.

NDT procedures,

e.

Welders and NDT operatives qualifications,

f.

Inspection and Test Plan (ITP) listing Hold Monitor and Witness points,

g.

3rd party fabrication release note,

h.

Technical queries/concession requests,

i.

As-built drawings,

j.

Design report.

9

12.7

THE CRANE VESSEL

12.7.1

Information shall be submitted on the crane vessel and the crane. This shall include, as appropriate:

Vessel general arrangement drawings and specification

12.7.2

12.7.3

12.7.4
12.7.5
12.7.6



Details of registry and class



Mooring system and anchors



Vessel station keeping procedures



DP operating and positioning procedures (as applicable) and station keeping analyses/rosettes



Vessel DP system FMEA



Operating and survival drafts



Crane specification and operating curves (including where necessary the dynamic crane
capacity / curve).



Details of any ballasting operations required during the lift.

The mooring arrangement for the operation and stand-off position shall be submitted. This should
include the lengths and specifications of all mooring wires and anchors, and a mooring plan showing
adequate horizontal clearances on all platforms, pipelines and any other seabed obstructions. An
elevation of the catenary for each mooring line, for upper and lower tension limits, shall demonstrate
adequate vertical clearance over pipelines and horizontal clearance to fixed installations and the
structure being lifted.
Mooring analyses shall be submitted based on the 10 year seasonal return data for the vessel in the
stand-off position, for moorings that are deployed for a period less than 30 days. The analysis shall
demonstrate that the mooring system is able to safely resist the environmental conditions, including
single line failure cases.
The mooring analysis shall also provide the limiting seastate for the crane vessel to remain in the
working position. The transient motions due to single line failure shall be considered.
Factors of safety shall meet the requirements of Ref. [7].
Anchors shall be selected with sufficient holding capacity for the soils expected based on the
geotechnical and geophysical data for the location.

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12.7.7

A site survey of the area encompassing the anchor pattern shall be provided to verify the location of all
subsea infrastructure with respect to the proposed vessel anchor patterns. The survey should
generally be carried out no less than 4 weeks prior to the start of installation.

12.8

PROCEDURES AND MANAGEMENT

12.8.1

Sufficient management and resources shall be provided to carry out the operation efficiently and
safely.
Quality, safety and environmental hazards shall be managed by a formal Quality Management system.
The management structure for the operation, including reporting and communication systems, and
links to safety and emergency services shall be demonstrated.
The anticipated timing and duration of each operation shall be submitted.
The arrangements for control, manoeuvring and mooring of barges and/or other craft alongside the
crane vessel shall be submitted.
A weather forecast from an approved source, predicting that conditions will be within the prescribed
limits, shall be received prior to the start of the operation, and at 12 hourly intervals thereafter, until the
operation is deemed complete, in accordance with Section 4.5.3.
In field monitoring of waves (height, direction and period) should be considered to enhance the 12
hourly forecast for each specific lift operation where a Certificate of Approval is required.
In field monitoring of currents (speed and direction) for subsea lifts in areas where it is known that high
currents exist in the water column should be considered to enhance the 12 hourly forecast where a
Certificate of Approval is required.
For marine operations that are planned to carried out in close proximity to fixed or moored installations,
appropriate risk assessments and vessel audits shall be carried out prior to issue of a certificate of
approval. This may include attendance at vessel annual DP trials and witnessing of in-field DP checks
that are scheduled for a specific marine operation.
Risk assessments, HAZOP/HAZID studies shall be carried out by the Contractor in the presence of the
Client, MWS and actual Contractor’s operational personnel. These studies shall be completed at an
early stage so that the findings can be incorporated into the operational procedures.

12.8.2
12.8.3
12.8.4
12.8.5
12.8.6

12.8.7
12.8.8

12.8.9

12.8.10

0027/ND REV 9

Page 40

9

GUIDELINES FOR MARINE LIFTING OPERATIONS
12.9

SURVEYS

12.9.1

Where GL Noble Denton approval is required the surveys shown in Table 12-1 will usually be needed:
Table 12-1

Typically Required Surveys

Survey

Time

Place

Sighting of inspection/test. certificates for
slings and shackles

Prior to departure of
structure from shore

GL ND / client's office or
fabrication yard

Sighting of inspection /test certificates or
release notes for lift points and attachments

Prior to departure of
structure from shore

GL ND / client's office or
fabrication yard.

Inspection of rigging laydown and
seafastening

Prior to departure of
structure from shore

Fabrication yard

Inspection of securing of loose items inside
module

Prior to departure of
structure from shore

Fabrication yard

Suitability survey of crane vessel, if required

Prior to start of marine
operations

As available

Inspection of preparations for lift, and issue
of Certificate of Approval

Immediately prior to
cutting seafastening

At lift site

Crane vessel mooring activities

Prior to start of marine
operations

At lift site

Crane vessel in field DP trials

Prior to start of marine
operations

At lift site

0027/ND REV 9

Page 41

GUIDELINES FOR MARINE LIFTING OPERATIONS

REFERENCES
[1]

GL Noble Denton Report 0013/ND - Guidelines for Loadouts.

[2]

ISO International Standard ISO 19901-5:2003 – Petroleum and natural gas industries – specific requirements
for offshore structures – Part 5: Weight control during engineering and construction.

[3]

The International Marine Contractors Association - Guidance on the Use of Cable Laid Slings and Grommets IMCA M 179 August 2005.

[4]

ISO International Standard ISO2408 - Steel wire ropes for General Purposes - Characteristics

[5]

ISO International Standard ISO 7531 - Wire Rope slings for General Purposes - Characteristics and
Specifications.

[6]

Lloyds Register - Code for Lifting Appliances in a Marine Environment

[7]

GL Noble Denton Report 0032/ND - Guidelines for Moorings

9

All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com.

0027/ND REV 9

Page 42

TECHNICAL POLICY BOARD
GUIDELINES FOR MARINE TRANSPORTATIONS

0030/ND

Once downloaded this document becomes UNCONTROLLED.
Please check the website below for the current version.

31 Mar 10

4

RLJ

Technical Policy Board

15 Apr 09

3

RLJ

Technical Policy Board

1 Apr 05

2

JR

Technical Policy Board

22 Sep04

1

RJP

Technical Policy Board

18 May 04

0

JR

Technical Policy Board

DATE

REVISION

PREPARED BY

AUTHORISED BY

www.gl-nobledenton.com

GUIDELINES FOR MARINE TRANSPORTATIONS

PREFACE
This document has been drawn with care to address what are likely to be the main concerns based on the
experience of the GL Noble Denton organisation. This should not, however, be taken to mean that this document
deals comprehensively with all of the concerns which will need to be addressed or even, where a particular matter is
addressed, that this document sets out the definitive view of the organisation for all situations. In using this
document, it should be treated as giving guidelines for sound and prudent practice on which our advice should be
based, but guidelines should be reviewed in each particular case by the responsible person in each project to ensure
that the particular circumstances of that project are addressed in a way which is adequate and appropriate to ensure
that the overall advice given is sound and comprehensive.
Whilst great care and reasonable precaution has been taken in the preparation of this document to ensure that the
content is correct and error free, no responsibility or liability can be accepted by GL Noble Denton for any damage or
loss incurred resulting from the use of the information contained herein.

© 2010 Noble Denton Group Limited, who will allow:



the document to be freely reproduced,
the smallest extract to be a complete page including headers and footers but smaller extracts may be
reproduced in technical reports and papers, provided their origin is clearly referenced.

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

CONTENTS
SECTION
1

2
3
4

5

6

7

PAGE NO.

SUMMARY
1.1
CONTENT AND SCOPE
1.2
THE APPROVAL PROCESS
1.3
DOCUMENTATION
1.4
METEOROLOGICAL CONDITIONS, VESSEL MOTIONS & LOADINGS, & SEAFASTENING
DESIGN
1.5
STABILITY
1.6
BARGE, TRANSPORT VESSEL & TUG SELECTION, TOWING EQUIPMENT, MANNED TOWS
1.7
PLANNING & CONDUCT OF THE TOWAGE OR VOYAGE
1.8
MULTIPLE TOWAGES
1.9
SPECIAL CONSIDERATIONS
INTRODUCTION
DEFINITIONS & ABBREVIATIONS
THE APPROVAL PROCESS
4.1
GENERAL
4.2
GL NOBLE DENTON APPROVAL
4.4
CERTIFICATE OF APPROVAL
4.5
SCOPE OF WORK LEADING TO AN APPROVAL
4.6
LIMITATION OF APPROVAL
CERTIFICATION AND DOCUMENTATION
5.1
GENERAL
5.2
DOCUMENTATION DESCRIPTION
5.3
ICE CLASS
5.4
TRANSPORTATION OR TOWING MANUAL
5.5
REQUIRED DOCUMENTATION
DESIGN ENVIRONMENTAL CONDITIONS
6.1
INTRODUCTION
6.2
OPERATIONAL REFERENCE PERIOD
6.3
WEATHER-RESTRICTED OPERATIONS
6.4
UNRESTRICTED OPERATIONS
6.5
CALCULATION OF “ADJUSTED” DESIGN EXTREMES, UNRESTRICTED OPERATIONS
6.6
CALCULATION OF EXPOSURE
6.7
CALCULATION OF VOYAGE SPEED
6.8
CALCULATION OF EXTREMES
6.9
COMPARISON WITH PERCENTAGE EXCEEDENCE
6.10
CRITERIA FROM TRANSPORT SIMULATIONS
6.11
METOCEAN DATABASE BIAS
6.12
DESIGN WAVE HEIGHT
6.13
DESIGN WIND SPEED
6.14
METOCEAN DATA FOR BOLLARD PULL REQUIREMENTS
MOTION RESPONSE
7.1
GENERAL
7.2
SEASTATE
7.3
PERIODS
7.4
VESSEL HEADING AND SPEED
7.5
THE EFFECTS OF FREE SURFACES
7.6
THE EFFECTS OF CARGO IMMERSION
7.7
MOTION RESPONSE COMPUTER PROGRAMS
7.8
RESULTS OF MODEL TESTS
7.9
DEFAULT MOTION CRITERIA

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7.10
DIRECTIONALITY AND HEADING CONTROL
LOADINGS
8.1
INTRODUCTION
8.2
LOADCASES
8.3
DEFAULT MOTION CRITERIA
8.4
LONGITUDINAL BENDING
8.5
CARGO BUOYANCY AND WAVE SLAM
DESIGN AND STRENGTH
9.1
COMPUTATION OF LOADS
9.2
FRICTION
9.3
SEAFASTENING DESIGN
9.4
CRIBBING
9.5
STRESS LEVELS IN CARGO, GRILLAGE & SEAFASTENINGS
9.6
SECURING OF PIPE AND OTHER TUBULAR GOODS
9.7
INSPECTION OF WELDING AND SEAFASTENINGS
9.8
FATIGUE
9.9
USE OF SECOND HAND STEEL SEAFASTENINGS
STABILITY
10.1
INTACT STABILITY
10.2
DAMAGE STABILITY
10.3
WIND OVERTURNING
10.4
DRAUGHT AND TRIM
10.5
COMPARTMENTATION AND WATERTIGHT INTEGRITY
TRANSPORT VESSEL SELECTION
11.1
GENERAL
11.2
SUITABILITY AND ON-HIRE SURVEYS
TOWING VESSEL SELECTION AND APPROVAL
12.1
GENERAL
12.2
BOLLARD PULL REQUIREMENTS
12.3
MAIN & SPARE TOWING WIRES & TOWING CONNECTIONS
12.4
TAILGATES / STERN RAILS
12.5
TOWLINE CONTROL
12.6
WORKBOAT
12.7
COMMUNICATION EQUIPMENT
12.8
NAVIGATIONAL EQUIPMENT
12.9
SEARCHLIGHT
12.10 PUMP
12.11 ADDITIONAL EQUIPMENT
12.12 BUNKERS & OTHER CONSUMABLES
12.13 TUG MANNING
TOWING & MISCELLANEOUS EQUIPMENT ON TOW
13.1
TOWING EQUIPMENT & ARRANGEMENTS - GENERAL
13.2
STRENGTH OF TOWLINE & TOWLINE CONNECTIONS
13.3
RELATIONSHIP BETWEEN TOWLINE LENGTH AND STRENGTH
13.4
TOWLINE CONNECTION POINTS
13.5
BRIDLE LEGS
13.6
BRIDLE APEX
13.7
SHACKLES
13.8
INTERMEDIATE PENNANT OR SURGE CHAINS
13.9
SYNTHETIC SPRINGS
13.10 BRIDLE RECOVERY SYSTEM
13.11 EMERGENCY TOWING GEAR
13.12 CERTIFICATION
13.13 NAVIGATION LIGHTS & SHAPES
13.14 ACCESS TO TOWS

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14

15

16

17

18

13.15 ANCHORING & MOORING EQUIPMENT
13.16 DAMAGE CONTROL & EMERGENCY EQUIPMENT
VOYAGE PLANNING
14.1
GENERAL
14.2
PLANNING
14.3
ROUTEING
14.4
WEATHER ROUTEING & FORECASTING
14.5
DEPARTURE
14.6
PORTS OF SHELTER, SHELTER AREAS, HOLDING AREAS
14.7
BUNKERING
14.8
ASSISTING TUGS
14.9
PILOTAGE
14.10 LOG
14.11 INSPECTIONS DURING THE TOWAGE OR VOYAGE
14.12 REDUCING EXCESSIVE MOVEMENT & THE SHIPPING OF WATER
14.13 NOTIFICATION
14.14 DIVERSIONS
14.15 RESPONSIBILITY
14.16 TUG CHANGE
14.17 HAZARDOUS MATERIALS
14.18 BALLAST WATER
14.19 RESTRICTED DEPTHS, HEIGHTS & MANOEUVRABILITY
14.20 UNDER-KEEL CLEARANCES
14.21 AIR DRAUGHT
14.22 CHANNEL WIDTH & RESTRICTED MANOEUVRABILITY
PUMPING AND SOUNDING
15.1
GENERAL
15.2
PURPOSE OF PUMPS
15.3
PUMPING SYSTEM
15.4
PUMP TYPE
15.5
PUMP CAPACITY
15.6
WATERTIGHT MANHOLES
15.7
SOUNDING PLUGS AND TAPES
15.8
VENTS
ANCHORS AND MOORING ARRANGEMENTS
16.1
EMERGENCY ANCHORS
16.2
SIZE AND TYPE OF ANCHOR
16.3
ANCHOR CABLE LENGTH
16.4
ANCHOR CABLE STRENGTH
16.5
ATTACHMENT OF CABLE
16.6
ANCHOR MOUNTING AND RELEASE
16.7
MOORING ARRANGEMENTS
MANNED TOWS AND TRANSPORTATIONS
17.1
GENERAL
17.2
INTERNATIONAL REGULATIONS
17.3
RIDING CREW CARRIED ON THE CARGO
17.4
SAFETY AND EMERGENCY EQUIPMENT
17.5
MANNED ROUTINE
MULTIPLE TOWAGES
18.1
DEFINITIONS
18.2
GENERAL
18.3
DOUBLE TOWS
18.4
TANDEM TOWS
18.5
PARALLEL TOWS
18.6
TWO TUGS (IN SERIES) TOWING ONE TOW

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21

22

18.7
MULTIPLE TUGS TO ONE TOW
82
SPECIAL CONSIDERATIONS FOR THE TRANSPORT OF JACK-UPS
83
19.1
GENERAL
83
19.2
MOTION RESPONSES
83
19.3
LOADINGS
83
19.4
HULL STRENGTH
83
19.5
STRESS LEVELS
84
19.6
STABILITY AND WATERTIGHT INTEGRITY
84
19.7
TUGS, TOWLINES AND TOWING CONNECTIONS
85
19.8
SECURING OF LEGS
85
19.9
DRILLING DERRICK, SUBSTRUCTURE AND CANTILEVER
85
19.10 HELIDECK
86
19.11 SECURING OF EQUIPMENT AND SOLID VARIABLE LOAD
86
19.12 SPUD CANS
86
19.13 PUMPING ARRANGEMENTS
87
19.14 MANNING
87
19.15 PROTECTION OF MACHINERY
87
19.16 ANCHORS
87
19.17 SAFETY EQUIPMENT
87
19.18 CONTINGENCY STAND-BY LOCATIONS
87
SPECIAL CONSIDERATIONS FOR THE TOWAGE OF SHIPS
88
20.1
GENERAL CONSIDERATIONS
88
20.2
TUG SELECTION
89
20.3
TOWLINES AND TOWING CONNECTIONS
89
20.4
STABILITY, DRAUGHT AND TRIM
90
20.5
COMPARTMENTATION AND WATERTIGHT INTEGRITY
90
20.6
ANCHORS
90
20.7
SECURING OF EQUIPMENT AND MOVEABLE ITEMS
90
20.8
EMERGENCY PUMPING
91
20.9
CARRIAGE OF CARGO
91
SPECIAL CONSIDERATIONS FOR THE TOWAGE OF FPSOS
92
21.1
GENERAL AND BACKGROUND
92
21.2
THE ROUTE AND WEATHER CONDITIONS
92
21.3
STRUCTURAL ISSUES
92
21.4
TUG SELECTION
93
21.5
BALLAST, TRIM AND DIRECTIONAL STABILITY
93
21.6
TOWING EQUIPMENT
94
21.7
SELF-PROPELLED OR THRUSTER-ASSISTED VESSELS
94
21.8
MANNING AND CERTIFICATION
94
21.9
EMERGENCY ANCHOR
94
21.10 MOORINGS & UNDER KEEL CLEARANCE
95
SPECIAL CONSIDERATIONS FOR THE TOWAGE OF VESSELS AND STRUCTURES IN ICE COVERED
WATERS
96
22.1
GENERAL
96
22.2
VESSEL ICE CLASSIFICATION
97
22.3
TOWAGE WITHOUT INDEPENDENT ICEBREAKER ESCORT
98
22.4
TOWAGE OPERATIONS WITH INDEPENDENT ICEBREAKER ESCORT
99
22.5
MANNING
100
22.6
MULTIPLE TOWS AND MULTI-TUG TOWS
100
22.7
TOWING EQUIPMENT
101
22.8
TUG SUITABILITY
104
22.9
CARGO LOADINGS
104
22.10 SEA-FASTENING DESIGN AND STRENGTH
104
22.11 STABILITY
104
22.12 BALLASTING
105

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GUIDELINES FOR MARINE TRANSPORTATIONS

23

22.13 VOYAGE PLANNING
22.14 WEATHER /ICE RESTRICTED OPERATIONS
22.15 DAMAGE CONTROL AND EMERGENCY EQUIPMENT
SPECIAL CONSIDERATIONS FOR CASPIAN SEA TOWAGES
23.1
BACKGROUND
23.2
REQUIREMENTS WITHIN NORTHERN CASPIAN SEA
23.3
REQUIREMENTS FOR REMAINING CASPIAN SEA AREAS
23.4
REQUIREMENTS FOR TOWAGES BETWEEEN CASPIAN SEA AREAS

105
106
107
108
108
109
110
110

REFERENCES

111

APPENDIX A - EXAMPLE OF MAIN TOW BRIDLE WITH RECOVERY SYSTEM
APPENDIX B - EXAMPLE OF EMERGENCY TOWING GEAR
APPENDIX C - EXAMPLE OF SMIT-TYPE CLENCH PLATE
APPENDIX D - EMERGENCY ANCHOR MOUNTING ON A BILLBOARD
APPENDIX E - ALTERNATIVES TO THE PROVISION & USE OF AN EMERGENCY ANCHOR
APPENDIX F - FILLET WELD STRESS CHECKING
APPENDIX G - TRANSPORTATION OR TOWING MANUAL CONTENTS

112
113
114
115
116
118
122

TABLES
Table 5-1
Table 5-2
Table 7-1
Table 7-2
Table 7-3
Table 9-1
Table 9-2
Table 10-1
Table 10-2
Table 12-1
Table 12-2
Table 12-3
Table 12-4
Table 13-1
Table 13-2
Table 13-3
Table 22-1
Table 22-2
Table 22-3
Table 22-4

Principal Documentation
Required Documentation
Value of JONSWAP γ, ratio of Tp:Tz and Tp:T1 for each integer value of K
Default Motion Criteria
Reduced Seastate v Heading
Maximum allowable coefficients of friction & minimum seafastening forces
Typical Friction Coefficients
Intact Stability Range
Minimum draught & trim
Towing Vessel Categories
Meteorological Criteria for Calculating TPR (Towline Pull Required)
Values of Tug Efficiency, Te
Selecting Bollard Pull from TPR for Hsig = 5 m
Minimum Towline Breaking Loads (MBL)
Fairlead Resolved ULC
Default Shackle SWL
Polar Class Descriptions
Previous Icebreaker Classifications
Previous Vessel Ice Classifications
Minimum Towline MBL in Ice

23
26
33
35
37
41
45
48
51
54
55
56
57
61
62
64
97
97
98
101

FIGURES
Figure 10-1
Figure 10-2
Figure 12-1
Figure 12-2
Figure 13-1
Figure 23-1

Wind Overturning Criteria (Intact Case)
Wind Overturning Criteria (Damaged Case)
Tug efficiencies in different sea states
Effective Bollard Pull in Different Sea States
Definition of angle  with and without a bridle
Northern Caspian Sea areas

50
50
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57
62
108

Figure F.1
Figure F.2
Figure F.3
Figure F.4

Effective Throat Dimension ‘a’ for concave and Convex Fillet Welds
Normal and Shear Stresses acting on the plane of Weld Throat
Bracket connected by double Fillet Weld
Stresses and Forces acting on Fillet Weld

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GUIDELINES FOR MARINE TRANSPORTATIONS

1

SUMMARY

1.1

CONTENT AND SCOPE

1.1.1

These guidelines will be used by GL Noble Denton for approval of specialised marine transportations,
including:
a.
Cargoes on ships or towed barges
b.

Towage of self-floating marine and oilfield equipment, civil engineering structures and ships

but are not normally intended to apply to “standard” cargoes such as bulk liquids, bulk solids,
refrigerated cargoes, vehicles or containers.
1.1.2
1.1.3

1.1.4

1.1.5

This Revision 4 includes changes described in Section 2.7.
It should be noted that this document cannot cover every case of all transportation types. The reader
should satisfy himself that the guidelines used are fit for purpose for the actual transportation under
consideration.
In general, in addition to compliance with these Guidelines, towing operations should comply with the
mandatory parts of relevant IMO documents. The approval of any transportation by GL Noble Denton
does not imply that approval by any other involved parties would be given. These Guidelines are
intended to ensure the safety of the transported equipment. They do not specifically apply to the
safety of personnel or protection of the environment, for which more stringent guidelines may be
appropriate.
These Guidelines are not intended to exclude alternative methods, new technology and new
equipment, provided an equivalent level of safety can be demonstrated.

1.2

THE APPROVAL PROCESS

1.2.1

A description of the Approval Process is included, for projects where GL Noble Denton is acting as a
Warranty Surveyor. The extent and limitations of the approval given are discussed.

1.3

DOCUMENTATION

1.3.1

The documents and certificates which are expected to be possessed or obtained for differing
operations/equipment are described and tabulated.

1.4

METEOROLOGICAL CONDITIONS, VESSEL MOTIONS & LOADINGS, & SEAFASTENING
DESIGN

1.4.1

Guidelines are presented for determining the design meteorological conditions, for differing operational
durations and exposures.
Alternative means of computing vessel motions are given, as are default motion criteria.
Methods of deriving the loadings resulting from vessel motions are stated.
Considerations are given for the design of grillage and seafastenings, and assessing the strength of
the cargo.

1.4.2
1.4.3
1.4.4

1.5

STABILITY

1.5.1

Guidelines for intact and damage stability are presented, with reference to International Codes where
appropriate.

0030/ND REV 4

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4

GUIDELINES FOR MARINE TRANSPORTATIONS
1.6

BARGE, TRANSPORT VESSEL & TUG SELECTION, TOWING EQUIPMENT, MANNED
TOWS

1.6.1
1.6.2
1.6.3

Considerations in the selection of a suitable transport barge or vessel are listed.
Tug specification, bollard pull requirements and equipment are stated.
Towing and miscellaneous equipment to be provided on the tow is also stated, including pumping
systems, anchoring and mooring systems.
Reasons for manning a tow in certain circumstances are discussed, and the equipment and
precautions to be taken in the event of manning.

1.6.4

1.7

PLANNING & CONDUCT OF THE TOWAGE OR VOYAGE

1.7.1

The planning and conduct of the towage or voyage are discussed in Section 14.

1.8

MULTIPLE TOWAGES

1.8.1

The different types of multiple towages are defined in Section 18, and the practical problems and
acceptability of each are discussed.

1.9

SPECIAL CONSIDERATIONS
Special considerations are given for:
a.

Transport or towage of jack-ups in Section 19.

b.

Towage of ships, including demolition towages in Section 20.

c.

Towage of FPSOs and similar vessels in Section 21.

d.

Towages of vessels and structures in ice covered waters in Section 22.

e.

Towages in the Caspian Sea in Section 23.

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

2

INTRODUCTION

2.1

This document describes the guidelines for approval of specialised marine transportations, including:
a.

Transportation of cargoes on towed barges

b.

Transportation of specialised cargoes on ships

c.

Transportation of specialised cargoes on submersible, heavy lift vessels

d.

Towage of ships including demolition towages

e.

Towages of self-floating marine and oilfield equipment such as mobile offshore drilling units
(MODUs), self floating jackets, floating docks, dredgers, crane vessels and Floating Production
Storage and Offload vessels (FPSOs)

f.

One-off towages of self-floating civil engineering structures such as caissons, power plants,
bridge components and submerged tube tunnel sections.

2.2

Where GL Noble Denton is acting as a consultant rather than a Warranty Surveyor, these Guidelines
may be applied, as a guide to good practice.

2.3

These Guidelines are not intended to be applicable to “standard” cargoes such as bulk liquids, bulk
solids, refrigerated cargoes, vehicles or containers.

2.4

The document refers to other GL Noble Denton guidelines as appropriate.

2.5

Revision 2 included an additional Section 22, relating to towages in ice covered waters. It also
superseded and replaced earlier Noble Denton guidelines:

2.6

a.

Guidelines for the transportation of specialised cargoes on ships and heavy transport vessels 0007/NDI

b.

Self-elevating platforms - guidelines for operations and towages (towage section only) 0009/ND [Ref. 1]

c.

Guidelines for Marine Transportations - 0014/NDI

d.

Guidelines for the Towage of Ships - 0026/NDI.

Revision 3 superseded Revision 2, and included:
a.

Modification of spectra definition in Section 7.3.5.

b.

Clarification of forward speed for motion analysis in Section 7.4.2.

c.

Minor changes to loadings in Sections 8.2, 8.3, and pump capacity in Section 15.5.1.

d.

Changes to friction in seafastenings in Section 9.2.

e.

Additional comments on the use of chain in seafastenings in Section 9.3.8.

f.

Changes of the use of 1/3 overload in Section 9.5.4 to 9.5.7

g.

Addition of Section 9.9 for use of second hand steel seafastenings.

h.

Default wind speed added for intact stability in Section 10.3.2.

i.

Removing the definition on “Field Move” for jack-ups and replacing it with 24-hour moves, with
revised bollard requirements in Section 12.2 and tug efficiencies in Table 12-3.

j.

Amplification of tug efficiencies in Sections 12.2.9 to 12.2.11.

k.

Clarification of the ULC for fairleads in Section 13.2.4.

l.

Implications of large bridle apex angles in Section 13.5.2.

m.

Introduction of surge chains in Section 13.8.5.

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GUIDELINES FOR MARINE TRANSPORTATIONS

2.7

n.

Increase in safety factor for bridle recovery .system in Section 13.10.5

o.

Addition of paragraphs on Hazardous materials in Section 14.17 and Ballast Water in Section
14.18.

p.

Addition of Sections 14.19 to 14.22 on vertical and horizontal clearances on passage.

q.

Changes to the philosophy of emergency anchors in Sections 16.1 and 16.2.

r.

Amplification of Flag State approval of riding crews on transported cargo. In Sections 17.1.3
and 17.1.4.

s.

Additional restriction for carrying drill pipe etc in the derrick for field moves (Section 19.9.3)

t.

Reference is made to the IMO Stability code for icing in Section 22.11.1.

u.

Introduction of the IACS Polar class for vessels operating in ice in Section 22.2.2

v.

Additional Reference documents in the Reference Section.

w.

Addition of fillet weld stress checking in Appendix F.

This Revision 4 supersedes Revision 3, and includes:
a.

The addition of Transportation / Towage Manuals in Section 5.4 and Appendix G.

b.

Updates to required documentation in Table 5-2.

c.

Clarification of design extremes in Sections 6.5.4 and 6.8.7.

d.

Clarification of Sections 7.2.2, 7.8.1 and 9.5.7.

e.

An additional option for design seastates in Sections 7.3.1 to 7.3.3.

f.

Additional default motion requirements in Section 7.9.1.

g.

Clarification of coupon testing results in Section 9.9.3.

h.

Minor changes for stability ranges in Table 10-1.

i.

Addition of towage requirements for concrete gravity units in Sections 12.1 and 14.20.

j.

Additional requirements for certificates in Sections 13.2.2 and 13.12.1.

k.

The addition of Section 23 for Towages in the Caspian Sea.

4

2.8

It should be noted that this document cannot cover every case of all transportation types. The reader
should satisfy himself that the guidelines used are fit for purpose for the actual transportation under
consideration.

2.9

Further information referring to other phases of marine operations may be found in:

2.10

a.

Self-elevating platforms – Guidelines for Elevated Operations 0009/ND [Ref. 1]

b.

Guidelines for Loadouts - 0013/ND [Ref. 2]

c.

Concrete Offshore Gravity Structures – Guidelines for Approval of Construction, Towage and
Installation - 0015/ND [Ref. 3]

d.

Seabed and Sub-Seabed Data Required for Approvals of Mobile Offshore Units (MOU) 0016/ND [Ref. 4]

e.

Guidelines for the Approvability of Towing Vessels - 0021/ND [Ref. 5]

f.

Guidelines for Lifting Operations by Floating Crane Vessels - 0027/ND [Ref. 6]

g.

Guidelines for the Transportation and Installation of Steel Jackets 0028/ND - [Ref. 7].

All current GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com.

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GUIDELINES FOR MARINE TRANSPORTATIONS
2.11

The approval of any transportation by GL Noble Denton does not imply that approval by designers,
regulatory bodies, harbour authorities and/or any other involved parties would be given, nor does it
imply approval of the seaworthiness of the vessel.

2.12

These Guidelines are intended to ensure the safety of the transported equipment. They do not
specifically apply to the safety of personnel or protection of the environment, which are covered by
other International and National Regulations. In some cases more stringent guidelines may be
appropriate in order to protect personnel and the environment.

2.13

These Guidelines refer both to towages of barges and other self-floating equipment, and to voyages of
self-propelled vessels. Where applicable, and unless particular distinction is required, the term
“vessel” may include “barge”, and “voyage” may include “towage”, and vice versa.

2.14

The “Special Considerations” Sections 19 through 23 may amend, add to or contradict the general
sections. Care should be taken to ensure that the special requirements are considered as appropriate.

2.15

These Guidelines are not intended to exclude alternative methods, new technology and new
equipment, provided an equivalent level of safety can be demonstrated.

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GUIDELINES FOR MARINE TRANSPORTATIONS

3

DEFINITIONS & ABBREVIATIONS

3.1

Referenced definitions are underlined.
Term or acronym

Definition

24-hour Move

A jack-up move taking less than 24 hours between entering the water and
reaching a safe airgap with at least two very high confidence good weather
forecasts for the 48 hours after entering the water, having due regard to
area and season.

ABS

American Bureau of Shipping

AISC

American Institute of Steel Construction

API

American Petroleum Institute

Approval

The act, by the designated GL Noble Denton representative, of issuing a
‘Certificate of Approval’.

ASPPR

Arctic Shipping Pollution Prevention Regulations

Assured

The Assured is the person who has been insured by some insurance
company, or underwriter, against losses or perils mentioned in the policy of
insurance.

Barge

A non-propelled vessel commonly used to carry cargo or equipment.

Benign area

An area that is free from tropical revolving storms and travelling
depressions, (but excluding the North Indian Ocean during the Southwest
monsoon season, and the South China Sea during the Northeast monsoon
season). The specific extent and seasonal limitations of a benign area
should be agreed with the GL Noble Denton office concerned.

BL /
Breaking Load

Breaking load (BL) = Certified minimum breaking load of wire rope, chain
or shackles, measured in tonnes.

BP /
Bollard Pull

Bollard pull (BP) = Certified continuous static bollard pull of a tug
measured in tonnes.

BV

Bureau Veritas

Cargo

Where the item to be transported is carried on a barge or a vessel, it is
referred to throughout this report as the cargo. If the item is towed on its
own buoyancy, it is referred to as the tow.

Cargo ship safety
certificates

Certificates issued by a certifying authority to attest that the vessel
complies with the cargo ship construction and survey regulations, has
radiotelephone equipment compliant with requirements and carries safety
equipment that complies with the rules applicable to that vessel type.

(Safety Construction)
(Safety Equipment)
(Safety Radio)

Certificate validities vary and are subject to regular survey to ensure
compliance.

CASPRR

Canadian Arctic Shipping Pollution Prevention Regulations

Certificate of Approval

A formal document issued by GL Noble Denton stating that, in its
judgement and opinion, all reasonable checks, preparations and
precautions have been taken to keep risks within acceptable limits, and an
operation may proceed.

Class

A system of ensuring ships are built and maintained in accordance with the
Rules of a particular Classification Society. Although not an absolute legal
requirement the advantages (especially as regards insurance) mean that
almost all vessels are maintained in Class.

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GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

COSHH

Control of Substances Hazardous to Health

Cribbing

An arrangement of timber baulks, secured to the deck of a barge or vessel,
formally designed to support the cargo, generally picking up the strong
points in vessel and/or cargo.

Demolition towage

Towage of a “dead” vessel for scrapping.

Deratisation

Introduced to prevent the spread of rodent borne disease, Certification
attesting the vessel is free of rodents (Derat Exemption Certificate) or has
been satisfactorily fumigated to derat the vessel (Derat Certificate).
Certificates are valid for 6 months unless further evidence of infestation
found.

Design environmental
condition

The design wave height, design wind speed, and other relevant
environmental conditions specified for the design of a particular
transportation or operation.

Design wave height

Typically the 10-year monthly extreme significant wave height, for the area
and season of the particular transportation or operation.

Design wind speed

Typically the 10-year monthly extreme 1-minute wind velocity at a
reference height of 10 m above sea level, for the area and season of the
particular transportation or operation.

DNV

Det Norske Veritas

Double tow

The operation of towing two tows with two tow wires by a single tug. See
Section 18.3.

Dry Towage (or Dry
Tow)

Transportation of a cargo on a barge towed by a tug. Commonly mis-used
term for what is actually a voyage with a powered vessel, more properly
referred to as ‘Dry Transportation’

Dry Transportation

Transportation of a cargo on a barge or a powered vessel.

Dunnage

See cribbing.

EPIRB

Emergency Position Indicating Radio Beacon

Flagged vessel

A vessel entered in a national register of shipping with all the appropriate
certificates.

Floating offload

The reverse of floating onload

Floating onload

The operation of transferring a cargo, which itself is floating, onto a vessel
or barge, which is submerged for the purpose.

FPSO

Floating Production, Storage and Offload vessel

GL

Germanischer Lloyd

GL Noble Denton

Any company within the GL Noble Denton Group including any associated
company which carries out the scope of work and issues a Certificate of
Approval, or provides advice, recommendations or designs as a
consultancy service.

GMDSS

Global Maritime Distress and Safety System

GPS

Global Positioning System

Grillage

A steel structure, secured to the deck of a barge or vessel, formally
designed to support the cargo and distribute the loads between the cargo
and barge or vessel.

GZ

Righting arm

IACS

International Association of Classification Societies

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GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

IMDG Code

International Maritime Dangerous Goods Code

IMO

International Maritime Organisation

Independent leg jackup

A jack-up where the legs may be raised or lowered independently of each
other.

Insurance Warranty

A clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent survey house.

IOPP Certificate

International Oil Pollution Prevention Certificate (see also MARPOL)

ISM Code

International Safety Management Code - the International Management
Code for the Safe Operation of Ships and for Pollution Prevention SOLAS Chapter IX [Ref. 8]

Jack-up

A self-elevating MODU, MOU or similar, equipped with legs and jacking
systems capable of lifting the hull clear of the water.

Line pipe

Coated or uncoated steel pipe sections, intended to be assembled into a
Pipeline

LOA

Length Over All

Load line

The maximum depth to which a ship may be loaded in the prevailing
circumstances in respect to zones, areas and seasonal periods. A
Loadline Certificate is subject to regular surveys, and remains valid for 5
years unless significant structural changes are made.

Loadout

The transfer of a cargo onto a barge or vessel by horizontal movement,
lifting, floatover etc.

Location move

A move of a MODU or similar, which, although not falling within the
definition of a field 24-hour move, may be expected to be completed with
the unit essentially in 24-hour field move configuration, without
overstressing or otherwise endangering the unit, having due regard to the
length of the move, and to the area (including availability of shelter points)
and season.

LRFD

Load and Resistance Factor Design

LRS

Lloyds Register of Shipping

Marine operation

See Operation

MARPOL

International Convention for the Prevention of Pollution from Ships
1973/78, as amended.

Mat-supported jack-up

A jack-up which is supported in the operating mode on a mat structure, into
which the legs are connected and which therefore may not be raised or
lowered independently of each other.

MBL

Minimum Breaking Load (see Sections 13.2.1 and 22.7.3.2)

MODU

See MOU

MOU

Mobile Offshore Unit. For the purposes of this document, the term may
include mobile offshore drilling units (MODUs), and non-drilling mobile
units such as accommodation, construction, lifting or production units

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GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

MPME /
Most Probable
Maximum Extreme

The value of the maximum of a variable with the highest probability of
occurring over a period of 3 hours.
NOTE The most probable maximum is the value for which the probability
density function of the maxima of the variable has its peak. It is
also called the mode or modus of the statistical distribution. It
typically occurs with the same frequency as the maximum wave
associated with the design seastate.

Multiple tow

The operation of towing more than one tow by a single tug. See Section
18.1.

NDT

Non Destructive Testing

Ocean towage

Any towage which does not fall within the definition of a restricted
operation, or any towage of a MODU or similar which does not fall within
the definition of a 24-hour move or location move.

Ocean transportation

Any transportation which does not fall within the definition of a restricted
operation

Off-hire survey

A survey carried out at the time a vessel, barge, tug or other equipment is
taken off-hire, to establish the condition, damages, equipment status and
quantities of consumables, intended to be compared with the on-hire
survey as a basis for establishing costs and liabilities.

Offload

The reverse of loadout

On-hire survey

A survey carried out at the time a vessel, barge, tug or other equipment is
taken on-hire, to establish the condition, any pre-existing damages,
equipment status and quantities of consumables. It is intended to be
compared with the off-hire survey as a basis for establishing costs and
liabilities. It is not intended to confirm the suitability of the equipment to
perform a particular operation.

Operation, marine
operation

Any activity, including loadout, transportation, offload or installation, which
is subject to the potential hazards of weather, tides, marine equipment and
the marine environment,

Operational reference
period

The planned duration of an operation including a contingency period.

Parallel tow

The operation of towing two tows with one tow wire by a single tug, the
second tow being connected to a point on the tow wire ahead of the first
tow with the catenary of its tow wire passing beneath the first tow. See
Section 18.1.4.

PIC

Person In Charge

Pipe carrier

A vessel specifically designed or fitted out to carry Line pipe

Port (or point) of
shelter

See Shelter point

Port of refuge

A location where a towage or a vessel seeks refuge, as decided by the
Master, due to events occurring which prevent the towage or vessel
proceeding towards the planned destination. A safe haven where a
towage or voyage may seek shelter for survey and/or repairs, when
damage is known or suspected.

Procedure

A documented method statement for carrying out an operation

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GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

Registry

Registry indicates who may be entitled to the privileges of the national flag,
gives evidence of title of ownership of the ship as property and is required
by the need of countries to be able to enforce their laws and exercise
jurisdiction over their ships. The Certificate of Registry remains valid
indefinitely unless name, flag or ownership changes.

Restricted operation

See Weather-restricted operation.

Risk assessment

A method of hazard identification where all factors relating to a particular
operation are considered.

SART

Search and Rescue Radar Transponder

Seafastening

The means of preventing movement of the cargo or other items carried on
or within the barge, vessel, or tow.

Semi-submersible

A MODU or similar designed to operate afloat, generally floating on
columns which reduce the water-plane area, and often moored to the
seabed when operating.

Shelter point (or
shelter port, or point
of shelter)

An area or safe haven where a towage or vessel may seek shelter, in the
event of actual or forecast weather outside the design limits for the
transportation concerned. A planned holding point for a staged
transportation

Single tow

The operation of towing a single tow with a single tug.

SLS

A design condition defined as a normal Serviceability Limit State / normal
operating case.

SMC /
Safety Management
Certificate

A document issued to a ship which signifies that the Company and its
shipboard management operate in accordance with the approved SMS.

SMS /
Safety Management
System

A structured and documented system enabling Company personnel to
implement the Company safety environmental protection policy.

SOPEP

Shipboard Oil Pollution Emergency Plan

Staged transportation

A transportation which can proceed in stages between shelter points, not
leaving or passing each shelter point unless there is a suitable weather
forecast for the next stage. Each stage may, subject to certain safeguards,
be considered a weather-restricted operation.

Submersible transport
vessel

A vessel which is designed to ballast down to submerge its main deck, to
allow self-floating cargoes to be on-loaded and off-loaded.

Suitability survey

A survey intended to assess the suitability of a tug, barge, vessel or other
equipment to perform its intended purpose. Different and distinct from an
on-hire survey.

Survey

Attendance and inspection by a GL Noble Denton representative.

Surveyor

The GL Noble Denton representative carrying out a Survey.
An employee of the fabrication or loadout contractor or Classification
Society performing, for instance, a dimensional, structural or Class survey.

Tandem tow

0030/ND REV 4

The operation of towing two or more tows in series with one tow wire from
a single tug, the second and subsequent tows being connected to the stern
of the tow ahead.

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GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

Te /
Tug efficiency (Te)

Defined as:

Tonnage

A measurement of a vessel in terms of the displacement of the volume of
water in which it floats, or alternatively, a measurement of the volume of
the cargo carrying spaces on the vessel. Tonnage measurements are
principally used for freight and other revenue based calculations. Tonnage
Certificates remain valid indefinitely unless significant structural changes
are made.

Tow

The item being towed. This may be a barge or vessel (laden or un-laden)
or an item floating on its own buoyancy. Approval by GL Noble Denton of
the tow will normally include, as applicable: consideration of condition and
classification of the barge or vessel; strength, securing and weather
protection of the cargo, draught, stability, documentation, emergency
equipment, lights, shapes and signals, fuel and other consumable
supplies, manning.

Towage

The operation of transporting a non-propelled barge or vessel (whether
laden or not with cargo) or other floating object by towing it with a tug.

Towing (or towage)
arrangements

The procedures for effecting the towage. Approval by GL Noble Denton of
the towing (or towage) arrangements will normally include consideration of
towlines and towline connections, weather forecasting, pilotage, routeing
arrangements, points of shelter, bunkering arrangements, assisting tugs,
communication procedures.

Towing vessel

See Tug

Towline connection
strength

Towline connection strength (TC) = ultimate load capacity of towline
connections, including connections to barge, bridle and bridle apex, in
tonnes.

TPR /
Towline pull required

The towline pull computed to hold the tow, or make a certain speed against
a defined weather condition, in tonnes.

Transportation

The operation of transporting a tow or a cargo by a towage or a voyage.

Tug

The vessel performing a towage. Approval by GL Noble Denton of the tug
will normally include consideration of the general design; classification;
condition; towing equipment; bunkers and other consumable supplies;
emergency and salvage equipment; communication equipment; manning.

TVAC /
Towing Vessel
Approvability
Certificate

A document issued by GL Noble Denton stating that a towing vessel
complied with the requirements of Ref [5] at the time of survey, or was
reportedly unchanged at the time of revalidation, in terms of design,
construction, equipment and condition, and is considered suitable for use
in towing service within the limitations of its Category, bollard pull and any
geographical limitations which may be imposed.

TVAS /
Towing Vessel
Approvability Scheme

The scheme whereby owners of towing vessels may apply to have their
vessels surveyed, leading to the issue of a TVAC.

0030/ND REV 4

Effective bollard pull produced in the weather considered
Certified continuous static bollard pull

Page 18

GUIDELINES FOR MARINE TRANSPORTATIONS
Term or acronym

Definition

ULC /
Ultimate Load
Capacity

Ultimate load capacity of a wire rope, chain or shackle or similar is the
certified minimum breaking load, in tonnes. The load factors allow for
good quality splices in wire rope.
Ultimate load capacity of a padeye, clench plate, delta plate or similar
structure, is defined as the load, in tonnes, which will cause general failure
of the structure or its connection into the barge or other structure.

ULS

A design condition defined as Ultimate Limit State / survival storm case.

Vessel

A self-propelled marine craft designed for the purpose of transportation by
sea.

Voyage

For the purposes of this report, the operation of transporting a cargo on a
powered vessel from one location to another.

Watertight

A watertight opening is an opening fitted with a closure designated by
Class as watertight, and maintained as such, or is fully blanked off so that
no leakage can occur when fully submerged.

Weather un-restricted
operation

An operation with an operational reference period generally greater than
72 hours. The design environmental condition for such an operation shall
be set in accordance with extreme statistical data.

Weather-restricted
operation

A marine operation which can be completed within the limits of an
operational reference period with a favourable weather forecast (generally
less than 72 hours), taking contingencies into account. The design
environmental condition need not reflect the statistical extremes for the
area and season. A suitable factor should be applied between the design
weather conditions and the operational weather limits.

Weathertight

A weathertight opening is an opening closed so that it is able to resist any
significant leakage from one direction only, when temporarily immersed in
green water or fully submerged.

WMO

World Meteorological Organisation

WPS

Welding Procedure Specification

WSD

Working Stress Design

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GUIDELINES FOR MARINE TRANSPORTATIONS

4

THE APPROVAL PROCESS

4.1

GENERAL

4.1.1

GL Noble Denton may act as a Warranty Surveyor, giving Approval to a particular operation, or as a
Consultant, providing advice, recommendations, calculations and/or designs as part of the Scope of
Work. These functions are not necessarily mutually exclusive.

4.2

GL NOBLE DENTON APPROVAL

4.2.1

GL Noble Denton approval means approval by any company within the GL Noble Denton Group
including any associated company which carries out the scope of work and issues a Certificate of
Approval.
GL Noble Denton approval may be sought where the towage, voyage or operation is the subject of an
Insurance Warranty, or where an independent third party review is required.
An Insurance Warranty is a clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent survey house. The requirement is normally
satisfied by the issue of a Certificate of Approval. Responsibility for interpreting the terms of the
Warranty so that an appropriate Scope of Work can be defined rests with the Assured.

4.2.2
4.3

4.3.1

GL Noble Denton approval may be required for the loadout and offload operations, either in addition to
the transportation, or where such operations are deemed to be part of the transportation.

4.4

CERTIFICATE OF APPROVAL

4.4.1
4.4.2

The deliverable of the approval process will generally be a Certificate of Approval.
The Certificate of Approval is the formal document issued by GL Noble Denton when, in its judgement
and opinion, all reasonable checks, preparations and precautions have been taken to keep risks within
acceptable limits, and an operation may proceed.
A Certificate confirming adequate preparation for a transportation will normally be issued by the
attending surveyor immediately prior to departure, when all preparations including seafastening and
ballasting are complete, the barge or vessel, cargo, tug and towing connections (as applicable) have
been inspected, and the actual and forecast weather are suitable for departure.

4.4.3

4.5

SCOPE OF WORK LEADING TO AN APPROVAL

4.5.1

In order to issue a Certificate of Approval, GL Noble Denton will typically require to consider, as
applicable, the following topics:
a.
History, condition and documentation of the tow or cargo
b.

Voyage or towage route, season and design environmental conditions, with shelter points if
applicable

c.

Capability of the vessel or barge to carry the cargo

d.

Vessel, barge or tow motions

e.

Strength of the tow, cargo, seafastening and cribbing to withstand static and motion induced
transportation loads

f.

Stability of the vessel, barge or tow

g.

Towing resistance and required bollard pull

h.

Towing vessel specification and documentation

i.

Towing connections and arrangements

j.

Weather protection of the tow or cargo

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GUIDELINES FOR MARINE TRANSPORTATIONS

4.5.2

4.5.3

4.5.4

4.5.5

4.5.6

4.5.7

4.5.8

k.

Seafastening of items and substructures within the tow or cargo

l.

Arrangements for receiving weather forecasts along the route

m.

Transportation or towing manual (see Section 5.4 and Appendix G).

4

If approval is also required for the onload and/or offload operations of a self-floating cargo onto/from a
submersible vessel or barge, then the following will typically require consideration:
a.
Location details, water depth, tidal conditions and meteorological exposure.
b.

Vessel or barge moorings.

c.

Stability and ballasting conditions during the load transfer operation and the critical parts of the
deballasting/ballasting operation.

d.

Cribbing position and securing during submergence.

e.

Towing and handling arrangements for the cargo.

f.

Cargo positioning arrangements.

g.

Reactions between vessel or barge and cargo.

h.

Limiting weather conditions for the operation.

If approval is required for loadout from the shore onto a vessel or barge, offload from a vessel or barge
to the shore, or lifting from a vessel or barge to a platform, reference should be made to documents
0013/ND [Ref. 2] and 0027/ND [Ref. 6] as appropriate.
Technical studies leading up to the issue of a Certificate of Approval for transportation may consist of:
a.
Reviews of specifications, procedures and calculations submitted by the client or his
contractors, or
b.

Independent analyses carried out by GL Noble Denton to verify the feasibility of the proposals,
or

c.

A combination of third party reviews and independent analyses.

Surveys required in order to issue a Certificate of Approval will typically include:
a.
Survey of the transport vessel or barge
b.

Survey of the tow or cargo

c.

Survey of completed seafastenings and other voyage preparations including vessel or barge
readiness, ballast condition, cargo securing, weather-tightness and internal seafastening

d.

Survey of tug and towing connections, if applicable

e.

Inspection of documentation for vessel, barge and tug as appropriate

f.

Review of actual and forecast weather for departure

The above surveys may be carried out immediately before departure, but the client may consider it in
his interests to have initial surveys carried out in advance, to reduce the risk of rejection of any major
item.
Tugs in possession of a GL Noble Denton Towing Vessel Approvability Certificate (TVAC) may be preapproved in principle in advance. It may be advisable to request a survey of an unknown tug prior to
mobilisation.
Whilst not forming part of the surveys required for approval, the client may also consider it in his
interests to have on- and off-hire surveys performed of equipment taken on charter, in order to
establish inventories of equipment and consumables, and liability for degradation or damage.

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GUIDELINES FOR MARINE TRANSPORTATIONS
4.6

LIMITATION OF APPROVAL

4.6.1
4.6.2

A Certificate of Approval is issued for a specific towage, voyage or operation only.
A Certificate of Approval is issued based on external conditions observed by the attending surveyor of
hull, machinery and equipment, without removal, exposure or testing of parts.
A Certificate of Approval shall not be deemed or considered to be a general Certificate of
Seaworthiness.
A Certificate of Approval for a towage or voyage does not include any moorings prior to the start of the
towage or voyage, or at any intermediate shelter, bunkering or arrival port, unless specifically approved
by GL Noble Denton.
No responsibility is accepted by GL Noble Denton for the way in which the towage or voyage is
conducted, this being solely the responsibility of the master of the tug or vessel.
The towage is deemed to be completed and the related Certificate of Approval invalidated when the
approved tug(s) is/are disconnected.
Fatigue damage is excluded from any GL Noble Denton approval, unless specific instructions are
received from the client to include it in the scope of work.
Any alterations in the surveyed items or agreed procedures or arrangements, after issue of a
Certificate of Approval, may render the Certificate void unless the alterations are specifically approved
by GL Noble Denton.
The Certificate covers the surveyed items within the agreed scope of work only. It does not, for
instance, cover any other cargo on board a vessel or barge, or any damage to the surveyed cargo as a
consequence of inadequacy of any other cargo or its seafastenings, unless specifically included in the
scope of work.

4.6.3
4.6.4

4.6.5
4.6.6
4.6.7
4.6.8

4.6.9

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5

CERTIFICATION AND DOCUMENTATION

5.1

GENERAL

5.1.1

In general, some or all of the documentation listed in the Table 5-1 and Table 5-2 below will be
required. Some documentation is mandatory to comply with international legislation and standards.
The documentation and certification requirements for any particular structure, vessel or operation
should be determined in advance. Where new documentation is needed, the issuing authority and the
Rules to be applied should be identified.

5.2

DOCUMENTATION DESCRIPTION

5.2.1

Principal documentation and certification is described in the following Table 5-1:
Table 5-1
Document / Certificate
Ship Safety Construction

Ship Safety Equipment

Class (Hull and machinery)

Customs clearance
De-rat, or De-rat Exemption

Garbage Management Plan
International Oil Pollution
Prevention

Lifesaving Appliances

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Principal Documentation

Description
Covers the hull, machinery and equipment of a ship, (over 500
gt) and shows that the ship complies with the construction and
safety regulations applicable to the ship and the voyages she is
to be engaged in. Issued by the Flag State, or appointed
Classification Society.
This is a record of the safety equipment carried on the vessel
(over 500 gt), in compliance with SOLAS, including life saving
appliances, fire fighting equipment, lights and shapes, pilot
ladders, magnetic compass etc. Issued by the Flag State, or
appointed Classification Society.
Vessels and their machinery, built and maintained in accordance
with the Rules of a Classification Society will be assigned a
class in the Society’s Register Book, and issued with the
relevant Certificates, which will indicate the character assigned
to the vessel and machinery. Issued by the Classification
Society.
Issued by Customs confirming that so far as they are concerned
the vessel is free to sail. Issued after light dues have been paid,
and on production of various other mandatory documentation.
A De-rat Certificate is issued after a vessel has been fumigated,
or dealt with be other means to rid her of rats. A De-rat
exemption is issued where inspection has shown no evidence of
rats on board. Issued by a Port medical officer.
A Class-approved document for management of waste.
Certifies that the vessel complies with international oil pollution
regulations (MARPOL Annex 1). Unless stated otherwise, all
vessels over 400 grt must comply with the requirements of the
code. Issued by the Flag State, or appointed Classification
Society.
Normally covered under Cargo Ship Safety Equipment
Certificate. Where temporary equipment, e.g. liferafts or fire
fighting equipment, is placed on a structure not in possession of
a Cargo Ship Safety Equipment Certificate, it is expected that
each would be individually certified, with an in-date inspection.

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GUIDELINES FOR MARINE TRANSPORTATIONS
Document / Certificate
Load Line

Load Line Exemption

Navigation Lights and Shapes

Panama Canal documentation
Registry

Safe Manning document
Safety Management Certificate
(SMC) - Document of
Compliance
Safety Radio
SOPEP
Tonnage

Transportation or towing manual
Trim and Stability booklet

0030/ND REV 4

Description
Issued after a vessel has been marked with her assigned load
line marks. The Certificate gives details of the dimensions
related to the freeboard, and the various special marks, e.g. TF
(Tropical Fresh), WNA (Winter North Atlantic) etc. The vessel
must be periodically inspected, to confirm that no changes have
occurred to the hull or superstructure which would render invalid
the data on which the assignment of freeboard was made.
Issued by the Flag State, or appointed Classification Society.
Where a vessel or structure is exempt from some or all of the
provisions of the above, it may be issued with a Load Line
Exemption Certificate, which will include any qualifying
provisions. Issued by the Flag State, appointed Classification
Society, or Port Authority.
Normally covered under Cargo Ship Safety Equipment
Certificate. Where temporary lights are placed on a structure
not in possession of a Cargo Ship Safety Equipment Certificate,
it is expected that they would be individually certified, or in
possession of a manufacturer’s guarantee of compliance.
For transit through the Panama Canal, drawings are required
showing the extent of visibility from the bridge, and the
extension of bilge keels, if fitted.
The Certificate of Registry is required by all commercial vessels.
It contains the details from the Flag State Register in which the
vessel has been registered, including principal dimensions,
tonnage, and ownership. Issued by the Flag State Register.
A document issued by Flag State, showing the minimum safe
manning for a vessel
A document issued to a ship which signifies that the Company
and its shipboard management operate in accordance with the
approved Safety Management System. Issued by the Flag
State, or appointed Classification Society.
Issued by the Flag State after survey of the vessel’s radio
installation, declaring that it is satisfactory for the intended
service.
Shipboard Oil Pollution Emergency Plan - Class approved
Shows the Tonnage as obtained by measurement, and is a
measure of volume rather that weight. 1 ton equals 2.83 cu.m
(100 cu.ft). Measured by a surveyor appointed by the Flag
State.
A manual providing the Master with the key information that he
needs, including the cargo and route.
A booklet setting out the vessel’s stability particulars, and
allowing the actual draught, trim and stability characteristics and
limitations to be determined for any cargo arrangement. Usually
prepared by designers, and must be approved by the Flag State.

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GUIDELINES FOR MARINE TRANSPORTATIONS
5.3

ICE CLASS

5.3.1

See the comments relating to Ice Class vessels in Section 22.2.

5.4

TRANSPORTATION OR TOWING MANUAL

5.4.1

A transportation or towing manual is required for all transportations or towages for the following
reasons:
a.
It shall provide the Master with the key information that he needs, including the cargo and route.

5.4.2

b.

It shall describe the structural and any other limitations of the cargo.

c.

It shall summarise contingency plans in the event of an emergency including contact details

d.

It shall give approving bodies the key information that they require for approval.

e.

It shall define the responsibilities of different parties if parts of the transport / tow and installation
are performed by different contractors. The scope split between the contractors shall be clearly
defined, to ensure that all parties are aware of their responsibilities, handover points and
reporting lines.

4

More details are given in Appendix G.

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GUIDELINES FOR MARINE TRANSPORTATIONS
5.5

REQUIRED DOCUMENTATION

5.5.1

In general the following documentation (shown as “”) will be required or recommended (those shown
as “*” will depend on the regulatory bodies) for the transportation of various types of vessels and
floating structures. Some regulatory bodies may require extra documentation.

Other towages

Demolition towages

FPSO /FPU etc
towages

Barges (Note 2)

Tugs (Note 1)

(Note 1)

Document

Required Documentation
Cargo vessels

Table 5-2

*



Certificate of registry
*
*




Certificate of class (hull)
*



Certificate of class (machinery)
*



Tonnage certificate
*
*



Cargo ship safety construction certificate
*
*



Cargo ship safety equipment certificate
*




Certificates for navigation lights & shapes




Load line certificate or load line exemption
*


Load line exemption (if unmanned)
*
Air Pollution Prevention (IAPP) certificate
*
*
*
*
*
*
*




IOPP Certificate


Safety Management Certificate (SMC)






Customs clearance





Deratisation certificate, or exemption


Radio certificate, including GMDSS




Trim and Stability booklet

Bollard pull certificate
Certificates for bridle, tow wires, pennants,





stretchers and shackles






Suez or Panama Canal documentation (if relevant)






Transportation or Towing manual
Manned towed objects






Load line or Load Line Exemption






Certificates for life saving appliances






Crew list






Radio Certificate
Notes:
1. Smaller vessels (typically < 500 gt) may be exempt from some Certification requirements.
2. Unmanned barges will not be required to have Safety Equipment Certificates, Derat Certificate or
IOPP, unless fitted with machinery.
3. Some documentation is not required for inland voyages or inland towages.

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GUIDELINES FOR MARINE TRANSPORTATIONS

6

DESIGN ENVIRONMENTAL CONDITIONS

6.1

INTRODUCTION

6.1.1

Each transportation shall be designed to withstand the loads caused by the most adverse
environmental conditions expected for the area and season through which it will pass, taking account
of any agreed mitigating measures.
For each phase of a transportation or marine operation, the design criteria should be defined,
consisting of the design wave, design wind and, if relevant, design current. It should be noted that the
maximum wave and maximum wind may not occur in the same geographical area, in which case it
may be necessary to check the extremes in each area, to establish governing loadcases.
Except as allowed by Sections 6.3 and 6.5 below, the transportation should generally be designed to
the 10-year monthly extremes for the area and season, on the basis of a 30 day exposure.

6.1.2

6.1.3

6.2

OPERATIONAL REFERENCE PERIOD

6.2.1

Planning and design of marine transportations shall be based on an operational reference period equal
to the planned duration of the operation plus a contingency period.
The planned duration for a transportation shall include, typically:
a.
The time anticipated, after the departure decision, preparing for departure or waiting for the
correct tidal conditions

6.2.2

6.2.3

b.

The time anticipated for the voyage or towage itself

c.

Time anticipated on arrival, waiting for the correct tidal conditions to enter harbour

d.

If the operation following the transportation is a weather-dependent marine operation such as
installation, the time required after arrival at the installation site to reach a safe condition.

The contingency period shall include, as appropriate, an allowance for:
a.
slower than predicted voyage or towing speed, because of adverse weather conditions or
vessel performance below specification
b.

the time required to reach and enter the planned shelter point, in worsening weather conditions
if the operation following the transportation is a weather-dependent marine operation such as
installation, and the contingency action is to return to shelter.

6.3

WEATHER-RESTRICTED OPERATIONS

6.3.1

A transportation with a reference period generally less than 72 hours may be classed as a weatherrestricted operation. The design environmental conditions for such an operation may be set
independent of extreme statistical data, provided that:
a.
The statistics indicate an adequate frequency and duration of the required weather windows
b.

Dependable weather forecasts are available

c.

The start of the operation is governed by an acceptable weather forecast, covering the
reference period

d.

A risk assessment has been carried out and the risks shown to be acceptable.

e.

Adequate marine procedures are in place.

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GUIDELINES FOR MARINE TRANSPORTATIONS
6.3.2

A transportation with a reference period greater than 72 hours may exceptionally be classed as a
weather-restricted operation, provided that:
a.
An adequate shelter point which can be entered in worsening weather is always available within
48 hours or the transport has sufficient speed to avoid the area of forecast severe weather
b.

An acceptable weather routeing service is contracted and is available for advice at any time

c.

Weather forecasts are received at appropriate intervals

d.

The weather forecast service is contracted to issue a warning should the weather forecast
deteriorate

e.

Management resources of interested parties are always available with the right authority level to
monitor any decision to proceed to shelter

f.

A risk assessment has been carried out and the risks shown to be acceptable.

g.

Adequate marine procedures and equipment are in place.

6.3.3

For weather-restricted operations, the maximum forecast operational criteria should be lower than the
design criteria by a margin depending on the area and season, the delicacy of the operation, and the
typical reliability of the forecast. The factor is dependent on the duration of the operation and the level
of the design criteria set. Typically a factor of 0.7 times the design maxima may be used to determine
the maximum forecast operational criteria.

6.4

UNRESTRICTED OPERATIONS

6.4.1

Except as allowed in Section 6.3.2, transportations with an operational reference period greater than
72 hours shall be defined as un-restricted operations.

6.5

CALCULATION OF “ADJUSTED” DESIGN EXTREMES, UNRESTRICTED OPERATIONS

6.5.1

The risk of encounter of extreme conditions by a particular transport is dependent on the length of time
that it spends in those route sectors where extreme conditions are possible. If the length of time is
reduced, then the probability of encountering extreme conditions is similarly reduced.
It is generally accepted that for a prolonged ocean transport the wind and wave design criteria should
be those with a probability of exceedance per voyage of 0.1 or less. For an ocean transport of 30 days
(or more), through meteorologically and oceanographically consistent areas, this corresponds to the 10
year monthly extreme.
Many transports last less than 30 days, or are potentially exposed to the most severe conditions for
less than 30 days. Consequently, for shorter exposures, the 10 year monthly extreme may be
adjusted for reduced exposure. This value is equivalent to the 10 voyage extreme and is also referred
to as the 10% risk level extreme. This must not be confused with the 10% exceedance value for the
transport, as discussed in Section 6.9.
When the 10% risk level extremes are less than the 1-year return monthly extremes, the 1-year
monthly extremes are the minimum that shall be used for design.
If the 10 year extremes are due to a tropical cyclone it may not be appropriate to design to adjusted
extremes. This is likely to be the case for barge or MODU towages that are not able to respond
effectively to weather routeing.

6.5.2

6.5.3

6.5.4
6.5.5

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GUIDELINES FOR MARINE TRANSPORTATIONS
6.6

CALCULATION OF EXPOSURE

6.6.1

For the purpose of the calculation of “adjusted” extremes the exposure time to potentially extreme or
near extreme conditions is calculated taking consideration of the points discussed below.
a.
The initial 48 hours of the transportation, is assumed to be covered by a reliable departure
weather forecast and is excluded
b.

The speed of the transport is reduced by taking the monthly mean wave heights along the route
into consideration as described in Section 6.7.2.

c.

The speed of the transport is adjusted to take into consideration the mean currents as
described in Section 6.7.3.

d.

A contingency time of 25 percent of the time is added. This allowance is to account for severe
adverse weather, for tug breakdowns or other operational difficulties

e.

A minimum exposure time of 3 days is considered.

6.7

CALCULATION OF VOYAGE SPEED

6.7.1

Voyage duration shall be calculated using the speed in the monthly mean sea state for each route
sector and shall allow for adverse currents as described below.
The effect of the mean sea state on the transport speed in each route sector is calculated assuming
that the wave height in which the transport will come to a dead stop is b (metres). This is typically 5m
for barge towages, and 8m for ships. The calm weather speed is multiplied by a factor, F, defined by:

6.7.2

H
F  1   m 
b


2

where Hm is the monthly mean wave height in that route sector.
6.7.3

The effect of the mean current on the transport speed in each route sector is calculated by adding the
current vector (resolved with respect to the transport heading). For the calculation of exposure to the
extreme conditions only negative currents which act to delay the transport shall be taken into account.

6.8

CALCULATION OF EXTREMES

6.8.1

The probability of non-exceedance of a value of wind speed or significant wave height in a particular
route sector is expressed as a cumulative frequency distribution (e.g. a Weibull distribution).
The probability that during some 3 hour period for waves (or 1 hour for wind) the transport will
experience a significant wave height (or wind speed) less than some value x is given by FX(x).
If it takes M hours to pass through the route sector and making the assumption that consecutive wave
height and wind speed events are independent then the probability of not exceeding the value x is
given by [FX(x)]N where N=M/T where T=1 hour is applied for winds and T=3 hours for waves, which
are a more persistent form of energy.
If it is reasonable to expect that extremes of wind speed or wave height could occur in more than one
route sector then the probability of not exceeding the value x is given by the product

6.8.2
6.8.3

6.8.4

F
i

6.8.5

Xi

( x) Ni

The probability of encountering an extreme value of wind speed or significant wave height, during a
particular transport, that is reached or exceeded once on average for every 10 transports is 0.1. The
value of x is varied until

1   FX i ( x) N i is equal to 0.1
i

to give the 10 transport extreme for the voyage or towage.

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GUIDELINES FOR MARINE TRANSPORTATIONS
6.8.6
6.8.7

This value is also referred to as the “adjusted” extreme for the transport, or as having a risk level of
10%. The method may be adjusted to give other risk levels (e.g. 1% or 5%).
The extremes used for design shall not be less than the 1-year return monthly extremes.

6.9

COMPARISON WITH PERCENTAGE EXCEEDENCE

6.9.1

Given a series of values of wind speed or significant wave height, as may be observed during a
complete transport, some value y will be exceeded at some times but not others and the percentage
exceedance of value y is equal to:

100  (number of times y exceeded )
total number of observations
6.9.2

6.9.3

6.9.4

If each observed value of wind speed or significant wave height is assumed to last for some duration
(typically 1 hour for winds and 3 hours for waves) then for example, during a transport lasting 10 days
there will be 240 wind events and 80 wave events. On the transport, if a wind speed greater than 30
knots is observed during 24 separate, hourly occasions then the percentage exceedance of 30 knots is
10%.
The 10% risk level (as defined in Section 6.5.3) for a transport along a specific route, departing on a
specific date is expected to occur only once, on average, in every 10 transports. However a value with
a 10% exceedance level for the same route and departure date is likely to occur on average for 10% of
the time on every transport.
Thus a 10% exceedance value is far more likely to occur than a 10% risk level value, or an adjusted,
10 year extreme value.

6.10

CRITERIA FROM TRANSPORT SIMULATIONS

6.10.1

If continuous time series of winds and waves are available along the entire transport route (e.g. from
hindcast data or satellite observations), an alternative way to develop criteria with a specified risk of
exceedance in a single transport is to perform tow simulations. A large number of simulations can be
performed, with uniformly spaced (in time) departure times during the specified month of departure
over the number of years in the database. For each simulated transport, the maximum wind speed
and the maximum wave height experienced somewhere along the tow route are retained. Then the
probability distribution of these transport-maxima can be used to determine the design value with a
specified risk of exceedance. For example, the value exceeded once in every 20 transports, on
average, can be determined by reading off the value of wave height from the distribution of transportmaximum wave heights at the 95th percentile level.
If fatigue during tow is an issue, the complete distributions of winds and waves experienced during the
simulated transports (not just the transport-maximum values) can be retained. These can be used to
give scatter diagrams of wave height against period and/or direction, and wind speed against direction.
The transport simulation method can be made to be very realistic and account for. variation of speed
due to inclement weather or ocean currents, weather avoidance en route through forecasting/routeing
services, or the use of safe havens, etc. If the transport simulator cannot accommodate all these
features, a reasonably conservative estimate of criteria can be derived by using a conservative (slow)
estimate of the average speed. Care should be taken when choosing the average speed estimate - a
slow speed may not be conservative if it results in the vessel apparently arriving in a route sector late
enough to miss severe weather, which might have been encountered if arrival had been earlier.

6.10.2

6.10.3

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GUIDELINES FOR MARINE TRANSPORTATIONS
6.11

METOCEAN DATABASE BIAS

6.11.1

Regardless of whether the method described in Section 6.8 or the method described in Section 6.10 is
used, it is important to know the accuracy of the metocean database being used. Specifically, if there
is a known bias in the wind or wave statistics for any segment of a tow, it is essential to adjust the
criteria accordingly.

6.12

DESIGN WAVE HEIGHT

6.12.1

The design wave height shall be the significant wave height (Hsig), where Hsig = 4m0 where m0 is the
sea surface variance. In sea states with only a narrow band of wave frequencies, Hsig is approximately
equal to H1/3 (the mean height of the largest third of the zero up-crossing waves). Advice should be
provided as to the appropriate spectra.

6.13

DESIGN WIND SPEED

6.13.1

The design wind speed shall be the 1 minute mean velocity at a reference height of 10m above sea
level. The 1 hour wind may also be needed in the calculation process.

6.14

METOCEAN DATA FOR BOLLARD PULL REQUIREMENTS

6.14.1

The design extremes are not normally used for calculation of bollard pull requirements, which are
covered in Section 12.2.

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GUIDELINES FOR MARINE TRANSPORTATIONS

7

MOTION RESPONSE

7.1

GENERAL

7.1.1

Design motions may be derived by means of motion response analyses, from model tank testing, or by
using the default equivalent motion values shown in Section 7.9.

7.2

SEASTATE

7.2.1

For the motion analyses, seastates shall include all relevant spectra up to and including the design
wave height for the most severe areas of the proposed voyage route. A wave height smaller than the
design wave height, at the natural period of roll and/or pitch of the tow, should also be checked if
necessary. "Long-crested" seas will be considered unless there is a justifiable basis for using "shortcrested" seas. Consideration should be given to the choice of spectrum which should be applicable to
the geographic area and Hsig of the design sea states.
The most probable maximum extreme (MPME) responses are to be based on a 3 hour exposure
period and shall be used for design.

7.2.2

7.3

PERIODS

7.3.1

The range of periods associated with the extreme seastate may be calculated in two different ways,
with due consideration given to the influence of swell.
In the simplest method the peak period (Tp) for all seastates considered, should be varied as:

7.3.2

 (13.Hsig) < Tp <  (30.Hsig)
where Hsig is in metres, Tp in seconds. The effects of swell should also be considered if not already
covered in this peak period range.
However, this method incorrectly assumes that all periods are equally probable. As a result this
method should generally produce higher design accelerations than would be the case when using the
more robust Hsig-Tp method described in the following section.
7.3.3

7.3.4

In the alternative method, a contour is constructed within the Hsig-Tp plane that identifies equally
probable combinations of Hsig & Tp for the design return period subject to theoretical constraints on
wave breaking. This contour should also cover swell. The combinations should be tested in motion
response calculations to identify the worst case response.
The relationship between the peak period Tp and the zero-up crossing period Tz is dependent on the
spectrum. For a mean JONSWAP spectrum (γ=3.3) Tp/Tz = 1.286; for a Pierson-Moskowitz spectrum
(γ=1) Tp/Tz = 1.41.

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GUIDELINES FOR MARINE TRANSPORTATIONS
7.3.5

The following Table 7-1 indicates how the characteristics of the JONSWAP wave energy spectrum
vary over the range of recommended seastates. The constant, K, varies from 13 to 30 as shown in the
equation in Section 7.3.1 above. T1 is the mean period (also known as Tm).
Value of JONSWAP γ, ratio of Tp:Tz and Tp:T1 for each integer value of K

Table 7-1
Constant K
13
14
15
16
17
18
19
20
21

γ
5.0
4.3
3.7
3.2
2.7
2.4
2.1
1.8
1.6

Tp/Tz
1.24
1.26
1.27
1.29
1.31
1.32
1.34
1.35
1.36

Tp/T1
1.17
1.18
1.19
1.20
1.21
1.23
1.24
1.25
1.26

Constant K
22
23
24
25
26
27
28
29
30

γ
1.4
1.3
1.1
1.0
1.0
1.0
1.0
1.0
1.0

Tp/Tz
1.37
1.39
1.40
1.40
1.40
1.40
1.40
1.40
1.40

Tp/T1
1.27
1.28
1.29
1.29
1.29
1.29
1.29
1.29
1.29

7.4

VESSEL HEADING AND SPEED

7.4.1

The analyses should be carried out for zero vessel speed for head, bow quartering, beam, stern
quartering and stern seas.
In addition the analysis should be carried out for non-beam sea cases for the maximum service speed
of the vessel or the maximum speed that can be maintained in the given seastate. The range of
probable peak wave periods, Tp, should be adjusted for the speed of the vessel as follows:

7.4.2

30 H sig
13H sig
 TP 
V
V
cos 
cos 
1  SHIP
1  SHIP
1.56 30 H sig
1.56 13H sig
where VSHIP is the ship speed in m/s and θ is the ship’s heading in degrees (0 = head seas, 180 =
following seas).

7.5

THE EFFECTS OF FREE SURFACES

7.5.1

The application of free surface corrections to reduce metacentric height (GM) and hence to increase
natural roll period will not generally be accepted. The effect of any reduction in GM must, however, be
considered in intact and damage stability calculations.

7.6

THE EFFECTS OF CARGO IMMERSION

7.6.1

The effect of cargo immersion in increasing GM and hence reducing natural roll period as well as
increasing damping should be considered in motion response analyses.

7.7

MOTION RESPONSE COMPUTER PROGRAMS

7.7.1

Computer programs shall be validated against a suitable range of model test results in irregular seas.
The validation is to be made available to GL Noble Denton and is to contain appropriate analytical
work which must be compared with applicable model tests.
When applying the results of a first-order motion response analysis program, heave shall be assumed
to be parallel to the global vertical axis. Therefore the component of heave parallel to the deck at the
computed roll or pitch angle (theta) is additive to the forces caused by the static gravity component and
by the roll or pitch acceleration.

7.7.2

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GUIDELINES FOR MARINE TRANSPORTATIONS
7.8

RESULTS OF MODEL TESTS

7.8.1

Model tests may be used to derive design motions, provided the tests pass the usual review of overall
integrity. Generally, for transportation analyses, the model test results should present the standard
deviation of the relevant responses. The standard deviation of the responses should then be multiplied
by (2.logn(N)), where N is the number of zero-upcrossings, to obtain the most probable maximum
extreme (MPME) in 3 hours, which is required for design. The individual measured maxima from
model tests should generally not be used in design as these vary between different realisations of the
same sea conditions, and are therefore unreliable for use as design values. These recommendations
apply to Gaussian responses, which is an appropriate assumption for most wave frequency motion
responses. If in the unlikely event that the response is significantly non-Gaussian, then alternative
methods should be used.
Maximum values of global loads, motions or accelerations from model test results can be used
provided ten similar realisations, or greater, are carried out to ensure that variations between individual
tests are accounted for. The mean and standard deviations of the maxima should be calculated. The
design value should be the mean plus two standard deviations.
Scale effects should also be accounted for by increasing the design loads by a further 10% or a
mutually agreed value.

7.8.2

7.8.3

7.9

DEFAULT MOTION CRITERIA

7.9.1

If neither a motions study nor model tests are performed, then for standard configurations and subject
to satisfactory marine procedures, the following motion criteria may be acceptable.

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Table 7-2
Nature of Transportation

Unrestricted

C
a
s
e

Default Motion Criteria

L/B[1]

Block
Coeff

1 > 140 and > 30

n/a

< 0.9

Full
cycle
period
(secs)
10

2

n/a

any

10

3

LOA
(m)

> 76

B[1]
(m)

and > 23

< 0.9

Heave

Roll

Pitch

20

10

0.2 g

20

12.5

0.2 g

15

0.2 g

30

≤ 76

or

≤ 23 ≥ 2.5

≤ 76

or

≤ 23 < 2.5

7

any

any

8

any

9

any

10

any

≥ 2.5
< 2.5,
≥ 1.4
≥ 2.5
< 2.5,
≥ 1.4

Inland and sheltered water transportations (see Section
7.9.2.f). For L/B < 1.4 use unrestricted case.

11

any

≥ 1.4

Independent leg jack-ups, ocean tow on own hull.

12

n/a

> 23

< 1.4

n/a

10

20

20

0.0

Independent leg jack-ups, 24-hour or location move.

13

n/a

> 23

< 1.4

n/a

10

10

10

0.0

4
5
6
Weather restricted operations in non-benign areas for a
duration <24 hours (see Section 7.9.2 d. For L/B < 1.4
use unrestricted case.
Weather restricted operations in benign areas (see
Section 7.9.2.e). For L/B < 1.4 use unrestricted case.

≥ 0.9
< 0.9

10

Single
amplitude

25
30

30

25

25

10

10

5

0.1 g

any

10

10

10

0.1 g

any

10

5

2.5

0.1 g

any

10

5

5

0.1 g

any

Static

≥ 0.9

10

Equivalent to
0.1 g in both
directions

0.2 g

4

0.0

Mat-type jack-ups, ocean tow on own hull.

14

n/a

> 23

< 1.4

n/a

13

16

16

0.0

Mat-type jack-ups, 24-hour or location move.

15

n/a

> 23

< 1.4

n/a

13

8

8

0.0

B = maximum moulded waterline breadth, L = waterline length. n/a = not applicable
Block coefficient = 0.9 is the cut-off between barge-shaped hulls (>0.9) and ship-shaped hulls.
[1]

7.9.2

The default motion criteria shown in Section 7.9.1, shall only be applied in accordance with the
following:
a.
Roll and pitch axes shall be assumed to pass through the centre of floatation.
b.

Heave shall be assumed to be parallel to the global vertical axis. Therefore the component of
heave parallel to the deck at the roll or pitch angles shown above is additive to the forces
caused by the static gravity component and by the roll or pitch acceleration.

c.

Phasing shall be assumed to combine, as separate loadcases, the most severe combinations of
 roll + heave
 pitch + heave

d.

For Cases 7 and 8, the departure shall be limited to a maximum of Beaufort Force 5, with an
improving forecast for the following 48 hours. The voyage duration including contingencies,
should not be greater than 24 hours.

e.

For Cases 9 and 10, the criteria stated is given as general guidance for short duration barge
towages and vessel transports. The actual criteria should be agreed with the GL Noble Denton
office concerned, taking into account the nature of the vessel or barge and cargo, the voyage
route, the weather conditions which may be encountered, the shelter available and the weather
forecasting services to be utilised.

f.

For Case 11, the design loading in each direction shall be taken as the most onerous due to:
 a 0.1g static load parallel to the deck, or
 the static inclination caused by the design wind, or
 the most severe inclination in the one-compartment damage condition.

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7.9.3

Alternative default motion criteria may be acceptable, as set out, for instance, in DNV Rules for the
Classification of Ships, January 2003, Part 3, Chapter 1, Section 4 [Ref. 9], or IMO Code of Safe
Practice for Cargo Stowage and Securing, 2003 Edition, Section 7 [Ref. 10]. Care should be taken to
ensure that the criteria adopted are applicable to the actual case in question.

7.10

DIRECTIONALITY AND HEADING CONTROL

7.10.1

The incident weather shall be considered to be effectively omni-directional, as stated in Section 7.4.
No relaxation in the design seastates from the bow-quartering, beam and stern-quartering directions
shall be considered for:
a.
Any transport where the default motion criteria are used, in accordance with Section 7.9, or
similar

7.10.2

b.

Single tug towages, or voyages by vessels with non-redundant propulsion systems (see Section
7.10.3 below).

c.

Any transport where the design conditions on any route sector are effectively beam on or
quartering, of constant direction, and of long duration, including, for example, crossing of the
Indian Ocean or Arabian Sea in the south-west monsoon

d.

Any towage in a Tropical Revolving Storm area and season

e.

Any un-manned towage.

f.

Any transport where the vessel does not have sufficient, redundant systems to maintain any
desired heading in all conditions up to and including the design storm, taking account of the
windage of the cargo.

Relaxation in the non-head sea cases may be considered for:
a.
Manned, multiple tug towages, where after breakdown of any one tug or breakage of any one
towline or towing connection, the remaining tug(s) still comply with the criteria of Section 12.2.
b.

7.10.3
7.10.4

Voyages by self-propelled vessels with redundant propulsion systems.
redundant propulsion system is defined as having, as a minimum:

A vessel with a



2 or more independent main engines



2 or more independent fuel supplies



2 or more independent power transmission systems



2 or more independent switchboards



2 or more independent steering systems, or an alternative means of operation of a single
steering system (but excluding emergency steering systems that cannot be operated from
the bridge)



the ability to maintain any desired heading in all conditions up to and including the design
storm, taking account of the windage of the cargo.

Any vessel not complying with all the above shall be considered non-redundant.
An advance survey may be required, to establish whether or not a vessel can be considered to have a
redundant propulsion system.

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7.10.5

In general, where a relaxation is allowed in accordance with Section 7.10.2, the following is a guide to
the acceptable sea state values. This should be confirmed as being suitable on a case-by-case basis.
Table 7-3

7.10.6
7.10.7
7.10.8

7.10.9
7.10.10

Reduced Seastate v Heading

Incident angle
(Head Seas = 0)

Applicable Hsig, as % of design sea state
(adjusted as appropriate)

0 - + 30

100%

+ (30 - 60)

Linear interpolation between 100% and 80%

+ 60

80%

+ (60 - 90)

Linear interpolation between 80% and 60%

+ 90

60%

+ (90 - 120)

Linear interpolation between 60% and 80%

+ 120

80%

+ (120 - 150)

Linear interpolation between 80% and 100%

+ (150 - 180)

100%

For any transport where a relaxation is allowed in accordance with Sections 7.10.2 and 7.10.5, a risk
assessment shall be carried out and the risks shown to be acceptable.
Such relaxation shall only apply to considerations of accelerations, loads and stresses. It shall not be
applied to considerations of stability.
For any transport where a relaxation is allowed in accordance with Sections 7.10.2 and 7.10.5, the
towage/voyage arrangements shall contain, in a format of use to the Master:
a.
The limitations on critical parameters
b.

Procedures for monitoring and recording of critical parameters

c.

Procedures for heading control

d.

Results of the risk assessment, and any recommendations arising

e.

Contingency actions in the event of any breakdown.

Critical parameters should preferably be ones the Master can observe or measure. The Master should
confirm that he can accept that the effects of these restrictions are practicable.
For any transport where a relaxation is allowed in accordance with Sections 7.10.2 and 7.10.5, it is
strongly recommended that an independent Company (Cargo Owner’s) Representative is on board to
witness events. He should be qualified to discuss with the Master weather conditions forecast and
encountered, routeing advice received and avoidance techniques adopted.

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8

LOADINGS

8.1

INTRODUCTION

8.1.1

The structure of the cargo or tow, including the legs, hull and jackhouses of self-elevating units, shall
be shown to possess adequate strength to resist the loads imposed due to the specified or calculated
motions and wind, combined with the additional loading caused by any overhang of the cargo over the
side of the vessel or barge.
The cargo shall be shown to possess adequate strength to withstand the local cribbing and
seafastening reactions.

8.1.2

8.2

LOADCASES

8.2.1

Loadcases for each heading shall be derived by the addition of fluctuating loads resulting from wind
and wave action to static loads resulting from gravity and still water initial conditions.
The fluctuating components shall be the worst possible combination of the loads resulting from
calculations or model tests carried out in accordance with Sections 7.1 through 7.8, with due account
to be taken of the effects of phase. All influential loadings shall be considered: however the following
static and environmental loadings are the most likely to be of importance:
S1: Loadings caused by gravity including the effects of the most onerous ballast condition on the
voyage.

8.2.2

F1: Loadings caused by the wind heel and trim angle.
F2: Loadings caused by surge and sway acceleration
F3: Loadings caused by pitch and roll acceleration
F4: Loadings caused by the gravity component of pitch and roll motion
F5: Loadings caused by direct wind
F6: Loadings caused by heave acceleration, including heave.sin(theta) terms
F7: Loadings caused by wave induced bending
F8: Loadings caused by slam and the effects of immersion.
8.2.3
8.2.3.1

One of the following three methods shall be used to determine the design loadings:
Except as noted in Section 7.9.2, the effects of phase differences between the various motions can be
considered, if resulting from model test measurements, or if the method of calculation has been
suitably validated.

8.2.3.2

In cases where it is not convenient or possible to determine the relative phasing of extreme wind
loadings and heave accelerations with roll/sway or pitch/surge maxima, a reduction of 10 percent may
be applied to fluctuating loadcases F1 through F8 which combine maximum wind and wave effects.
However, if wind induced or wave induced loads individually exceed the reduced load, then the
greatest single effect shall be considered.

8.2.3.3

Alternatively, the total loads may be calculated by combination of loads as follows:
S1 + F1(1hr) + F5(1hr) +  {[F2+F3+F4+F6]2 + [F1(1min)+F5(1min)–F1(1hr)–F5(1hr)]2}
Where:
F(1hr)

=

Loads based on 1 hour mean wind speed

F(1min)

=

Loads based on 1 minute mean wind speed.

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8.3

DEFAULT MOTION CRITERIA

8.3.1

For loads computed in accordance with Section 7.9, the loads applied to the cargo shall be:
S1 + F 1 + F 3 + F 4 + F 6
where: S1, F1, F3, F4 and F6 are as defined in Section 8.2.2. The effects of buoyancy and wave slam
loading shall also be considered if appropriate.
As stated in Section 7.9.2 c) roll and pitch cases are to be considered separately. Combined roll and
pitch are not required.

8.4

LONGITUDINAL BENDING

8.4.1

The potential effects of longitudinal wave bending effects need to be considered if:
a.
The towed hull is not a classed, seagoing vessel or barge, or

8.4.2

b.

The cargo is longer than about 1/3rd of the transport barge or vessel length, or

c.

The cargo is supported longitudinally on more than 2 groups of supports, or

d.

The relative stiffness of the hull and cargo could cause unacceptable stresses to be induced in
either, or

e.

The seafastening design allows little or no flexibility between cargo and barge.

8.4.3

Some cargoes, such as large steel jackets, may be inherently much stiffer than the barge, and will
reduce barge deflections, at the expense of increased cargo stresses.
See also Sections 9.2.2 for friction, 9.3 for seafastening design and 19.4 for jack-ups.

8.5

CARGO BUOYANCY AND WAVE SLAM

8.5.1

Cargo overhangs which are occasionally immersed, and which may receive loadings due to wave slam
and/or immersion, will require special consideration.
Buoyant cargoes, particularly where the buoyancy contributes to stability requirements, shall be
adequately secured against lift-off unless it can be shown that lift-off will not occur.

8.5.2

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9

DESIGN AND STRENGTH

9.1

COMPUTATION OF LOADS

9.1.1

The loads acting on grillages, cribbing, dunnage, seafastening and components of the cargo shall be
derived from the loads acting on the cargo, according to Sections 6, 7 and 8, as applicable.
The loads shall include components due to the distribution of mass and rotational inertia of the cargo.
This is of particular importance in the calculation of shear forces and bending moments in the legs of
self-elevating units and similar tall structures.
If the computed loads are less than the “Minimum allowable seafastening force” shown in Table 9-1,
then the values in the Table shall apply.
Care should be taken in cases where the cargo may be designed for service loads in the floating
condition, but is being dry-transported. Its centre of gravity may be higher above the roll centre in the
dry-transportation condition than in any of its floating service conditions. Even though the
transportation motions may appear to be less than the service motions, the loads on cargo
components and ship-loose items may be greater.

9.1.2

9.1.3
9.1.4

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9.2

FRICTION

9.2.1

For certain cargo weights, cargo overhangs and arrangements of cribbing and seafastenings, the
effects of friction may be used, as shown in the following Table 9-1 and subject to Section 9.2.2, to
resist part of the computed loadings on the cribbing and seafastenings. This shows the maximum
coefficient of friction which may be considered, and the minimum required seafastening force,
expressed as a percentage of cargo weight, below which the actual seafastening design capability
shall not be allowed to fall.
Table 9-1

Overhang

Maximum allowable coefficients of friction & minimum seafastening forces

<100

Cargo weight, W, tonnes
100
1,000
5,000
10,000< 20,000<
<W<
<W<
<W<
W<
W<
1,000
5,000
10,000
20,000
40,000
Maximum allowable coefficient of friction

> 40,000

None

0

0.10

0.20

0.20

0.20

0.20

0.20

< 15 m

0

0

0.10

0.20

0.20

0.20

0.20

15 – 25 m

0

0

0

0.10

0.20

0.20

0.20

25 – 35 m

0

0

0

0

0.10

0.20

0.20

35 - 45 m

0

0

0

0

0

0.10

0.10

> 45 m

0

0

0

0

0

0

0

Minimum required seafastening force, %W
Transverse

10%

10%

10%

10%

10%

Longitudinal

5%

5%

5%

5%

See Note
2

See Note
1
See Note
3

5%
1.5%

Notes:
1. For 20,000 ≤ W < 40,000 tonnes, the minimum required seafastening force, transversely, shall be
not less than 15 - W/4,000 (%W)
2. For 10,000 ≤ W < 20,000 tonnes, the minimum required seafastening force, longitudinally, shall be
not less than 7.5 - W/4,000 (%W)
3. For 20,000 ≤ W < 40,000 tonnes, the minimum required seafastening force, longitudinally, shall be
not less than 3.5 - W/20,000 (%W)
4. For transport of pipes and similar tubular goods, the above table does not apply. See Section 9.6.
5. The friction coefficient may be interpolated as a function of overhang using the maximum cargo
overhang.

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9.2.2

Friction is allowed as a contribution to seafastening restraint subject to the following:
a.
Loadings are computed in accordance with Sections 7.2 though 7.8 and 8.2 above. Friction
may not be used if the loadings are computed in accordance with the default criteria in Sections
7.9 and 8.3, except as allowed by Section 9.6.
b.

Friction forces shall be computed using the normal reaction between the vessel and cargo
compatible with the direction of the heave.sin(theta) term used in computing the forces parallel
to the deck in Section 8.2.2. Thus, when heave.sin(theta) increases the force parallel to the
deck, it also increases the normal reaction and vice-versa.

c.

The cargo is supported by wood dunnage or cribbing – friction is not allowed for steel to steel
interfaces.

d.

The overhang is the distance from the side of the vessel to the extreme outer edge of the cargo.

e.

For wood cribbing less than 600 mm high, with a width not less than 300 mm, the friction force
due to the friction coefficient permitted in Table 9-1 may be assumed to act in any direction
relative to the cribbing provided that:

f.

(i)

the cribbing is reasonably well balanced in terms of the proportion in the fore-aft and
transverse directions, AND

(ii)

each of these groups is reasonably well balanced about the cargo CoG in plan.

Provided that the conditions in (e) above are met, for cribbing heights between 600 and 900
mm, with a width not less than 300 mm, then the percentage computed friction force at right
angles to the longitudinal axis of a cribbing beam shall not exceed (900 - H)/3 %, where H = the
height of cribbing above deck, in mm. In the direction of the longitudinal axis of a cribbing
beam, the full friction force can be used.

g.

For wood cribbing over 900 mm high, or with a width less than 300 mm, no friction force is
assumed to act in a direction at right angles to the longitudinal axis of a cribbing beam.

h.

If greater cribbing friction is required than available according to (f) and (g) above, stanchions
may be fitted to provide transverse cribbing restraint. Where such stanchions are fitted, they
should be designed to carry loads due to a friction coefficient of 0.5 (to ensure they are able to
carry loads due to upper-bound friction assumptions).

i.

The underlying assumption in the approach given above is that the seafastenings have
sufficient flexibility to deflect in the order of at least 2mm without failing. This will be reasonable
in most cases, but when this is not the case the more detailed approach given in (j) below shall
be used.

j.

As an alternative to (e) through (h) above, a more detailed approach may be used. In such
cases, the friction permitted in Table 9-1 can be doubled, but the relative flexibility of the
cribbing and seafastenings shall be taken into account. The arrangements shall be such as to
ensure that the required lateral load can be carried by the combination of friction & seafastening
reactions BEFORE the seafastenings are overstressed. Where stanchions are used, they shall
comply with (h) above.

k.

The “Minimum allowable seafastening force” is the minimum allowable value of seafastening
restraint, expressed as a percentage of cargo weight, in the event that the total required
seafastening force, as computed, is less than this value.

l.

For very short duration moves in sheltered water, such as turning a barge back alongside the
quay after a loadout, then friction may be allowed to contribute. The entire load path, including
the potential sliding surfaces, shall be demonstrated to be capable of withstanding the loading
generated.

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9.3

SEAFASTENING DESIGN

9.3.1

In this context, seafastenings include any grillage, dunnage, cribbing or other supporting structure, roll,
pitch and uplift stops, and the connections to the barge or vessel.
Seafastenings shall be designed to withstand the global loadings as computed in Sections 7 and 8.
Seafastenings shall be designed to accept deflections of the barge or vessel in a seaway, principally
due to longitudinal bending. In general, longitudinal bending should be considered for the cases
described in Sections 8.4.1 and 8.4.2.
Where longitudinal bending is a consideration, suitable seafastening designs include:
a.
Chocks which allow some movement between the barge and cargo

9.3.2
9.3.3

9.3.4

9.3.5

9.3.6

9.3.7

9.3.8

9.3.9

9.3.10

9.3.11
9.3.12

b.

Pitch stops at one point only along the cargo, with other points free to slide or deflect
longitudinally

c.

Vertical supports at only 2 positions longitudinally

d.

An integrated structure of barge-seafastenings-cargo, capable of resisting the loads induced by
bending and shear.

Additionally, for towed objects such as FPSOs, which may have permanently installed modules with
piping or other connections between them, there should be adequate flexibility in the connections to
avoid overstress. It should be noted that the transport wave bending condition may be more severe
than the operating condition. In long modules carried as cargo, internal pipework should be similarly
considered.
In the absence of more detailed information, it should be assumed that the barge will incur bending
and shear deflection as if unrestrained by the cargo. Quasi-static barge hogging and sagging should
be considered in a wave of length L equal to the barge length, and height = 0.61L, metres.
Grillage and seafastening design is frequently influenced by the loadout method. Cargoes lifted onto
the transport barge or vessel, or floated over a submersible barge or vessel, are frequently supported
by timber cribbing or dunnage to distribute the loads and allow for minor undulations in the deck
plating. Cargoes loaded by skidding normally remain on, and are seafastened to, the skidways.
Cargoes loaded out by trailers normally need a grillage structure higher than the minimum trailer
height. The grillage or cribbing height must allow for any projections below the cargo support line.
Welded steel seafastenings are preferred, but for smaller cargoes, typically of less than 100 tonnes,
chain or wire lashings with suitable tensioning devices may be acceptable. Chain binders or
turnbuckles shall be tensioned before departure to spread the load between the seafastenings and
secured so that they cannot become slack. Lashings should be inspected regularly and after bad
weather to ensure that tension is maintained. Wire lashings are not recommended for unmanned
transportations unless such inspections can be made. Guidance on good practice for lashings and
similar devices may be found in the IMO Code of Safe Practice for Cargo Securing and Stowing, 2003
Edition [Ref. 10].
The design load in any chain used for seafastening should not exceed the certified (lifting) WLL or
SWL of the chain. When the WLL /SWL is not known, it shall be taken as no more than the certified
BL / 2.25.
Connections to the deck of a barge or vessel should be carefully considered, particularly tension
connections. Calculations should be presented to justify all connections. It should not be assumed,
without inspection, that underdeck connections between deck plating and stiffeners or bulkheads are
adequate. Seafastenings landing on doubler plates are not generally acceptable as tension
connections.
Care should be taken to avoid welding onto fuel oil tanks or oil cargo tanks, unless the tanks are
empty, and gas free certification has been obtained.
Final welded connections, particularly those which may be influenced by longitudinal deflections of the
barge or vessel, should be carried out with the barge or vessel ballasted to the transportation
condition, or as close as draught limitations permit.

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9.3.13

9.3.18

Welding of seafastenings should not be carried out in wet conditions. Weather protection should be
used to minimise the effects of wet conditions.
For cargoes that will be removed offshore, the seafastenings should be capable of being released in
stages, such that the cargo is secure for a 10 degree static angle until the release of the final stage.
The release of seafastenings, and the removal of any one item, should not disturb the seafastenings of
any other item.
Where a lift is made onto a barge offshore, the seafastenings should be designed accordingly,
normally by means of guides or a cradle, which will hold the cargo whilst it is being seafastened.
Items of the cargo which are vulnerable to wave action, wetting or weather damage shall be suitably
protected. This may require provision of breakwaters or waterproofing of sensitive areas.
Internal seafastenings may be needed to prevent items moving inside structures or modules. See also
the caution in Section 9.1.4 for dry transportations.
Guide posts should not be used for seafastenings unless specifically designed for that purpose.

9.4

CRIBBING

9.4.1

Where the cargo is supported on wooden cribbing or dunnage, rather than steel-to-steel supports, then
sufficient material should be provided to ensure an adequate distribution of load to the underside of the
cargo and to the deck of the transport vessel, under the static loadings and the design environmental
loadings as shown in Sections 7 and 8.
Cribbing designed to pick up structural members in the underside of the cargo, the transport vessel
deck, or both, and fixed to the deck of the vessel, should not normally be less than 200 mm high. See
also the comments on cribbing width in Sections 9.2.2.f and 9.2.2.g.
A minimum clearance of 0.075 m should be provided between the lowest protrusion of the cargo and
the deck of the barge or vessel.
The nominal bearing pressure on the cribbing should not normally exceed 4 N/mm2 for softwood.
Should it be demonstrated that the cargo, vessel and cribbing, without crushing, can withstand a higher
pressure, then this may be acceptable. The cribbing pressure should be calculated taking into account
the deadweight of the cargo plus the loads caused by the design environmental loadings.
Ideally the type of timber selected should withstand the computed cribbing pressures without crushing.
Localised crushing to accommodate cargo and cribbing imperfections is permissible. A satisfactory
arrangement may consist of hardwood for the main cribbing structure, topped by a soft packing layer,
say 50 mm thick.
In the case of a random or herring-bone dunnage layout supporting a flat-bottomed cargo, without
taking into account the strong points, then the maximum cribbing pressures should not exceed 1
N/mm2, subject to consideration of the overall allowable loads on the deck of the vessel and the
underside of the cargo.
For cargoes floated on and/or off a grounded or partially grounded transport barge or vessel, the
cribbing should be designed to withstand loads caused by point loads and trim or heel angles during
on-load and off-load. A minimum of 5º should be considered.

9.3.14

9.3.15
9.3.16
9.3.17

9.4.2

9.4.3
9.4.4

9.4.5

9.4.6

9.4.7

9.5

STRESS LEVELS IN CARGO, GRILLAGE & SEAFASTENINGS

9.5.1

The cargo, grillage and seafastenings shall be shown to possess adequate strength to resist the loads
imposed during the voyage. Any additional loadings caused by any overhang of the cargo over the
side of the transport vessel, buoyancy forces and wave slam loadings shall be included.
The cargo shall be shown to have adequate strength to withstand the local cribbing and seafastening
loads.
Stress levels shall be within those permitted by the latest edition of a recognised and applicable
offshore structures code.

9.5.2
9.5.3

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GUIDELINES FOR MARINE TRANSPORTATIONS
9.5.4

The structural strength of high quality structural steelwork with full material certification and NDT
inspection certificates showing appropriate levels of inspection (see Section 9.7) shall be assessed
using the methodology of a recognised and applicable offshore code including the associated load and
resistance factors for LRFD codes or safety factors for ASD/WSD codes. Traditionally AISC has also
been considered a reference code. If the AISC 13th Edition is used, the allowables shall be compared
against member stresses determined using a load factor on both dead and live loads of no less than:
WSD option
SLS:
ULS:

9.5.5

1.0
0.75

1.60
1.20

Stress in fillet fillet welds for brackets loaded by a force acting in a direction parallel to the weld bead
shall be assessed using the method presented in Appendix F. The allowables shall be compared
against member stresses determined using a load factor on both dead and live loads of no less than
SLS:
ULS:

9.5.6
9.5.7

LRFD Option

1.40
1.05

Any load case may be treated as a normal serviceability limit state (SLS) / Normal operating case.
Most probable maximum extreme (MPME) load cases, (which typically occur at the same frequency as
the maximum wave associated with the design seastate) may be treated as an ultimate limit state
(ULS) / Survival storm case provided that they are dominated by environmental forces. This does not
apply to:
 Steelwork subject to deterioration and/or limited initial NDT unless the condition of the entire
loadpath has been verified, for example the underdeck members of a barge or vessel.


Steelwork subject to NDT prior to elapse of the recommended cooling and waiting time as defined
by the Welding Procedure Specification (WPS) and NDT procedures. In cases where this cannot
be avoided by means of a suitable WPS, it may be necessary to increase the strength or impose
a reduction on the design/permissible seastate.

9.6

SECURING OF PIPE AND OTHER TUBULAR GOODS

9.6.1

This section refers to the transport of tubulars, including line pipe, casing, drill pipe, collars, piles,
conductors marine risers and similar, hereafter called “pipes”, on vessels and barges. Transport of drill
pipe, collars etc on jack-ups is covered in Section 19.11. The degree and design of securing required
will depend on the type of vessel, the nature of the cargo, the duration of the towage or voyage, and
the weather conditions expected.
For these types of cargoes, friction may be assumed to resist longitudinal seafastening loads, and
Sections 9.2.1 and 9.2.2.a do not apply. The following friction coefficients may be used, as examples:

9.6.2

Table 9-2

Typical Friction Coefficients

Materials in contact

Friction coefficient

Concrete coated pipe - concrete coated pipe

0.5

Concrete coated pipe - timber

0.4

Timber - timber

0.4

Uncoated steel - timber

0.3

Uncoated steel - uncoated steel

0.15

Epoxy coated pipe - timber

0.1

Epoxy coated pipe - epoxy coated pipe

0.05

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9.6.3
9.6.4
9.6.5

9.6.6

Caution should be exercised where sand may be present between the friction surfaces as this may
considerably reduce the friction coefficient.
Generally speaking, pipes should be stowed in the fore and aft direction.
Where pipes are stacked in several layers, the maximum permissible stacking height shall be
established, in order to avoid overstress of the lower layers. Reference may be made to API RP 5LW
“Recommended practice for transportation of line pipe on barges and marine vessels” [Ref. 14].
Smaller diameter pipes such as drill pipe may be stacked without individual chocking arrangements
and restrained transversely by means of vertical stanchions. Timber dunnage or wedges shall be used
to chock off any clearance between the pipes and the stanchions. The stanchions, taken collectively,
shall be capable of resisting the total transverse force computed.
a.
For weather-restricted operations, and 24-hour or location moves of jack-ups, the stack may be
secured by means of transverse chain or wire lashings over the top, adequately tensioned.
Provided it can be demonstrated that sufficient friction exists to prevent longitudinal movement,
no end stops need be provided.
b.

9.6.7

Line pipe on pipe carrier vessels may be stacked between the existing stanchions/crash barriers, on
the wooden sheathed deck. Timber dunnage or wedges should be used to chock off any clearance
between the pipes and the stanchions.
a.
For weather restricted operations, provided it can be demonstrated that adequate friction exists
to prevent longitudinal movement, no end stops need be provided. This is likely to apply to
concrete coated pipe, but uncoated or epoxy coated pipe should be treated with caution.
b.

9.6.8

9.6.9

9.6.10
9.6.11

For unrestricted operations, steel strongbacks should be fitted over the top layer, and each stow
set up hard by driving wooden wedges between the strongbacks and the top layer of pipe. End
stops or bulkheads shall be provided.

Larger diameter pipes such as piles are often individually chocked, and end stops provided, often at
one end only. Unless it can be demonstrated that the piles cannot roll out of the chocks further
restraints may be necessary, such as individual wire or chain lashings, stanchions or strongbacks.
In all cases of transportation of coated line pipe, the transportation and securing arrangements must be
designed so that the coating will be protected from damage. The manufacturer’s and/or shipper’s
recommendations should be sought.
Where end stops are provided for pipes with prepared ends, the end preparation should be protected,
either with protectors on the pipe, or by wood sheathing on the end stops.
When open ended pipes are carried as deck cargo and the pipes could become partially filled with
water, care should be taken to ensure that:
a.
the vessel’s stability meets the requirements of Section 10, with particular reference to the
effects of entrapped water, and
b.

9.6.12

For unrestricted operations, including ocean transportations of jack-ups, steel strongbacks
should be fitted over the top layer, and each stow (group of pipes) set up hard by driving
wooden wedges between the strongbacks and the top layer of pipe. End stops or bulkheads
shall be provided.

the deck and pipe layers are not overstressed.

Otherwise, it may be necessary to seal the ends of at least the lowest level of the stack.
Note: the trim and stability booklet of some vessels may include suitable example loading conditions
and should be considered.

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9.7

INSPECTION OF WELDING AND SEAFASTENINGS

9.7.1

For newly-constructed cargoes, an adequate system of construction supervision, weld inspection and
testing shall be demonstrated. For other cargoes, the extent of inspection and testing shall be agreed.
Principal seafastening welds shall be visually checked and the weld sizes confirmed against the
agreed design.

9.7.2
9.7.3

9.7.4

Non-destructive testing (NDT), by a suitable and agreed method, shall be carried out on the structural
members of the seafastenings. NDT acceptance criteria should be to EEMUA 158 “Construction
specification for fixed offshore structures in the North Sea” [Ref. 15], AWS D1.1 “Structural welding
code – steel” [Ref .16] or equivalent. The following is a guide to the minimum recommended extent of
NDT:
a.
100% visual
b.

Penetration welds - 40% UT and 20% MPI

c.

Fillet welds - 20% MPI

d.

All welds to barge/vessel deck - 100% MPI with additional 40% UT for penetration welds

e.

In any case, the extent of NDT should be not less than the Project specification requirements

f.

For critical areas or where poor welding quality is suspected, then 100% inspection may be
required.

9.7.5

Care should be taken where the seafastening load path depends on the tension connection of the deck
plating of a barge or vessel to underdeck stiffeners or bulkheads. In cases of any doubt about the
condition, an initial visual inspection should be undertaken, to establish that fully welded connections
exist, and that the general condition is fit for purpose. Further inspection may be required, depending
on the stress levels imposed and the condition found.
Any faulty welds discovered shall be repaired and re-tested.

9.8

FATIGUE

9.8.1

Notwithstanding the exclusion in Section 4.6.7, clients may wish the effects of fatigue on the towed
object, cargo and/or seafastenings to be considered, in which case they should instruct GL Noble
Denton accordingly.

9.9

USE OF SECOND HAND STEEL SEAFASTENINGS

9.9.1

When second hand steel seafastenings are used, any wastage caused during previous removal(s) or
use should not affect its fitness for purpose, and there should be sufficient documentation to ensure
the traceability of the steel and in particular documentation relating to the grade of steel.
There should be NDT inspection reports for areas of previous fabrication, old welds, burnt off
attachments etc, to demonstrate no cracking or lamellar tearing in critical areas.
Should sufficient documentation of the type of steel (e.g. EN10025) be unavailable, coupon testing is
acceptable to determine the steel type. The guaranteed minimum properties of this type of steel are to
be used, not the tested values which may not be representative of the rest of the steel.

9.9.2
9.9.3

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10

STABILITY

10.1

INTACT STABILITY

10.1.1

The intact range of stability, defined as the range between 0º degrees heel or trim and the angle at
which the righting arm (GZ) becomes negative, shall not be less than the values shown in the following
Table 10-1. Objects which do not fall into the categories shown in the Table, which are nonsymmetrical, or which have an initial heel or trim which is not close to 0º, may require special
consideration. Where there is a significant difference between the departure, arrival or any
intermediate condition, then the most severe should be considered, including the effects of any ballast
water changes during the voyage.
Table 10-1

Intact Stability Range

Vessel or towed object, type and size

Intact range

Large and medium vessels,

LOA > 76 m and B[1] > 23 m

36

Large cargo barges,

LOA > 76 m and B[1] > 23 m

36

Small cargo barges,

LOA <76 m or

< 23 m

40

Small vessels,

LOA <76 m or B[1] < 23 m

44

Jack-ups with

B[1], [2]

B[1]

> 23 m for ocean towages

Jack-ups with B[1], [2] > 23 m for 24-hour or location moves

36

Inland and sheltered water (in ice areas)

28
36

Inland and sheltered water (out of ice areas)

24

Notes:
1. B = maximum moulded waterline beam
2. Jack-ups with B < 23 m and without radiused bilges shall be considered as small barges. Those
with radiused bilges shall be considered as small vessels.
10.1.2

Alternatively, if maximum amplitudes of motion for a specific towage or voyage can be derived from
model tests or motion response calculations, the intact range of stability shall be not less than:
(20 + 0.8θ)
where θ = the maximum amplitude of roll or pitch caused by the design seastate as defined in Section
6.1.3, plus the static wind heel or trim caused by the design wind, in degrees.

10.1.3

10.1.4
10.1.5
10.1.6

10.1.7

Metacentric height (GM) shall be positive throughout the range shown in Section 10.1.1 or 10.1.2. The
initial metacentric height, GM0, should include an adequate margin for computational and other
inaccuracies. A GM0 of around 1.0 m will normally be required, and in any case shall not be less than
0.15 m.
Cargo overhangs shall generally not immerse as a result of heel from a 15 m/s wind in still water
conditions.
Subject to Sections 8.5 and 10.1.4, buoyant cargo overhangs may be assumed to contribute to the
range of stability requirement of Section 10.1.1.
The effects of free surface shall be considered in the stability calculations. The effects of free surface
liquids in the cargo must also be taken into account, as must residual free surface due to incomplete
venting, such as may occur if ballasting when trimmed.
Vessels shall comply with the mandatory parts of the International Maritime Organisation (IMO)
Resolution A.749 (18) as amended by Resolution MSC.75 (69) - “Code on Intact Stability” [Ref. 17],
and the IMO International Convention on Load Lines, Consolidated Edition 2002 [Ref 18].

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10.1.8

In areas and seasons prone to icing of superstructures, the effects of icing on stability should be
considered as described in Section 22.11.

10.2

DAMAGE STABILITY

10.2.1

Except as described in Sections 10.2.4 and 10.2.5 below, towed objects, including cargo barges,
MODUs and structures towed on their own buoyancy, shall have positive stability with any one
compartment flooded or broached. Minimum penetration shall be considered to be 1.5 metres. Two
adjacent compartments on the periphery of the unit shall be considered as one compartment if
separated by a horizontal watertight flat within 5 m of the towage waterline.
The emptying of a full compartment to the damaged waterline shall be considered if it gives a more
severe result than the flooding of an empty compartment.
If buoyancy of the cargo has been included to meet intact stability requirements, then loss of cargo
buoyancy or flooding of cargo compartments, shall be considered as a damage case, as appropriate.
One-compartment damage stability is not always achievable without impractical design changes, for
the following and similar structures:
a.
Concrete gravity structures, particularly when towing on the columns

10.2.2
10.2.3
10.2.4

10.2.5

10.2.6
10.2.7
10.2.8

b.

Submerged tube tunnel sections

c.

Bridge pier caissons

d.

Outfall or water intake caissons.

For those structures listed in Section 10.2.4, or similar, damage stability requirements may be relaxed,
provided the towage is a one-off towage of short duration, carried out under controlled conditions, and
suitable precautions are taken, which may include:
a.
Areas vulnerable to collision should be reinforced or fendered to withstand collision from the
largest towing or attending vessel, at a speed of 2 metres/second, and:
b.

Projecting hatches, pipework and valves are protected against collision or damage from towing
and handling lines.

c.

Emergency towlines are provided, with trailing pick-up lines, to minimise the need for vessels to
approach the structure closely during the tow.

d.

Emergency pumping equipment is provided.

e.

Potential leaks via ballast or other systems are minimised.

f.

Ballast intakes and discharges, and any other penetrations through the skin of the vessel or
object, shall be protected by a double barrier system, or blanked off.

g.

Vulnerable areas are conspicuously marked.

h.

Masters of all towing or attending vessels are aware of the vulnerable areas.

i.

A guard vessel is available to warn off other approaching vessels.

j.

A risk assessment is carried out and the risks shown to be acceptable.

The extent and adequacy of the precautions necessary for a particular towage will be assessed on a
case-by-case basis.
The relaxations allowed by Sections 10.2.4 and 10.2.5 do not apply in ice-affected areas, where the
vessel or structure should comply with Section 22.11.
The damage stability recommendations of this Section do not apply to transport of cargoes on flagged
trading vessels, sailing at the assigned ‘B’ freeboard or greater. The ‘B’ freeboard is the minimum
freeboard assigned to a Type B vessel, which is generally defined as any vessel not carrying a bulk
liquid cargo. Reduced freeboards may be assigned to a Type B vessel over 100 m in length,
depending on the arrangements for protection of crew, freeing arrangements, strength, sealing and

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security of hatch covers, and damage stability characteristics. See the IMO International Convention
on Load Lines, Consolidated Edition 2002, [Ref. 15] for further details.

10.3

WIND OVERTURNING

10.3.1

For the intact condition, the area under the righting moment curve shall be not less than 40% in excess
of the area under the wind overturning arm curve. The areas shall be bounded by 0º heel or trim, and
the second intercept of the righting and wind overturning arm curves, or the downflooding angle,
whichever is less.
The wind velocity used for intact wind overturning calculations shall be the 1-minute design wind
speed, as described in Section 6.13. In the absence of other data, 50 metres /second shall be used.

10.3.2

(A + B) > 1.4 (B + C)
0.8

Downflooding
angle

RIGHTING ARM (GZ)

Intact GZ

A

Wind
Overturning
Arm

Intercept angle

C

B

0.0

HEEL ANGLE (DEGREES)

0

40

Figure 10-1 Wind Overturning Criteria (Intact Case)
10.3.3

For the damage condition, the area under the righting moment curve shall be not less than 40% in
excess of the area under the wind overturning arm curve. The areas shall be bounded by the angle of
loll, and the second intercept of the righting and wind overturning arm curves, or the downflooding
angle, whichever is less.
(A + B) > 1.4 (B + C)
0.6

RIGHTING ARM (GZ)

Damaged GZ
Angle of
Loll

Downflooding
angle

A

Wind
Overturning
Arm

Intercept angle

C

B

0
0

HEEL ANGLE (DEGREES)

40

Figure 10-2 Wind Overturning Criteria (Damaged Case)
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10.3.4

The wind velocity used for overturning moment calculations in the damage condition shall be 25
metres /second, or the wind used for the intact calculation if less.

10.4

DRAUGHT AND TRIM

10.4.1

For vessels and barges with a load-line certificate, the draught shall never exceed the appropriate
load-line draught, except for temporary on-load and off-load operations under controlled conditions.
The draught should be small enough to give adequate freeboard and stability, and large enough to
reduce motions and slamming. Typically, for barge towages, it will be between 35% and 60% of hull
depth, which is usually significantly less than the load-line draught.
For barges and large towed objects, such as FPSOs, the draught and trim should be selected to
minimise slamming under the forefoot, to give good directional control, and to allow for the forward trim
caused by towline pull.
For guidance, and for discussion with the Master of the tug, the tow should be ballasted to the
following minimum draughts and trims:

10.4.2

10.4.3

10.4.4

Table 10-2

10.4.5

10.4.6
10.4.7
10.4.8

Minimum draught & trim

Length of Towed Vessel

Minimum Draught Forward

Minimum Trim by Stern

30 metres

1.0 metre

0.3 metre

60 metres

1.7 metres

0.6 metre

90 metres

2.4 metres

0.8 metre

120 metres

3.1 metres

1.0 metre

150 metres

3.7 metres

1.2 metres

200 metres

4.0 metres

1.5 metres

Where barges with faired sterns are fitted with directional stabilising skegs, it may be preferable to
have no trim. This should normally be documented in the Trim and Stability booklet. However
allowance should be made for trim caused by the towline force and there should be adequate
freeboard at the bow (and possibly a breakwater) to minimise damage from “green water” coming over
the bow.
It may be preferable to tow structures such as floating docks, at minimum draught with zero trim, in
order to minimise longitudinal bending moments.
Draught marks forward and aft shall be easily readable and, if necessary, re-painted in the area above
the waterline.
Where the tow is unmanned, and in order that the tug may monitor any increased draught during the
towage, it may be advantageous to paint a broad distinctive line of contrasting colour around the bow
approximately 0.5 metre above the waterline.

10.5

COMPARTMENTATION AND WATERTIGHT INTEGRITY

10.5.1

Where the watertight integrity of any tow is in question, particularly for demolition tows, part built ships
and MODUs, it shall be checked by visual inspection, chalk test, ultrasonic test, hose test or air test as
considered appropriate by the attending surveyor.
Any opening giving an angle of downflooding less than 20 degrees, or (θ + 5) degrees if less than 20
degrees, where θ is the angle as defined in Section 10.1.2, shall be closed and watertight, or protected
by automatic closures in operable condition.
Hatches, ventilators, gooseneck air pipes and sounding pipes shall be carefully checked for proper
closure and their watertight integrity confirmed. Where such equipment could be damaged by sea
action or movement of loose equipment, then additional precautions should be considered.

10.5.2

10.5.3

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10.5.4

10.5.5
10.5.6

10.5.7
10.5.8
10.5.9
10.5.10
10.5.11

10.5.12
10.5.13

Outboard accommodation doors shall be carefully checked for proper closure and their weathertight
integrity confirmed. All dogs shall be in good operating condition and seals shall be functioning
correctly.
Watertight doors in holds, tween decks and engine room bulkheads, including shaft alleyway and boiler
room spaces, shall be checked for condition and securely closed.
Any watertight doors required to be opened for access during the transportation, shall be marked, on
both sides, “To be kept closed except for access” or words to that effect. In some cases a length of
bar or pipe may be required to assist opening and closing.
Portholes shall be checked watertight. Porthole deadlights shall be closed where fitted. Any opening
without deadlights that may suffer damage in a seaway shall be plated over.
Windows which could be exposed to wave action shall be plated over, or similarly protected.
All tank top and deck manhole covers and their gaskets shall be in place, checked in good condition,
and securely bolted down.
All overboard valves shall be closed and locked with wire or chain. Where secondary or back-up
valves are fitted for double protection, they shall also be closed.
Closure devices fitted to sanitary discharge pipes, particularly near the waterline, shall be closed. Any
discharge pipe close to the waterline not fitted with a closure device, may need such a facility
incorporated, or be plated over.
All holds, void spaces and engine room bilges shall be checked before departure and should be
pumped dry.
All other spaces shall be sounded prior to departure. It is recommended that all spaces should be
either pressed up or empty. Slack tanks should be kept to a minimum.

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11

TRANSPORT VESSEL SELECTION

11.1

GENERAL

11.1.1

The following points should be considered in the selection of a suitable transport barge or vessel:
a.
Is there adequate deck space for all the cargo items planned, including room for seafastenings,
access between cargo items, access to towing and emergency equipment, access to tank
manholes, installation of cargo protection breakwaters if needed, and for lifting offshore if
required?
b.

Has the barge or vessel adequate intact and damage stability with the cargo and ballast as
planned, including any requirement for ballast water exchange?

c.

Does the barge or vessel as loaded have sufficient freeboard to give reasonable protection to
the cargo?

d.

If a floating loadout is planned, is there sufficient water depth to access and leave the loadout
berth? Can the loadout be carried out in accordance with GL Noble Denton document 0013/ND
- Guidelines for Loadouts [Ref. 2]

e.

If a submerged loadout is planned, can the barge or vessel be submerged, within its Class
limitation, so as to give adequate clearance over the deck, and adequate stability at all stages,
within the water depth limitations of the loadout location?

f.

Is the deck strength adequate, including stiffener, frame and bulkhead spacing and capacity, for
loadout and transportation loads?

g.

For a vessel, does securing of seafastenings require welding in way of fuel tanks?

h.

For a barge, is it properly equipped with main and emergency towing connections, recovery
gear, pumping equipment, mooring equipment, anchors, lighting and access ladders?

i.

Will the motion responses as calculated cause overstress of the cargo?

j.

Is all required equipment and machinery in sound condition and operating correctly?

k.

Does the barge or vessel possess the relevant, in date, documentation as set out in Section 5?

11.2

SUITABILITY AND ON-HIRE SURVEYS

11.2.1

In his interest, the charterer is advised to have a suitability survey and an on-hire survey of the barge
or vessel carried out prior to acceptance of the charter.

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12

TOWING VESSEL SELECTION AND APPROVAL

12.1

GENERAL

12.1.1

The tug(s) selected should comply with the minimum bollard pull requirements shown in Section 12.2
below, and should also comply with the appropriate Category in Section 3 of GL Noble Denton
document 0021/ND - Guidelines for the Approvability of Towing Vessels [Ref. 5]. The categories are
summarised in the following table. The appropriate category should be agreed with the GL Noble
Denton office concerned.
Table 12-1
Category
ST – Salvage Tug
U - Unrestricted

12.1.2

12.1.3

12.1.4

12.1.5

Towing Vessel Categories

Used for
Single tug towages in benign or non-benign weather areas

C - Coastal

Towages in benign weather areas or weather routed

R1 - Restricted

Assisting in multi-tug towages

R2 - Restricted

Benign weather area towages

R3 - Restricted

Assisting in multi-tug towages in benign weather areas

The tug(s) used for any towage to be approved by GL Noble Denton should be inspected by a
surveyor nominated by GL Noble Denton before the start of the towage. The survey will cover the
suitability of the vessel for the proposed operation, its seakeeping capability, general condition,
documentation, towing equipment, manning and fuel requirements.
For tugs entered in the GL Noble Denton Towing Vessel Approvability Scheme (TVAS), it will generally
be possible to issue a statement of acceptability in principle, prior to departure. The extent and
frequency of surveys as required by the TVAS is defined in Ref. [5]. A survey on departure will still be
required, to ensure that the vessel still complies with the rules of the scheme.
Vessels not entered into the scheme will require to be surveyed before any formal opinion on
acceptability or approvability can be issued. For vessels not known to GL Noble Denton, a survey well
in advance of departure is recommended.
An additional tug may be recommended for high value tows or towages through areas with limited
searoom, to carry out the following duties:
a.
Act as a Guardship, to protect the tow, and advise approaching vessels they may be running into
danger
b.

In the event of mechanical failure or towline breakage, assist in removing the failed tug from the
towing spread

c.

Take over the duties of the failed tug

e.

Provide any other required assistance in an emergency.

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12.2

BOLLARD PULL REQUIREMENTS

12.2.1

The following Table summarises the different conditions to be considered. The most severe conditions
that apply to a particular towage should be used. The conditions are described in more detail in the
indicated sections.
Table 12-2

Meteorological Criteria for Calculating TPR (Towline Pull Required)

Section

Condition

Hsig (m)

Wind (m/sec)

12.2.2

Limited searoom

Design

Design
(1 hour mean)

12.2.3

Continuous adverse
current or weather

12.2.4

Standard

5

20

12.2.5

24-hour jack-up move

3

15

12.2.6

Benign weather areas

As agreed with the GL Noble Denton office concerned but not less than:
2
15
0.5

12.2.7

Sheltered from waves

As agreed with the GL Noble Denton office concerned.

12.2.2

12.2.3

12.2.4

12.2.5

Current (m/sec)
0.5
or predicted current if greater

As agreed with the GL Noble Denton office concerned to ensure a
reasonable speed in moderate weather.
0.5
0.5
or predicted current if greater

For towages which pass through an area of restricted navigation or manoeuvrability, outside the
validity of the departure weather forecast and which cannot be considered a weather-restricted
operation, the minimum Towline Pull Required (TPR) should be computed for zero forward speed
against the following acting simultaneously:
 the design wave height (see Section 6), and


1 hour design wind speed (see Section 6), and



0.5 metres/second current, or the maximum predicted surface current if greater.

If the tow route passes through an area of continuous adverse current or weather, or if a particular
towing speed is required in calm or moderate weather, a greater TPR may be appropriate and agreed
with the GL Noble Denton office concerned. In any event, an assessment should be made that a
reasonable speed can be achieved in moderate weather.
For towages where adequate searoom can be achieved within the departure weather forecast and
maintained thereafter, the TPR shall be computed for zero forward speed against the following acting
simultaneously:
 5.0 metre significant seastate, and


20 metres/second wind, and



0.5 metres/second current, or the maximum predicted surface current if greater.

For 24-hour moves of jack-ups the following reduced criteria, acting simultaneously, may be used for
the calculation of TPR:
 3.0 metres significant seastate, and


15 metres/second wind, and



0.5 metres/second current, or the maximum predicted surface current if greater.

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12.2.6

12.2.7
12.2.8

For benign weather areas, the criteria for calculation of TPR shall be agreed with the GL Noble Denton
office concerned. Generally these should not be reduced below:
 2.0 metres significant seastate, and
 15 metres/second wind, and
 0.5 metres/second current.
For towages partly sheltered from wave action, but exposed to strong winds, the criteria shall be
agreed with the GL Noble Denton office concerned.
TPR shall be related to the continuous static bollard pull of the tug(s) proposed (BP) by:
TPR = (BP x Te/100)
where:

12.2.9

Te = the tug efficiency in the sea conditions considered, %
(BP x Te/100) is the contribution to TPR of each tug
 means the aggregate of all tugs assumed to contribute.

Tug efficiency, Te, depends on the size and configuration of the tug, the seastate considered and the
towing speed achieved. In the absence of alternative information, Te may be estimated for good
ocean-going tugs according to the following Table 12-3. However tugs with less sea-kindly
characteristics will have significantly lower values of Te in higher sea states.
Values of Tug Efficiency, Te

Table 12-3

Tug Efficiency, Te %

Continuous Bollard
Pull (BP), tonnes

12.2.10

Calm

Hsig = 2 m

Hsig = 3 m

Hsig = 5 m

BP < 30

80

50 + BP

30 + BP

BP

30 < BP < 90

80

80

52.5 + BP/4

7.5 + 0.75 x BP

BP > 90

80

80

75

75

These efficiencies are shown graphically in the following Figure.
100

TUG EFFICIENCY, Te %

90

calm

80

2m Hsig

70
60
50

3m Hsig

40

5m Hsig

30
20
10
0
0

10

20

30

40

50

60

70

80

90

100

STATIC CONTINUOUS BOLLARD PULL (tonnes)

Figure 12-1 Tug efficiencies in different sea states
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12.2.11

The resulting effective bollard pull in the different sea states is shown in the following Figure:

EFFECTIVE BOLLARD PULL (tonnes)

80
70
60
50

< 2 m Hsig
40

5m Hsig

30

3m Hsig
20

Calm
10

2m Hsig
0
0

10

20

30

40

50

60

70

80

90

100

STATIC CONTINUOUS BOLLARD PULL (tonnes)

Figure 12-2 Effective Bollard Pull in Different Sea States
12.2.12

Alternatively, for the Hsig = 5.0 m case, BP can be related to TPR by:
Table 12-4

Selecting Bollard Pull from TPR for Hsig = 5 m

Towline Pull Required (TPR), tonnes

Continuous Bollard Pull (BP), tonnes

TPR < 9

(100 x TPR)

9 < TPR < 67.5

[25 + (300 x TPR) /2.25] - 5

TPR > 67.5

TPR /0.75

12.2.13

Only those tugs connected so they are capable of pulling effectively in the forward direction shall be
assumed to contribute. Stern tugs shall be discounted in the above calculation.

12.3

MAIN & SPARE TOWING WIRES & TOWING CONNECTIONS

12.3.1

The main and spare towing wires, pennants and connections shall be in accordance with Section 13.

12.4

TAILGATES / STERN RAILS

12.4.1

Where a towing tailgate or stern rail is fitted, the radius of the upper rail shall be at least 10 times the
diameter of the tug’s main towline, and adequately faired to prevent snagging.

12.5

TOWLINE CONTROL

12.5.1

Where a towing pod is fitted, its strength shall be shown to be adequate for the forces it is likely to
encounter. It should be well faired and the inside and ends must have a minimum radius of 10 times
the towline diameter.

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12.5.2

12.5.3

Where no pod is fitted, the after deck should be fitted with a gog rope, mechanically operated and
capable of being adjusted from a remote station. If a gog rope arrangement is fitted then a spare shall
be carried. Where neither a towing pod nor gog rope is fitted, then an alternative means of centring
the tow line should be provided.
On square-sterned towing vessels, it is preferred that mechanically or hydraulically operated stops be
fitted near the aft end of the bulwarks, to prevent the towline slipping around the tug's quarter in heavy
weather.

12.6

WORKBOAT

12.6.1

A powered workboat must be provided for emergency communication with the tow, and must have
adequate means for launching safely in a seastate associated with Beaufort Force 4 to 5. An inflatable
or RIB may be acceptable provided it has flooring suitable for carriage of emergency equipment to the
tow.

12.7

COMMUNICATION EQUIPMENT

12.7.1

In addition to normal Authorities’ requirements, the tug shall carry portable marine VHF and/or UHF
radios, for communication with the tow when tug personnel are placed on board for inspections or
during an emergency. Spare batteries and a means of recharging them shall be provided.

12.8

NAVIGATIONAL EQUIPMENT

12.8.1

Towing vessels shall be provided with all necessary navigational instruments, charts and publications
that may be required on the particular towage, including information for possible diversion ports and
their approaches.

12.9

SEARCHLIGHT

12.9.1

The tug shall be fitted with a searchlight to aid night operations and for use in illuminating the tow
during periods of emergency or malfunction of the prescribed navigation lights. The searchlight(s)
should provide illumination both forward and aft, thereby allowing the tug to approach the tow either
bow or stern on.

12.10

PUMP

12.10.1

On any tow outside coastal limits, the tug shall carry at least one portable pump, equipped with means
of suction and delivery and having a self contained power unit with sufficient fuel for 12 hours usage at
the pump’s maximum rating. The pump shall be suitable for the requirements outlined in Section
15.2.1.e through 15.2.1.h, but may not be considered to be a substitute for the pump(s) required by
Section 15. The methods and feasibility of deployment should be considered.

12.11

ADDITIONAL EQUIPMENT

12.11.1
12.11.2

Anti-chafe gear should be fitted as necessary. Particular attention should be paid to contact between
the towline and towing pods, tow bars and stern rail.
All tugs should be equipped with burning and welding gear for use in emergency.

12.12

BUNKERS & OTHER CONSUMABLES

12.12.1

The tug should carry fuel and other consumables including potable water, lubricating oil and stores, for
the anticipated duration of the towage, taking into account the area and season, plus a reserve of at
least 5 days supply. If refuelling en route is proposed, then suitable arrangements must be made
before the towage starts, and included in the towing procedures.

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12.13

TUG MANNING

12.13.1

Notwithstanding minimum manning levels for tugs as described in Ref. [5], or those required by State
or Port Authorities, consideration shall be given to the fact that in an emergency situation, two or more
of the tug crew may need to board and remain on the tow for an extended period. This should be
taken into account when approving the manning level of a towing vessel.

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13

TOWING & MISCELLANEOUS EQUIPMENT ON TOW

13.1

TOWING EQUIPMENT & ARRANGEMENTS - GENERAL

13.1.1

Towage should normally be from the forward end of the barge or tow via a suitable bridle as shown in
Appendix A. The components of the system are:
a.
Towline connections, including towline connection points, fairleads, bridle legs and bridle apex

13.1.2

13.1.3
13.1.4

13.1.5
13.1.6

b.

Intermediate pennant

c.

Bridle recovery system

d.

Emergency towing gear.

There may be a case for towing some structures by the stern. These could include:
a.
Part-built or damaged ships, or any structure when the bow sections could be vulnerable to
wave damage.
b.

Part-built ships, converted ships or FPSOs without a rudder or skeg, or with a turret or spider
fitted forward, where better directional stability may be obtained if towed by the stern.

c.

Any structure with overhanging or vulnerable equipment near the bow, which could be
vulnerable to wave damage, or could interfere with the main and emergency towing
connections.

A decision whether to tow by the stern should be based on the results of a risk assessment which shall
be presented to GL Noble Denton for review.
If two tugs are to be used for towing, then in general the larger tug should be connected to the bridle,
and the smaller tug to a chain or chain/wire pennant set to one side of the main bridle. Alternatively
two bridles may be made up, one for each tug. For two balanced tugs, the bridle may be split and the
tugs should tow off separate bridle legs, via intermediate pennants. This is not generally preferred for
tows with rectangular bows. Whichever system is used, a recovery system should be provided for the
connection point for each tug.
For tows where a bridle is not appropriate, such as multiple tug towages, then normally each tug
should tow off a chain pennant and an intermediate wire pennant.
It is normal that the towline and the intermediate pennant are supplied by the tug. However, the
strength requirements are presented here, to bring together the requirements for towlines and towing
connections.

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13.2

STRENGTH OF TOWLINE & TOWLINE CONNECTIONS

13.2.1

The Minimum Breaking Loads (MBL) of the main and spare towlines, and the ultimate load capacity of
the towline connections to the tow including each bridle leg, shall be related to the actual continuous
static bollard pull (BP) of the tug as follows, (BP, MBL and ULC are in tonnes):
a.
Towline breaking load MBL shall be computed as follows:
Table 13-1

b.

Minimum Towline Breaking Loads (MBL)

Bollard Pull (BP)

Benign Areas

Other Areas

BP < 40 tonnes

2.0 x BP

3.0 x BP

40 < BP < 90 tonnes

2.0 x BP

(3.8 - BP/50) x BP

BP > 90 tonnes

2.0 x BP

2.0 x BP

The Ultimate Load Capacity (ULC), in tonnes, of towline connections to the tow, including bridle
legs, chain pennants, and fairleads, where fitted, shall be not less than:
ULC = 1.25 x MBL

(for MBL < 160 tonnes) or

ULC = MBL + 40

(for MBL >160 tonnes)

See Section 13.5.2 for bridle apex angle >120o.
13.2.2

13.2.3
13.2.4

A certificate to demonstrate the MBL of each towline shall be available. MBL may be obtained by
testing, or by showing the aggregate breaking load of its component wires, with a spinning reduction
factor. This certificate shall be issued or endorsed by a body approved by an IACS member or other
recognised certification body accepted by GL Noble Denton.
Each bridle leg, and the connections to which it is attached, shall be designed to the full value of ULC,
as shown in Section 13.2.1.b.
Fairleads, where fitted, shall be designed to take loadings as the tug deviates from the nominal towing
direction, as follows, where:
 = a.

the horizontal angle of towline pull from the nominal towing direction when a bridle is
not used, as shown in Figure 13-1, or
b. the horizontal angle of the bridle leg from its normal direction (with bridle apex angles
of less than 120o - see Section 13.5.2).
ULC is as defined in Section 13.2.1.b.

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Deviated
towline
direction

Nominal
towing
direction



Nominal towing
direction with bridle

Deviated bridle
leg direction



Figure 13-1 Definition of angle  with and without a bridle
Table 13-2

13.2.5
13.2.6
13.2.7

13.2.8

13.2.9

13.2.10

Fairlead Resolved ULC

Horizontal angle, 

Fairlead ultimate load capacity, resolved as appropriate

0 <  < 45

ULC

45 <  < 90

Linear interpolation with  between ULC and (0.5 x ULC)

 > 90

0.5 x ULC

Where no fairleads are fitted, the towing connections shall be similarly designed.
If a fairlead or towing connection is to be used either with or without a bridle, it should be designed for
both cases.
For tows where it may be operationally necessary to apply the full value of towline pull at any angle,
the connections and fairleads may require special consideration, and the reduction shown in Section
13.2.4 may not be appropriate.
Where towing connections or fairleads may be subjected to a vertical load, the design shall take
account of the connection or fairlead elevation, the proportion of bridle and towline weight taken at the
connection or fairlead, and the towline pull, at the maximum pitch angle computed.
It should be noted that the above requirement represents the minimum values for towline connection
strength. It may be prudent to design the main towline connections to allow for the use of tugs larger
than the minimum required.
In particular circumstances, where the available towing vessel is oversized with regard to TPR (see
Section 12.2), and the towline connections are already fitted to the tow, then the towline connections
(but not the towline itself) may be related to the required BP rather than the actual BP. Such relaxation
shall be with the express agreement of the Master of the tug, and shall be noted in the towing
arrangements. It shall not apply for towages in ice areas.

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13.3

RELATIONSHIP BETWEEN TOWLINE LENGTH AND STRENGTH

13.3.1

Except in benign areas and sheltered water towages, the minimum length available of each of the main
and spare towlines (L) shall be determined from the “European” formula:
L > (BP/MBL) x 1800 metres

13.3.2

except that in no case shall the available length be less than 650 metres, apart from coastal towages
within a good weather forecast when this may be reduced to 500m.
For benign areas, the minimum length available shall be not less than:
L > (BP/MBL) x 1200 metres

13.3.3

13.3.4

except that in no case shall the available length be less than 500 metres.
The available length shall take into account the minimum remaining turns on the winch drum, and the
distance from the drum to the stern rail or roller. One full strength wire rope pennant which is
permanently included in the towing configuration may be considered when determining the available
length.
MBL as shown in Section 13.2.1 shall be increased if required for L to comply with Section 13.3.1 or
13.3.2 as appropriate. ULC shall be correspondingly increased.

13.4

TOWLINE CONNECTION POINTS

13.4.1

Towline connections to the tow shall be of an approved type. Preferably they should be capable of
quick release under adverse conditions, to allow a fouled bridle or towline to be cleared, but must also
be secured against premature release. A typical bracket design is shown in Appendix C.
Towline connections and fairleads shall be designed to the requirements of Section 13.2.
Sufficient internal/underdeck strength must be provided for all towline connections and fairleads.
Where fitted, fairleads should be of an approved type, located close to the deck edge. They should be
fitted with capping bars and sited in line with the towline connections, to prevent side load on the
towing connections.
Where the bridle might bear on the deck edge, the deck edge should be suitably faired and reinforced
to prevent chafe of the bridle.
Where towing connections are of a quick-release type, then the fairlead design shall allow all the
released parts to pass easily through the fairlead.

13.4.2
13.4.3
13.4.4

13.4.5
13.4.6

13.5

BRIDLE LEGS

13.5.1

13.5.3
13.5.4

Each bridle leg should be of stud link chain or composite chain and wire rope. If composite, the chain
should of sufficient length to extend beyond the deck edge and prevent chafing of the wire rope.
The angle at the apex of the bridle should normally be between 45 and 60 degrees. If it exceeds 120o
then the strength of the bridle legs, fittings and towing connections will need to be increased to allow
for the increased resolved load in the bridle from the towline force.
The end link of all chains shall be a special enlarged link, not a normal link with the stud removed.
All wire ropes shall have hard eyes or sockets.

13.6

BRIDLE APEX

13.6.1

The bridle apex connection should be a towing ring or triangular plate, often called a Delta, Flounder or
Monkey Plate, or an enlarged bow shackle.

13.7

SHACKLES

13.7.1

The breaking load of shackles forming part of the towline shall be at least 110% of the actual breaking
load of the towline to be used.

13.5.2

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13.7.2
13.7.3

The breaking load of shackles forming part of the bridle shall be not less than 110% of the required
breaking load of the connected parts.
If the breaking load of a shackle cannot be identified then the minimum Safe Working Load (SWL) may
be related to the continuous static bollard pull (BP) of the largest tug proposed, as follows:
Table 13-3

Default Shackle SWL

Continuous bollard pull, BP, tonnes

Minimum Safe Working Load,
SWL, tonnes

BP < 40

1.0 x BP

BP > 40

(0.5 x BP) + 20

13.8

INTERMEDIATE PENNANT OR SURGE CHAINS

13.8.1

An intermediate wire rope pennant should be fitted between the main towline and the bridle or chain
pennant. Its main use is for ease of connection and reconnection. All wire rope pennants shall have
hard eyes or sockets, and be of the same lay (i.e. left or right hand) as the main towline.
A synthetic spring, if used, should not normally replace the intermediate wire rope pennant.
The length of the wire pennant for barge tows is normally 10-15 metres since this can be handled on
the stern of most tugs without the connecting shackle reaching the winch. Longer pennants may be
needed in particular cases.
The breaking strength of the wire rope pennant shall not be less than that of the main towline with the
possible exceptions in Section 13.8.6.
A surge chain may be used, especially in shallow water when a long towline catenary cannot be used,
to provide shock absorption. If a surge chain is supplied then the MBL shall not be less than that of the
main towing wire. The surge chain shall be a continuous length of welded studlink chain with an
enlarged open link at each end (see Section 13.5.3). A method of recovery of the chain shall be
provided in case a tow wire breaks.
GL Noble Denton may approve a “fuse” or “weak link” pennant provided that:
a.
The strength reduction is not more than 10% of the actual strength of the main towline, and

13.8.2
13.8.3

13.8.4
13.8.5

13.8.6

b.

The resulting strength of the pennant is at least equal to that required for the towline.

13.9

SYNTHETIC SPRINGS

13.9.1

Where a synthetic spring is used, its breaking load shall be at least 1.5 times that required for the main
towline. As synthetic springs have a limited life due to embrittlement and ageing, they must be in good
condition, and have been stored to protect them from wear, solvents and sunlight. See Section 22.7.7
for towages when icing can occur.
If used, a synthetic spring should normally be connected between the main towing wire and the
intermediate pennant, rather than connected directly into the bridle apex.
All synthetic springs shall have hard eyes. A synthetic spring made up as a continuous loop with a
hard eye each end is generally preferable to a single line with an eye splice each end.

13.9.2
13.9.3

13.10

BRIDLE RECOVERY SYSTEM

13.10.1

A system shall be fitted to recover the bridle or chain pennant, to allow reconnection in the event of
towline breakage. The preferred type of bridle recovery system is shown in Appendix A. It consists of
a winch and a recovery line connected to the bridle apex, via a suitable lead, preferably an A-frame.
The recovery winch shall be capable of handling at least 100% of the weight of the bridle, plus
attachments including the apex and the intermediate pennant. It shall be suitably secured to the
structure of the tow. Except for very small barges, the winch should have its own power source. It

13.10.2

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13.10.3
13.10.4
13.10.5

should be noted that an adequate winch will be useful for initial connection of the towline. Adequate
fuel should be carried.
If the winch is manually operated, it should be fitted with ratchet gear and brake, and should be geared
so that the tow bridle apex can be recovered by 2 persons.
Should no power source be available, and manual operation is deemed impractical, then arrangements
shall be made, utilising additional pennant wires as necessary, which will allow the tug to reconnect.
The breaking load of the recovery wire, shackles, leads etc shall be at least 6 times the weight of the
bridle, apex and intermediate pennant. The winch barrel should be adequate for the length and size of
the wire required.

13.11

EMERGENCY TOWING GEAR

13.11.1

Emergency towing gear shall be provided in case of towline failure, bridle failure or inability to recover
the bridle. Preferably it should be fitted at the bow of the tow. It may consist of a separate bridle and
pennant or a system as shown in Appendix B. Precautions should be taken to minimise chafe of all
wire ropes.
The emergency system will typically consist of the following:
a.
Towing connection on or near the centreline of the tow, over a bulkhead or other suitable strong
point

13.11.2

13.11.3

13.11.4

13.11.5

13.11.6

13.11.7
13.11.8
13.11.9

b.

Closed fairlead

c.

Emergency pennant, minimum length 80 metres, with hard eyes or sockets, preferably in one
length. This length may be reduced for small barges and in benign areas

d.

Extension wire, if required, long enough to prevent the float line chafing on the stern of the tow

e.

Float line, to extend 75-90 metres abaft the stern of the tow

f.

Conspicuous pick-up buoy, with reflective tape, on the end of the float line.

The strength of items a, b and c above should be as for the main towline connections, as shown in
Section 13.2.1. The breaking load of the handling system, items d and e above should be not less
than 25 tonnes, and must be sufficient to break the securing devices.
If the emergency towline is attached forward, it must be led over the main tow bridle. It should be
secured to the outer edge of the tow, outside all obstructions, with soft lashings, or metal clips opening
outwards, approximately every 3 metres.
If the emergency towing gear is attached aft, the wire rope should be coiled or flaked near the stern, so
that it can be pulled clear. The outboard eye should be led over the deck edge to prevent chafe of the
float line.
For towage of very long vessels, alternative emergency arrangements may be approvable but any
arrangement shall be agreed with the Master of the tug to ensure that reconnection is possible in an
emergency.
Whatever the arrangement agreed, care shall be taken that no chafe can occur to the floating line
when deployed.
It is good practice to have swivels at the connection of the float line to the pennant line or extension
wire, and at the connection of the float line to the buoy.
The following reconnection equipment should also be considered, and placed on board if the duration
and area of the towage demand it:
a.
Heaving lines
b.

Line throwing equipment

c.

Spare shackles.

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13.12

CERTIFICATION

13.12.1

Valid certificates shall be available for all chains, wires and shackles utilised in the towing
arrangement. Where certification is not available or attainable for minor items the surveyor may
recommend that oversized equipment shall be fitted. Certificates shall be issued or endorsed by
bodies approved by an IACS member or other recognised certification bodies accepted by GL Noble
Denton.
The GL Noble Denton surveyor may reject any items that appear to be unfit for purpose, or are lacking
valid certification.

13.12.2

13.13

NAVIGATION LIGHTS & SHAPES

13.13.1

The tow shall carry the lights and shapes required by the International Regulations for Preventing
Collisions at Sea, 1972 amended 1996 (COLREGS [Ref. 19]) and any local regulations.
Navigation lights shall be independently powered (e.g. from an independent electric power sources or
from gas containers). Fuel or power sources shall be adequate for the maximum duration of the
towage, plus a reserve. Spare mantles or bulbs should be carried, even if the tow is unmanned.
It is desirable that a duplicate system of lights be provided.
Towed objects which may offer a small response to radar, such as barges or concrete caissons with
low freeboard, should be fitted with a radar reflector. The reflector should be mounted as high as
practical. Octahedral reflectors should be mounted in the “catch-rain” orientation.

13.13.2

13.13.3
13.13.4

13.14

ACCESS TO TOWS

13.14.1

13.14.8

Whether a tow is manned or not, suitable access must be provided. This may include at least one
permanent steel ladder on each side, from main deck to below the waterline.
Where practical, ladders should be recessed, back painted for ease of identification, be clear of
overhanging cargo, and faired off to permit access by the tug’s workboat.
Alternatives may be accepted if it can be demonstrated that they will provide a safe and reliable means
of access during the towage. For example, a pilot ladder on each side or over the stern, secured to
prevent it being washed up on deck, may be accepted for short tows or where it can be deployed from
a manned tow.
Objects with high freeboard (e.g. over about 10 m) may need special consideration. Ladders should
be enclosed, except within 5 m of the towage waterline, with resting platforms every 10 metres. Where
practical, stairways are preferable to ladders.
Where practical, a clear space should be provided and appropriately marked, with access ladders if
necessary so that, in an emergency, men may landed or recovered by helicopter. If it is required to
land a crew on board prior to entering port, for instance to start pumps and reduce draught, then a
properly marked and certified helideck or landing area would be an advantage.
A boarding party should be appropriately equipped with survival suits, lifejackets and communication
equipment.
Even if the tow is not manned, consideration should be given to placing life saving appliances on
board, appropriate to the hazards a boarding party may face once aboard.
Not withstanding the potential for piracy in some areas, means of boarding shall still be available.

13.15

ANCHORING & MOORING EQUIPMENT

13.15.1

See Section 16.

13.14.2
13.14.3

13.14.4

13.14.5

13.14.6
13.14.7

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13.16

DAMAGE CONTROL & EMERGENCY EQUIPMENT

13.16.1

When the length and area of the towage demand it, the following equipment should be carried on the
tow in suitable packages or in a waterproof container secured to the deck:
a.
Burning gear
b.

Welding equipment

c.

Steel plate - various thicknesses

d.

Steel angle section - various sizes and lengths

e.

Plywood sheets - 25 mm thick

f.

Lengths of 3” x 3” (75mm x 75mm) timber

g.

Caulking material

h.

Sand and cement (suitably packaged)

i.

Nails - various sizes

j.

Wooden plugs – various sizes

k.

Wooden wedges – various sizes

l.

A selection of tools, including a hydraulic jack, hammers, saws, crowbars, Tirfors.

m.

Portable coamings 60 cm minimum height, with a flange and boltholes to suit the manhole
design. The top should be constructed to avoid damage to hoses and cables

n.

A sounding tube extension, of 60 cm minimum height, threaded so that it can be screwed into
all sounding plug holes

o.

Sounding tapes

p.

Fire fighting equipment as appropriate

q.

Personal protection equipment - gloves, goggles, hard hats, survival suits etc

r.

Emergency lighting.

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14

VOYAGE PLANNING

14.1

GENERAL

14.1.1

The following recommendations apply with respect to the way in which the towage or voyage is
conducted. The Certificate of Approval is based on agreed towage or voyage arrangements, which
shall not be deviated from without good cause, and where practical with the prior agreement of
GL Noble Denton.

14.2

PLANNING

14.2.1

Planning of the voyage or towage shall be carried out in accordance with the requirements of the IMO
International Safety Management Code [Ref. 8].

14.3

ROUTEING

14.3.1

14.3.2

Routeing procedures shall be agreed with the Master prior to commencement of the towage or voyage,
taking into account the transport vessel or tug’s capacity and fuel consumption, the weather and
current conditions and normal good navigation and seamanship.
Piracy in some areas, for instance South East Asia, is prevalent, and slow moving vessels or tows are
particularly at risk. Maintaining sufficient distance from land throughout the tow will reduce this risk
and also ensure there is sufficient sea room in case of emergency. Guidance on prevention of piracy
may be found in IMO MSC/Circ.623 - Piracy and armed robbery against ships [Ref. 20].

14.4

WEATHER ROUTEING & FORECASTING

14.4.1

Weather forecasts for the departure area should be commenced at least 48 hours before the
anticipated departure date. Whenever possible a second weather forecast should be obtained from a
different independent source prior to departure.
For any towage, the weather conditions for departure from the departure port or any intermediate port
or shelter area shall take into account the capabilities of the towing vessel, the marine characteristics
of the tow, the forecast wind direction, any hazards close to the departure port or shelter area and the
distance to the next port or shelter area. A suitable weather forecast may be one that predicts a
minimum 48 hour period with winds not in excess of Beaufort Force 5 and a favourable outlook for a
further 24 hours.
If appropriate, a weather routeing service, provided by a reputable company, should be arranged prior
to the start of the towage or voyage. The utilisation of a weather routeing service may be a
requirement of the approval. See also Section 6.3.2. In any event, every effort shall be made by the
Master to obtain regular and suitable weather forecasts from a reputable source during the towage.

14.4.2

14.4.3

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14.5

DEPARTURE

14.5.1

Prior to departure, a departure condition report for the tow or vessel shall be provided by the owners or
their agents, for the Master and the GL Noble Denton surveyor. This report should contain as a
minimum:
a.
The documentation referred to in Section 5 as appropriate

14.5.2
14.5.3

14.5.4
14.5.5

b.

Lightship weight

c.

Tabulation and distribution of ballast, consumables, and cargo, including any hazardous
materials

d.

Calculated displacement and draughts

e.

Actual draughts and displacement

f.

For ships, a statement that the longitudinal bending and shear force are within the allowable
seagoing limits

g.

Calculated VCG

h.

Calculated GM and confirmation that it is within allowable limits

i.

GZ Curve and confirmation that it is within allowable limits.

Departure condition shall be verified to be satisfactory regarding the stability of the tow with proper
allowance made for any slack tanks.
If no stability documentation is available then it may be necessary to perform an inclining experiment to
check that the GM is satisfactory. Calculations may be needed to establish righting and overturning
lever curves.
It shall be verified that the tow floats in a proper upright attitude and at a draught and trim appropriate
to the calculated weight and centre of gravity.
The Certificate of Approval shall be issued on agreed readiness for departure and on receipt of a
suitable weather forecast.

14.6

PORTS OF SHELTER, SHELTER AREAS, HOLDING AREAS

14.6.1

Ports of shelter, or shelter areas on or adjacent to the route, with available safe berths, mooring or
holding areas, shall be agreed before departure and all necessary permissions obtained.
Where such shelter points are required as part of a weather-restricted operation, as described in
Section 6.3, they shall be capable of entry in worsening weather.

14.6.2

14.7

BUNKERING

14.7.1

Bunkering ports, if required, shall be agreed before departure. If it is not practical to take the tow into
port, then alternative arrangements must be agreed which may include:
a.
Where the towage is by more than one tug, each tug in turn may be released to proceed to a
nearby port for bunkers, subject to a favourable weather forecast. The remaining tug(s) should
meet the requirements of Section 12.2, or some other agreed criterion.

14.7.2

b.

Relief of the towing tug by another suitable tug, which itself is considered suitable to undertake
the towage, so that the towing tug may proceed to a nearby port for bunkers.

c.

Bunkering at sea from a visiting vessel, subject to suitable procedures and calm weather
conditions.

Such procedures shall form part of the approved towage or voyage arrangements.

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14.8

ASSISTING TUGS

14.8.1

Assisting tugs shall be engaged at commencement of the towage, at any intermediate bunkering port
and at the arrival destination, as appropriate.

14.9

PILOTAGE

14.9.1

The Master shall engage local pilotage assistance during the towage or voyage, as appropriate.

14.10

LOG

14.10.1

A detailed log of events shall be maintained during the towage or voyage.

14.11

INSPECTIONS DURING THE TOWAGE OR VOYAGE

14.11.1

14.11.3

Unless the tow is manned, it should be boarded on a regular basis by the crew of the tug, particularly
after a period of bad weather, in order to verify that all the towing arrangements, condition of the cargo,
seafastenings and watertight integrity of the tow are satisfactory. Suitable access shall be provided see Section 13.14.
For manned tows, and self propelled vessels, the above inspections should be carried out on a daily
basis as relevant - see also Section 17.5.
Any adjustable seafastenings or lashings should be re-tensioned as necessary.

14.12

REDUCING EXCESSIVE MOVEMENT & THE SHIPPING OF WATER

14.12.1

The Master should take any necessary measures to reduce excessive movement or the shipping of
water which may damage the cargo, cribbing or seafastenings. This may entail changes of course, or
speed, or both.

14.13

NOTIFICATION

14.13.1

After departure of an approved towage or voyage, regular notification shall be sent to GL Noble Denton
regarding progress, the reporting of any unusual or abnormal events, or necessary deviation from the
agreed towing arrangements.

14.14

DIVERSIONS

14.14.1

Should any emergency situation arise during the towage or voyage which necessitates diversion to a
port of refuge, then GL Noble Denton shall be advised. GL Noble Denton will review and advise on the
validity of the existing Certificate of Approval for continuing the towage or voyage depending on the
circumstances of the case. A further attendance at the port of refuge may be required in order to revalidate the Certificate of Approval.

14.15

RESPONSIBILITY

14.15.1

The Towmaster is responsible for the overall conduct of a tow, and towing arrangements during the
towage.
If any special situations arise during the towage or voyage and it is not possible to comply with any
specific recommendations, agreed procedures or International Regulations, then such measures as
appropriate for the safety of life and property shall be taken. GL Noble Denton shall be informed as
soon as practical of any such circumstances.
Nothing in this document shall set aside or limit the authority of the Master who remains solely
responsible for his vessel during the voyage in accordance with maritime laws.

14.11.2

14.15.2

14.15.3

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14.16

TUG CHANGE

14.16.1

The tug(s) approved for any towage, as noted on the Certificate of Approval, shall be the only tug(s)
approved for that specific towage and should remain with the tow throughout the towage. Should it be
required to change the tug(s) for any reason, except in emergency or where special arrangements
have been agreed for bunkering, the replacement tug must be approved by GL Noble Denton and a
new Certificate of Approval issued.

14.17

HAZARDOUS MATERIALS

14.17.1

Hazardous substances may be considered as materials which, when released in sufficient quantities or
improperly handled, have the potential to cause damage to the asset, personnel or the environment
through chemical means or combustion. Unless it is necessary the carriage of such materials should
be avoided, unless it can be shown that the substances are effectively controlled. Stowage of such
materials should take into account that the transportation may be unmanned and therefore remedial
action in the case of inadvertent release will be limited.
The properties of such material should be contained in the COSHH (Control of Substances Hazardous
to Health) data sheets and the recommended method of stowage and handling is found in the IMDG
(International Maritime Dangerous Goods) Code.
Where identifiable hazardous material is found on board prior to a tow / transportation taking place, it
should be controlled either through isolation or removal ashore.

14.17.2

14.17.3

14.18

BALLAST WATER

14.18.1

14.18.3

The IMO Ballast Water Convention of 2004 (Resolution A.868(20)) requires the monitoring and
recording of ballasting and de-ballasting operations. Vessels flagged in signatory states are required
to have on board and to implement a Ballast Water Management Plan. This plan is specific to each
vessel and the record of ballast operations may be examined by the Port State Authorities.
Vessels may need to change ballast water before or at their arrival port for operational reasons
(loading /discharging). There may be local laws that will have an impact on these activities. In the
U.S.A. there are numerous state laws that cover these operations. Compliance with these rules may
need to become part of the voyage planning.
The necessary ballast plan and records should be available for any attending surveyor.

14.19

RESTRICTED DEPTHS, HEIGHTS & MANOEUVRABILITY

14.19.1

The following recommended clearances are general, and each towage should be assessed on its own,
taking into account
a.
environmental conditions,

14.18.2

14.19.2
14.19.3

b.

length of areas of restricted manoeuvrability,

c.

any course changes within the areas of restricted manoeuvrability,

d.

cross section of areas of restricted manoeuvrability in relation to underwater area/shape of the
base structure, and

e.

capability of the tugs.

The recommended values give guidance. If it can be proved that smaller values give the same or even
better level of confidence these values should be taken.
For areas where the under-keel or side clearance is critical, a survey report that is not older than 3
months shall be available. If not, the tow route should be surveyed with a width of 5 times the beam,
with a minimum of 500 metres. Side-scan sonar and bathymetric data should be provided. The
equipment used should be of a recognized industry standard. The spacing between depth contour
lines should be appropriate for the purpose. Current surveys should be made in restricted parts of the
tow route.

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14.19.4
14.19.5

The survey requirements can be relaxed if it can be shown that the on-board bathymetry measurement
systems and position management systems have sufficiently high precision.
Ideally passages through areas of restricted manoeuvrability and passing under bridges and power
cables should not take place in darkness.

14.20

UNDER-KEEL CLEARANCES

14.20.1

The under-keel clearance allowing for protrusions below the hull shall account for the effects of
a.
Roll, pitch and initial heel and trim,
b.

heave,

c.

tow-line pull,

d.

inclination due to wind,

e.

tolerance on bathymetry,

f.

changes in draught of the transport or towed object,

g.

differences in water density,

h.

low water tidal height variations,

i.

squat effects,

j.

deflections of the structure

k.

errors in measurement, and

l.

negative surge.

4

and shall include a margin of not less than the greater of one metre or ten percent of the maximum
draught. The 10% may be reduced in very benign conditions after agreement with the GL Noble
Denton office concerned.
14.20.2
14.20.3

14.20.4
14.20.5

Under-keel clearances for departure from dry-docks or building basins are covered in 0015/ND [Ref 3].
If sections of the passage are tidally dependent, safe holding areas should be identified in the vicinity
with adequate sea room and water depth to keep the structure afloat at low tide, while maintaining the
minimum under-keel clearance. Any delay time waiting for the tide must be included in the overall
planning.
Immediately before critical sections of the passage the tidal level shall be confirmed by measurement.
Use of an air cushion to reduce draft to assist in crossing localised areas of restricted water depth may
be considered subject to:
a.
Any conceivable loss of air not increasing the draft by more than the reserve on underkeel
clearance, and
b.

The recommendations contained in 0015/ND [Ref 3] on air cushions.

14.21

AIR DRAUGHT

14.21.1

When passing under bridges and power cables, the overhead clearance shall be calculated allowing a
margin of not less than one metre plus dimensional tolerances on the items listed in Section 14.20.1
excluding squat. Where clearance is limited then a dimensional survey of the barge/vessel and
structure shall take place just prior to sailaway in order to ensure that the required clearance exists.
Power cables need a 'spark gap', as well as a physical clearance; the transmission company will have
their own criteria on the minimum allowable clearance. It should be noted that the catenary of the
power cable will change depending on the load being carried in the cable; the lowest position should
be used.
The actual clearance shall be confirmed with all appropriate authorities including those responsible for
the obstruction.

14.21.2

14.21.3

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14.21.4

Immediately before the passage the tidal level shall be confirmed by measurement.

14.22

CHANNEL WIDTH & RESTRICTED MANOEUVRABILITY

14.22.1

The minimum channel width along any inshore legs of the tow route with the underkeel clearance and
air draught required in Sections 14.20 and 14.21 should be three times the maximum width of the
towed object after allowances for yaw. Additional channel width may be required in exposed areas, if
there are significant cross currents or if needed for the tugs to manoeuvre safely.
Side clearances for departure from dry-docks or building basins are covered in 0015/ND [Ref 3].

14.22.2

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15

PUMPING AND SOUNDING

15.1

GENERAL

15.1.1
15.1.2

Emergency-pumping arrangements should be available for any tow.
Pumps in accordance with this section are primarily required for barges. The need for, and
specification of, pumps for other tows, including self-floating objects, MODUs, FPSOs and ships, will
be assessed on a case-by-case basis, depending on the nature of the towage and the extent and
availability of any installed system.
Some relaxation may be possible, agreed on a case-by-case basis, for a towage considered as a
weather-restricted operation.
Whatever pumping system is agreed, and whether or not a tow is manned, the pumping system shall
be available at short notice. Any time required for connection or warm-up should be included in the
pumping times and capacities shown in Section 15.5.
Where a tow is not manned, then the tug master and chief engineer shall be aware of the available
pumping system. Members of the tug crew shall be familiar with the systems, and be able to board the
tow and run the pumps at short notice. Procedures for pumping shall be known and available,
including any restrictions arising from considerations of stability or hull stresses, and any vents, which
must be opened before pumping starts.

15.1.3
15.1.4

15.1.5

15.2

PURPOSE OF PUMPS

15.2.1

Pumps may be required for the following:
a.
Ballasting before, during and after loadouts

15.2.2

15.2.3

b.

Ballasting to the agreed departure condition

c.

Restoration of draught and trim after discharge (especially at sea)

d.

Deballasting to reduce draught to enter port

e.

Damage control, including counterflooding

f.

Deballasting after accidental grounding

g.

Trimming to allow inspection and repair below normal waterline

h.

Access to a flooded compartment (e.g. pump room, anchor winch room).

The use of a barge compressed air system may not be practicable for all these cases, especially if
manhole covers have been removed, or the barge is holed above the waterline. A compressed air
system should have a compressor on board and available, connected into the permanent lines.
It should be possible to sound and pump into or from critical compartments (defined in Section 15.3.2)
in severe weather. The following shall be provided:
a.
Pumping system
b.

Watertight manholes

c.

Portable coamings

d.

Sounding plugs, extensions and tapes or rods. An additional remote sounding system may be
needed for compressed air ballasting systems

e.

Vents to all compartments.

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15.3

PUMPING SYSTEM

15.3.1

It is recommended that barges have one of the following systems, able to pump into and from all
critical spaces, in order of preference:
a.
Two independent pumprooms or one protected pumproom, as described below

15.3.2

b.

An unprotected pumproom with an independent emergency system that can pump out the
pumproom

c.

A system of portable pumps.

A critical space is defined as any tank or compartment which:
1. when flooded or emptied, at any stage of the voyage, may lead to:
a.
non compliance of intact or damage stability criteria, or
b.

non compliance of structural load limits, or

c.

heeling or trimming that may prevent the tow from continuing its passage safely and free
from obstructions in shallow water, or

d.

maximum allowable transit draught being exceeded.

2. may be required for ballasting / de-ballasting so that the barge or vessel can safely continue her
passage after any single compartment is damaged.

15.3.4

Independent pumprooms should have separate power supply, pumps, control and access. Each
pumproom should be able to work into all spaces.
To be considered protected, a pumproom, and any compartment required for access, should be
separated from the bottom plating by a watertight double bottom not less than 0.60 m deep and from
the outer shell by other compartments or cofferdams not less than 1.5 metres wide.

15.4

PUMP TYPE

15.4.1

If portable pumps are used then either they should be portable enough to be moved around the barge
(and cargo) by two men, or enough pumping equipment should be carried so that any critical
compartment can be reached.
Each portable pump should be able to pump out from the deepest space (with portable coaming
installed). This requires submersible pumps for barges over about 6 metres depth, due to suction
head. Portable submersible pumps must be able to fit through tank manholes.

15.3.3

15.4.2

15.5

PUMP CAPACITY

15.5.1

The total capacity of the fixed or portable pumps should be such that any one wing space (or other
critical tank or pumproom) can be emptied or filled in 4 hours for an unmanned tow, or 12 hours for a
manned tow. At least two pumps shall be provided, except where there is a protected pump room.
Whatever type of pumps are fitted or supplied, sufficient fuel shall be carried for at least 72 hours
continuous operation.

15.5.2

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GUIDELINES FOR MARINE TRANSPORTATIONS
15.6

WATERTIGHT MANHOLES

15.6.1

15.6.6

If manholes to critical compartments are covered by cargo then either alternative manholes should be
fitted, or cutting gear should be installed and positions marked for making access. Welding gear and
materials shall be carried to restore watertight integrity.
Where the barge is classed, the owner should inform the classification society in good time of any
holes to be cut or any structural alterations to be made.
Access shall always be available to pumprooms and other work areas.
Ladders to the tank bottom are required from each manhole position.
Suitable tools shall be provided for removal and refastening of manhole covers and sounding plugs.
All manhole covers should be properly secured with bolts and gaskets, renewed as necessary.
Portable coamings to suit the manhole design should be carried, if required by Section 13.16.1.m.

15.7

SOUNDING PLUGS AND TAPES

15.7.1

15.7.3

For vessels or barges with compressed air ballast systems, gauges should be provided in lieu of
sounding pipes.
A sounding plug shall be installed in each compartment (in manhole covers if necessary) to avoid
removing manhole covers. Sounding tapes and chalk shall be carried on board the tow.
For spaces that will be sounded regularly, a tube and striker plate are recommended.

15.8

VENTS

15.8.1

All compartments connected to a pumping system should have vents fitted, preferably of an approved,
automatic, self-closing type. If not automatic, then the vents should be sealed for towage with wooden
bungs or steel blanks, but with a 6 mm diameter breather hole fitted. This will give audible warning or
reduce pressure differentials in event of mishap, and compensate for temperature changes. The
breather hole can be drilled into the gooseneck of the vent or through the wooden bung used to close
the vent.

15.6.2
15.6.3
15.6.4
15.6.5

15.7.2

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16

ANCHORS AND MOORING ARRANGEMENTS

16.1

EMERGENCY ANCHORS

16.1.1

16.1.4

Emergency anchors have traditionally been required to reduce the risk of a tow running aground if a
towing vessel is disabled or a towline broken. However in many cases the disadvantages (described
in Section E.4 of Appendix E) associated with using such anchors may outweigh the advantages.
If a tow passes through an area of restricted sea room, a comparative risk assessment should be
performed to determine the preferred arrangements. Appendix E sets out topics to be taken into
account in this risk assessment. One possible outcome may be the provision of suitably sized extra
tugs in some sectors of the tow.
The same requirements apply for towed ships, including demolition towages. See Section 20.6.
Where such towages may need to wait for a few days on arrival at the end of a voyage before
documentation is completed then, if this is in a high-current area, anchoring or mooring arrangements
may be required.
For self-elevating platforms, see also Section 19.16.

16.2

SIZE AND TYPE OF ANCHOR

16.2.1
16.2.2

For classed vessels and barges, the anchor(s) fitted in accordance with Class requirements will
generally be acceptable unless there is deck cargo.
In other cases the minimum weight of the emergency anchor should be 1/10 of the towline pull
required (TPR) for the tow, as defined in Section 12.2. A high holding power anchor with anti-roll
stabilisation is preferred.

16.3

ANCHOR CABLE LENGTH

16.3.1

The normal minimum effective length of anchor cable required is 180 metres, preferably mounted on a
winch. If the cable runs through a spurling pipe, or other access, to storage below decks, then the pipe
or access should be capable of being made watertight.

16.4

ANCHOR CABLE STRENGTH

16.4.1

For cable on a winch, or capstan, which can be paid out under control, the minimum breaking load of
the cable should be 15 times the weight of the anchor, or 1.5 times the holding power of the anchor if
greater.
For cable flaked out on deck, the minimum breaking load of the cable should be 20 times the weight of
the anchor, or twice the holding power if greater, to allow for the extra shock load.
The last few flakes of cable on deck should have lashings that will break and slow down the cable
before it is fully paid out.

16.1.2

16.1.3

16.4.2
16.4.3

16.5

ATTACHMENT OF CABLE

16.5.1

The inboard end of the cable should be led through a capped fairlead near the barge centre line and
be securely fixed to the barge. Precautions should be taken to minimise chafe of the cable.
The breaking load of the connections of the cable to padeye or winch, and padeye or winch to the
barge structure should be greater than that of the cable.
For towed ships, and tows with similar arrangements, the anchor cable(s) shall be properly secured,
with the windlass brake(s) applied. Any additional chain stopper arrangements that are fitted shall be
utilised, or alternatively, removable preventer wires should be deployed.
Spurling pipes into chain lockers should be made watertight with cement plugs, or another satisfactory
method.

16.5.2
16.5.3

16.5.4

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16.6

ANCHOR MOUNTING AND RELEASE

16.6.1

If there is no suitable permanent anchor housing the anchor should be mounted on a billboard, as
shown in Appendix D, at about 60 degrees to the horizontal.
The anchor should be held on the billboard in stops to prevent lateral and upwards movement. It
should be secured by wire rope and/or chain strops that can be easily released manually without
endangering the operator.
The billboard should normally be mounted on the stern. It should be positioned such that on release
the anchor will drop clear of the barge and the cable will pay out without fouling.
For any system, it shall be possible to release the anchor safely, without the use of power to release
pawls or dog securing devices. If the anchor is held only on a brake, an additional manual quick
release fastening should be fitted.
The anchor arrangement should be capable of release by one person. Adequate access shall be
made available.

16.6.2

16.6.3
16.6.4

16.6.5

16.7

MOORING ARRANGEMENTS

16.7.1

All vessels and floating objects should be provided with at least four mooring positions (bollards /
staghorns etc.) on each side of the barge unless it is impracticable to moor them, e.g. because of
draught limitations.
If fairleads to the bollards are not installed then the bollards should preferably be provided with capping
bars, horns, or head plate to retain the mooring lines at high angles of pull. Suitable chafe protection
should be fitted as required e.g. to the deck edge for low angles of pull.
At least four mooring ropes in good condition of adequate strength and length, typically about 50-75
mm diameter polyprop or nylon, and each 60-90 metres long, should be provided.
Mooring ropes should be stowed in a protected but accessible position.
Objects with very large freeboard such as FPSOs may advantageously be fitted with mooring and
towing connection points along the side, at a convenient height above the towage waterline. These
may provide a more convenient connection for mooring lines and harbour tugs than bollards at deck
level. Care should be taken that the connection points cannot damage, or be damaged by, attending
vessels.

16.7.2

16.7.3
16.7.4
16.7.5

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17

MANNED TOWS AND TRANSPORTATIONS

17.1

GENERAL

17.1.1

17.1.5
17.1.6

Manning of tows should generally be limited to those where early intervention by a riding crew can be
shown to reduce the risks to the tow, for example tows of MODUs, passenger ships and Ro-Ro
vessels.
Where a riding crew is carried on a tow for commissioning and/or maintenance, sufficient marine
personnel shall be included to operate the equipment listed in Section 17.4 and to carry out the duties
in Section 17.5. A riding crew may be carried on an FPSO for similar reasons.
There is sometimes a requirement for a riding crew on a dry transportation to maintain or commission
systems or to carry out general maintenance. Riding crew carried on any dry transportation must be
within the carrying vessel’s Flag State limits for life saving appliances; any exceedance of the Flag
State limit must be approved by the Flag State in advance.
GL Noble Denton will only be able to approve the transport with respect to the riding crew when the
documented flag state approval for the proposed number of riding crew has been seen. The
transportation contractor is therefore advised to obtain this Flag State approval in good time. The
underwriters should also be informed if a large riding crew is proposed.
The health and safety of the riding crew shall be assured at all times.
A risk assessment shall be carried out to demonstrate the acceptability of the proposed arrangements.

17.2

INTERNATIONAL REGULATIONS

17.2.1

Accommodation, consumables, lifesaving appliances, pumping arrangements and communication
facilities with the tug shall comply with International Regulations.

17.3

RIDING CREW CARRIED ON THE CARGO

17.3.1

Where a riding crew is carried on the cargo, for instance a maintenance crew on a dry-transported
jack-up rig, the total number of persons on board may exceed the capacity of the vessel or barge.
Subject to Flag State approval (see Section 17.1.3) this may be permissible. Additional precautions
which may be necessary include:
a.
Access to/from the cargo /rig forward and aft, and to the liferaft launching area

17.1.2

17.1.3

17.1.4

b.

The cargo /rig’s liferafts and lifeboats should be relocated and the falls lengthened, if necessary,
so that on launching they will land in the water.

c.

A firewater supply should be made available to the cargo /rig.

d.

The cargo /rig’s and vessel’s alarm systems should be linked, so that an alarm on the cargo /rig
is repeated on the vessel, and vice versa.

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17.4

SAFETY AND EMERGENCY EQUIPMENT

17.4.1

Notwithstanding the requirements of SOLAS and any or all international regulations for Life Saving
Appliances and Fire Fighting Equipment, the minimum complement of safety and emergency
equipment carried aboard the tow shall be as follows:
a.
Certified liferafts located on each side of the tow, clear of any possible wave action, provided
with means of launching and fitted with hydrostatic releases. The liferaft or liferafts on each
side of the tow shall be capable of taking the full crew complement. Adequate means of access
to the water shall be provided
b.

4 lifebuoys, two located on each side of the tow and including two fitted with self igniting lights
and two with a buoyant line

c.

Approved life jackets to be provided for each crew member plus 25% reserve

d.

If appropriate, a survival suit to be provided for each crew member

e.

First aid kit

f.

Fire fighting equipment, which may consist of an independently powered fire pump with
adequate hoses, and portable fire extinguishers as appropriate.

g.

6 parachute distress rockets and 6 hand held flares

h.

A daylight signalling lamp and battery

i.

2 portable VHF radios, fitted with all marine VHF channels, with appropriate battery charging
equipment

j.

Hand held GPS (Global Positioning System) receiver

k.

GMDSS radio (Global Maritime Distress and Safety System)

l.

Charts covering the route

m.

An EPIRB (Emergency Position Indicating Radio Beacon) emergency transmitter

n.

2 SARTs (Search and Rescue Radar Transponder)

o.

Heaving line(s) and/or line throwing apparatus if appropriate.

17.4.2

All members of the riding crew shall be adequately trained in the use of the safety equipment. At least
1 crew member shall possess the appropriate radio operator’s licences.

17.5

MANNED ROUTINE

17.5.1

The riding crew shall take the following actions during the towage:
a.
Maintain a daily log and include all significant events
b.

Inspect towing arrangements and navigation lights

c.

Inspect all seafastenings and any other accessible, critical structures

d.

Tension any adjustable seafastenings or lashings as necessary

e.

Check soundings of all bilges and spaces

f.

Monitor any unexpected or unexplained ingress of water

g.

Pump out any ingress of water

h.

Maintain regular contact by radio with the tug, reporting any abnormalities.

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18

MULTIPLE TOWAGES

18.1

DEFINITIONS

18.1.1
18.1.2

This section expands on the definitions in Section 3 for multiple towages:
Double tow – 2 tows each connected to the same tug with separate towlines. One towline is of
sufficient length that the catenary to the second vessel is below that of the first.
Tandem tow – 2 (or more) tows in series behind 1 tug, i.e. the second and following tows connected to
the stern of the previous one.
Parallel tow – the method of towing 2 (or more) tows, using one tow wire, where the second (or
subsequent) tow(s) is connected to a point on the tow wire ahead of the preceding tow, and with each
subsequent towing pennant passing beneath the preceding tow.
Two tugs (in series) towing one tow – where there is only 1 towline connected to the tow and the
leading tug is connected to the bow of the second tug.
More than 1 tug (in parallel) towing one tow – each tug connected by its own towline, pennant or
bridle to the tow.

18.1.3
18.1.4

18.1.5
18.1.6

18.2

GENERAL

18.2.1

Compared with single towages, multiple towages have additional associated problems including those
of:

18.2.2
18.2.3

18.2.4
18.2.5
18.2.6
18.2.7

18.2.8

18.2.9

18.2.10
18.2.11

a.

Manoeuvring in close quarter situations

b.

Reconnecting the towlines after a breakage

c.

Maintaining sufficient water depth for the longer and deeper catenaries required.

With the exception of the cases described in Section 18.1.6, multiple towages may only be approvable
in certain configurations, areas and seasons, and subject to a risk assessment.
When approval is sought, then full details of the operation, including detailed drawings, procedures and
equipment specifications shall be submitted to GL Noble Denton for review and comment. An initial
assessment of the method will then be made, and if the basic philosophy is sound, recommendations
may be made for the approval process to continue.
Approval may be rejected if any doubt exists as to the viability of the operation proposed.
For those multiple towages that are approvable, each tow shall be prepared as described in these
Guidelines.
Additional factors may be applied to the towing arrangements, so that the probability of breakage is
further reduced.
The bollard pull requirement of the tug shall be according to the number and configuration of the tows
connected. The Towline Pull Required (TPR) should be the sum of those required for each tow. The
towing arrangements on each tow shall have sufficient capacity for the Bollard Pull (BP) of the tug(s).
The tug shall be equipped as in Ref. [5], although additional or stronger equipment and longer towlines
may be necessary. Where longer towlines are required, these may be formed by the utilisation of
pennant wires of no less Ultimate Load Capacity than the main tow wires.
Where the towing configuration requires the use of 2 towlines from 1 tug, a third tow wire shall be
carried on board the tug, stowed in a protected position, whence it can be safely transferred at sea to
either towing winch.
It may be necessary to include (surge) chain or a stretcher to improve the spring, or to provide the
required catenary in any towing arrangement.
If a synthetic stretcher is included in any towing arrangement, it shall comply with Section 13.9. A
spare stretcher shall be carried aboard the tug for each stretcher utilised in the towing arrangement.

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18.2.12
18.2.13
18.2.14

Multiple tows being towed behind a single tug may yaw in different directions. Special arrangements
shall be made on the deck of the tug to separate the towlines.
It is particularly difficult to reconnect to a tow that has broken loose when another tow or tows are
connected to the same tug. Special procedures must be agreed for reconnection.
Due to the difficulties that will be encountered if a towline breakage should occur, GL Noble Denton
may recommend a higher total number of crew on the tug.

18.3

DOUBLE TOWS

18.3.1

These are usually only considered as acceptable:
a.
In benign areas
b.

For short duration towages covered by good weather forecasts

c.

Where there is sufficient water depth along the tow route to allow for the catenary required for
the second tow.

18.3.2

The tug should be connected to each tow with a separate towline on a separate winch drum. It shall
also carry a spare towline, stowed on a winch, or capable of being spooled onto a winch at sea.

18.4

TANDEM TOWS

18.4.1
18.4.2

These are normally only acceptable in very benign areas or in ice conditions where the towed barges
will follow each other.
In ice conditions the towlines between tug and lead tow and between tows will normally be short
enough for the line to be clear of the water. Care must be taken to avoid tows over-running each
other, or the tug.

18.5

PARALLEL TOWS

18.5.1

This method is generally only approvable in extremely benign areas, and may be subject to additional
safety factors with respect to the capacity of the towing arrangements.

18.6

TWO TUGS (IN SERIES) TOWING ONE TOW

18.6.1

This is usually only feasible when a small tug is connected to the bow of a larger, less manoeuvrable
tug to improve steering.
This configuration is generally only acceptable if:

18.6.2

a.

All the towing gear (towline/pennants/bridles/connections etc.) between the second tug and the
tow is strong enough for the total combined bollard pull

b.

The second tug is significantly heavier than the leading tug (to avoid girding the second tug).

18.7

MULTIPLE TUGS TO ONE TOW

18.7.1

This is generally considered acceptable, provided that each tug has a separate towline to the vessel
(via bridles or pennants as required). Care must be taken that the tugs do not foul each other or their
towing equipment.
Consideration should be given to matching the size and power of the tugs.
The use of eccentric bridles may be advantageous but care must be taken to avoid chafe.
Normally there will not be more than 3 tugs, except for the towage of very large objects, such as
FPSOs and concrete gravity structures.

18.7.2
18.7.3
18.7.4

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19

SPECIAL CONSIDERATIONS FOR THE TRANSPORT OF JACK-UPS

19.1

GENERAL

19.1.1

19.1.2

This Section is intended to cover the special requirements of jack-up platforms, not covered by other
sections. The terms 24-hour move, location move, ocean towage and ocean transportation have the
meanings shown in Section 3.
Reference [24] – “UKOOA Guidelines for Safe Movement of Self-Elevating Offshore Installations” and
Reference [25] “The Safe Approach, Set-Up And Departure of Jack-Up Rigs to Fixed Installations”
describe good practice for jack-up moves within the North Sea and many of these practices can be
usefully followed in other areas.

19.2

MOTION RESPONSES

19.2.1

The motion responses for towage of a jack-up on its own hull, or for transport on a barge or vessel,
may be derived from Section 7, either by calculation, from the standard motion criteria in Section 7.9,
or by model tests.

19.3

LOADINGS

19.3.1

Loads in legs, guides, jack-houses and jack-house connections into the hull, as appropriate, shall be
derived in accordance with one of the methods set out in Section 8.
For jack-ups transported on a barge or vessel, the loads in cribbing and seafastenings shall be
similarly derived in accordance with Section 8.

19.3.2

19.4

HULL STRENGTH

19.4.1

For units transported on their own buoyancy, either the hull shall be built to the requirements of a
recognised Classification Society, and be in Class or verified to comply with Class building and
inspection requirements. Otherwise the requirements of Section 19.4.2 through 19.4.5 shall apply.
If not in Class, the hull shall be demonstrated to be capable of withstanding the following loadings:
a.
Static loading, afloat in still water, with all equipment, variable load and legs in towage position,
plus either:

19.4.2

19.4.3

b.

Longitudinal or transverse bending, as derived from Section 19.4.3, or

c.

Loads imposed on the hull and guide support structures by the legs, when subjected to the
agreed motion criteria.

Longitudinal and transverse bending may be derived by quasi-static methods, assuming a wave
length, Lw, equal to the unit’s length or beam, and height:
Hw = 0.61Lw,
where Lw is in metres.

19.4.4

19.4.5

External plating shall be demonstrated to have adequate strength to withstand the hydrostatic loads
due to the immersion of the section of shell plating considered, to a depth equivalent to that which
would be caused by inclining the hull, in towage condition, to the static angle equal to the amplitude of
motion as considered in Section 7.9.1.
Hull and superstructure construction, details, materials and workmanship shall be shown to be in
accordance with sound marine practice, and shall be in sound condition.

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19.5

STRESS LEVELS

19.5.1

Stress levels in legs, guides, jack-houses, hull and all temporary securing arrangements shall comply
with Section 9.5. The hull in way of seafastenings to a barge or transportation vessel shall also be
checked to comply with Section 9.5. See also the caution for dry transportations in Section 9.1.4.
A critical motion curve may be drawn up, or provided in the Operations Manual, reflecting the motion
limits for the legs or any other component. This may be used as a guide during the towage or voyage,
indicating whether course or speed should be changed, or the legs lowered, as appropriate.
Prior to an ocean transportation of a jack-up, an inspection programme, including non-destructive
testing, for critical structural areas shall be implemented. Typically, this should include, as appropriate,
the areas of legs from just below the lower guides to 2 bays above the upper guides, with the legs in
any proposed transport condition. It should also include the guide connections, the jack-house
connections to the deck and connections of the spudcans to the leg chords.
The exclusion stated in Section 4.6.7 regarding fatigue damage should be noted. Local areas of jackup platforms may be particularly prone to fatigue damage. The effects of fatigue damage will be
excluded from any Certificate of Approval issued by GL Noble Denton unless specific instructions are
received from the client.

19.5.2

19.5.3

19.5.4

19.6

STABILITY AND WATERTIGHT INTEGRITY

19.6.1

For units transported on their own buoyancy, the following shall apply:
a.
The intact stability requirements set out in Sections 10.1 and 10.3.
b.

19.6.2

19.6.3
19.6.4
19.6.5

The damage stability requirements of Sections 10.2 and 10.3.

For ocean towages, the compartmentation and watertight integrity requirements of Section 10.5 shall
be particularly addressed. Engine room intake vents and exhausts, shall comply with Section 10.5.2.
Other special considerations for jack-ups include:
a.
All compartments and their vents, intakes, exhausts and any other appurtenances or openings
shall be effectively watertight up to the waterline associated with the minimum required
downflooding angle (see Section 10.5.2), or 3 m above main deck level, whichever is the
higher.
b.

All compartments and their vents, intakes, exhausts and any other appurtenances or openings
shall be structurally capable of withstanding hydrostatic pressure due to inclination to the
minimum required downflooding angle, and direct loadings from green water.

c.

All air intakes and exhausts for equipment that must be kept running and/or which must be
available for emergency use must extend above the waterline associated with the minimum
required downflooding angle, or 3 m above main deck level, whichever is the higher.

d.

Any jetting lines and pumping nipples in lines shall be checked closed and watertight before
departure.

e.

All pre-load dump valves shall be closed and secured.

f.

Mud return lines from shale shaker pumps etc, leading below main deck, shall be blanked off.

g.

Dump valves in mud pits shall be checked closed secured.

h.

Overboard discharges shall be blanked off, or fitted with non-return valves.

For all towages, liquid variable loads shall be minimised and shall be in pressed up tanks where
possible.
Free surface in the mud pits is not generally acceptable, except for very short 24-hour moves in
controlled conditions.
Free surface effects of all remaining liquid variables, except those in pressed up tanks, shall be taken
into account in the stability calculations.

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19.6.6

Stability calculations shall accurately reflect the position and buoyancy of the spud cans. Spud can
water shall be taken into account in weight and centre of gravity calculations, where appropriate.

19.7

TUGS, TOWLINES AND TOWING CONNECTIONS

19.7.1

Tugs shall be selected in general accordance with Section 12, using the categories required in Section
4 of 0021/ND - Ref [5] as applicable to:
a.
ocean towages
b.

19.7.2

19.7.3

24-hour or location moves.

The particular requirements for manoeuvring on and off location may be taken into account when
selecting the towing fleet, unless additional tugs are used for manoeuvring. Similarly additional tugs
may be required when in congested waters or when approaching a lee shore when there may not be
sufficient time to reconnect a tug after a broken towline or breakdown in the forecast weather
conditions.
Towlines and towing connections shall, as a minimum, be in accordance with Section 13. The
cautions in Section 13.2.8 (for vertical loads) and 13.2.9 (for larger tugs) should be noted.

19.8

SECURING OF LEGS

19.8.1

For ocean transportations, legs shall be properly secured against excessive horizontal movement by
means of shimming in the upper and lower guides, or by means of an approved locking device. Shim
material specification should take into account the pressures expected, particularly for units with
guides having a small contact area.
For 24-hour and location moves, leg position and securing arrangements shall be agreed, and shall
comply with designers’ recommendations.
For electric jacking systems, all motors should be checked for torque and equalised in accordance with
manufacturers’ instructions.
Hydraulic and pneumatic jacking systems shall be secured in accordance with manufacturers’
recommendations.
For jacking systems fitted with elastomeric pads, clearances should be shimmed or preload applied in
accordance with the manufacturer’s specifications.
For tilt-leg jacking systems, tie bars shall be fitted to by-pass the tilt mechanism.
Where lowering of legs or jacking on a standby location is envisaged during the towage, then any leg
securing arrangements shall be quickly removable.
Where a critical motion curve, or equivalent limitation, is provided for the legs, it may be necessary to
lower the legs in order to comply. Instructions and limitations for this operation shall be clearly defined
in the Operations Manual, taking into account any lesser motion limitation during the lowering
operation. The lowering operation shall be carried out well before the onset of forecast bad weather.

19.8.2
19.8.3
19.8.4
19.8.5
19.8.6
19.8.7
19.8.8

19.9

DRILLING DERRICK, SUBSTRUCTURE AND CANTILEVER

19.9.1

The drilling derrick, substructure and cantilever shall be shown to be capable of withstanding the
motions as derived from Sections 7 and 19.2. For 24-hour and location moves the crown block may be
left in place. For ocean transportations the derrick shall be considered in the condition proposed for
transportation, with the crown block lowered if required. Other machinery and equipment are to be
similarly considered.
For ocean transportations and location moves, no setback shall be carried.

19.9.2

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19.9.3

19.9.4
19.9.5

For 24-hour moves, towage with setback in the derrick may be considered, provided it can be
demonstrated that all of the following apply:
a.
The derrick, with the setback proposed and after suitable allowance for wear, corrosion or
fatigue, can withstand the motion criteria derived from Section 19.2.
b.

All pipe, collars and other equipment racked in the derrick are secured to meet the same
criteria.

c.

The seabed conditions at the arrival location are confirmed as presenting virtually zero risk of a
punch-through.

d.

The stability of the unit can meet the requirements of Section 19.6.

e.

The carriage of setback in the derrick is clearly documented. The limitations thereof, the
securing method, and any special precautions shall be clearly stated.

For ocean transportations the travelling block and/or topdrive should be lowered and secured. The drill
line should be tightened, and secured against movement.
The cantilever and substructure shall be skidded to their approved positions for tow, and secured in
accordance with manufacturers’ recommendations.

19.10

HELIDECK

19.10.1

For ocean towages, it shall be shown that at an inclination in still water of 20 degrees about any
horizontal axis, no part of the helideck plating or framing is immersed.
Alternatively, model tests may be used to demonstrate that the helideck remains at least 1.5 m clear of
wave action, in any seastate up to the design seastate as defined in Section 6.
If neither Section 19.10.1 nor 19.10.2 can be satisfied, then all or part of the helideck shall be removed
for the towage.

19.10.2
19.10.3

19.11

SECURING OF EQUIPMENT AND SOLID VARIABLE LOAD

19.11.1

19.11.7

Weight of equipment variable load carried on board shall not exceed the maximum variable load
allowed for jacking.
All items of equipment above and below decks shall be secured to resist the motions indicated in
Sections 7 and 19.2.
For 24-hour and location moves, drill pipe, collars and other tubulars shall be properly stowed on the
pipe deck and in the bays provided with stanchions erected. Chain lashings over each stack shall be
used. See also Section 9.6.
For ocean transportations, drill pipe, collars and other tubulars shall be stowed in the piperacks, to a
height above the rack beams of no more than 1.8 metres. Drill pipes should normally be stowed on top
of collars. Timber battens should be placed between each layer of pipe. See also Section 9.6.
For ocean transportations, the well logging unit shall be secured in position and stops fitted to prevent
rotation.
All crane and lifting derrick booms shall be laid in secure boom rests. For ocean transportations, the
booms should be shimmed or wedged against transverse and vertical movements, but left free to
move axially. Fitted brake systems for prevention of crane rotation shall be implemented. Electric
power shall be isolated at the main switchboard. Cranes shall not be used at sea except in an
emergency.
Deepwell and leg well pumps shall be fully raised and secured.

19.12

SPUD CANS

19.12.1

For 24-hour and location moves, the spud cans should normally be full. See also Section 19.6.6 for
stability calculations.

19.11.2
19.11.3

19.11.4

19.11.5
19.11.6

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19.12.2

19.12.3

For ocean towages, the spud cans may be full or empty. See also Section 19.6.6. If empty, and if the
towage procedures call for lowering of legs (see Section 19.8.7), then the lowering procedures must
include procedures for filling the spud cans.
For dry transports, the spud cans should be empty and vented. Safety notices should be posted at
each spudcan, and at the control panel.

19.13

PUMPING ARRANGEMENTS

19.13.1

For units transported on their own buoyancy, the general pumping requirements of Section 15 shall
apply. The requirements of Sections 19.13.2 and 19.13.3 shall also apply.
All spaces should be capable of being pumped by the unit’s own pumping systems. Sufficient
generator capacity should be available to operate bilge and ballast systems simultaneously.
Additionally for ocean towages, 2 no x 3 inch portable, self-contained, self-priming salvage pumps shall
be on board, with not less than 30 metres each of suction and delivery hose.

19.13.2
19.13.3

19.14

MANNING

19.14.1
19.14.2

Units transported on their own buoyancy should usually be manned, and the general manning
requirements of Section 17 shall apply.
Units transported on a barge or vessel need not be manned. However, it may be advantageous for
person(s) familiar with the unit’s structure, machinery and systems to be on board the tug or the
transport vessel, and to inspect the unit periodically.

19.15

PROTECTION OF MACHINERY

19.15.1
19.15.2

Where practical, and where the unit is manned, main and auxiliary machinery should be run
periodically during the transportation.
For ocean transportation, electrical equipment which cannot be run, including motors, switchgear and
junction boxes, should have dehumidifying chemicals placed inside, and then be wrapped against
wetting damage. Heaters, where fitted, should be run periodically.

19.16

ANCHORS

19.16.1
19.16.2

The general emergency anchor /risk assessment requirements of Section 16 shall apply.
For ocean towages where anchors are fitted, the forward anchors should normally be removed, and
secured on deck. The aft anchors should be left in place and stopped on the racks to prevent lateral
movement. A retaining wire tightened by a turnbuckle and incorporating a quick-release system
should be passed through the anchor shackle and secured on deck. The turnbuckle and quick-release
system shall be on deck and accessible.

19.17

SAFETY EQUIPMENT

19.17.1

For towages on a unit’s own buoyancy, safety equipment in accordance with SOLAS and any or all
regulations for Life Saving Appliances and Fire Fighting Equipment shall be carried. Consideration
should be given to any additional safety and emergency equipment listed in Section 17.4.1.
For ocean towages, it may be necessary to relocate liferafts stowed forward or overboard to a secure
area protected from wave action. Securing arrangements for liferafts stowed aft should be checked.

19.17.2

19.18

CONTINGENCY STAND-BY LOCATIONS

19.18.1

Where the towing arrangements envisage jacking up at any intermediate location, suitable procedures
shall be written to cover location feasibility, preloading requirements, airgap requirements, local
clearances and Customs formalities etc.

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20

SPECIAL CONSIDERATIONS FOR THE TOWAGE OF SHIPS

20.1

GENERAL CONSIDERATIONS

20.1.1

This Section sets out the technical and marine aspects, which would be considered by GL Noble
Denton for approval of the towage of ships, including demolition towages and as appropriate, towages
of FPSOs.
It is recognised that all ships are different and these guidelines are therefore general in nature. Each
specific approval depends on a survey to identify any particular problems which may exist for the
vessel(s) in question.
It is preferred that any towed vessel should be in Class with a recognised Classification Society, and
possess a current Load Line or Load Line Exemption Certificate. It is recognised that for demolition
towages, the Class and other documentation may have expired, and renewal may be impractical.
Minimum certification and documentation requirements are shown in Section 5.
The existence of current classification and certification will be taken into account when determining the
extent of survey required.
After carrying out an inspection, and in order to verify that the structural strength and watertight
integrity of the tow is approvable for the intended voyage, the attending surveyor may require one or
more of the following:
a.
An extended, in depth, survey of the vessel structure involving one or more specialist
surveyor(s). Facilities for close-up survey of inaccessible parts of the hull structure may be
required.

20.1.2

20.1.3

20.1.4
20.1.5

20.1.6

20.1.7

20.1.8

20.1.9

b.

Thickness determination (gauging) of specified areas of the vessel structure. This survey may
be in limited areas or extend over large parts of the hull structure. Such surveys shall be
carried out by a reputable independent company. An existing survey report may be acceptable
provided that it is not more than 1 year old, and there is no evidence of damage or significant
deterioration since that date.

c.

A GL Noble Denton review of classification society approved scantling drawings.

d.

Calculations to show that the structural strength of particular local areas of the vessel is
adequate. The extent of the calculation required to be determined by the results of the surveys.

Should any doubt exist as to the ability of the vessel to complete the proposed towage, after all the
necessary surveys and calculations have been undertaken, a dry dock survey of the vessel may be
necessary.
After complying with the requirements of Sections 20.1.2 through 20.1.6 above, GL Noble Denton may
deem that the vessel is unfit for tow and decline to issue a Certificate of Approval. Alternatively the
vessel may only be considered fit for tow after specified repairs or temporary strengthening have been
carried out.
The towage of any vessel which is damaged below the waterline, is suspected of being damaged
below the waterline or has suffered other damage or deterioration which could affect the structural
strength will not normally be approved except where it is clearly shown by survey and calculation that
the strength of the vessel and its watertight integrity is satisfactory for the intended towage.
Passenger ships and warships, because of the complex nature of their systems, pose particular
problems with respect to their compartmentation, and require special consideration. Ro-Ro ships may
also pose particular problems, on account of the potentially large free surface in the event of flooding.
Passenger ships and Ro-Ro ships will generally only be approved for towage if the tow is manned, to
permit early intervention in the event of any problems.

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GUIDELINES FOR MARINE TRANSPORTATIONS
20.1.10

20.1.11

Any heavy fuel oil within the tanks of the vessel must be identified, and shall be minimised where
possible. In the event of heavy fuel oil being carried, possible limitations on entry to ports of refuge
and ports of shelter shall be noted and taken into account in the towage procedures. To minimise the
risk of pollution, the requirements of the IMO “Guidelines for Safe Ocean Towing” [Ref. 21], paragraph
13.19, shall be taken into account so far as is practical.
These guidelines assume that the tow will be towed from its forward end or bow. If a stern-first towage
is required (see Section 13.1.2) then approval may be given and the basic guidance contained in this
report is valid. In this case, and depending on the circumstances, special care shall be taken
regarding towing connections, draught, trim and the control and protection of the tow during the
towage.

20.2

TUG SELECTION

20.2.1

Tug selection, including specification and bollard pull, shall be in accordance with Section 12.

20.3

TOWLINES AND TOWING CONNECTIONS

20.3.1

Each ship or vessel towage is unique and it is therefore not possible to specify the connection
equipment to be used and how it is to be attached for every case. The guidelines hereunder are
therefore general in nature. In any event, any equipment used for the towage must be fit for purpose
and must be agreed between the Owner of the tow, the tug master and the GL Noble Denton surveyor.
Towlines, towline connections, recovery systems and emergency towing gear shall be in general
accordance with Sections 13.1 through 13.12.
Unless the tow has been fitted with proper towing brackets, or the anchor chain and windlass are used,
it may be necessary to utilise attachments such as mooring bitts to connect to the tow. In such cases it
shall be shown that the mooring equipment has sufficient ultimate strength, above and below deck, to
comply with Section 13.2.1. If necessary, reinforcements shall be fitted to achieve the required
capacity, otherwise alternative arrangements must be made.
The configuration of the attachments to the tow may be one of the following depending on the
circumstances and equipment available:
a.
Chain bridle with bridle leg from each side of the bow

20.3.2
20.3.3

20.3.4

20.3.5
20.3.6
20.3.7

20.3.8

b.

Single chain from centre line location or forward fairlead

c.

Anchor chain(s) from vessel’s hawse pipe(s)

d.

Single continuous chain with the ends extending out from each bow

e.

Single continuous chain, or chain and wire combination, around a part of, or the whole
superstructure of the vessel.

Chain may be substituted by wire rope of the required ultimate load capacity, but only where chafe
cannot occur.
Chafe of chain or wire may occur when unsuitable fairleads have to be used, or the tow yaws
significantly. In these cases, consideration should be given to providing oversize chain or wire.
A bridle is most suitable for tows which have a wide bow. In any event the angle at the apex of the
bridle should not exceed 60º. A triangle plate, delta plate or towing ring shall be fitted at the apex of
the bridle.
For tows which have a sharp bow configuration a single chain pennant passing through a bow centre
line or forward fairlead may be preferred.

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20.3.9

20.3.10

20.3.11

20.3.12

If deemed appropriate an anchor chain from the tow may be used after removal of the associated
anchor. The condition and capacity of the chain shall be assessed with reference to Section 13.2. If
such a method is utilised then appropriate safety measures shall be applied as follows:
a.
Windlass in gear
b.

Windlass brake applied

c.

Chain claw or stopper deployed

d.

Back-up wire to connect chain to base of windlass or other suitable securing point.

A single chain passing through one side fairlead, around a strongpoint such as the windlass base and
out of a fairlead on the other side may be approvable. An alternative arrangement may consist of a
single chain passing up one hawse pipe and out of the other. In either case the outboard ends should
be made up into a bridle. Each leg should have preventers on the inboard side to stop the chain
sliding and it should not interfere with the vessel’s emergency anchoring arrangements.
On a vessel which is not provided with suitable attachments, or where the anchoring arrangements do
not permit the single chain method described above, a chain, or a combination of chain and wire may
be positioned around a part of, or the whole superstructure of the vessel and made up into a bridle at
the bow.
Where mooring bitts are utilised to secure chain to the tow, and in order to ensure that the towing
arrangement is securely anchored on the vessel and does not slip on the bitts, the chain should be
backed-up to further bitts abaft the main connection points using suitable wire pennants locked into
position with clips. If such an arrangement is used then the first bitts used must have the required
ultimate capacity, unless positive load-sharing can be achieved. Bitts and fairleads shall be capped
with welded bars or plates of sufficient strength to prevent equipment jumping off or out of the
arrangement.

20.4

STABILITY, DRAUGHT AND TRIM

20.4.1

Stability, draught and trim shall be in accordance with Sections 10.1 through 10.4.

20.5

COMPARTMENTATION AND WATERTIGHT INTEGRITY

20.5.1

Compartmentation and watertight integrity shall be in accordance with Section 10.5.

20.6

ANCHORS

20.6.1

An emergency anchor shall be provided if required as a result of the risk assessment described in
Section 16.1 and appropriate access afforded for deployment by one person.
Port and starboard anchor cables shall be properly secured with the windlass brake applied. Any
additional chain stopper arrangements that are fitted shall be utilised or, alternatively, removable
preventer wires shall be deployed.
Spurling pipes into chain lockers shall be made watertight with cement plugs or other satisfactory
method.

20.6.2

20.6.3

20.7

SECURING OF EQUIPMENT AND MOVEABLE ITEMS

20.7.1

In general, all equipment shall be secured to meet the appropriate motion requirements of Section 7,
and seafastenings of loose items designed in accordance with Sections 8 and 9.
See Section 19.11.6 for securing and use of cranes and lifting derricks.
The rudder shall be positioned in the amidships position, or as agreed with the Tug Master, and
immobilised.
The propeller shaft shall be immobilised, or disconnected, to prevent damage to machinery during the
towage.

20.7.2
20.7.3
20.7.4

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20.7.5

20.7.7

Every effort shall be made to limit the carriage of any loose deck equipment to an absolute minimum.
Where equipment must be carried on an exposed deck then it shall be protected and secured against
movement using welded brackets, chain or wire. Equipment in other areas shall also be secured.
For large equipment, engineering calculations shall be carried out in order to verify that the securing of
items is satisfactory.
Additional protection or securing may be required for equipment exposed to wave slam.

20.8

EMERGENCY PUMPING

20.8.1

Emergency pumping arrangements shall be available on the tow, in general accordance with Section
15.

20.9

CARRIAGE OF CARGO

20.9.1

The carriage of manifested cargo on the tow shall not normally be approved unless the tow is manned
and is fully classed by a Classification Society, including the possession of a current International Load
Line Certificate.
International Load Line Regulations shall be strictly followed. Approval shall not be given to any
towage where the prescribed Load Line draught is exceeded.
A cargo plan shall be provided for agreement by the attending surveyor.
The cargo shall be loaded in a seaman-like manner making proper allowances for load distribution
both during loading and for the duration and route of the towage. Longitudinal strength requirements
shall be complied with.
Bulk cargoes shall be properly trimmed to prevent shifting in a seaway. Shifting boards or other
preventative methods shall be utilised where appropriate.
All other cargoes shall be secured in accordance with Sections 7, 8 and 9.
Particular attention shall be paid to the securing of scrap steel, which if carried shall be properly
seafastened. If carried in a hold, it shall not be treated as a bulk cargo.

20.7.6

20.9.2
20.9.3
20.9.4

20.9.5
20.9.6
20.9.7

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21

SPECIAL CONSIDERATIONS FOR THE TOWAGE OF FPSOS

21.1

GENERAL AND BACKGROUND

21.1.1

21.1.5

Many of the foregoing guidelines apply equally to the towage of FPSOs, and similar large vessels. The
aim of this Section is to address the specific marine-related issues associated with the towage of these
units. Although it is recognized that there are many more marine activities in an FPSO development,
towage to field is a critical and often long operation, which must be addressed by the project team
early in the schedule.
Some FPSO developments are ‘fast-track’, resulting in construction and commissioning activities being
completed during the tow.
New-build or converted FPSOs usually undertake a limited number of towages only, following
construction or conversion. There may be a further towage at the end of their working life.
Frequently the design weather conditions for towage are more severe than the service conditions.
There is a natural reluctance to build in additional strength or equipment which will have no practical
value during the service life.
Project-specific fit-for-purpose guidelines must be agreed in each case.

21.2

THE ROUTE AND WEATHER CONDITIONS

21.2.1

Metocean design criteria should be carefully established early in the project, in accordance with
Section 6. In many cases, the field’s operational criteria may be less onerous than the tow-to-field
criteria, so temporary-phase operational limits may define structural load cases and equipment motion
criteria.
Mitigation of the design extremes may be achieved by the use of a staged towage, in accordance with
Section 6.3.
In such cases the towage route must be planned to incorporate a series of safe-havens, meaning
sheltered locations where the tow can safely ride out severe weather. It may also be necessary to
identify suitable bunker ports. These requirements may conflict with the requirement for adequate
searoom, and such conflicts should be resolved.
Passage through restricted or busy waters should be considered, and the need for appropriate
additional tugs determined.

21.1.2
21.1.3
21.1.4

21.2.2
21.2.3

21.2.4

21.3

STRUCTURAL ISSUES

21.3.1

FPSOs are intended to remain at sea without dry-docking for their entire working life, usually in the
order of 20 years. In this respect the integrity of the hull must be maintained and precautions taken to
ensure no damage occurs during the tow. A commercial vessel is usually assumed, for design
purposes, to spend about 20% of its life in port, and is periodically dry-docked. These differences
place much greater emphasis on the reliability, integrity and quality of the hull including its coating.
These qualities must not be compromised during the tow other than by reasonable wear and tear.
For long towages, fatigue damage may need to be considered.
The capability of the FPSO to withstand design towage conditions shall be demonstrated. Checks
should include hull girder strength, local plating strength, operating limit states for process equipment
including rotating machinery.
Equipment foundations shall be designed for the temporary phase operations. Fatigue damage to the
connections between the topsides and hull should be considered.
Any temporary equipment aboard shall be secured to withstand the design conditions. If construction,
completion, or commissioning work is performed during tow, then all the scaffolding, temporary power
packs, work containers etc shall be installed to withstand the design criteria. Any scaffolding or other
temporary works which cannot comply with the design criteria shall be dismantled or removed.

21.3.2
21.3.3

21.3.4
21.3.5

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21.3.6

Green water damage or slamming damage on temporary equipment should be considered in the
location of equipment.

21.4

TUG SELECTION

21.4.1

Tugs shall be selected, as a minimum, in accordance with Section 12, but with regard to the comments
on redundancy below.
Redundancy in the towing fleet is recommended.
The use of additional tug(s) may be required in restricted waters.
Redundancy of towing vessels gives greater freedom for bunkering, where one tug may divert to
bunker whilst the other(s) continue(s) with the towage.
A concern in multiple-tug towages relates to emergency procedures in the event of loss of a tug's
power. If, for example, the lead tug in a three-tug spread blacks out, then it could be over-ridden by
the FPSO, with catastrophic consequences. Suitable emergency procedures and tow equipment will
be required to mitigate such a possibility.
Additional or larger tugs may be required if it is not possible or practical to provide an emergency
anchor. See also Section 21.9.

21.4.2
21.4.3
21.4.4
21.4.5

21.4.6

21.5

BALLAST, TRIM AND DIRECTIONAL STABILITY

21.5.1

Directional stability under tow may be compromised resulting in the FPSO veering off the course line.
This is due to various factors related to the design and construction of the FPSO, including but not
limited to:
a.
The presence of a mooring or riser turret, below the keel of the vessel, generally at the forward
end or midlength.

21.5.2

b.

The removal of the vessel’s rudder, where the FPSO is a conversion

c.

The hull design of purpose-built FPSOs

d.

High windage structure at the fore end.

The lack of directional stability can be hazardous due to:
a.
Lack of sea room in congested and/or confined waters, e.g. Dover Strait
b.

21.5.3

21.5.4
21.5.5

Accelerated deterioration of the towing gear caused by excessive movement, especially wear of
chains.

To limit the loss of directional stability the hull must be carefully ballasted, trimmed by the stern and in
the case of a ship-shape hull with the forefoot well immersed. This will also reduce slamming in heavy
weather. The ballast distribution must be checked to ensure that the shear and longitudinal bending
moment are within acceptable limits.
Consideration may also be given to attaching a towing vessel at the stern of the FPSO (see also
Section 21.5.5 below).
Careful design of the towing gear may mitigate the problem. Consideration may be given to towing by
the stern. If this is proposed then any motions analysis or model testing shall recognise this
configuration. The strength of the hull in way of the stern shall be checked to ensure that:
a.
The stern can withstand the anticipated slamming loads
b.

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Suitably sized towing connections and fairleads are or can be attached.

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21.6

TOWING EQUIPMENT

21.6.1

Requirements for assisting tugs to provide additional manoeuvring control, and to assist with berthing
or connection to the permanent mooring system shall be assessed for:
a.
Departure

21.6.2

21.6.3

b.

Any intermediate ports

c.

Any shelter areas

d.

Bunkering

e.

Arrival.

The towing equipment shall be configured to accommodate additional and assisting tugs and to allow
connection and disconnection when required. These activities may dictate the equipment on board the
unit. For example, tugger winches, davits or cranes could be needed.
As noted in Section 21.5, FPSOs may exhibit a lack of directional stability during towage. There are
two key tow-gear-related issues to address this problem and minimise the risk of gear failure:
a.
The towing brackets on the vessel need to be wide-spaced, preferably more than one-half of
the beam
b.

The chafe chains should be generously oversized (typically +50%) to allow for accelerated wear
during the voyage.

21.6.4

At least one emergency towline is mandatory, and means to recover each bridle after any breakage
shall be provided. The possible manning of the vessel will influence the type and location of any
recovery gear.

21.7

SELF-PROPELLED OR THRUSTER-ASSISTED VESSELS

21.7.1

21.7.3

In some cases, the FPSO may have its own propulsion, which may be either the original ship’s system
or thruster units to be used in service. If these are to be used for the voyage to site, the vessel must
comply fully with all regulatory requirements.
The specification of the thruster units, power supplies and manning should be reviewed, to ensure that
they are compatible with the voyage requirements.
A risk assessment shall be undertaken to determine the need for assisting tugs.

21.8

MANNING AND CERTIFICATION

21.8.1

Most FPSOs are not classed as ships during their service life. The documentation set out in Section 5
shall be provided.
If the towage is to be manned, then the requirements of Section 17 shall be considered.
Regardless of the presence of construction or commissioning personnel, a dedicated marine riding
crew is recommended, as shown in Section 17.1.4.
In all cases, whether manned or unmanned, the unit must be fitted with appropriate means of boarding,
in accordance with Section 13.14.

21.7.2

21.8.2
21.8.3
21.8.4

21.9

EMERGENCY ANCHOR

21.9.1
21.9.2

The general emergency anchor requirements of Section 16 shall apply.
FPSO mooring systems (whether turret-type or spread), being only for in-place conditions, are not
configured to act as emergency moorings during transit. On a conversion the permanent anchors will
often be removed. For many designs the deck space where an emergency anchor might be sited is
taken up with the permanent mooring equipment.

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21.10

MOORINGS & UNDER KEEL CLEARANCE

21.10.1

The need for moorings before, during or immediately after the towage shall be considered. Design and
layout of such quayside moorings should be incorporated into the overall arrangement of the vessel as
described in Section 16.7.
Wherever an FPSO hull is moored in shallow water, a minimum of 1m underkeel clearance must be
maintained at all levels of tide for the duration of the vessel’s stay in a particular location. The
clearance should be calculated after consideration of:
a.
Lowest predicted astronomical tide,

21.10.2

b.

Maximum negative surge

c.

Other environmental factors,

d.

Weight growth due to construction activities and loading of modules,

e.

Ballast, trim and heel changes,

f.

Bottom protrusions,

g.

Hull girder bending,

h.

Water density,

i.

Squat (when moored in a river or tidal stream),

j.

Seabed conditions.

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22

SPECIAL CONSIDERATIONS FOR THE TOWAGE OF VESSELS AND
STRUCTURES IN ICE COVERED WATERS

22.1

GENERAL

22.1.1

This Section sets out the special technical and marine aspects and issues not covered elsewhere in
these Guidelines, that will be considered by GL Noble Denton for the approval of the towage of ships,
barges, MODU’s and any other floating structure towed in ice-covered waters.
It is recognized that towing in ice-covered water is a unique marine operation and that all vessels and
towages in ice are different - making these guidelines general in nature. Each approval will depend on
the result of an in-depth review of the tow-plan as well as an equipment inspection/attendance by a
surveyor to identify any particular problems that may exist for the specific vessel(s) and towage in
question.
Structural safety and towing performance will require careful consideration of the size and shape of the
vessel being towed, especially with respect to the beam of the towed vessel in comparison to the beam
of the towing vessel and the shape of the bow of the towed unit. The beam difference will affect the
level of ice protection provided by the tug to the tow, as well as the ice interaction and towing
resistance caused when the beam of the tow is greater than that of the tug and/or of any independent
icebreaker support. In addition, special towing techniques used in ice and manoeuvrability restrictions
caused by the ice require that experienced personnel plan and execute the tow.
Except as allowed by Section 22.1.5, any vessel that is operated and/or towed in ice shall be in Class
with a recognized Classification Society and have a current Load Line Certificate.
Special cases may be considered for the towage of vessels with a Load Line Exemption Certificate or
for objects with no classification such as caissons and vessels with expired classification such as a
demolition towage. In such special cases an inspection will be carried out and, in order to verify if the
structural strength and watertight integrity of the tow is approvable for the intended voyage, the
attending surveyor may require one or more of the following:
a.
An extended, in depth, survey of the vessel structure involving one or more specialist
surveyor(s). Facilities for a close-up survey of inaccessible parts of the hull structure may be
required.

22.1.2

22.1.3

22.1.4
22.1.5

22.1.6

22.1.7

b.

Thickness determination (gauging) of specified areas of the vessel structure. This survey may
be in limited areas or extend over large parts of the hull structure. Such surveys shall be
carried out by a reputable independent company. An existing survey report may be acceptable
provided that it is not more than 1 year old, and there is no evidence of damage or significant
deterioration since that date.

c.

A GL Noble Denton review of classification society approved scantling drawings.

d.

Calculations to show that the structural strength of particular local areas of the vessel is
adequate. The extent of the calculation required to be determined by the results of the surveys
and drawings review.

Should any doubt exist as to the ability of the vessel (object) to complete the proposed towage, after all
the necessary surveys and calculations have been undertaken, a dry dock survey of the vessel may be
necessary.
After complying with the requirements of Sections 22.1.2 to 22.1.4 listed above, GL Noble Denton may
deem that the vessel/object is unfit for tow and decline to issue a Certificate of Approval. For example,
the towage of any vessel or object which is damaged below the waterline, is suspected of being
damaged below the waterline or has suffered other damage or deterioration which could affect the
structural strength and/or watertight integrity will not be approved for towage in ice. Alternatively, the
vessel/object may only be considered fit for tow after specified repairs and suitable ice strengthening
has been carried out.

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22.2

VESSEL ICE CLASSIFICATION

22.2.1

The tug(s) and towed vessel shall have an appropriate ice classification or equivalent for transit
through the anticipated ice conditions identified in the Tow Plan and verified by GL Noble Denton.
The International Association of Classification Societies (IACS) introduced “Requirements concerning
Polar Class” in 2007 [Ref 23] which came into effect on ships contracted for construction on and after 1
March 2008. These are described in the following Table:

22.2.2

Table 22-1
Polar Class

22.2.3
22.2.4

22.2.5

Polar Class Descriptions

Ice Description (based on WMO Sea Ice Nomenclature)

PC 1

Year-round operation in all Polar waters

PC 2

Year-round operation in moderate multi-year ice conditions

PC 3

Year-round operation in second-year ice which may include multiyear ice
inclusions

PC 4

Year-round operation in thick first-year ice which may include old ice inclusions

PC 5

Year-round operation in medium first-year ice which may include old ice
inclusions

PC 6

Summer/autumn operation in medium first-year ice which may include old ice
inclusions

PC 7

Summer/autumn operation in thin first-year ice which may include old ice
inclusions

The following tables summarize the previous nominal ice classification equivalencies for some
classification societies and regulators.
It is important to note that the structural requirements of various classification societies are different
and that many requirements have changed substantially over the years so that the ‘equivalencies’
shown in the tables should only be used for general guidance. This may result in a vessel’s ice
capability being interpreted by GL Noble Denton to be different to that indicated by the table.
Vessels classed as Ice breakers:
Table 22-2
Polar
Classes
PC 5
PC 4
PC 3
PC 2
PC 1

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Russian

(LL4)
LU6
(LL3)
LU7
(LL2)
LU8
(LL1)
LU9

LRS

C1

Previous Icebreaker Classifications
Canadian
Arctic Class
CASPRR

CAC4

Operating Criteria
DNV

Ice 05
Ice 10
Ice 15
Polar 10

AC1.5

CAC3

AC2

CAC2

Polar 20

AC3

CAC1

Polar 30

Typical WMO ice
type & thickness
capability
Winter ice with
pressure ridges
Thick first year ice
with old ice inclusions
Multi-year ice floes
and glacial ice
inclusions

Ice
thickness
0.5 m
1.0 m
1.5 m
2.0 m
3.0 m

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22.2.6

Vessels classed For Ice Navigation:
Table 22-3
Canada
(ASPPR)

GL

E

E

D

E1

C

E2

B

E3

A

E4

Russian
(L4)
LU
(L3)
LU2
(L2)
LU3
(L1)
LU4
(UL/ULA)
LU5

Previous Vessel Ice Classifications
ABS

BV

DNV

LRS

D0

1D

Ice C

1D

1C

1C

1C

1B

1B

1B

1A

1A

1A

1AA

1A
Super

1A*

1C
(Ice 3)
1B
(Ice 2)
1A
(Ice 1)
1A
Super

Typical WMO ice type
and thickness capability
Grey
(0.0 m - 0.15 m)
Grey white
(0.15 m - 0.3 m)
Thin first year (1st stage 0.3 m - 0.5 m)
Thin first year (2nd stage 0.5 m - 0.7 m)
Medium first year
(0.7 m - 1.2 m)

For Russian Classes L-ICE U-REINFORCED A-ARCTIC

22.3

TOWAGE WITHOUT INDEPENDENT ICEBREAKER ESCORT

22.3.1

Where no independent icebreaker escort is identified in the tow-plan for the intended voyage, the tug
and tow must be of appropriate ice classification and power to maintain continuous headway in the
anticipated ice conditions. When a tow is anticipated to take more than three (3) days (the maximum
for a reasonably accurate weather/ice forecast) or longer in ice conditions that includes a concentration
of five (5) tenths or more of limiting ice types, the tow-plan must indicate the location of the nearest
icebreaker support and the anticipated time before independent icebreaker assistance (Coast Guard or
Commercial) can be provided.
With the exception of a vessel pushed ahead (push-towed), the ice classification requirement for the
towed object may be considered for reduction if it is determined that the tug has a higher than
necessary level of ice classification and can protect the tow from potentially damaging ice interaction.

22.3.2

22.3.3

CONVENTIONAL TOW OPERATIONS:
a.
the tug must have sufficient power and hull strength (ice classification) to be capable of safely
maintaining continuous towing headway through the worst anticipated ice conditions including, if
necessary, the breaking of large diameter floes and deformed ice with no requirement for
ramming and:
b.

22.3.4
22.3.4.1

the tow-plan must show that the towage should not be subjected to ice pressure.

CLOSE-COUPLE TOWING OPERATIONS
Close-couple towing is an operation that allows a specially designed icebreaker to combine towing and
icebreaking assistance. The stern of the icebreaker has a heavily fendered ‘notch’ into which the bow
of a ship is pulled by the icebreaker’s towline. The towline remains attached and the icebreaker
steams ahead, usually with additional power provided by the towed vessel in the notch. In this way an
icebreaker can tow a low-powered and low ice classed ship quickly (up to 3 times faster than
conventional towing in ice) and safely (better protection of the towed vessel and less risk of collision
due to over-running) through high concentrations of difficult ice. For close-couple towages:
a.

The beam of the icebreaker must be more than that of the towed ship in order to avoid shoulder
damage to the towed vessel and excessive towline stress and:

b.

The icebreaker is fitted with a constant tension winch or equipment that will reduce the effects
of shock-loading:

c.

The bow of the towed ship must be compatible with the notch design of the icebreaker.
Preferably the entrance of the towed ship is not so sharp as to apply excessive force on the

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stem when going straight ahead. Freedom of movement of the towed ships bow can cause
manoeuvring difficulties as well as applying heavy side forces on the towed ships bow when
turning. The bow should not be so bluff that all the force is concentrated in localized areas. In
addition the towed ship cannot have a bulbous bow because the underwater protrusion could
damage the icebreakers propellers and:
d.

The displacement and freeboard of the towed vessel should not be so disproportionate with that
of the icebreaker that the manoeuvring characteristics of the icebreaker are seriously
compromised:

e.

The anticipated ice conditions should not require ramming or passage through areas where
high levels of ice pressure may be experienced without independent icebreaker assistance.

22.3.5
22.3.5.1

PUSH-TOW OPERATIONS
Push-Tow operations can be carried out using rigid connection (composite unit) or flexible connections
(a push-knee erected at the stern of the pushed vessel). In some cases where the design and ice
strength of the tug and tow is appropriate a tug may opt to push rather than tow in ice, especially when
experiencing ice pressure, so that headway can be maintained and to remove the stress from the
towline.

22.3.5.2

In some cases a push-tow is a more efficient and a more desirable method of ice transit to
conventional towing, however, in all circumstances where the push-towing technique may be used, it is
important that the pushed vessel has appropriate ice strengthening, particularly in the bow and
shoulder areas.

22.3.5.3

The ice classification of a tug that is engaged in a ‘push-tow’ operation with no independent icebreaker
support can be reduced if:
a.

the vessel being pushed has appropriate ice classification and strength for unescorted transit in
the anticipated ice conditions and:

b.

the beam of the pushed vessel is greater than that of the tug. The beam of the pushed vessel
should be at least one third greater than that of the tug to allow suitable manoeuvring for a
flexible connection and:

c.

the connection between tug and tow is of suitable strength for emergency stops and:

d.

the tow-plan shows that the ‘push-tow’ will not enter, or be exposed to, an area where ice
pressure may be encountered of sufficient severity to stop the continuous forward progress of
the push-tow without independent icebreaker assistance.

22.4

TOWAGE OPERATIONS WITH INDEPENDENT ICEBREAKER ESCORT

22.4.1

The ice classification requirements indicated in Section 22.2.2 for the tug(s) and towed vessel(s) may
be considered for reduction if it is determined that appropriate icebreaker escort assistance is provided
for the duration of the tow in ice and that:
a.
The icebreaker(s) has sufficient capability to allow the towage to maintain continuous headway
through all of the anticipated ice conditions and,
b.

The icebreaker(s) has a beam equal to, or greater than, the tug and tow combination or:

c.

The icebreaker(s) is fitted with suitable and operational equipment such as azimuthing main
propulsion units or compressed air systems that are capable of opening the track wider than the
beam of the escorted towage in the anticipated ice conditions or:

d.

More than one icebreaker will be used to provide a broken track equal to, or wider than, the
beam of the tug and tow combination.

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22.5

MANNING

22.5.1

In addition to Section 12.13 concerning manning, special consideration should be given to the number,
qualification and experience of personnel required on the navigating bridge to ensure safe navigation
including steering and engine control, lookout, operation of searchlights and, emergency operation of
the towing winch abort system.
The master in charge of a tow (tow-master) should typically have at least 3 years experience of towing
in ice conditions similar to those anticipated for the proposed towage. Other navigating officers on tugs
involved in a towage in ice should also have previous experience of towages in ice.

22.5.2

22.6

MULTIPLE TOWS AND MULTI-TUG TOWS

22.6.1

Multiple Towages in ice are subject to the appropriate provisions set out in this section regarding ice
classification, equipment and suitable propulsion power as well as the general provisions (particularly
those presented in Section 18). However, only in exceptional circumstances of very light ice and/or
very low ice concentration (trace) will a Double Tow (Section 18.1.1) or a Parallel Tow (Section 18.1.4)
be considered for approval. An in-depth risk assessment would be required and the risks shown to be
acceptable.
In addition to the provisions presented in Section 18 concerning towing operations that use more than
one tug or multiple tows:
a.
To avoid collision or over-running each tug shall have a quick release and re-set system as
described in Sections 22.7.2.1 and 22.7.2.2.

22.6.2

b.

The most experienced tug Master shall be designated as the tow-master and give directions to
the other vessels. All other tug Masters and senior navigating officers involved in the multi-tug
towage should have an appropriate level of experience of towing in ice and be familiar with the
associated difficulties and hazards.

c.

A multi-tug tow-plan that is presented to GL Noble Denton for approval that does not include
independent icebreaker escort assistance shall demonstrate clearly why it is not considered
necessary. As an acceptable example, the tow could be configured such that one or more tugs
with the capability to perform ice management (escort duties) can be released, and the
remaining tug(s) have sufficient BP to continue making towing progress. In some
circumstances a tow-plan can include the contingency of releasing one or more tugs that are
towing in the conventional manner to push-tow provided that:


the towed vessel is appropriately ice strengthened:



the towed vessel is appropriately designed and strengthened in the pushing location(s):



the tugs are designed and adequately fendered for pushing:



such action would only be considered in a high ice concentration where there is no
influence by sea or swell.

d.

When two tugs are towing in series as described in Section 18.6 in an ice infested area, special
attention shall be given to the strength of the towing connections on the foredeck of the second
tug in case it is necessary for the lead tug to break through ice floes of varying thickness that
may cause shock-loading.

e.

A tandem tow of barges as described in Section 18.4.2 is sometimes referred to as ice-coupled.
Where the presence of ice increases the potential for rapid changes to the towing speed, this
type of close connection necessitates good fenders to be in place between each unit in the tow.

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22.7

TOWING EQUIPMENT

22.7.1
22.7.1.1

GENERAL
The towing techniques that are used in ice typically require a short distance between the tug and tow
to increase manoeuvrability and so that the propeller wash from the towing vessel can assist in
clearing ice accumulation around the bow of the towed vessel. Because of the short towing distance
and reduction of towline catenary it is necessary for the towing arrangement to be suitable for the
additional stress that can be experienced. The stress on the towing arrangement can vary
considerably with:
a.

the thickness and concentration of ice as well as ice pressure,

b.

the difference in beam between the tug and tow resulting in ice interaction on the shoulders of
the towed vessel and ice accumulation in front of the tow as well as the use and effectiveness
of independent icebreaker escort and

c.

large heading deviations due to manoeuvring through and around ice and

d.

unintentional tug interaction with heavy ice floes which can result in shock-loading to towing
components due to whiplash and the tow taking charge.

It is for these reasons that additional provisions concerning towing equipment strength, type and
configuration are necessary.
22.7.2
22.7.2.1

ADDITIONAL EQUIPMENT REQUIREMENTS FOR TOWING IN ICE
In addition to Section 12.5 (Tow-line Control), a tug involved in towing in ice infested waters must be
fitted with an operational towline quick release/reset system (tow-wire abort system):
a.

when towing in ice that could rapidly reduce towing speed or

b.

when a tug is involved in a multiple tow or

c.

when a tug is involved with a multi-tug tow.

22.7.2.2

The towline quick release system should be capable of immediate winch brake release for pay out of
tow-wire as well as winch brake re-set from the navigation bridge and the winch control station (if
different).

22.7.2.3

With reference to Section 12.9, a tug involved in a towage in ice should be fitted with at least two
searchlights that can be directed from the navigation bridge.

22.7.2.4

As recommended in Sections 12.11.2 and 13.16, every tug that is towing in ice shall be equipped with
burning and welding gear for ice damage control and repair.

22.7.3

STRENGTH OF TOWLINE

22.7.3.1

With reference to Section 13.2.1 (a):
For a tug that is planning a conventional single towline towage in ice the Minimum Towline Breaking
Load (MBL) should be computed as follows:
Table 22-4

0030/ND REV 4

Minimum Towline MBL in Ice

Bollard Pull (BP)

MBL (tonnes)

BP ≤ 40 tonnes

3.7 x BP + 12

40 < BP ≤ 90 tonnes

(4.2 – BP/50) x BP + 24

BP > 90 tonnes

2 x BP + 60

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22.7.3.2

An exception can be made for short tows in very thin ‘new’ ice or in very low concentrations (<3/10ths)
of medium or thick ‘rotten’ ice. In these circumstances the Minimum Towline Breaking Load (MBL)
should be computed as shown for a ‘non-benign’ tow in Section 13.2.

22.7.3.3

The strength of all other towing connections and associated equipment should be appropriately
calculated as required by the provisions of Section 13.2.

22.7.3.4

Further, ALL tugs involved in a towage in ice must carry a spare tow-wire of the same length and
strength as the main tow-wire that is immediately available on a reel to replace the main tow-wire. In
addition, there must be enough competent personnel, equipment and spares on board to crop and resocket the main tow-wire at least once.

22.7.4
22.7.4.1

SPECIAL CASES OF REDUCED TOW-WIRE STRENGTH
The minimum size of tow-wire that is typically used by icebreaking tugs of 160te BP for close-couple
towing is for example, 64mm EIPS rove through a multiple sheave floating ‘Nicoliev Block’ system. In
this system a single bridle wire, usually of the same size and strength as tug's main tow-wire, is made
fast to each bow of the vessel being towed.. The tow-wire goes from the towing winch to the floating
block on the bridle and back via a fairlead to a towing damper on the tug. For larger powered tugs, the
tow-wire may be doubled up again by passing the wire through a standing block on the tug’s deck and
around a second sheave on the floating block before it is made fast to the towing damper. This makes
the bridle wire the ‘weak link’ in the system and because of this an icebreaking tug shall carry sufficient
spare bridle wires, typically at least 6.

22.7.4.2

To meet the minimum towline strength criteria a tug that has an appropriate bollard pull may, in
exceptional circumstances, be considered for approval of a conventional towage in calm waters
containing ice using two towlines provided that:
a.

Each of the two independent towlines is a minimum of 90% of the required strength and

b.

Each tow-wire is on a separate towing winch that can be adjusted, quick released and reset
independently from the other and

c.

Each tow-wire meets the requirements of a single tow-wire in terms of minimum length,
construction etc. and

d.

Each tow-line has a monitoring system to enable load sharing.

22.7.5
22.7.5.1

TOWING WINCHES
Towing winches are required due to the typical manoeuvring restrictions and hazards that are inherent
to towing in ice. Towing hooks do not allow for the rapid adjustment of towline length.

22.7.5.2

Each towing winch should have sufficient pull to allow the towline to be shortened under tension.
When possible, the navigating bridge and winch operator should be provided with continuous readouts
of towline length deployed and towline tension.

22.7.5.3

Winch controls and winch operating machinery should be suitably protected from environmental
conditions, particularly low temperatures that can result in winch malfunction.

22.7.5.4

Towing winches shall have a quick release and re-set system as described in Sections 22.7.2.1 and
22.7.2.2.

22.7.6
22.7.6.1

CHAIN BRIDLES
A chain bridle is typically used for a towage in ice with a chain pigtail connected to a ‘fuse wire’ or
directly to the towline. In some circumstances where high shock loads are anticipated, an extra long
chain pigtail may be considered appropriate. Wire pennants and bridles are sometimes used for small
barge and vessel tows, especially when the close-couple or ice-couple towing technique is anticipated.

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22.7.7
22.7.7.1

SYNTHETIC ROPE
Synthetic rope is prone to rapid cutting both internally by ice crystals and externally by ice edges and
therefore is not approved for use in a towing system for an in-ice towage. Sections 13.8.2 and all parts
of Section 13.9 do not apply in ice transits or in very low temperatures where icing can occur.

22.7.8
22.7.8.1

BRIDLE RECOVERY SYSTEM
In addition to the requirements of Section 13.10:
a.

To reduce direct ice interaction and disconnection of the bridle recovery wire, the wire should be
lightly secured to one leg of the bridle and the end shackled onto the apex or a chain link close
to the apex of the tri-plate.

b.

The fuel mentioned in Section 13.10.2 for a motorized recovery winch shall be appropriate for
the anticipated temperatures.

22.7.9
22.7.9.1

EMERGENCY TOWING GEAR
With reference to Section 13.11, special arrangements may be required for the emergency towing
gear, especially on an unmanned tow proceeding in ice. For all towages in ice the emergency towing
gear should be fitted and arranged to tow from the bow unless it can be shown that the object being
towed is designed for multi-directional towing.

22.7.9.2

A floating line and pick-up buoy are susceptible to being cut and lost or snagged by ice and pulled
clear of the soft lashings or metal clips. It is recommended that a different arrangement is employed in
high concentrations of ice. For example, an intermediate wire may be attached to the end of the
emergency tow-wire and lightly secured to a pole extended astern at least 5 metres. The eye of the
intermediate wire is suspended above the surface of the ice approximately 1 metre above the aft
working deck of the tug where it can be captured for connection to a tugger-winch wire. The float line
and pick-up buoy are shackled to the emergency tow-wire in the same way as described in Section
13.11.2, but remain coiled on the deck of the tow for deployment once the towage arrives in open
water.

22.7.10
22.7.10.1

ACCESS TO TOWS
With reference to Section 13.14, whether a tow is manned or not, suitable access must be provided.
For towages in ice, a permanent steel ladder should be provided at the stern from the main deck to just
above the waterline. As discussed in Section 13.14.2, ladders, particularly side ladders should be
recessed to avoid ice damage. A tug workboat should carry suitable equipment to de-ice recessed
access arrangements and ladders to tows. Pilot ladders used as a short term alternative should be
closely inspected for ice damage before being used. Typically, a pilot ladder secured at the stern of
the tow is subject to the least amount of ice interaction.

22.7.11
22.7.11.1

TOWING EQUIPMENT CERTIFICATION AND SPECIAL PRECAUTIONS
As described in Section 13.12, all equipment used in the main and emergency towing arrangements
for a towage in ice shall have valid certificates. Special precautions are necessary for equipment that
has been, or will be, used in extremely low temperatures. Regardless of anticipated temperatures
during the proposed towage, a GL Noble Denton surveyor may request to have sockets, chains,
flounder plates and shackles used in the towing process non-destructively tested (NDT). Based on the
results of a visual inspection of the tow-wire, the surveyor may also require that the tow-wire is cropped
and re-socketed prior to the towage.

22.7.12
22.7.12.1

RECOMMENDED SAFETY EQUIPMENT FOR THE WORKBOAT
In addition to Section 12.6, sufficient Arctic survival suits shall be carried on board the tug for all
personnel that may be operating the workboat and personnel transferred to the tow by the work boat.
These additional survival suits should be fitted with hard soled boots, belts and detachable gloves.

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22.8

TUG SUITABILITY

22.8.1

The tug shall have a bollard pull appropriate for the anticipated ice and weather conditions. The
calculated BP should never be less than that necessary for an open ocean towage, as shown in
Section 12.2.

22.8.2
22.8.2.1

OVERSIZED TUG
For all towages in ice, Section 13.2.10 concerning towing connections does not apply. In the case of
an oversized tug (in terms of TPR) all connections should be at least equal to the MBL of the tow-wire
in use. The tow-master must be fully aware of any strength reduction to the connections, carry
adequate replacement spares and the towing procedures should identify the maximum power setting
that may be applied.

22.9

CARGO LOADINGS

22.9.1
22.9.2

Special attention should be given to cargo overhangs on a case-by-case basis.
In general, cargo overhang for a towage in ice will not be approved unless it can be shown that the
cargo is adequately protected such that no ice interaction can occur.
To determine the potential for ice interaction, calculations must show that the cargo has at least three
meters clearing height above the maximum height of ice deformity that can be experienced during the
tow. In all ice concentrations this minimum clearing height will be maintained in all conditions of roll,
pitch and heave (see Sections 7 and 8). Due to the potential for ice impact and resulting damage
cargo overhang cannot be allowed to immerse under any circumstance, so that Sections 7.6, 8.5,
10.1.4 and 10.1.5 are not applicable.

22.9.3

22.10

SEA-FASTENING DESIGN AND STRENGTH

22.10.1

The motions of a vessel transiting through low concentrations of ice should be assumed to be as
severe as those experienced in clear open water storm conditions. Swell waves can persist for many
miles even into an ice edge of very high ice concentration. In high ice concentrations where no waves
are evident, impact or over-running of thick ice floes can cause sudden deceleration, heading
deflections, listing and rolling of the tow. For these reasons the strength of cargo and sea-fastenings
for transportation in ice conditions should be of appropriate design and not less than that required for
unrestricted transportations in non-benign areas - see Sections 7 and 8. The cargo mass shall include
the effect of ice accretion calculated in accordance with the IMO Intact Stability Code [Ref. 17],
Chapter 5.

22.10.2
22.10.2.1

INSPECTION OF WELDING AND SEAFASTENINGS
With reference to Section 9.7, consideration of special welding procedures and techniques may be
necessary for sea-fastenings installed in very cold temperatures.

22.10.3
22.10.3.1

PIPES AND TUBULARS
With reference to Section 9.6.4 - stress on pipes in a stack, and Section 9.6.10 - open ended pipes,
special consideration should be given to pipes filling with ice due to freezing spray and/or wave action
in low temperatures and the potential to overstress lower levels of pipe, seafastenings and deck
structures. The effect on the vessel stability should also be considered.

22.11

STABILITY

22.11.1

Stability calculations for vessels, including tugs and tows, operating in very cold temperatures and in
ice conditions shall be submitted to GL Noble Denton for review against the IMO Intact Stability Code
[Ref. 17], Chapter 5.
The intact range of stability of a towed vessel (see Section 10.1.1) shall never be less than 36 degrees,
including inland and sheltered towages.

22.11.2

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22.11.3

22.11.4
22.11.5
22.11.6
22.11.7

22.11.8

22.11.9

For transit in ice-infested waters, the statement in Section 10.1.4 of these guidelines shall be modified
to read ‘Cargo overhangs shall be such that no immersion is possible in the anticipated environmental
conditions’.
Section 10.1.5 referring to buoyant cargo overhangs does not apply to transits in ice.
In addition to the requirements of Section 10.2.1, towed objects shall have positive stability with any
two compartments flooded or broached.
The damaged stability relaxations for towed objects referenced in Sections 10.2.4 and 10.2.5 do not
apply in any area where ice interaction can occur. See also Section 10.2.7.
The integrity of all underwater compartments of a tug and compartments subject to down-flooding must
be safeguarded from flooding by watertight doors and hatches that access such compartments. This is
a critical requirement for an approval to conduct a towage in ice. All compartment accesses must be
checked for watertight integrity and kept closed at all times throughout the towage.
The draughts mentioned in Section 10.4.4 are the minimum for open water operations. In an ice
environment, additional consideration must be given to the location of any specially strengthened ‘ice
belt’ and to the exposure of areas vulnerable to ice damage such as propulsion and steering
equipment that may require specific and/or deeper overall ice transit draughts.
A vessel being towed or pushed (regardless of being self propelled) shall not be excessively trimmed.
On manned tows the trim should be appropriate to provide watch personnel with as much forward
visibility as possible for observation of approaching ice conditions and the movements of other vessels
involved in the towage to reduce the potential for ice impact and/or collision damage.

22.12

BALLASTING

22.12.1

Ballasting of the forepeak (to above the waterline) of a tug and towed vessel is done to assist with ice
impact load dispersal. This also provides protection against developing excessive trim by the head in
the event that a forward compartment is breached by ice and flooded. In addition, the emptying of a
ballasted forward compartment can assist with exposing damage for emergency repair or to raise the
damaged area clear to avoid continued ice interaction and escalation of damage.
Special precautions should be taken to avoid structural damage caused by pressurizing compartments
when ballasting and deballasting due to water freezing in tanks or inside tank vent pipes. This is in
addition to the freezing of tank vents from coating with freezing spray in very low temperatures.

22.12.2

22.13

VOYAGE PLANNING

22.13.1

In addition to the requirements listed in Section 14, a written voyage plan or tow-plan should be
submitted for review and comment by GL Noble Denton in advance of a proposed towage in an iceinfested region.
The plan should include:
a.
A general description of the proposed voyage (manned/unmanned towage etc)

22.13.2

b.

Tug and tow particulars including ice classifications and certification

c.

Research documentation indicating the anticipated ice/weather conditions

d.

Routeing including shelter and holding locations

e.

Navigation and communications equipment appropriate for the region

f.

Summary of tow-master and senior officer experience

g.

Arrangements for receiving weather and ice information and/or routeing

h.

Voyage speed and fuel calculations including any bunkering requirements and procedures to
comply with National regulations

i.

Contingency fuel, hydraulic & lubricating oils of suitable viscosity for the low ambient
temperatures

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j.

Main and emergency towing arrangements and certification

k.

Stability calculations and location of all cargoes, consumables, ballast and pollutants for the tug
and tow

l.

Sea-fastening (cargo securing) arrangements

m.

Arrangements for assist tugs for docking etc and for ice management as required

n.

Damage and pollution control equipment as applicable

o.

Contingency procedures for ice damage, tug breakdown, fire, broken tow, man overboard and
the nearest icebreaker assistance.

22.13.3

In addition to the list in Section 14.5.1, prior to departure the tow-master of an unmanned towage
should be supplied with the appropriate drawings that indicate the basic structure, watertight
compartments, ballast system, cargo securing arrangements on the tow, and manuals that provide the
tug crew with operating procedures for emergency equipment such as ballast pumps (see Section 15),
the emergency generator, the emergency anchor system and the tow bridle retrieval system.

22.13.4
22.13.4.1

RE-FUELLING THE TUG
The tow-plan should indicate the calculated fuel usage during the tow for the required power in the
anticipated ice conditions.

22.13.4.2

For the portion of the voyage that will be carried out in ice conditions, in addition to the times listed in
Section 6.2.2 - the operational reference period, and Section 6.7 – calculation of voyage speed, the
planned duration will include:
a.

typical towing speeds of not more than 2 knots in ice covered areas as a conservative estimate
where the actual towing distance is unlikely to be direct. A towing speed of 5 knots may be
used where it can be shown that the tow will only encounter very thin new ice or alternatively
very low concentrations (<3/10ths) of thick rotting ice and:

b.

waiting for appropriate ice conditions for departure, transit and arrival and:

c.

up to 25% additional fuel (and other consumables) may be required (see Sections 6.2 and
12.12).

22.13.4.3

The tow-plan must indicate compliance with the International, National and Local regulations and
guidelines concerning the carriage of oil cargoes, the allowable quantity and distribution of fuel oil or
any other pollutant or dangerous cargo. In addition, where a tow-plan indicates the requirement to refuel the tug from the tow or from another vessel this will normally require special approval from a
National authority and also require that the tug carries appropriate pollution containment and clean-up
equipment. The re-fuelling approval from the appropriate jurisdiction, as well as the re-fuelling
procedure and equipment, shall be provided in the tow-plan for review.

22.14

WEATHER /ICE RESTRICTED OPERATIONS

22.14.1

In addition to the requirements of Section 6.3, for a towage in an ice infested area, dependable ice
forecasts must be available and the tug must have appropriate equipment on board to receive ice
information including ice maps, bulletins, advisories and forecasts.

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22.15

DAMAGE CONTROL AND EMERGENCY EQUIPMENT

22.15.1

Special consideration should be given to the remoteness of the area and the anticipated ice conditions
where a towage will take place to determine the availability of emergency response, assistance and
equipment. In addition to the damage control equipment listed in Section 13.16, additional equipment
is recommended for a towage in ice:
a.
Portable generator
b.

Portable compressor

c.

Portable salvage pump(s)

d.

Bracing shores

e.

Portable de-icing equipment

f.

Space heaters

g.

Extension ladders

h.

Chain falls

i.

Collision mat materials.

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23

SPECIAL CONSIDERATIONS FOR CASPIAN SEA TOWAGES

23.1

BACKGROUND

23.1.1

For the purposes of these guidelines the Caspian Sea has been divided into the shallow Northern area
(North of 45oN latitude as shown in Figure 23.1), an Intermediate area between 45oN and Kuryk
(approximately 43oN), and the Southern area. The Intermediate area has been introduced for vessels
travelling between the Northern and the Southern areas with relaxations subject to suitable weather
routeing.

Astrakhan

NORTHERN AREA
5m WD

45oN

4
Bautino
10m WD
Astrakhan
sea buoy

INTERMEDIATE AREA

Aktau

Kuryk
43oN

Figure 23-1 Northern Caspian Sea areas
23.1.2

The Northern area contains 25% of the total Caspian Sea area but only 5% of the water volume. The
shallow water (typically 3 to 5 m deep, and very rarely more than 10 m) is a feature of the area which
leads to the ready formation of ice in the winter months. Although winds can be very strong, the limited
fetches and shallow water do not allow significant wave heights above about 3.5 to 4 metres.

23.1.3

Because the water level depends on river inflows balancing the evaporation, there are long term and
seasonal rises and falls in the mean sea level and seawater density. As at 2005, the mean sea level
(MSL) was 27 metres below Baltic Datum (equivalent to global mean sea level) and 1.0m above
Caspian Datum.

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23.1.4

The whole Caspian Sea suffers from a large number of unmarked fishing nets which provide a serious
hazard to tugs which can be immobilised by these nets fouling their propellers. Therefore single
propeller tugs are not recommended, unless there are suitable additional (redundant) tugs in
attendance to replace them.

23.1.5

Many of the tugs found in this region are pusher tugs which should not be used for pushing in open
waters.

23.2

REQUIREMENTS WITHIN NORTHERN CASPIAN SEA

23.2.1

GENERAL The following departures from the requirements shown in Sections 5 to 22 of these
guidelines may be accepted for tows that take place totally within the Northern area (North of 45oN
latitude).

23.2.2

BOLLARD PULL REQUIREMENTS Because of the limited wave heights (due to the shallow water)
the meteorological criteria for calculating the Towline Pull Required (TPR) referred to in Section 12.2.7,
when there is no ice, may be taken as:
Hsig

= 2.5 m

Wind

= 20 m/sec

Current

= 0.5 m/sec

provided that the tow will have adequate sea room after the initial departure. If there will not be
adequate searoom, then Section 12.2.2 will apply.
23.2.3

TOWLINE LENGTHS Because of the very shallow water depths and limited wave heights the
minimum towline lengths required in Section 13.3.1 may be reduced within this area as follows. The
minimum length available for each of the main and spare towlines (L) shall be determined from the
“European” formula:
L > (BP/MBL) x 1,200 metres
except that in no case shall the available length be less than 200 metres.

23.2.4

TOWLINE STRENGTH Because of the short towlines there will be little catenary to absorb shock
loads in bad weather. Unless other methods of reducing the shock loads are used, the towline MBL
shall be increased in line with Section 13.3.2. As an example, a deployed towline length of 200m will
require a towline MBL of 6 (=1,200/200) times the continuous static bollard pull. The towing
connection capacities in Section 13.2.1 b shall be related to the increased required towline MBL.

23.2.5

TOWING CONNECTIONS Suitably positioned, purpose-built quick-release towing connections are
preferred. Where bollards have to be used as the towline connection:


The capacity of the bollards and their foundations must comply with the requirements of Section
13.4.



Suitable fairleads and anti-chafe arrangements must be used.



A keeper plate, capping bar or other means of keeping the towing bridle connected to the
bollards must be provided and this must be suitable for any vertical loads likely to be
encountered.



The design must also allow for quick release of the keeper plate, capping bar or another proven
method to rapidly clear a fouled bridle.

23.2.6

23.2.7

WORKBOAT A twin screw tug fitted with a bow thruster and two anchors in accordance with Class
requirements may be exempt from the requirement for a workboat in Section 12.6 provided the voyage
can be completed within a favourable weather forecast. The tug must also be able to come alongside
the barge at sea so that crew can board with any necessary equipment for pumping, repairs, dropping
the barge’s anchor or reconnecting a towline.

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23.2.8

BUNKERS The requirement for 5 days reserve in Section 12.12 may be reduced to 3 days (pumpable
reserve) provided that:


the towage can be completed within a good weather forecast period, and



there are suitable bunkering ports within 3 days sailing at all times, and



there are suitable tugs available to take over the tow if required during a diversion for refuelling.

23.2.9

TOWAGES IN ICE Section 22 applies.

23.3

REQUIREMENTS FOR REMAINING CASPIAN SEA AREAS

23.3.1

All tows in this area should follow the requirements in Sections 5 to 22 of these guidelines for
unrestricted ocean tows outside benign weather areas, as applicable.

23.3.2

In addition, tugs with a single propeller are not recommended, unless there are suitable additional
(redundant) tugs in attendance to replace them.

23.4

REQUIREMENTS FOR TOWAGES BETWEEEN CASPIAN SEA AREAS

23.4.1

Many shallow draft tugs that are designed for working in the shallow Northern area will be unable to
carry towing gear suitable for towing in the Southern area. When it is not practicable for towages to
change tugs when travelling between these areas whilst within the intermediate area defined in Section
23.1.1, and subject to suitable weather routeing, the following relaxations may be accepted:

23.4.2

4



Deployable towline length to be at least 400 m, and



Towline and towing connection strength requirements of Sections 22.3.4 and 23.2.5 will apply,
and



Minimum bollard pull requirements as in Section 23.2.2.

Weather routeing will include:


Voyage planning to avoid travelling too close to a lee shore and to identify sufficient suitable
safe places of shelter for different weather directions, and



Receipt of regular marine weather forecasts and a commitment to go to a suitable safe place of
shelter on receipt of a bad weather forecast.

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

REFERENCES
[1]

GL Noble Denton document 0009/ND - Self-Elevating Platforms - Guidelines for Elevated Operations

[2]

GL Noble Denton document 0013/ND - Guidelines for Loadouts

[3]

GL Noble Denton document 0015/ND - Concrete Offshore Gravity Structures - Guidelines for Approval of
Construction and Installation

[4]

GL Noble Denton document 0016/ND - Seabed and Sub-Seabed data required for Approvals of Mobile
Offshore Units (MOU)

[5]

GL Noble Denton document 0021/ND - Guidelines for the Approval of Towing Vessels

[6]

GL Noble Denton document 0027/ND - Guidelines for Marine Lifting Operations

[7]

GL Noble Denton document 0028/ND - Guidelines for the Transportation and Installation of Steel Jackets

[8]

IMO International Safety Management Code - ISM Code - and Revised Guidelines on Implementation of the
ISM Code by Administrations - 2002 Edition

[9]

DNV Rules for the Classification of Ships, January 2003, Part 3, Chapter 1, Section 4

[10]

IMO Code of Safe Practice for Cargo Securing and Stowing - 2003 Edition

[11]

API Recommended Practice 2A-WSD (RP 2A-WSD), Twenty First Edition, December 2000, Errata and
Supplement 1, December 2002.

[12]

API Recommended Practice 2A-LRFD (RP 2A-LRFD), First Edition, July 1, 1993

[13]

AISC Allowable Stress Design and Plastic Design, July 1, 1989, with Supplement 1

[14]

API RP 5LW - Recommended Practice for Transportation of Line Pipe on Barges and Marine Vessels

[15]

EEMUA 158 - Construction Specification for Fixed Offshore Structures in the North Sea,

[16]

AWS D1.1 - Structural Welding Code - steel

[17]

IMO Resolution A.749 (18) as amended by Resolution MSC.75(69) - Code on Intact Stability

[18]

International Convention on Load Lines, Consolidated Edition 2002

[19]

International Regulations for Preventing Collisions at Sea, 1972 (amended 1996) (COLREGS)

[20]

IMO MSC/Circ.623 - Piracy and armed robbery against ships - guidance to ship-owners and ship operators,
shipmasters and crews on preventing and suppressing acts of piracy and armed robbery against ships

[21]

IMO Document Ref. T1/3.02, MSC/Circ.884 - Guidelines for Safe Ocean Towing

[22]

IMO BWM/CONF/36 - International Convention for the Control & Management of Ships' Ballast Water &
Sediments, 2004

[23]

IACS Requirements concerning Polar Class Oct 2007

[24]

UKOOA Guidelines for Safe Movement of Self-Elevating Offshore Installations (Jack-ups) April 1995

[25]

UK HSE circular “The Safe Approach, Set-Up And Departure of Jack-Up Rigs to Fixed Installations” Sept 03
from www.hse.gov.uk/foi/internalops/hid/spc/spctosd21.pdf

[26]

Eurocode 3: Design of steel structures - Part 1-8: Design of Joints (BS EN 11993-1-8:2005)

All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX A - EXAMPLE OF MAIN TOW BRIDLE WITH RECOVERY SYSTEM

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX B - EXAMPLE OF EMERGENCY TOWING GEAR

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX C - EXAMPLE OF SMIT-TYPE CLENCH PLATE

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX D - EMERGENCY ANCHOR MOUNTING ON A BILLBOARD

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX E - ALTERNATIVES TO THE PROVISION & USE OF AN EMERGENCY
ANCHOR
E.1

An anchor may be required in an emergency situation, for instance in the event of a broken towline, or
tug failure due to breakdown or fire. The requirement for an emergency anchor in areas of restricted
searoom may be determined as a result of a risk assessment as set out in Section 16.1.2 and which
should satisfy all parties that the precautions proposed are adequate.

E.2

For very large tows, such as GBS’s, TLP’s and FPSO’s, an emergency anchor may be impractical, and
alternative means of achieving an equivalent level of safety should be sought.

E.3

FPSO mooring systems (whether turret-type or spread), being only for in-place conditions, are not
normally configured to act as emergency moorings during transit. On a conversion the permanent
gear is usually removed. For many designs the deck space where an emergency anchor might be
sited is taken up with the permanent mooring equipment.

E.4

For any tow, there are arguments for and against the provision of anchors:
For:
a.
Conventional marine and insurance industry practice is that an anchor is provided, and any
alternative arrangement must be justified.
b.

Once access is gained to the tow, or if the tow is manned, an anchor may provide a “last resort”
method of controlling the tow.

Against:
a.
A chain locker must be provided together with an anchor windlass, chain stoppers etc. and
these will be for one use only. A billboard arrangement, as shown in Section 16.6 and
Appendix D would almost certainly be ineffective for large tows.
b.

Whereas ships and ship-FPSO conversions may retain a hawse pipe, chain locker, anchor
windlass, chain stoppers etc, most new build FPSO’s are not fitted with these facilities.

c.

For most of an ocean towage, and close to steep-to coastlines, the depth of water will be too
great for an anchor to be effective.

d.

If the tow is not manned, then boarding it in bad weather could pose an unacceptable hazard to
the boarding crew, and deploying the anchor may prove to be impossible. In this respect a
spare tug rather than an anchor would be more useful.

e.

In some restricted areas, especially with pipelines, cables or subsea equipment, anchoring is
prohibited, even in emergency situations.

f.

Unless the anchor can be paid out under control, the shock loads when the anchor beds in and
the cable comes taut may be excessive, and could result in damage, loss of the anchor or
unacceptable risk to the riding crew.

g.

Under adverse conditions the anchor may drag, and the tow could still be lost.

h.

If 2 or more tugs are towing, then it is unlikely that any attempt to deploy an anchor would be
made until all tugs or towlines had failed. If, for instance, 2 tugs were towing, dropping an
anchor after a single towline failure would seriously hamper the efforts of the remaining tug to
control the situation. An anchor will probably only be dropped, therefore, if all towlines break.

i.

After deployment of an anchor the towage must resume at some point. The anchor must either
be retrieved or cut and abandoned for later retrieval. It is probable that the tow would then be
lacking an anchor, at least for a time. It is suggested that any anchor used is fitted with a
retrieval pennant and buoy.

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS
E.5

If sufficient towing capacity and redundancy is provided, in the towing spread, tugs will provide a more
flexible and manoeuvrable means of controlling the tow. Reaction time will be faster and control
should be possible in all water depths.

E.6

Proposed criteria, if anchor(s) are not used, include:
a.

Provision of at least N main towing tugs, any (N-1) of which comply with the requirements of
Section 12.2, or:

b.

Provision of at least 2 main towing tugs, which together comply with the requirements of Section
12.2, and:

c.

If 1 or 2 main towing tugs are provided, an additional tug will be required to escort the tow, if the
tow comes within an agreed distance of any coastline or offshore hazard. (48 nautical miles is
suggested as a minimum, assuming the tow may drift uncontrollably at 2 knots for 24 hours).

d.

The escort tug should be approximately equal in specification to the larger main towing tug.

e.

The escort tug is not always required to hook up for escort duties, but contingency plans and
equipment must allow for it to be connected rapidly, either in place of one of the other two tugs,
or in addition, such that the configuration is still reasonably balanced.

f.

In restricted waters, if one of the main towing tugs has a breakdown, it may be preferable to
connect the escort tug to the bow of the broken-down tug, rather than to the tow

g.

The towage route must be drawn up showing the proximity to coastlines or other hazards, and
the route sectors where an escort tug is required. Planning should ensure that the escort tug
has time to arrive and connect up before the searoom is below the agreed limits.

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX F - FILLET WELD STRESS CHECKING
F.1

The effective length of a fillet weld, l, should be taken as the length over which the fillet is full-size.
This may be taken as the overall length of the weld reduced by twice the effective throat thickness a.
Provided that the weld is full size throughout its length, including starts and terminations, no reduction
in effective length need be made for either the start or the termination of the weld.

F.2

The effective throat thickness, a, of a fillet weld should be taken as the height of the largest triangle
(with equal or unequal leg) that can be inscribed within the fusion faces and the weld surface,
measured perpendicular to the outer side of this triangle, see Figure F.1.

a

Figure F.1
F.3

a

Effective Throat Dimension ‘a’ for concave and Convex Fillet Welds

A uniform distribution of stress is assumed on the throat section of the weld, leading to the normal and
shear stresses shown in Figure F.2.

σ┴ =

normal stress perpendicular to the throat

σ║ = normal stress parallel to the axis of the weld
τ┴ = shear stress (in the plane of the throat) perpendicular to the axis of the weld
τ║ = shear stress (in the plane of the throat) parallel to the axis of the weld

0030/ND REV 4

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GUIDELINES FOR MARINE TRANSPORTATIONS

σ║

σ┴

τ║
τ┴

Figure F.2

Normal and Shear Stresses acting on the plane of Weld Throat

F.4

The normal stress σ║ parallel to the axis is not considered when verifying the design resistance of the
weld.

F.5

The two stress conditions perpendicular to the axis of the weld, σ┴ and τ┴ may be considered to be
equal in magnitude in the case where the load P acting on the bracket is applied parallel to the axis of
the weld. This can be seen in the assumption in Figure F.2 that the load vectors should be drawn with
the symmetry that is illustrated.

F.6

The design resistance of the fillet weld will be sufficient if the following is satisfied:



2




 3      11
2

2



0.5

  m   yield

Eqn

1

Where:

σyield is the yield stress of the material
γm is the appropriate material factor selected
Fillet Welded Bracket
F.7

For a bracket subjected to a load P parallel to the weld line as shown in Figure F.3 and where the base
structure to which the bracket is welded is adequately stiff the bending load applied to the weld line can
be considered to vary linearly and the shearing load at the weld to be constant, as shown in the figure.

F.8

In this case the maximum perpendicular load per unit weld length, fv, can be described as shown in
Eqn 2.

fv  6  P  h 
F.9

1
l2

Eqn 2

The uniform shear load per unit weld length, fh, is given by

fh 

0030/ND REV 4

P
l

Eqn 3

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GUIDELINES FOR MARINE TRANSPORTATIONS

P

h

a

Plane of
throat of
weld

l

a.t - = shear force per unit length

fv = 6.P.h/(l2)= max bending tension
per unit length

Figure F.3

Bracket connected by double Fillet Weld

Double Fillet
F.10

For a double fillet weld as shown in Figure F.4 the force fv may be considered as being resisted by a
combination of normal and shear stresses acting on the throat of the weld as illustrated in the diagram.
The applied load also produces a shear stress on the weld throat of τ║ acting at right angles to the
other shear stress τ┴.

F.11

These stresses can be combined to form the von Misses equivalent stress (see Eqn 1). The equations
for σ┴, τ┴ and τ║ are given in Eqn 4 and Eqn 5.

  

 ll 

0030/ND REV 4

3
2



Ph
al2

P
2 al

Eqn

4

Eqn

5

Page 120

GUIDELINES FOR MARINE TRANSPORTATIONS
fv = 6.P.h/(l2)
a.σ┴
Fillet weld #1
a.τ┴

Weld #1

Weld #2

fv = 6.P.h/(l2)

a.τ┴
Fillet weld #2

a.τ┴

a.τ┴

a.σ┴

a.σ┴

a.σ┴

Stresses and
Resultant Forces

Figure F.4

F.12

Vector Force Diagram

Stresses and Forces acting on Fillet Weld

The resulting limiting value for the weld throat thickness, a, is given in Eqn 6.



P
. 
a
  


l
yield
 m


2


18   h   3 

4 
l


Eqn 6

Single Fillet
F.13

For a bracket with a single fillet weld of length l the resulting limiting value for the weld throat thickness,
a, is given in Eqn 6.



P
. 
a
  


l
m
yield



2


h


 72     3 


l



Eqn 6

Selection of Yield Stress and Material Factor
F.14

The yield stress used should be the lowest of the yield stress values of the weld itself and the two parts
of metal welded together.

F.15

The material factor, γm, shall be taken as 1.0.
Note: The applied loads shall be increased by the following factors:
1.40 for serviceability limit state (SLS) checks and
1.05 for ultimate limit state (ULS) checks.

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GUIDELINES FOR MARINE TRANSPORTATIONS

APPENDIX G - TRANSPORTATION OR TOWING MANUAL CONTENTS
G.1

The purpose of the transportation or towing manual described in Section 5.4 is to give to:
 the vessel or tug Master and
 Persons In Charge (PIC), or Responsible Persons ashore for emergency response planning in
the event of an incident or accident,
information about:

G.2

1.

The cargo,

2.

Routeing, including possible deviations to shelter points if required,

3.

What to do in an emergency,

4.

Contact details (client, owner, local authorities, Marine Warranty Surveyor etc.),

5.

Organogram showing the scope split between different contractors (if applicable). These must be
clearly defined, to ensure that all parties are aware of their responsibilities, handover points and
reporting lines.

The contents of the manual shall be in a form and language that can be clearly understood by the
Master and senior officers undertaking the operations.. Revisions should be clearly marked and
attached drawings, with their revision numbers noted in the main text.

G.3

Where a manual has been produced to satisfy local authority requirements then this should take
precedence, providing it satisfies the main requirements detailed below.

G.4

The list below is what the Marine Warranty Surveyor would expect to see in the transportation or
towage manual. The list also includes the essential details needed by the vessel’s Master. Detailed
calculations and other documents may be in separate manuals referenced in the transportation or
towage manual.
1.
2.
3.
4.
5.
6.
7.
8.

9.
10.
11.
12.

13.
14.
15.

0030/ND REV 4

Introduction. What is the cargo, where is it being transported or towed, who for and why.
Description of the vessel and cargo.
Proposed route (with plot or chart) including waypoints and any refuelling arrangements,
anticipated departure date and speed.
Metocean conditions for the route for anticipated departure date.
Any limiting criteria and motions (roll, pitch and period etc) for the transport or tow, weather
forecasting arrangements and weather routeing details if applicable.
Contact details and responsibilities.
Reporting details: who to, how often and content.
Summary of ballast conditions and stability (usually including anticipated departure and arrival
loading conditions) with corresponding stability calculations and GZ curves. Calculations should
also be provided for any ballasting required for loading or discharging where applicable.
Motions and strength - detailed supporting calculations for the motions and accelerations,
longitudinal strength and strength of the seafastening and cribbing/grillage.
Arrival details, contacts, field plan etc.
Contingency arrangements.
Drawings to include, where applicable, cargo, GA and other key drawings of vessel and cargo,
stowage plan, towing arrangement, cribbing /grillage arrangement, load-out /discharge plan,
seafastening arrangement, guidepost details etc.
Reference documents.
Tug bollard pull calculation (if applicable).
Tug or transport vessel specification.

Page 122

4

TECHNICAL POLICY BOARD

GUIDELINES FOR MOORINGS

0032/ND

Once downloaded this document becomes UNCONTROLLED.
Please check the website below for the current version.

6 Dec 10

0

RK

Technical Policy Board

Date

Revision

Prepared by

Authorised by

www.gl-nobledenton.com

GUIDELINES FOR MOORINGS

CONTENTS
SECTION
1

2
3
4

5

6

7

8

9

10

SUMMARY
1.1
Scope
1.2
Contents
INTRODUCTION
DEFINITIONS
THE APPROVAL PROCESS
4.1
General
4.2
Scope of work leading to an approval
CODES AND STANDARDS
5.1
General
5.2
Offshore moorings
5.3
Inshore moorings and quayside moorings
INFORMATION REQUIRED
6.1
General
6.2
Operation
6.3
Design criteria
6.4
Location
6.5
Design environmental conditions
6.6
Vessel
6.7
Mooring system
DESIGN ENVIRONMENTAL CONDITIONS
7.1
General
7.2
Unrestricted operations
7.3
Weather-restricted operations
7.4
Use of seasonal / directional Metocean data
7.5
Wind
7.6
Current
7.7
Waves
7.8
Tide
ENVIRONMENTAL LOADS AND MOTIONS
8.1
General
8.2
Wind loads
8.3
Current loads
8.4
Wave loads
8.5
Wave frequency motions
8.6
Low frequency motions
MOORING ANALYSIS
9.1
General
9.2
Analysis cases
9.3
mooring Line length/tension adjustment
9.4
Analysis techniques
DESIGN AND STRENGTH
10.1
General
10.2
Redundancy
10.3
mooring pattern
10.4
Mooring line and connection strength
10.5
Anchor capacity

0032/ND Rev 0

PAGE NO.
5
5
5
6
7
10
10
10
11
11
11
11
13
13
13
13
13
13
14
14
15
15
15
15
16
17
17
17
17
18
18
18
18
18
19
19
20
20
20
21
21
23
23
23
23
23
24

Page 2

GUIDELINES FOR MOORINGS
11

CLEARANCES
11.1
General
11.2
Horizontal anchor clearances
11.3
Horizontal Wire or Chain clearances
11.4
Line vertical clearances
11.5
Line-line clearances
11.6
Installing Anchors
12
MOORING EQUIPMENT
12.1
Mooring integrity
12.2
Certification
12.3
Anchors
12.4
Chain
12.5
Wire rope
12.6
Fibre rope
12.7
Connectors
12.8
Buoys (surface and subsurface)
12.9
Vessel connection points
12.10 Fendering
13
PROCEDURAL CONSIDERATIONS
13.1
General
13.2
Anchor proof loading
13.3
Manning
13.4
Inspection, monitoring and maintenance
14
DOCUMENTATION
14.1
Leading to approval
14.2
Office review
14.3
On site
15
SPECIAL CONSIDERATIONS FOR INSHORE AND QUAYSIDE MOORINGS
15.1
Background
15.2
Locations within harbour limits
15.3
Contingency arrangements
15.4
Mooring considerations
15.5
Shore mooring points / bollards / winches
15.6
Procedures
15.7
Cold stacking
15.8
Ice loading
16
SPECIAL CONSIDERATIONS FOR PERMANENT MOORINGS
16.1
General
REFERENCES

26
26
27
27
27
28
28
29
29
29
29
29
29
29
29
30
30
30
32
32
32
32
32
33
33
33
33
34
34
34
34
34
35
35
35
35
36
36
37

TABLES
Table 7-1
Table 7-2
Table 9-1
Table 9-2
Table 10-1
Table 10-2
Table 10-3
Table 10-4
Table 11-1

Environmental Return Periods
Seastate Reduction Factors for 24 hour Operational Duration
Recommended Analysis Methods and Conditions
Types of Analyses
Line Tension Limits and Design Safety Factors
Drag Anchor Holding Capacity Design Safety Factors
Design Safety Factors for Holding Capacity of Anchor Piles and Suction Piles
Design Safety Factors for Holding Capacity of Gravity and Plate Anchors
Summary of Minimum Mooring Clearances

15
16
20
22
24
24
24
25
26

FIGURES
Figure 11.1

Minimum Horizontal Anchor Clearances from Pipelines or Cables

27

0032/ND Rev 0

Page 3

GUIDELINES FOR MOORINGS

PREFACE
This document has been drawn with care to address what are likely to be the main concerns based on the
experience of the GL Noble Denton organisation. This should not, however, be taken to mean that this document
deals comprehensively with all of the concerns which will need to be addressed or even, where a particular matter is
addressed, that this document sets out the definitive view of the organisation for all situations. In using this
document, it should be treated as giving guidelines for sound and prudent practice on which our advice should be
based, but guidelines should be reviewed in each particular case by the responsible person in each project to ensure
that the particular circumstances of that project are addressed in a way which is adequate and appropriate to ensure
that the overall advice given is sound and comprehensive.
Whilst great care and reasonable precaution has been taken in the preparation of this document to ensure that the
content is correct and error free, no responsibility or liability can be accepted by GL Noble Denton for any damage or
loss incurred resulting from the use of the information contained herein.

© 2010 Noble Denton Group Limited, who will allow:
 the document to be freely reproduced,
 the smallest extract to be a complete page including headers and footers, but smaller extracts may be
reproduced in technical reports and papers, provided their origin is clearly referenced.

0032/ND Rev 0

Page 4

GUIDELINES FOR MOORINGS

1

SUMMARY

1.1

SCOPE

1.1.1

This document describes the guidelines which will be used by GL Noble Denton for the approval of
moorings, including:
a.
Offshore catenary or taut leg moorings of mobile offshore units (MOU)
b.
Offshore catenary or taut leg mooring of floating offshore installations (FOI)
c.
Inshore mooring of MOUs and FOIs, e.g. for stacking
d.
Temporary mooring of offshore installations in an afloat condition during construction,
installation or decommissioning
e.
Quayside mooring of MOUs and FOIs, e.g. during maintenance or conversion
f.
Mooring of vessels during loadouts and installation operations.

1.2

CONTENTS

1.2.1

The following aspects of moorings are described:
a.
The approval process
b.
Codes and standards
c.
Information required
d.
Design environmental conditions
e.
Environmental loads
f.
Motion response
g.
Mooring analysis
h.
Design and strength
i.
Clearances
j.
Mooring equipment
k.
Procedural considerations
l.
Documentation
m.
Special considerations for inshore and quayside moorings
n.
Special considerations for permanent moorings.

0032/ND Rev 0

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GUIDELINES FOR MOORINGS

2

INTRODUCTION

2.1

This document describes the guidelines which will be used by GL Noble Denton for the approval of
moorings, including:
a.
Offshore catenary or taut leg moorings of mobile offshore units (MOU)
b.
Offshore catenary or taut leg mooring of floating offshore installations (FOI)
c.
Inshore mooring of MOUs and FOIs, e.g. for stacking
d.
Temporary mooring of offshore installations in an afloat condition during construction,
installation or decommissioning
e.
Quayside mooring of MOUs and FOIs, e.g. during maintenance or conversion
f.
Mooring of vessels during loadouts and installation operations.

2.2

Where GL Noble Denton is acting as a consultant rather than a Warranty Surveyor, these Guidelines
may also be applied as a guide to good practice.
This document is not intended to apply to “standard”, temporary moorings such as ships in port or
anchored or moored by the bow where the vessels are fully manned, have a full marine watch, live
engines and tugs available.
This document does not cover all types of mooring and every mooring application. Readers should
therefore satisfy themselves that the Guidelines used are fit for purpose for the actual mooring under
consideration.
This document refers to recognised standards and design codes and to other GL Noble Denton
Guidelines as appropriate. All current GL Noble Denton Guideline documents can be downloaded
from www.gl-nobledenton.com.
This document gives guidance on engineering analysis and practical marine considerations, both of
which will form the basis for any approval.
These Guidelines are intended to lead to an approval by GL Noble Denton. Approval by GL Noble
Denton does not necessarily imply that submitted proposals will comply with the requirements of any
other party or organisation (e.g. as defined by codes, national legislation, guidelines, etc).
This document is submitted for general guidance and it should be noted that each mooring will differ in
design due to the nature of the moored structure and the particulars of the location. This document
therefore contains general guidance and detailed recommendations that will apply to individual cases.
These Guidelines are not intended to exclude alternative methods, new technology and new
equipment, provided that an equivalent level of safety can be demonstrated.

2.3

2.4

2.5

2.6
2.7

2.8

2.9

0032/ND Rev 0

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GUIDELINES FOR MOORINGS

3

DEFINITIONS
Referenced definitions are underlined.

0032/ND Rev 0

Term or Acronym

Definition

Approval

The act, by the designated GL Noble Denton representative, of issuing a
‘Certificate of Approval’.

ATA

Automatic Thruster Assist

Barge

A non-propelled vessel commonly used to carry cargo or equipment.
(For the purposes of this document, the term Barge can be considered to
include Vessel or Ship where appropriate).

Benign Area

An area that is free from tropical revolving storms and travelling
depressions, (excluding the North Indian Ocean during the Southwest
monsoon season and the South China Sea during the Northeast
monsoon season). The specific extent and seasonal limitations of a
benign area should be agreed with the GL Noble Denton office
concerned.

Certificate of Approval

A formal document issued by GL Noble Denton stating that, in its
judgement and opinion, all reasonable checks, preparations and
precautions have been taken to keep risks within acceptable limits, and
an operation may proceed.

Client

The company to which GL Noble Denton is contracted to perform marine
warranty or consultancy activities.

Cold Stacking

Cold stacking is where the unit is expected to be moored up for a
significant period of time and will have minimum or, in some cases, no
services or personnel available.

DNV

Det Norske Veritas

DP

Dynamic Positioning

FLS

Fatigue Limit State

FOI

Floating Offshore Installation

FOS

Factor of Safety

GL Noble Denton

Any company within the GL Noble Denton Group including any
associated company which carries out the scope of work and issues a
Certificate of Approval, or provides advice, recommendations or designs
as a consultancy service.

HAZID

Hazard Identification

Hot Stacking

Hot stacking may be defined as mooring the vessel in a manned
functional condition, with the option to run machinery to provide sufficient
power to operate all mooring winches, thrusters, etc as may be required.

IACS

International Association of Classification Societies.

Inshore Mooring

A mooring operation in relatively sheltered coastal waters, but not at a
quayside.

Insurance Warranty

A clause in the insurance policy for a particular venture, requiring the
approval of a marine operation by a specified independent survey house.

Loadout

The transfer of a major assembly or a module onto a barge, e.g. by
horizontal movement or by lifting.

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Term or Acronym

Definition

MBL

Certified Minimum Breaking Load (of a wire, chain or other mooring
system component).

Mobile Mooring

Mooring system, generally retrievable, intended for deployment at a
specific location for a short-term duration, such as those for mobile
offshore units.

MODU

Mobile Offshore Drilling Unit

Mooring System

Consists of all the components in the mooring system including shackles
windlasses and other jewellery and, in addition, rig/vessel and shore
attachments such as bollards.

MOU

Mobile Offshore Unit

n/a

Not Applicable

NMD

Norwegian Maritime Directorate.

Operational Reference
Period

The planned duration of the operation, including a contingency period.

OCIMF

Oil Companies International Marine Forum.

Permanent Mooring

Mooring system normally used to moor floating structures deployed for
long-term operations, such as those for a floating production system.

PSA

Petroleum Safety Authority Norway

QTF /
Quadratic Transfer
Function

Refers to the matrix that defines second order mean wave loads on a
vessel in bi-chromatic waves. When combined with a wave spectrum the
mean wave drift loads and low frequency loads can be calculated.

Quayside Mooring

A mooring that locates a vessel alongside a quay (usually at a sheltered
location).

RAO /
Response Amplitude
Operator

Defines the vessel’s (first order) response in regular waves and allows
calculation of vessel wave frequency (first order) motion in a given
seastate using spectral analysis techniques.

Redundancy Check

Check of the failure loadcase associated with the applicable extreme
(survival) environment, e.g. the one leg damaged case.

Semi-Submersible Unit

A floating structure normally consisting of a deck structure with a number
of widely spaced, large cross-section, supporting columns connected to
submerged pontoons.

Self-Elevating Unit

More commonly know as a ‘Jack-up’. It is a Marine Unit equipped with
legs and jacking systems capable of lifting the hull clear of the water. A
‘Jack-up’ unit may be used as a production platform, drilling platform,
construction support platform or accommodation platform.

SLS /
Serviceability Limit
State

A design condition defined as a normal Serviceability Limit State / normal
operating case.

Survey

Attendance and inspection by a GL Noble Denton representative. Other
surveys which may be required for a marine operation, including
suitability, dimensional, structural, navigational, and Class surveys.

Surveyor

The GL Noble Denton representative carrying out a survey. An employee
of a contractor or Classification Society performing, for instance, a
suitability, dimensional, structural, navigational or Class survey.

TA

Thruster Assist

UKCS

United Kingdom Continental Shelf
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Term or Acronym

Definition

ULS /
Ultimate Limit State

The intact loadcase associated with the applicable extreme (survival)
environment.

VLA

Vertical Load Anchors.

Vessel

Within the scope of this document refers to any structure which is being
moored.

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4

THE APPROVAL PROCESS

4.1

GENERAL

4.1.1

GL Noble Denton may act as a warranty surveyor, issuing an approval for a particular mooring or
mooring operation, or as a consultant providing advice, recommendations, calculations and/or designs
as part of the scope of work. These functions are not necessarily mutually exclusive.
Agreement is required on the start point (or point of no return) for the mooring or mooring operation
and the end point (or termination) which may apply to each issued certificate of approval.

4.1.2

4.2

SCOPE OF WORK LEADING TO AN APPROVAL

4.2.1

Technical studies leading to the issue of a certificate of approval may consist of:
a.
Reviews and audits of procedures, calculations and/or physical model tests submitted by the
client or his contractors, or
b.
Independent analyses carried out by GL Noble Denton to verify the feasibility of the proposals,
or
c.
A combination of third party reviews and independent analyses.

4.2.2

Surveys and attendances carried out as part of GL Noble Denton's scope of work typically include:
a.
Site survey or examination of the mooring system, confirming that it complies with mooring
design as submitted to GL Noble Denton
b.
Review of the certification of all component parts of the system
c.
Confirmation of the general condition of the vessel in terms of machinery and manning
d.
Inspection and verification of procedures for maintenance and operation of mooring equipment
and actions in an emergency including availability of tugs, etc.
e.
Discussions with the local port authority or pilots as appropriate
f.
Examination and/or function testing of any key items of equipment, vessels, etc. to be employed
during the installation of the mooring system or in the as installed operational condition
g.
Attendance at HAZIDs, risk assessment meetings as required
h.
Attendance and witnessing mooring installation activities, including deployment, test tensioning,
etc.

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5

CODES AND STANDARDS

5.1

GENERAL

5.1.1

A number of recognised standards and design codes covering moorings are already in existence. It is
not intended that this document should redefine recommendations in areas already well covered by
established codes. The default standard for mooring system design and approval is ISO 19901-7.
Although many aspects of mooring design and practice are covered by existing codes, it is often
necessary to draw upon more than one source. This document aims to collate relevant guidance from
several sources where necessary. Care shall be taken to use coherent input data, analysis methods
and safety factors; in general this means that these should be taken together from a single source.
Combining the least conservative options from different sources is not acceptable.
References to guidance on best practice relating to specific issues are provided in this document
wherever possible.
In some subject areas, particularly in relation to inshore or quayside moorings of offshore units, there is
little relevant guidance available. It is intended that this document be a primary source of reference for
these areas.

5.1.2

5.1.3
5.1.4

5.2

OFFSHORE MOORINGS

5.2.1

The International Standard ISO 19901-7, Ref. [2], represents the most modern and widely accepted
set of criteria and guidelines for offshore moorings. GL Noble Denton considers ISO 19901-7 to be the
preferred code for the design of all mooring systems.
API Recommended Practice 2SK (RP 2SK), Ref. [3] is to be incorporated within, and superseded by,
ISO 19901-7 but at present it includes extensive guidance that is not included within the International
Standard. This document makes reference to API RP 2SK guidance on some subjects not covered in
detail by ISO 19901-7:2005.
DNV OS E301, Position Mooring (POSMOOR E301), Ref. [6], is considered by GL Noble Denton to be
an acceptable alternative to ISO 19901-7 when used in conjunction with DNV RP C205.
DNV Rules for the Classification of Mobile Offshore Units, Part 6, Chapter 2: Position Mooring
(POSMOOR ‘96), Ref. [6] has been superseded by DNV Offshore Standard E301. However
POSMOOR ‘96 still remains the de facto standard code in some regions. GL Noble Denton will accept
its use in some circumstances, such as if specifically requested by a field operator for MOUs with
existing POSMOOR notation under the Rules for the Classification of Mobile Offshore Units Ref. [6].

5.2.2

5.2.3
5.2.4

5.3

INSHORE MOORINGS AND QUAYSIDE MOORINGS

5.3.1

Although the environmental loads experienced by a vessel moored in a sheltered inshore location or
alongside a quayside are likely to be significantly lower than those it may experience offshore, the risk
profile of these types of mooring is high due to a combination of the following factors:
a.
Offshore mooring systems are generally designed for large deployed lengths of mooring wire or
chain whereas inshore moorings will generally have short taut lines which can lead to very high
tensions and can result in uplift on anchors
b.
High consequence of failure given the proximity to shore, other assets and limited response
time
c.
Potential lack of suitable or degraded connection points on the vessel and onshore, e.g.
quayside
d.
Uncertainty in the calculation of environmental forces due to wind shear effects and shallow
water blockage effects
e.
Potential limitations on the ability to adjust moorings and balance the line tensions in adverse
weather conditions
f.
Potential difficulty in knowing the actual tensions in the lines, in other words a lack of
instrumentation
g.
Potential for failures due to chafe points and abrasion (especially for quayside moorings).

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5.3.2

5.3.3

5.3.4

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The basic approach to the review and approval of inshore and quayside moorings will be similar to that
for offshore moorings, and the basic design philosophy should be the same although suitably modified
to take account of the key features of these applications. Acceptance criteria (safety factors, etc.)
should be based upon either the codes discussed in Section 5.2 (subject to the limitations stated
therein) or those given in Sections 5.3.4 and 10 of this Guideline.
BS6349-6 “Design of Inshore Moorings and Floating Structures”, Ref. [7], whilst somewhat outdated in
a number of aspects (material selection and analytical techniques being two primary areas) provides
suitable guidance for the assessment of pontoons, floating docks and Admiralty-type buoy moorings. If
used, the general philosophy must be consistent with that laid out in this guideline.
OCIMF, Ref. [11], is considered appropriate for evaluating quayside mooring requirements of marine
vessels such as tankers. It also provides good guidance on the use of quayside moorings and on
design factors of safety for common vessel connections such as bitts, Smit brackets and Panama
chocks.

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6

INFORMATION REQUIRED

6.1

GENERAL

6.1.1
6.1.2

This section outlines the information required for the approval of a mooring or for carrying out mooringrelated consultancy work.
Where relevant the approved operations manual should be submitted, for example, where it contains
details of approved wind and current load coefficients, motions response amplitude operators, wave
drift coefficients, etc. The manual is also likely to be relevant where it defines any limitations,
guidelines or performance criteria relating to the active control of winches, windlasses and thrusters.

6.2

OPERATION

6.2.1

Details of the operation to be undertaken should be established, including:
a.
Nature of operation
b.
Timing, e.g. dates
c.
Duration
d.
Any operational mooring system performance criteria
e.
Whether the mooring system will be active or passive; an active system allows line
tension/length adjustment
f.
Manned or unmanned and, if manned, whether on a 24 hour basis.

6.3

DESIGN CRITERIA

6.3.1

All relevant design criteria should be established, including the code or standard to which the design
has been carried out.

6.4

LOCATION

6.4.1

All relevant details of the mooring location should be established including
a.
Geographical location, e.g. grid coordinates and possible local currents e.g. river outflows
b.
Water depth including bathymetry covering the full area of the mooring spread
c.
Seabed conditions, e.g. soil type
d.
Geotechnical information, e.g. soil properties derived from core samples, if required
e.
Details of any existing installations or infrastructure on the surface and subsea, documented by
reliable surveys
f.
For inshore or quayside moorings some details of the local topography may be required to help
determine the wind sheltering effects and the wind shear profiles that should be applied
g.
Quay wall section drawings detailing water levels and elevation of fendering arrangements
h.
Capacity of quayside bollards (see Section 15.5).

6.4.2

Further details of seabed and geotechnical data requirements are given in GL Noble Denton Guideline
0016/ND, Ref [9] “Seabed and Sub-seabed Data Required for Approvals of Mobile Offshore Units
(MOU)”.

6.5

DESIGN ENVIRONMENTAL CONDITIONS

6.5.1

The environment considered in any analysis is dependent on the design criteria used but, in general,
environmental information should include the following:
a.
Design seastate is usually characterised by significant wave height and mean zero-crossing
period, together with a parametric wave spectrum, e.g. JONSWAP spectrum
b.
Design wind speed and, if applicable, gust spectrum
c.
Design current and, if applicable, current profile
d.
Long period swell and direction,

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e.

Minimum temperature if below 0oC.

6.6

VESSEL

6.6.1

The type and characteristics of the vessel to be moored should be established. The required
information can be broadly categorised as shown below.
Vessel condition:
a.
Intended draught(s)
b.
Details of loading condition, if required.

6.6.2

6.6.3

Environmental loading and response characteristics (for all relevant draughts):
a.
Response Amplitude Operators (RAOs)
b.
Quadratic Transfer Functions (QTFs)
c.
Wind load coefficients
d.
Current load coefficients
e.
Displacement and frequency dependent added mass and damping.

6.6.4

Vessel mooring points:
a.
Fairleads - type, positions and documented structural capacity including supporting structure
b.
Winches or windlasses - number, type, brake capacity, stopper capacity, stall capacity, pawl
details, etc.
c.
Position and capacity of onboard bollards, mooring bitts or Smit brackets
d.
Dimensions, condition and load capacity of anchor racks (cow catchers).

6.6.5

Propulsion and dynamic positioning systems:
a.
Thrusters - number, type, thrust and positions and operational; status
b.
Control system - manual joystick or fully dynamically positioned (TA / ATA)
c.
Critical failure modes - thrust available following a worst case single point failure.

6.7

MOORING SYSTEM

6.7.1

Details of mooring system components including:
a. Anchors - number, type and weight
b. Mooring line make-up, length, type and age of each component
c. Mooring line diameter, area, minimum breaking load, axial stiffness and weight per length
d. Latest mooring line inspection report
e. Details of any buoys or clump weights
f. Details of any connecting hardware
g. Condition and operational status of equipment.

6.7.2

If GL Noble Denton is undertaking a mooring analysis, details of any Operator or Drilling Contractor
preferred or standard anchor patterns should be supplied.

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7

DESIGN ENVIRONMENTAL CONDITIONS

7.1

GENERAL

7.1.1

Moorings shall be designed to withstand the loads caused by the most adverse environmental
conditions expected for the location and duration of the mooring. Guidance and requirements relating
to the design environment are included in most of the mooring codes, and these should be referred to
in the first instance. This section contains general information and additional specific guidance
covering situations outside the scope of existing codes.

7.2

UNRESTRICTED OPERATIONS

7.2.1

An unrestricted operation is one which is effectively free of any environmental limits. An unrestricted
mooring is designed to be able to withstand a design environment with a large return period such that
the probability of it being encountered is suitably small.
The following table identifies minimum return periods generally applicable to a variety of mooring types
and durations.

7.2.2

Table 7-1

Environmental Return Periods

Mooring Type

10 year[1]

Offshore - Mobile near another asset

10 year

Offshore - Mobile in Open Location
[1]

7.2.4
7.2.5

7.2.6

< 6 months

Quayside / Inshore
Offshore - Permanent

7.2.3

Mooring Duration

N/A
5 year

6m ≤ t < 20 yr

≥ 20 years

100 year
See Section
7.2.3

100 year
100 year
N/A

A longer return period will be required when the moored item is high-value, e.g. a concrete production
platform under construction

For mooring durations greater than 6 months, 100 year return period can be used. Alternatively a
project specific return period environmental return period may be determined to give risk levels
equivalent to those of systems designed to 20 year exposure with 100 year return period.
Joint probability data should only be used when permitted by the referenced standard.
Mobile moorings should generally be designed with reference to a 10 year return period when in the
vicinity of any other infrastructure. Where a mobile mooring is in an open location, with reduced
consequence from mooring failure, a five year return period may be acceptable. Where applicable
seasonal/monthly and/or directional metocean data as in Section 7.4 can be used with the specified
return period.
When evaluating the consequence of failure, consideration should be given to whether risers will be
connected, proximity to other installations and the type of operation being undertaken. For pipe laying
operations, the expected duration of the operation, plus a suitable contingency value should be
addressed.

7.3

WEATHER-RESTRICTED OPERATIONS

7.3.1

Where a weather restricted mooring is to be approved, procedures addressing all the issues identified
in this section shall be provided for office review together with the mooring analysis.
A weather restricted operation is one in which a design environmental limit for an operation is
identified, independent of extreme statistical data.
In general weather restricted operations will be operations with a total duration less than 72 hours.
To undertake any operation, the “operation criteria” shall be less than the “design criteria”. The margin
is a matter of judgement, dependent on factors specific to each case, but should be documented.
Unless agreed otherwise with GL Noble Denton, for marine operations with an operational duration of
no more than 24 hours the maximum forecast seastate shall not exceed the design seastate multiplied

7.3.2
7.3.3
7.3.4
7.3.5

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by the applicable (sometimes called alpha, α) factor from Table 7-2 below. For operations with other
durations alternative factors apply and should be agreed with GL Noble Denton. The forecast wind
and current shall be similarly considered when their effects on the operation or structure are significant.
Table 7-2

Seastate Reduction Factors for 24 hour Operational Duration

Weather Forecast Provision

7.3.6

7.3.7

Reduction Factor

No project-specific forecast (in emergencies only)

0.50

One project-specific forecast source

0.65

One project-specific forecast source plus in-field wave monitoring (wave
rider buoy)

0.70

One project-specific forecast source plus in-field wave monitoring and
offshore meteorologist

0.75

In tropical and sub-tropical regions the short term extreme weather conditions are likely to be
associated with the possibility of thunderstorm activity and the squalls associated with the passage of a
storm front. Unless local weather radar is available together with an on site forecaster, it is difficult to
predict the onset and severity of these squalls and even then there can be considerable uncertainty.
Conduct of operations for design conditions below the 10 year seasonal squall may, therefore, be
highly restricted during some seasons.
Planning and design of moorings shall be based on the length of time that the vessel is to be moored.
Short term moorings of less than 72 hours (e.g. during a loadout) may be deemed weather-restricted
operations provided that:
a.
Metocean statistics indicate an adequate frequency and duration of the required weather
windows
b.
Regular, reliable weather forecasts for the specific location are readily available
c.
The start of the operation is governed by an acceptable weather forecast covering the reference
period
d.
A documented risk assessment has been carried out and the results accepted by GL Noble
Denton
e.
Reference is made to an appropriate code
f.
Detailed marine procedures are in place for the operation, including contingency plans in the
event that the weather or the weather forecast deteriorates after the mooring has been
established.

7.3.8

The length of time required to complete an operation is referred to as the reference period. When
calculating the operational reference period, allowance should be made for:
a.
The time anticipated, after the decision to commence the operation, for preparing to start or
waiting for appropriate environmental conditions
b.
The time anticipated for the operation itself
c.
The time anticipated, upon completion, for awaiting correct tidal conditions for departure and for
recovering the mooring spread
d.
A contingency period allowing for over-run of the operation
e.
The time required for intervention in the event of mooring component or equipment failure.

7.4

USE OF SEASONAL / DIRECTIONAL METOCEAN DATA

7.4.1

Metocean data specific to the month(s) or season(s) during which the mooring will be utilised may be
used where appropriate.
Directional metocean data may also be used with suitable spreading functions to reflect directional
divergence in the design environment.

7.4.2

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7.5

WIND

7.5.1
7.5.2

Wind speeds should be referenced at 10m above the still water level.
For permanent moorings the more onerous of the following should be considered:
a.
Steady one minute mean velocity; or
b.
One hour mean plus a suitable gust spectrum.

7.5.3

Generally the ISO 19901 gust spectrum Ref. [2] would be applicable to 7.5.2b unless an alternative
can be clearly justified.
For mobile moorings either a steady state wind speed or a suitable gust spectrum may be used
depending upon the stiffness of the mooring system. The 10 minute averaged wind speed can be
used to analyse catenary moorings if the effect of wind dynamics on the line tension is shown to be
insignificant.
For inshore or quayside moorings care must be taken to ensure that all natural periods of response of
the system have been considered. Some of the mooring system response periods may be shorter
than one minute but on the other hand the use of shorter gust periods may not represent a sustained
design wind that will act at the same time across the whole of the structure. The representative design
wind sampling period, therefore, has to be carefully established on a case by case basis for inshore
and quayside moorings.

7.5.4

7.5.5

7.6

CURRENT

7.6.1

The design current shall taking account of mean spring tide, the return period storm surge, fluvial
(river) and wind-driven components.

7.7

WAVES

7.7.1

For mobile moorings it is generally acceptable to consider a single extreme significant wave height and
associated zero crossing period corresponding to the relevant return period for a location.
For permanent moorings a number of Hs-Tz combinations along the 100 year return period contour
line have to be considered for the analysis. If a contour plot is not available, a sensitivity study by
varying peak period for the 100 year return period sea state is required. This is to ensure that extreme
line tensions due to low frequency motion at lower periods are captured in the analysis, especially for
ship shaped floaters.

7.7.2

7.8

TIDE

7.8.1

For moorings at locations where the tidal range is greater than 10% of the water depth, the highest and
lowest still water levels at the location for the duration of the mooring should be established and
considered in the analysis of the mooring.
For quayside moorings the effect of tide should always be considered including possible means to
adjust line lengths for locations subject to substantial tidal variations and also to monitor line tensions
with the possible provision of an alarm system (24 hour monitoring required) when tensions approach
pre-specified levels.

7.8.2

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8

ENVIRONMENTAL LOADS AND MOTIONS

8.1

GENERAL

8.1.1

This section addresses the calculation of forces imposed by the environment upon a moored vessel, its
mooring spread and appendages, such as risers and umbilicals.
Unless it is clearly demonstrated that any of the following forces or motions are insignificant, they
should always be considered in any mooring analysis.
Drag coefficients or model tests should be representative of the vessel at the draught(s) under
consideration. Line tensions should be evaluated for all possible vessel draughts.

8.1.2
8.1.3

8.2

WIND LOADS

8.2.1

Wind loads should be considered to have a variable component modelled by an appropriate gust
spectrum.
Wind loads may be determined through model tests, by numerical modelling (computational fluid
dynamics analysis), or by calculation using accepted drag coefficients.
Offshore wind shear profiles may also not be appropriate for inshore or quayside moorings. The use of
an offshore design wind with an offshore shear profile will always be conservative for an inshore
location unless it is exposed to funnelling or squalling effects. Conversely the use of an inshore
sheltered wind extreme with an offshore wind shear profile may be non-conservative because of
substantially different wind shear profiles that are typical of inshore locations.
Wind loads are likely to be the dominant source of loading for inshore and quayside moorings.
Therefore the design wind conditions need to be very carefully established.

8.2.2
8.2.3

8.2.4

8.3

CURRENT LOADS

8.3.1

Current loads may be determined through model tests, by numerical modelling or by calculation using
accepted drag coefficients.
If current profile information is available it should be utilised when calculating current loads and/or
damping associated with mooring lines. Only the surface current speed need be considered when
calculating current loads on conventional draught vessels (ship-shaped, barges, semi-submersibles).
Current loads upon mooring lines, risers, umbilicals and power cables shall be assessed and their
effects must be taken into account in a mooring analysis unless they have been shown to have
negligible effect.
Any increase in the effective drag diameter of mooring line and risers due to marine growth shall be
taken into account when analysing a permanent mooring. Guidance on estimating the effect of marine
growth can be found in Section 6.7.4 of DNV RP C205.
When mooring takes place in shallow water depths (<75m) account should be taken of increase in
current loads due to current blockage effects. Note that additional blockage effects will also arise
when mooring alongside a quay.

8.3.2

8.3.3

8.3.4

8.3.5

8.4

WAVE LOADS

8.4.1

In addition to causing motions (see Section 8.5) waves also impose mean and slowly varying loads
upon a vessel. The mean wave drift force contributes to the mean environmental load. The slowly
varying loads contribute to low frequency motions of a moored vessel at its natural periods, sometimes
called slow drift behaviour.
Wave drift forces are generally calculated from the wave spectrum and QTFs.
The direct effect of waves upon mooring lines can generally be neglected.
Shallow water corrections will be required for vessels in water depths less than 100m.
The possible impact of long period swell should be checked.

8.4.2
8.4.3
8.4.4
8.4.5

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8.5

WAVE FREQUENCY MOTIONS

8.5.1

Forces imposed by waves upon a vessel lead to a wave frequency motion response of the vessel. The
magnitude and phase of this response is generally calculated from the wave spectrum and the vessel’s
RAOs. RAOs may be derived from the results of model tests, or by numerical analysis (e.g. diffraction
analysis taking a suitable level of damping into account). The RAOs should be determined at the
relevant vessel draughts.
Where moorings take place in areas where the seas can be considered short crested, a reduction in
the first order motion may be justifiable, e.g. in line with Section A.8.7 of ISO 19901-1, Ref. [1]. In
cases where short-crestedness increases the responses this should be taken into account.
When mooring takes place in shallow water depths (<100m), account should be taken of increase in
wave frequency motions due to elliptical particle orbits and attenuation of motions due to reduced wave
energy for standard wave height.
For quayside moorings in relatively exposed locations the impact of long period swell should be taken
into account, preferably by a time domain analysis (see Section 15.4.1).

8.5.2

8.5.3

8.5.4

8.6

LOW FREQUENCY MOTIONS

8.6.1

Catenary moored vessels (i.e. not moored against a fixed structure) are often subject to low frequency
surge, sway, and yaw motions. These are due to the excitation of the combined vessel / mooring
system, at periods close the natural frequency of the overall system, by low frequency variable loads
including
a.
Varying wind load (due to gust spectrum);
b.
Frequency difference components of the wave drift force.

8.6.2

Low frequency motions often have a marked influence on mooring line tensions, particularly in deeper
water. Unless it is clearly demonstrated that second order motions are not significant they should
always be considered in any mooring analysis.

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GUIDELINES FOR MOORINGS

9

MOORING ANALYSIS

9.1

GENERAL

9.1.1

This section addresses the calculation of mooring line tensions based on environmental loads
evaluated using the methods described in the preceding section.

9.2

ANALYSIS CASES

9.2.1

To ensure that redundancy requirements discussed in Section 10.2 are met, mooring analyses should
include, as a minimum, an examination of the following cases for each environment direction (at least
every 45 degrees, and including the directions of environmental maxima):
a.
The mooring system as designed (intact case)
b.
For each line, as the environment is applied round the clock, but with one of the loaded lines
removed from the analysis (single line failure case / redundancy check)
c.
If thruster assistance is being considered, the system as designed, with available thrust reduced
to that available following the worst case single point failure in the propulsion or DP system.

9.2.2

In cases where the moored vessel is in close proximity to a structure (other than a quayside) or
specific operational constraints upon the vessel offset exist (e.g. a connected drilling riser), the vessel’s
trajectory immediately following each single point failure should be calculated (transient analysis).
Relevant closest points of approach and maximum offsets of points of interest should be extracted
from the output of the transient analysis.
Full guidance on expected analysis cases is given in Section 6.2 of ISO 19901-7, Ref. [2] and Table 1
therefrom is reproduced below:

9.2.3

Table 9-1
Type of Mooring

Limit State

Analysis Method

Dynamic

Transient[1]

Quasi-Static or Dynamic

FLS

Intact

Dynamic

SLS

No guidance given

No guidance given

Intact / Redundancy Check

Quasi-static or Dynamic

Transient[1],[2]

Quasi-static or Dynamic

FLS

Not required

Not applicable

SLS

No guidance given

No guidance given

ULS
Mobile Mooring

Conditions to be Analysed

Intact / Redundancy Check

ULS
Permanent
Mooring

Recommended Analysis Methods and Conditions

NOTES

0032/ND Rev 0

[1]

Applicable only if another installation is in proximity to the mooring.

[2]

Applicable for MODUs drilling in deepwater where excessive transient motions can cause
stroke-out of the riser slip joint.

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GUIDELINES FOR MOORINGS
9.3

MOORING LINE LENGTH/TENSION ADJUSTMENT

9.3.1

ISO 19901-7, Ref [2] permits only the consideration of adjustments “for operational reasons and/or in
advance of foreseeable environmental events” not “the modelling of active adjustments of line tension
during the analysis of design situations”. This is interpreted as follows:
a.
Line manipulations to maintain vessel position, etc, in operating (SLS) cases ARE permitted
provided that tension levels remain below winch stall capacities
b.
A reduction in line pretensions in advance of worsening weather or on moving to survival draft
IS permitted provided a single adjusted spread is used for all environmental loadcases
c.
Line adjustments following line failure ARE NOT permitted
d.
Line adjustments to optimise tensions in particular loadcases, e.g. windward / leeward line
manipulations ARE NOT permitted.

9.3.2

Where it is permissible under the selected code and is permitted by the vessel mooring equipment
classification and where a policy of leeward line slackening has been demonstrated to be actively
employed on a vessel, it is considered acceptable to take account of this in a survival analysis,
provided:
a.
Line manipulations are only performed in the intact case
b.
Due consideration is made regarding to winch/windlass stall limits
c.
The adjustments performed are intuitive and with regard to the intact mooring system only (i.e.
not with regard to optimising tension distributions after line failure)
d.
The operations are carried out in advance of any worsening weather conditions that have been
forecast. Note location specific forecasts are required.
e.
Adequate trained and experienced personnel are available on board (24 hour call off basis) to
carry out mooring line adjustment operations.

9.4

ANALYSIS TECHNIQUES

9.4.1

Two principal classes of analytical technique for the calculation of mooring line tensions are in common
use. The advantages, limitations and validity of each technique are briefly described below. Further
guidance on analytical methods is available in Section 5 of API RP 2SK 3rd Edition (2005), Ref. [3].
In quasi-static analysis, the mean environmental force is applied and the mean vessel offset
calculated. The low frequency and wave frequency responses in the horizontal plane are combined to
find the maximum instantaneous offset. The wave frequency response shall be determined taking the
effects of the mooring system into account when these are significant. Mooring line tensions are then
calculated statically for this maximum offset position. Quasi-static analysis is known to increasingly
underestimate line tensions as water depth increases. Design codes generally allow for this by
requiring higher safety factors to be applied to the results of quasi-static analyses. However, in deeper
water this is no longer a conservative approach.
In contrast, dynamic analysis takes account of both moored vessel responses and line dynamics
resulting from the fairlead motions and the hydrodynamic forces on the mooring lines. It is generally
more accurate than quasi-static analysis, particularly so in deep water.
Frequency domain analysis is significantly faster with respect to computation time than time domain
analyses, but generally cannot handle nonlinear systems as accurately.
For most moorings a frequency domain analysis is adequate - for long term or non standard moorings
the adequacy of results should be confirmed with a check of key cases by a time domain simulation.

9.4.2

9.4.3

9.4.4
9.4.5

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GUIDELINES FOR MOORINGS
9.4.6

Not withstanding any specific code requirements, the types of analysis shown in Table 9-2 are
generally considered suitable:
Table 9-2
Type of Analysis

Types of Analyses
Quasi-Static

Dynamic
Frequency

Time







Short Term Offshore Open Location







Short Term Offshore alongside a Fixed
Installation







Short Term Offshore Vessel alongside
a Floating Offshore Installation







Long Term Offshore







Quayside / Inshore

Key:  = Normally Preferred

 = Normally acceptable

 = Not suitable

9.4.7

A recognised dynamic analysis method should be used, unless:

it can be demonstrated that quasi-static analysis yields line tension capacity utilisations that are
not significantly less than those produced by dynamic analysis, or

code requirements dictate otherwise.

9.4.8

If dynamic analysis of line tensions is carried out, any increase in the effective drag diameter of
mooring lines, risers, umbilicals and power cables due to marine growth shall be taken into account.
Guidance on estimating the effect of marine growth can be found in Section 6.7.4 of DNV RP C205,
Ref. [4]
Care should be taken when undertaking mooring analyses of systems with fibre ropes due to their
nonlinear stiffness characteristics. Fibre rope conditioning and fibre rope storm stiffness should be
addressed in the analyses.
Guidance on calculating the design maximum combined low frequency and wave frequency motion of
a moored vessel is given in Section 8.10.2 of ISO 19901-7:2005, Ref. [2].

9.4.9

9.4.10

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GUIDELINES FOR MOORINGS

10

DESIGN AND STRENGTH

10.1

GENERAL

10.1.1

This section discusses how the design forces on mooring components may be calculated. It provides
guidance on determining the acceptability of these calculated forces, together with guidance on
general design considerations.

10.2

REDUNDANCY

10.2.1

The mooring system must have sufficient built in redundancy, such that the failure of any single
component will not result in a loss of ability to maintain station or an infringement of safe clearances
from other structures.
Failure cases should consider the worst potential failure case which may include shore or vessel
connection points.
Mooring systems without single point failure capacity may be found acceptable and approved, provided
that both the following are submitted:
a.
Emergency response procedures showing that suitable arrangements are in place, e.g. 24-hour
manning / monitoring, vessel assistance on standby and other practical arrangements to ensure
that any loss of position can be identified and controlled;
b.
A risk assessment that has been or can be accepted by GL Noble Denton; this shall include the
effect of losing buoys if these are used.
Note: The approach of simply doubling the safety factor requirements to compensate for lack of
redundancy is not acceptable for systems, including chain and associated connectors, because
mooring failures are not always directly related to a design overload. A case by case review taking into
account the age and condition of all the mooring line components should be carried out.

10.2.2
10.2.3

10.3

MOORING PATTERN

10.3.1

The mooring pattern chosen should be balanced, with line pretensions as evenly distributed as is
practicable. Patterns should be as close to symmetrical as practicable taking into account the actual
surveyed sea-bed infrastructure.
The methods for achieving design pretensions and sensitivity to variations therein will be of particular
importance in quayside moorings where the typically short line lengths and highly asymmetric mooring
arrangements can lead to very uneven load sharing between the lines.
Mooring line bearing angles should be selected to avoid placing out-of-plane loads on all components
including padeyes and pivoting fairleads, which have limited rotation angles.
In deeper water analytical checks must be carried out to confirm that mooring lines do not make
contact with the vessel itself or with the anchor racks/bolsters, as the resulting abrasive wear can
damage both the mooring line(s) and the vessel.

10.3.2

10.3.3
10.3.4

10.4

MOORING LINE AND CONNECTION STRENGTH

10.4.1

For quayside moorings the implications of tidal variation and how this could potentially result in chafing
and abrasion of moorings should be taken into account with respect to line protection and the
arrangements for mooring line adjustment, monitoring and maintenance.
The maximum analysed line tensions, when multiplied by a recognised appropriate safety factor shall
not exceed the MBLs of the mooring lines and the ultimate strength of the connections and
attachments, taking their present condition into account.
Mooring line tension safety factors for various analysis methods and cases are given in Section 10.2 of
ISO 19901-7:2005, Ref. [2].

10.4.2

10.4.3

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GUIDELINES FOR MOORINGS
Table 10-1
Analysis Condition

10.4.4
10.4.5

10.4.6

10.4.7

Line Tension Limits and Design Safety Factors
Line Tension Limit
(percent of MBL)

Analysis Method

Design Safety Factor

Intact

Quasi-Static

50%

2.00

Intact

Dynamic

60%

1.67

Redundancy Check

Quasi-Static

70%

1.43

Redundancy Check

Dynamic

80%

1.25

Transient

Quasi-Static

95%

1.05

The above safety factors are applicable to wire, chain and fibre rope mooring lines.
Certification of minimum breaking strength of fibre ropes shall be according to Section 12.6.3. Where
the minimum breaking strength of fibre ropes does not conform to this certification criteria or where
equivalent reliability cannot be established (either on breaking strength or stiffness), the design safety
factors in Table 10-1 shall be doubled.
The safety factors specified in design codes are intended for mooring hardware that is regularly
inspected and maintained. The breaking loads used with these factors should account for any
reduction in the diameter of the mooring lines due to mechanisms including wear and corrosion.
If inspection or maintenance is not proposed an additional agreed allowance shall be made for wear
and corrosion. This also applies to quayside moorings if replacement lines are not readily available in
case of chafing or abrasion damage.

10.5

ANCHOR CAPACITY

10.5.1

It shall be demonstrated that the design environment does not lead to anchor forces in excess of the
holding capacity of the anchors, including a recognised safety factor.
The following safety factors, consistent with ISO 19901-7, Ref. [2], should be considered applicable in
the absence of other code specific requirements:

10.5.2

Table 10-2

Drag Anchor Holding Capacity Design Safety Factors

Condition

Quasi-Static

Dynamic Analysis

Intact Condition

n/a

1.50

Redundancy Check

n/a

1.00

Intact Condition

1.00

0.80

Redundancy Check

Not required

Not required

Permanent Mooring

Mobile Mooring

Table 10-3

Design Safety Factors for Holding Capacity of Anchor Piles and Suction Piles
Permanent Moorings

Analysis Condition

0032/ND Rev 0

Axial
Loading

Lateral
Loading

Mobile Moorings
Axial
Loading

Lateral
Loading

Intact Condition

2.00

1.60

1.50

1.20

Redundancy Check

1.50

1.20

1.20

1.00

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GUIDELINES FOR MOORINGS
Table 10-4

Design Safety Factors for Holding Capacity of Gravity and Plate Anchors
Gravity Anchors
Permanent
Moorings

Analysis Condition

Axial

10.5.3

10.5.4

10.5.5

10.5.6
10.5.7

10.5.8

0032/ND Rev 0

Lateral

Plate Anchors

Mobile Moorings
Axial

Lateral

Permanent
Moorings

Mobile
Moorings

Intact Condition

2.00

1.60

1.50

1.20

2.00

1.50

Redundancy Check

1.50

1.20

1.20

1.00

1.50

1.20

Anchor forces may be reduced by friction between the grounded portion of the mooring line and the
seabed. Guidance on mooring line seabed friction is given in Annex A.10.4.5 of ISO 19901-7:2005,
Ref. [2]
Anchor holding capacity for mobile moorings may be determined by referring to manufacturer’s
datasheets for the size and type of anchor under consideration taking into account the seabed soil type
determined by location survey findings.
Where seabed conditions are unknown, or of a type not characterised by typical manufacturer data,
anchor capacity should be demonstrated by proof loading; normally, to the maximum intact tension
determined in the mooring analysis.
For permanent moorings and those utilising VLAs (Vertical Load Anchors), e.g. DENLA / StevManta or
pile anchors, detailed soil data and a full geotechnical assessment will generally be required.
It is generally accepted that modern drag embedment anchors (e.g. Stevpris Mk V and Bruce FFTS)
are capable of resisting significant uplift forces. It is considered acceptable that this vertical load
capacity is utilised, provided that the calculation is based on recognised guidelines, e.g. Appendix D of
API RP 2SK 3rd Edition (2005), Ref. [3].
If traditional drag embedment anchors (not specifically designed to resist vertical uplift forces) are
used, it must be shown that sufficient mooring line is deployed to prevent uplift in the intact case. In
the single line failure case it is generally acceptable to have some uplift, provided that the vertical force
at the anchor is much less than the submerged weight of the anchor.

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GUIDELINES FOR MOORINGS

11

CLEARANCES

11.1

GENERAL

11.1.1

The clearances stated below are given as guidelines to good practice. The specific requirements and
clearances should be defined for each project and operation, taking into account particular
circumstances such as:

water depth

proximity of subsea assets

survey accuracy

the station keeping ability of the anchor handling vessel

seabed conditions and slope

estimated anchor drag during embedment

single mooring line failure

the probable weather conditions during anchor installation

11.1.2

Field operators and subsea asset owners may have their own requirements which differ from those
stated below, and should govern if more conservative. Agreement should be obtained from such
operators and/or owners in advance if the moorings will be close to their assets.
If any of the clearances specified below are impractical because of the proposed mooring configuration
or seabed layout a risk assessment shall be carried out to determine the necessary precautions. The
results of the risk assessment shall be agreed with the relevant GL Noble Denton office.
Moorings should be designed and laid in such a way that there is positive clearance with any subsea
asset during installation.
The following Table 11-1 summarises the minimum clearances described in the Sections below. The
minimum clearances are based on the worst intact configuration accounting for external loads.

11.1.3

11.1.4
11.1.5

Table 11-1

Summary of Minimum Mooring Clearances
Minimum Clearance

0032/ND Reference
Section

50 m (typical)

11.2.1

Anchor horizontal distance from a subsea asset

100 m

11.2.2

Horizontal distance to pipeline or asset in line of
anchor drag

300 m

11.2.2

Line horizontal to subsea wellhead, manifold or
other asset

100 m

11.3.1

Line/Vessel horizontal to platform*

10 m

11.3.2

Line above pipeline ≥40m WD

10 m

11.4.1

Line above pipeline <40m WD

25% WD,
but not less than 5 m

11.4.1

20 m
(30 m - if repositioning by
winching)

11.5.1

Condition

Allowance for anchor placing inaccuracy

Line to line

* This is only for platforms which project above Water Level (WL)

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GUIDELINES FOR MOORINGS
11.2

HORIZONTAL ANCHOR CLEARANCES

11.2.1

Adequate clearance shall be maintained between anchors and any associated laydown pennants
(where applicable) and seabed infrastructure. Allowance must be made for inaccuracies and
unpredictability in the laying and embedment of drag anchors (typically 50m in the most critical
direction).
Anchors should not be placed within 100m of a subsea asset. Additionally where the drag path of the
anchor is towards the asset, drag embedment anchors should be located more than 300m radially from
the point where the anchor line crosses the pipeline, cable or subsea structure as shown in the
following Figure 11.1. These distances must be maintained throughout the mooring life.

11.2.2

Figure 11.1

Minimum Horizontal Anchor Clearances from Pipelines or Cables

11.3

HORIZONTAL WIRE OR CHAIN CLEARANCES

11.3.1
11.3.2

Moorings shall never be run over subsea assets, other than pipelines or cables, or within 100m
horizontally from them.
In the absence of code specific requirements minimum horizontal clearances of 10m should be
maintained both above and below the water line between the line and any structure that projects above
the water level (structures that are fully submerged are classed as subsea assets).

11.4

LINE VERTICAL CLEARANCES

11.4.1

In the absence of code specific requirements minimum vertical clearances of 10m over pipelines
should be maintained at any tension in the intact condition. In shallow water depths of less than 40m
the minimum clearance should not be less than 25% of the water depth, but not be less than 5.0m.
Any reduction in clearance to less than that specified shall be based on a documented risk assessment
(GL Noble Denton present) and provision for constant monitoring of the clearances during the
operation of the unit.
A reduced vertical clearance may be justified for fibre rope due to the greatly reduced weight of the
material provided that the fibre rope connections are maintained clear of the thrash zone and the
pipeline / umbilical / subsea infrastructure.

11.4.2

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GUIDELINES FOR MOORINGS
11.4.3

Temporary lay-down of an anchor wire or fibre rope (but not chain) over a pipeline, umbilical, spool or
cable may be acceptable subject to all of the following being submitted to review:

Evidence that there is no other practicable anchor pattern that would avoid the lay-down.

The status of a pipeline or spool (e.g. trenched, live, rock-dumped, on surface) and its contents
(e.g. oil, gas, water) and internal pressure.

Procedures clearly stating the maximum duration that the anchor wire/fibre rope is in contact
with the pipeline, umbilical, spool or cable and the reason for the contact.

Written evidence that the pipeline owner accepts laying down of the anchor wire over their
pipeline, umbilical spool or cable and has contingency measures in place in case of damage
and a possible hydrocarbon leak.

Evidence that the anchor wire will be completely slack i.e. no variation in tension.

Evidence that the seastate during the lay-down will be restricted to an acceptable value.

Documentation demonstrating that the anchor wire or its weight will not overstress or damage
the coating on the pipeline, umbilical, spool or cable.

11.5

LINE-LINE CLEARANCES

11.5.1

Crossed mooring lines are generally not acceptable except:
a.
Where crossing points are visible and contact avoided / wear mitigated with suitable protection;
b.
Where a minimum line-line clearance requirement of 20 m (or 30 m if repositioning by
winching), can be demonstrated for the combinations of tensions and vessel motions that are
most critical from the clearance perspective. This would normally apply to independently
moored vessels.

11.6

INSTALLING ANCHORS

11.6.1

Whenever an anchor is run out over a pipeline, flowline or umbilical, the anchor shall be securely
stowed on the deck of the anchor handling vessel. In circumstances where either gravity anchors or
closed stern tugs (tugs without stern rollers) are used, and anchors cannot be stowed on deck, the
anchors shall be double secured through the additional use of a safety strap or similar.
At no time shall an anchor wire come in contact with a pipeline, cable or subsea structure while running
out or retrieving an anchor.

11.6.2

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12

MOORING EQUIPMENT

12.1

MOORING INTEGRITY

12.1.1

Whilst the selection of a mooring system to meet code requirements is imperative to ensure the overall
safety of a moored structure, it should be borne in mind that inappropriate selection of materials
(connections and jewellery, etc) and inadequate inspection and maintenance programmes are likely to
be the primary factors in most failures.
Care shall be taken such that all mooring hardware is used in strict accordance with the manufacturer’s
recommendations and best industry practice.
Experience is required to assess the suitability of a proposed mooring system for a long term
application. Reference should be made to the principal findings from Noble Denton’s Phase 1 and
Phase 2 Mooring Integrity Joint Industry Projects (JIPs). See Refs [12] and [13].

12.1.2
12.1.3

12.2

CERTIFICATION

12.2.1

All components of a mooring system should be certified and their certificates available for inspection by
an attending surveyor.

12.3

ANCHORS

12.3.1

Anchors should be of a type approved by a recognised classification society and suitable for the
seabed composition at the location. In particular, at locations where the seabed is hard, anchors
capable of taking the full load through the fluke tips alone should be used.
Where applicable, anchors should be correctly configured for the seabed composition at the location,
e.g. fluke angle should be set as per manufacturer’s recommendations.

12.3.2

12.4

CHAIN

12.4.1

Mooring chain shall be manufactured in accordance with an appropriate standard for offshore mooring
chain (such as an IACS classification society) and certified by an IACS member or other recognised
certification body accepted by GL Noble Denton.

12.5

WIRE ROPE

12.5.1

Wire rope mooring components for offshore mooring shall comply with the requirements of Section
11.1.2 of ISO 19901-7, Ref. [2] (Stationkeeping Systems) and be certified by an IACS member or other
recognised certification body accepted by GL Noble Denton.

12.6

FIBRE ROPE

12.6.1

In general, contact between fibre rope and the seabed should be avoided in normal operating
conditions.
Given the nonlinear stiffness characteristics of fibre ropes, it is essential that appropriate data is
obtained on the stiffness characteristics under load.
Minimum breaking strength of fibre ropes shall be certified in accordance with a standard industry
practice (such as API RP 2SM) by bodies approved by an IACS member or other recognised
certification body accepted by GL Noble Denton.

12.6.2
12.6.3

12.7

CONNECTORS

12.7.1
12.7.2

Mooring chains should be composed of continuous lengths of chain where practicable.
Where it is necessary to use in-line connectors, the mooring pattern should be designed, so as to
ensure that no connecting hardware is subjected to thrashing against the seabed. If this is not
possible this should be risk assessed on a case by case basis and suitable contingency measures put
in place in case of failure at this location.
Only classification society approved Long Term Mooring (LTM) connectors should be used where a
double locking mechanism has been employed to restrain the main load bearing pins of the connector.

12.7.3

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GUIDELINES FOR MOORINGS
12.8

BUOYS (SURFACE AND SUBSURFACE)

12.8.1

Spring buoys should be designed in accordance with the requirements of a recognised design code.
Guidance on spring buoy design is given in Section 11.1.5 of ISO 19901-7, Ref. [2], (Stationkeeping
Systems).
It should be ensured that any subsurface buoy is supplied with a suitable submersion rating for the
intended application.
For long term applications, the dynamic response of the buoy and the resulting fatigue implications for
all connections should be addressed. Experience has shown that such analyses are complex and time
consuming and do not necessarily predict possible failure modes which may be experienced in the
field.
Where buoys are used to provide clearances, means to detect their loss should be provided e.g.
tension monitoring (this should reveal a loss), transponders, etc. The operating procedures should
document the loss monitoring procedure and the remedial actions required. Suitable spares should
also be readily available and stored in a convenient location.

12.8.2
12.8.3

12.8.4

12.9

VESSEL CONNECTION POINTS

12.9.1

Where vessel connections are to fairleads / winches / windlasses that make up part of a classed
mooring system for a vessel, e.g. under POSMOOR notation, it is acceptable to assume that these
have adequate strength (as the capacities of these are specified under the class rules in relation to the
MBL of the vessel’s mooring lines).
Vessel connections points (including windlasses, winches, fairleads, Smit brackets, bollards, bitts etc)
should generally be designed for a load equal to 1.1 times the MBL of the connected mooring line.
The foundation structure must also be demonstrated to be suitable for the same design loads.
Where design calculations and/or certificates are unavailable, it may be acceptable to demonstrate
adequate connection capacity through proof loading. OCIMF, Ref. [11], gives some guidance on
suitable levels of proof loading for common vessel connections (e.g. double bitts, panama chocks etc).
Proof loading is potentially hazardous and a detailed, risk assessed procedure, will be required before
commencing such proof loading operations.
Notwithstanding any class requirements, winches/windlasses should have a stall capacity sufficiently in
excess (typically 20%) of the maximum line tensions in the limiting operating environment to allow the
vessel to safely move to the standby/survival condition (as applicable).

12.9.2

12.9.3

12.9.4

12.10

FENDERING

12.10.1

When a vessel is to be moored against another structure such as a quayside, adequate fendering shall
be provided to prevent damage to the vessel and structure.
In cases where fendering must restrain the vessel (e.g. when the vessel is blown on to the quay),
fenders shall be considered to be structural elements of the mooring system and shall be subject to the
same redundancy requirements as mooring lines.
It must be demonstrated that the maximum analysed load upon any fender when multiplied by the
appropriate safety factor (see Table 10-1) does not exceed the static reaction force rating of the
fender.
The pressure exerted by a fender on the hull of the vessel and the quay shall be calculated, and it shall
be demonstrated that this pressure is not in excess of that which the vessel’s structure and the quay
are designed to resist.
The rated energy absorption capacity of the fendering shall be at least twice the energy associated
with the vessel’s peak velocity due to the environment or wake induced motion from passing traffic.
Structural elements of fendering (e.g. pressure membranes) shall be protected (e.g. with sacrificial
elements such as tyres) such that they are not damaged through contact with the vessel or quayside.
Moveable fenders shall be restrained to prevent excessive movement. Restraints shall be designed to
resist a load equal to the maximum analysed load on the fender multiplied by the maximum coefficient
of friction between the fender and vessel.

12.10.2

12.10.3

12.10.4

12.10.5
12.10.6
12.10.7

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12.10.8

12.10.9

0032/ND Rev 0

Particular care should be taken where it is intended to employ a spacer barge as a fender. These
arrangements have historically proven to have high failure potential and should, therefore, always be
the subject of careful design and independent scrutiny.
Fenders should be arranged to avoid the possibility of a vessel “hang up” against the quayside. The
fender arrangement should be subject to a local site inspection. This is particularly relevant for loadout
operations where “hung up” barges may suddenly come free as the load of a module is being
transferred from the quayside to a barge.

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GUIDELINES FOR MOORINGS

13

PROCEDURAL CONSIDERATIONS

13.1

GENERAL

13.1.1

The planning and preparation for mooring a vessel should be carried out sufficiently in advance of the
operation such that the analyses described in this document can be carried out.
Non-standard mooring operations such as quayside moorings of MODUs shall be risk assessed to
confirm that all factors relating to the security of the vessel have been taken into account and that the
level of risk is controlled. The risk assessment shall be submitted for approval by GL Noble Denton.
The risk assessment should also take into account political or crime related security risks associated
with the location.
Prior to designing a mooring spread a mooring analysis needs to be carried out and the factors
detailed in Sections 7, 8 and 9 are to be taken into account.

13.1.2

13.1.3

13.2

ANCHOR PROOF LOADING

13.2.1

After installation, anchors should be proof load tested to ensure adequate embedment. Proof loads
should be maintained for at least 15 minutes.
For mobile moorings in open locations, proof loads will generally be to the maximum expected
operating tension at a location.
For mobile moorings in proximity to other installations, proof load is expected to be the maximum intact
tension identified in a mooring analysis.
Mooring test loading for permanent moorings shall be in accordance with Section 10.4.6.2 of ISO
19901-7, Ref [2].

13.2.2
13.2.3
13.2.4

13.3

MANNING

13.3.1

The level of manning shall be sufficient in terms of numbers, skill competency and experience to
operate all the relevant machinery and to manage the mooring system and emergency systems, on a
twenty-four hour basis, without the need for any personnel to work excessively long hours. The
numbers shall be sufficient to take appropriate action in the case of any emergency to ensure the
safety and security of the crew, the vessel and the location infrastructure (including port facilities,
moored vessels and environmental considerations).
Where appropriate shore-side assistance should be available on a 24-hour basis with direct lines of
communication to the moored vessel.

13.3.2

13.4

INSPECTION, MONITORING AND MAINTENANCE

13.4.1

Where practicable, an inspection, monitoring and maintenance programme should be in place to
ensure that all mooring components are in a serviceable condition and that their certified MBLs remain
valid. Discard criteria shall be documented and applied in line with recognised industry standards

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14

DOCUMENTATION

14.1

LEADING TO APPROVAL

14.1.1

For GL Noble Denton to issue approval, the following documentation must be provided.

14.2

OFFICE REVIEW

14.2.1

Mooring analysis report detailing:
a.
Location and Vessel Data (see Sections 6 and 7);
b.
Environmental Loads and Motions (see Section 8);
c.
Mooring Analysis Results (see Sections 9, 10, 11 and 12).

14.2.2
14.2.3

Mooring plan detailing vessel location and mooring arrangement.
Supporting procedures and risk assessments (particularly where the mooring is weather restricted or is
not fully redundant).

14.3

ON SITE

14.3.1

Certification for all mooring components including vessel and shore connection points. These
certificates shall be issued or endorsed by bodies approved by an IACS member or other recognised
certification bodies accepted by GL Noble Denton. If the certification is old, on site inspection by a
competent person should have been carried out to check the present condition of connection points,
etc.
Details of manning and emergency response plan.

14.3.2

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GUIDELINES FOR MOORINGS

15

SPECIAL CONSIDERATIONS FOR INSHORE AND QUAYSIDE MOORINGS

15.1

BACKGROUND

15.1.1

The engineering, design, verification and execution of inshore and especially quayside moorings is
very frequently underestimated leading to a gap between the strict requirements for approval and what
the client / contractor may wish to provide. The default standards used often fall below the
requirements of a 10 year return period design to recognised codes.

15.2

LOCATIONS WITHIN HARBOUR LIMITS

15.2.1

The intended location of the unit within the port area should be established with the Port Authority. In
some cases the Port Authority will have determined this well in advance and it will not be subject to
change. In some Ports, where commercial shipping forms the core of their business, the berth
selected by the Port may be subject to change. In all cases discussions should be held with the Port
Authority to determine the berth likely to be selected and its characteristics and those of any likely
alternatives.
If the Port Authority is reluctant to commit to a particular berth the importance of the details of the berth
in the project planning and design should be emphasised in discussions with the Port Authority. In
order to avoid delays it may be necessary to undertake analyses for not only the most probable berth
but also a number of contingencies.
The potential for surge due to passing traffic, particularly if moored in a river or canal, should be
assessed. The unit may experience surge up and down the berth and may be drawn off it.
The Port Authority should be requested to issue a Notice to Mariners requesting passing marine traffic
to reduce their speed to limit any effect of surge on the moorings.

15.2.2

15.2.3
15.2.4

15.3

CONTINGENCY ARRANGEMENTS

15.3.1

Details of tug capacity and shore-based manpower, their availability, call out times, phone numbers
and port emergency procedures should all be provided for review and taken into account in the risk
assessment (see Sections 13.1.2 and 13.3).

15.4

MOORING CONSIDERATIONS

15.4.1

Even very small magnitude motions induced by waves or long period swell, can result in very large
tensions on the short, stiff mooring lines commonly utilised in quayside moorings. This effect should
be evaluated closely (see Section 8.5.4).
Motions will also increase the likelihood of abrasion damage particularly in fibre ropes. Chafe chain,
stretchers and adequate protection should be employed to minimise chafe points. Chafe points should
be regularly inspected and if significant damage is found the damaged components should be replaced
as a matter of priority. Thus, adequate contingency spares are required at the site of the mooring.
Wind loads shall take account of all construction phases and can be increased due to scaffolding, wind
and weather protection, etc.
It is often impossible to properly tension and adjust moorings at quayside. It is therefore necessary to
take account of large variations in working tension in the mooring analysis. A suitable method for
achieving and verifying the design pretension should be considered during mooring design. In practice
a smaller number of high capacity, lines with similar lengths and pretensions is better than multiple
small ones in an asymmetric arrangement.
In some cases a mooring is simply not feasible without some means of adjustment and this can be
somewhat difficult and expensive to provide if it is not available on the vessel. It, however, represents
a wise investment given the likely value of the moored object.
Quayside moorings will often necessitate the use of multiple connections, strops etc to make up the
mooring lines. These need to be reviewed carefully to ensure that there are no unforeseen failure
modes. All connections shall be properly matched and all soft rope to hard tackle connections shall
have properly fitted hard eyes.

15.4.2

15.4.3
15.4.4

15.4.5

15.4.6

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GUIDELINES FOR MOORINGS
15.4.7

15.4.8

15.4.9

Adequate fendering is hard to achieve on larger vessels, semi-submersibles, etc. because the loads
involved can be large. Spacer barges, in particular, have a poor record in operation and proposals to
use spacer barges should always be carefully engineered. If possible, some means of holding the
vessel off the quay as well as the fenders should be provided. Laying offshore anchors on a semisubmersible moored at the quayside can provide an additional contingency.
Inshore and especially quayside moorings will typically require a careful local study of environmental
design extremes. Usually it is not feasible to design the mooring to resist the omni-directional
extremes so some form of directional metocean study is required. It is rare to have available a full set
of data on current and tides, and it may be necessary to take some local measurements to determine
the actual current at the quayside.
Quayside moorings typically have short natural periods. Therefore the wind and wave excitation
frequencies need to be carefully established.

15.5

SHORE MOORING POINTS / BOLLARDS / WINCHES

15.5.1

The capacity of shore mooring points and winches, including their foundations, should be
demonstrated by certification or by design. Where these are unavailable, proof loading may be
undertaken to demonstrate capacity. Proof loads should be a minimum of 1.25 times the maximum
intact tension for that line calculated in the mooring analysis. Proof loading operations can be
potentially very hazardous and should be carefully planned taking into account the possibility of
catastrophic failure of connection points. A suitable, risk assessed, proof testing procedure should be
available.

15.6

PROCEDURES

15.6.1

Procedures should detail and quantify, where applicable,

mooring tension monitoring, inspection, line adjustment and

emergency response arrangements, including spare equipment and availability of tugs and
shore-based manpower as described in Section 15.3.

mooring line tending arrangements to account for predicted variations in tidal height

safe access to vessels accounting for potentially significant tidal variations.

15.7

COLD STACKING

15.7.1

Approval for cold stacking can only be given when it can be demonstrated that all of the factors
mentioned in this document have been taken into account and it can be demonstrated by a risk
assessment accepted by GL Noble Denton that cold stacking presents no substantially increased risk
to the unit. It is clear, however, that moorings on cold stacked units still require regular inspection and
it should be documented that steps have been put in place for this to be carried out.

15.8

ICE LOADING

15.8.1

For locations where loading from drifting ice is expected on a moored structure the impact on mooring
line tensions shall be assessed.
Mooring lines employed in locations where sea ice is expected shall be qualified by the manufacturers
for the range of temperatures expected in the region. The mooring lines shall be resistant to abrasion.

15.8.2

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GUIDELINES FOR MOORINGS

16

SPECIAL CONSIDERATIONS FOR PERMANENT MOORINGS

16.1

GENERAL

16.1.1

Requirements for permanent moorings are fairly comprehensively covered in the industry standard
codes referred to previously.
Additional considerations over mobile moorings are likely to include the following with further
information available in the Mooring Integrity JIP OTC papers, Ref. [12] and [13]:

Fatigue (axial, bending and torsion)

Marine growth and how to r remove it for inspection to take place

Wear and corrosion including , microbial induced corrosion (MIC)

Mooring line failure detection and instrumentation

Spring buoy failure detection.

16.1.2

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GUIDELINES FOR MOORINGS

REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]

ISO IS 19901-1: Petroleum and Natural Gas Industries — Specific Requirements for Offshore Structures
— Part 1: Met ocean Design and Operating Conditions.
ISO IS 19901-7: Petroleum and Natural Gas Industries — Specific Requirements for Offshore Structures
— Part 7: Stationkeeping Systems for Floating Offshore Structures and Mobile Offshore Units.
API RP 2SK 3rd Edition (2005): Design and Analysis of Station keeping Systems for Floating Structures.
DNV RP C205 (2007): Environmental Conditions and Environmental Loads. Det Norske Veritas,
DNV OS E301 (2008): Position Mooring. Det Norske Veritas
DNV Rules for Classification of Mobile Offshore Units, Part 6, Chapter 2 (1996): Position Mooring
(POSMOOR).
BS 6349-6 (1989): Maritime Structures — Design of Inshore Moorings and Floating Structures.
GL Noble Denton 0013/ND “Guidelines for Loadouts”
GL Noble Denton 0016/ND “Seabed and Sub-seabed Data Required for Approvals of Mobile Offshore Units
(MOU)”
IMCA M 179 (2005): Guidance on the Use of Cable Laid Slings and Grommets.
OCIMF Mooring Equipment Guidelines, Second Edition 1997
“Floating Production Mooring Integrity JIP – Key Findings” Martin G. Brown, Tony D. Hall, Douglas G. Marr,
Max English and Richard O. Snell, OTC 17499, 2005
“Phase 2 Mooring Integrity JIP – Summary of Findings” Martin G. Brown, Andrew P. Comley, Morten
Eriksen, Ian Williams, Philip Smedley, Subir Bhattacharjee, OTC 20613, 2010
All GL Noble Denton Guidelines can be downloaded from www.gl-nobledenton.com

0032/ND Rev 0

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