DISCLAIMER: This material is for information purposes only. It is in no way intended by the author to be complete and accurate. It is based only on the experience of the author, information gained from product manufacturers, and/or other entities. No responsibility is assumed for any person or persons attempting to use products or methods that have been described in this document. Introduction: The K-28 is a minimalist pocket cruiser / daysailer based on the 15 Square Meter Skerry Cruisers. Hull form and rig proportions are true to the requirements of the Square Meter Rule, while just about everything else has been changed from the Rule requirements. More information and Designer's Comments can be found at http://www.pkboatplans.com/K-28.html. There are some significant design features incorporated in the K-28 that need to be considered by the builder. The hull is single skin fiberglass throughout with no core. The deck is fiberglass sandwich construction with foam core. The mast is deck stepped. Ballast is an internal lead casting; no keel bolts. Rudder stock and "paddle" are silicon bronze, and chainplates are silicon bronze. Single skin fiberglass hull construction was chosen for several reasons. The relatively large keel and keel reinforcement area has to be single skin regardless, single skin construction has greater impact resistance than cored construction, and eliminating the core from the hull eliminates all risk of water damage to the hull core. The deck stepped mast simplifies construction and eliminates any possibility of deck leaks at the mast. The mast section needs to be stronger and heavier than a keel stepped mast, but the K-28 rig is so small the weight difference is not significant. One nice thing about a deck stepped mast is there are no leaks from a mast collar. The K-28 requires no wiring in the mast, so there are no leaky wire penetrations in the deck. A keel stepped mast will leak rain water into the boat through internal halyard openings. Not so with a deck stepped mast. The minimum mast weight allowed by the Square Meter Rule is 2.53 kilograms per meter. The conservatively designed K-28 mast weight is only about 1.90 kilograms per meter, depending on the selected mast section. Silicon bronze is used instead of stainless steel for highly loaded metal parts exposed to the elements. Although stainless steel has become ubiquitous in its use in the marine environment, it has a big problem. Stainless steel requires the presence of oxygen to create a chromium-oxide film which inhibits corrosion. If stainless steel is deprived of oxygen it can pass into its active state and corrode freely. This is commonly known as "crevice corrosion". Because of this, the rudder stock, chainplates, and chainplate bolts on the K-28 are silicon bronze, not stainless steel. In my experience there are several recurring issues in small boat construction that add to the cost and time of building a one-off custom boat. Fairing the hull to a perfect yacht finish, not having parts and materials available when they are needed, building the components out of sequence, and requiring the highest paid people in the shop to spend time creating construction details left out by the designer are time consuming, expensive, and very common. I have attempted to address all these issues in the plans and 1
documentation for the K-28 to reduce building costs and simplify the construction process. Plans: Plans and CNC Pattern files for the K-28 can be downloaded at http://www.pkboatplans.com/K-28_Download.html and http://pkboatplans.com/K28_Build.html. The plans are in PDF format and the full size sheets are 24" x 36". You can get them printed at a commercial printing or copying business. Also, 11" x 17" reduced size prints are readable and are handy for reference and study purposes. The plans need to be printed in color, not black and white, to get the gray lines to show up properly. The first thing to do is to go over all the drawings and be sure to read all the General Notes. The General Notes contain critical information and must not be overlooked. Because the plans for the K-28 are absolutely free, there is no designer support for the builder. It is the responsibility of the builder to identify and resolve any discrepancies in the plans. Be sure to read the CNC DXF File Notes for information regarding full size patterns or CNC cut files for station molds and bulkheads. The accuracy of the CNC patterns for the K-28 has not yet been verified. It is the builder's responsibility to verify the accuracy of the CNC patterns before construction of the hull mold, deck mold, rudder, bulkheads, or ballast casting. Use the CNC DXF files at your own risk. Construction Sequence: A simple rule of thumb for an efficient way to build a boat is: Build the Hull Last. The idea is to have all the structural components; rudder, ballast casting, bulkheads, joiner panels, etc. ready to be installed when the hull is completed. Once the structural components are installed, the deck part needs to be complete and ready to be bonded to the hull. With that in mind the suggested construction sequence for the K-28 is: 1. Order the ballast casting. 2. Build the rudder and tiller. 3. Build the bulkheads, partial bulkheads, and bunk top. 4. Order the batteries, interior access hatches, electrical, and plumbing components to be delivered before completion of the hull. 5. Build the strongback for the hull and deck molds. 6. Build the deck mold. 7. Laminate the deck, allow to cure, and paint the inside of the deck and cockpit. Remove the deck part from the deck mold. 8. Order the deck hardware to be delivered before installation of the deck part. 9. Take apart the deck mold and save strongback for the hull mold. 2
10. Build the hull mold. 11. Laminate the hull and allow to cure. 12. Fair the hull. 13. Build the hull cradle. 14. Unfasten the station molds from the strongback and roll the hull with the hull mold intact. 15. Take apart the hull mold. 16. Install the bulkheads. 17. Install the sheer clamp. 18. Install the lead ballast casting. 19. Install the keel floors and transverse frames. 20. Install the partial bulkheads at stations 3 and 4. 21. Pour the buoyancy foam. 22. Install the bunk top, seats, and cabin sole. 23. Paint the hull interior. 24. Install the interior access hatches, batteries, and cockpit drain thru-hulls. 25. Order the spars, rigging, and sails to be delivered before the boat is launched. 26. Glue and bond the deck part to the hull and bulkheads. 27. Bond the bulkheads to the deck and cockpit. 28. Install the partial bulkhead at station 7. 29. Fair the hull to deck joint. 30. Fair the deck and cockpit 31. Install the rudder tube, rudder bearings, and plywood gussets. 32. Paint the hull and deck exterior. 33. Dry-fit the chainplates, and deck hardware. 34. Apply the deck and cockpit sole non-skid. 3
35. Install the deck hardware. 36. Install the bilge pumps, bilge pump piping, and cockpit drain piping. 37. Install the 12 VDC electrical system. 38. Install the rudder, shaft collar, tiller head, and tiller at the launch site. 39. Step the mast at the launch site. Install the boom vang and mainsheet. Install the VHF whip antenna. 40. Launch. Step 1 - Order the ballast casting Ballast for the K-28 is a one piece lead casting internally set into the keel. The mass of the lead casting is 432 kg (952 lb). Dimensions of the lead casting are given on dwg no 06-A5, Ballast Casting Geometry and CNC patterns are in 06-BLST-CNC.dxf. See also the General Notes on dwg 06-A3, Keel and Rudder Details. Note the CNC patterns are to the finished surface of the ballast casting. A foundry specializing in casting lead sailboat keels should have no problem building the patterns and casting the ballast from the drawings and DXF file. The ballast is one of the first things to go into the completed hull, so it needs to be ordered with enough lead time to be delivered just before the hull is turned over. The primary reason for locating the ballast internally on the K-28 is to avoid keel bolts altogether. Eliminating the keel bolts simplifies the construction and does away with stress concentrations and maintenance issues associated with keel bolts. The down side is the center gravity of the ballast is a bit higher, but this is acceptable in the K-28 because of the relatively small sail plan. One of the advantages of taking a minimal sail area approach to the design is less ballast is needed and stresses on the hull and rig are reduced. Step 2 - Build the rudder and tiller The first thing that needs to be done to build the rudder is to buy the tiller head. The tiller head called out on the Deck Plan is a Lewmar 25 mm. Use the tiller head to verify the machining of the end of the rudder stock. The 1 1/2" diameter rudder stock and 1/8" plate "paddle" are silicon bronze fabricated as shown in dwg no 06-A3, Keel and Rudder Details. The rudder core is high density (20 lb/ft^3) foam. I think something like General Plastics LAST-A-FOAM would work well here. One way to build the rudder core is in longitudinal sections with 3/4" thick material. The inner pieces are cut out for the rudder stock and and routered 3/32" deep for the 1/8" plate with the outline matching the rudder profile. The outline of the outer pieces are cut to the 3/4" buttock line. The rudder core is then shaped to match the waterline patterns and glassed as called out on the drawing. Use the same fairing compound to be used in Step 12 to fair the rudder. Coat the faired rudder with epoxy primer.
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Build the tiller from wood such as mahogany. The tiller width needs to fit the tiller head. Length of the tiller is 996 mm from the centerline of the rudder stock to the end of the tiller.
Step 3 - Build the bulkheads, partial bulkheads, and bunk top The bulkheads, partial bulkheads at stations 3 and 4, and the bunk top panels can be pre cut from the CNC pattern DXF files. Cutouts in the bulkheads and panels should be bullnosed with a router. All the bulkheads and panels are to be cut with a 3 mm gap between the plywood and inside of the hull or deck surface. The CNC pattern DXF files already include a deduction for the 3 mm gap. The bulkheads and panels are to be coated with WEST System, System Three, or equal epoxy. Leave the perimeter bonding width + 12 mm dry for the bonding laminate. The bulkhead to hull / deck bonding will not stick to the cured epoxy, so it is important to leave the perimeter bare. See dwg no 06-C3, Construction Details, Details C-7 and B-2, and dwg no 06-C1, Framing Plan, Detail B-8 for bulkhead and bunk top bonding widths. Locate and mark the centerline and 1200 DWL on bulkheads A, B, and C. Step 4 - Order the batteries, interior access hatches, electrical, and plumbing components to be delivered before completion of the hull All the stuff that goes into the boat after the hull is complete but before the deck goes on needs to be ordered in time to be delivered before the hull is turned over. The idea is to not have an empty hull gathering dust while waiting for items that need to be installed. The following needs to be installed in the hull before the deck goes on: Batteries and battery boxes Cockpit drain thru-hull fittings Bilge pump overboard thru-hull fittings Knot log thru-hull Access plates for bulkheads A and D Access opening for bunk top The following should be standing by to be installed just after the deck is bonded to the hull and bulkheads: 12 VDC distribution panel Battery disconnect switch Battery cables Interior light 5
Compass light junction box 12 VDC outlet VHF radio 12 VDC wire Adhesive cable tie mounts Bilge pumps Bilge hose Cockpit drain hose Rudder tube Rudder bearings Step 5 - Build the strongback for the hull and deck molds The same strongback can be used for both the hull and deck molds. Strongback construction details are shown on dwg no 06-M1, Hull Mold Construction, and dwg no 06-M2, Deck Mold Construction. It is important to follow these drawings if the CNC pattern DXF files are used to produce the mold stations. 6 - Build the deck mold For purposes of this document it is assumed the hull mold and deck mold will use the same strongback. Therefore, the hull and deck will be built one part at a time rather than simultaneously. I suggest building the deck part first and setting it aside until the hull is complete since the deck part will take up less space than the hull. The deck mold should be built in accordance with dwg no 06-M2, Deck Mold Construction. The deck mold stations and cross beams are located on the strongback in the same positions as the hull mold stations. This is so the strongback can be re-used for the hull mold. Each station mold is to be marked with a centerline and horizontal plane reference line. The horizontal plane 222 mm above the bottom of the strongback can be used as a reference plane, since this is where the station molds will be cut if the CNC pattern files are used. The cross beams on the strongback are to be marked with a centerline reference. Set up each station mold with proper alignment of the centerline and vertical reference marks. Use additional bracing if required to keep the station molds absolutely vertical. Build the deck mold surface with the material thicknesses indicated on the Deck Mold Construction drawing. This is important if the CNC pattern DXF files are used to ensure the final size of the deck part is correct. I would consider building the hatch flat surfaces first, extending the forward hatch flat from station 2 to station 7 and the aft hatch flat from station 10 to station 13. Next build the cockpit surfaces. The forward and aft cockpit surfaces are located in accordance with dwg no 06-A2, Deck Lines. Build the deck surfaces and add the forward and aft hatch flat faces. Finally, add the 1/8" (3.2 mm) hardboard around the perimeter of the deck mold. This forms the recess for the hull to deck joint. Finish the surface of the mold in accordance with the Deck Mold Drawing. Important: Make up a test sample FRP laminate to be sure the deck part will release from the mold. Use drywall screws to attach the hardboard to the station molds. Use as few fasteners as possible; it all has to be taken apart later. No glue should be used anywhere in the deck mold or strongback. 6
Step 7 - Laminate the deck, allow to cure, and paint the inside of the deck and cockpit. Remove the deck part from the deck mold Vinylester resin is preferred for the deck part, but polyester is acceptable. The E-LTM 1808 material used in the deck laminate should be oriented transversely across the width of the deck mold. Do NOT orient the material diagonally. Do not lap the edges of the material, use butt joints to avoid bumps in the laminate. Stagger the butt joints. The outside skin of the deck / cockpit is laid up by hand in accordance with the laminate schedule on dwg no 06-C1, Framing Plan. The plywood core in the hatch flats is glued in place with thickened epoxy resin, making sure there are no voids between the plywood and fiberglass. The deck / cockpit foam core may be glued in place by hand with ATC Core-Bond core adhesive or vacuum bagged. Follow the manufacturer's instructions for the use of Core-Bond. The foam core around the deck edge is reduced in thickness to allow for the hull to deck bonding overlap. See Detail A-5 on dwg no 06-C3, Construction details. The inside skin of the deck / cockpit is a hand layup similar to the outrside skin. An additional inner layer of E-LTM 1808 at the deck reinforcement and at the corner of the hatch flats is to be added to the inside skin as shown on the Construction Sections, Detail C-2 and Framing Plan. Install the cockpit drain tubes as shown on dwg no 06-E2, Piping Plan, Detail C-7. Now is a good time to paint the inside of the deck part. Mask off 1" around the perimeter of the deck and mask the bonding widths at the bulkheads before painting. Also mask the area under the cockpit sole where the partial bulkhead at station 7 will be bonded, and mask the area where the rudder tube will be bonded to the deck. There is no need to paint the inside of the deck forward of bulkhead A or aft of bulkhead D. Follow the paint manufacturer's instructions for preparation and priming of the surface to be painted. Gel coat is an acceptable coating for the inside of the deck. After the deck part is removed from the mold, add the additional E-LTM 1808 at the mast step and the additional layer of E-LTM 1808 in the deck reinforcement area to the outside skin. Step 8 - Order the deck hardware to be delivered before installation of the deck part Make sure all the hardware and fittings to be mounted on the deck are ordered in time to be delivered before the deck is bonded to the hull and bulkheads. A complete list of hardware is included on dwg no 06-B2, Deck Plan. The fasteners for the hardware and fittings need to be ordered as well. Ordering the custom pulpits on dwg no 06-D3, Bow and Stern Pulpits and the custom chainplates on dwg no 06-D2, Chainplates should also be done. Note the shroud chaiplates are not symmetrical and the port shroud chainplate is not identical to the starboard shroud chainplate. The port and starboard shroud chainplates are mirror images of each other. Now is a good time to fabricate the toe rails so they are ready when the deck hardware is installed. See Detail A-15 on dwg no 06-B2, Deck Plan. Step 9 - Take apart the deck mold and save strongback for the hull mold Once the deck part is complete and removed the deck mold can be disassembled. Be sure to mark the station locations on the deck part before removing it from the mold. Unfasten the station molds from the cross beams and leave the cross beams and strongback rails intact for the hull mold. 7
Step 10 - Build the hull mold The hull mold should be built in accordance with dwg no 06-M1, Hull Mold Construction. The strongback built in Step 5 will be used for the hull mold. Each station mold is to be marked with a centerline and horizontal plane reference line at the 1200 DWL. The 1200 DWL is located 950 mm above the bottom of the strongback rails as shown on the Hull Mold Construction drawing. The cross beams on the strongback are to be marked with a centerline reference. Set up each station mold with proper alignment of the centerline and vertical reference marks. Use additional bracing if required to keep the station molds absolutely vertical. Build the hull mold surface with the material thicknesses indicated on the Hull Mold Construction drawing. This is important if the CNC pattern DXF files are used to ensure the final size of the hull is correct. The mold planking within 65 mm of the underside of deck is planed down to 16 mm thick as shown on Detail C-7 of the Hull Mold Construction drawing. This forms the recess for the hull to deck joint bonding, but also introduces reverse draft into the mold surface. The reverse draft requires the hull mold be disassembled after the hull is complete and rolled upright. This is not a major issue since the mold should be left intact while the hull is turned over anyway. Finish the surface of the mold in accordance with the Hull Mold Drawing. Important: Make up a test sample FRP laminate to be sure the hull mold can be pulled from the hull part. Use drywall screws to attach the hull mold planking and 1/4" hardboard to the station molds. Use as few fasteners as possible; it all has to be taken apart later. No glue should be used anywhere in the hull mold or strongback. Step 11 - Laminate the hull and allow to cure The K-28 hull is single skin with no core, so it can be laminated start to finish without stopping if desired. Use vinylester resin for the hull laminate. The hull laminate schedule is included in dwg no 06-C1, Framing Plan. The E-LTM 2408 material used in the hull laminate should be oriented longitudinally along the length of the hull mold. Do NOT orient the material diagonally. Do not lap the edges of the material, use butt joints to avoid bumps in the laminate. Stagger the butt joints. Start by laying up 2 layers of ELTM 2408 on top of the cap piece at the bottom of the keel. Next lay up 2 layers of ELTM 2408 at the bottom and sides of the keel, and in the bottom reinforcement area. End the first layer of bottom reinforcement 30 mm from the transition to the regular hull laminate, and the second layer at the transition. Now lay up 4 layers of E-LTM 2408 over the entire hull mold. Do not increase the laminate thickness along the hull centerline; it is not required and will add weight unnecessarily. Finally, add 2 additional layers of E-LTM 2408 at the chainplate reinforcement area. Step 12 - Fair the hull Fairing the hull can be time consuming and very expensive in terms of labor hours. Faring and painting a custom boat to a perfect yacht finish can add up to be 20% of the total cost of the boat. And a high gloss paint job applied to hull that is less than perfectly fair looks terrible. In keeping with the minimalist philosophy of the K-28, I suggest planning on a semi-gloss finish with reasonable (not perfect) hull fairing. If a perfect yacht finish is a "10", fair the hull to an "8" and walk away.
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A lot of builders like to mix up their own fairing compound, and that is fine. Ready made fairing compound should be something like Awlgrip Awl-Fair. Start by masking off the recess for the hull to deck bonding at the sheer. Apply an epoxy primer like Awlgrip 545 to the hull surface. Apply the fairing compound and go through the process of fairing the hull. Hopefully, the hull is already fair to the point of only having to fill the weave of the woven roving to achieve an "8" out "10" fairing job. Once the hull is satisfactorily faired, seal the sanded fairing compound with Awlgrip 545 or equal epoxy primer. Always follow the manufacturer's instructions when applying primer and fairing compound. Step 13 - Build the hull cradle A hull cradle must be built to support the completed hull after it is turned upright and the hull mold is removed. The hull will be somewhat flexible until the floors, frames, bulkheads, and sheer clamp are installed. The hull cradle will help the hull hold its shape while the internal structural components are installed. A suggested means of building the hull cradle is shown in dwg no 06-M3, Hull Cradle Details. The cradle should be built to support the bottom of the boat up to the 1200 DWL at station 4 and station 10. The cradle should have reference marks to allow the hull to be easily located and leveled after it is turned over. A good method for building the cradle pads is given in the book "Fiberglass Boatbuilding for Amateurs" by Ken Hankinson: "Place strips of parting film over the hull where the cradle supports will be positioned. Then use scrap pieces of foam or strips of carper taped in place over the parting strips and saturate the exposed surface (the carpet backing in the case of the carpet strips) with resin and several layers of mat. Place the cradle supports over these strips and use bonding angles of (E-LTM 1808) to secure the cradle supports to the foam or carpet." Step 14 - Unfasten the station molds from the strongback and roll the hull with the hull mold intact Once the hull has been faired and primed, it needs to be turned upright and leveled. It must be rolled with the mold structure intact to prevent distortion of the hull before the internal structural components are installed. Mark the station locations and 1200 DWL location on the hull before the station molds are unfastened from the strongback. The station molds are then unfastened from the strongback, then the hull and hull mold are turned over and placed into the hull cradle. Use the station and 1200 DWL reference marks to level the hull fore and aft and athwartships. It is up to the builder to determine the best way to roll the hull over. The method used will depend on the available space and equipment on hand. The total mass of the hull and hull mold (without strongback) is approximately 900 kg (1,980 lb) assuming medium density particle board is used for the station molds. The center of gravity of the hull and hull mold (without strongback) is 340 mm aft of station 6 and 140 mm below the 1200 DWL reference plane with the hull upside down. Step 15 - Take apart the hull mold Once the hull and hull mold have been turned over, placed in the cradle, and leveled, the hull mold can be disassembled. Start by removing the butt blocks at station molds 5 through 8. Cut out the station molds with a Sawzall as close to the mold planking as 9
practicable. Then pull away the mold planking. The keel section of the hull mold can be pulled up and out of the hull part. Step 16- Install the bulkheads The bulkheads should be complete and ready to be placed and bonded to the hull at this time. Locate the bulkheads as shown on the Framing Plan. The bulkheads can be clamped to temporary cross members located at each bulkhead station. Use small wood wedges to fill the 1/8" gap between the bulkhead and the hull. Glue the bulkheads in place with dabs of thickened resin in 4 to 6 spots on each bulkhead. Remove the wedges and add a thickened resin fillet around the perimeter of the bulkhead. Bond the bulkheads to the hull in accordance with Detail C-7 on dwg no 06-C3, Construction Details. Step 17 - Install the sheer clamp The sheer clamp can be beveled and bull-nosed prior to installation. The top bevel is 9o from horizontal and the bull-nose radius is 6 mm. Glue and hold the sheer clamp in place with clamps. See also Detail A-5 on the Construction Details drawing. The sheer clamp may be installed in sections with butt joints; its primary purpose is to provide a landing for the deck part. The inboard corner of the top bevel will probably have to be shaved down somewhat at the extreme bow and stern for the deck part to fit properly. Step 18 - Install the lead ballast casting The lead ballast casting ordered in Step 1 should have a threaded hole for a 1/2" diameter steel eyebolt. The eyebolt must have a "shoulder" to bear against the top of the lead casting. Coat the inside of the keel in way of the ballast location with thickened resin. Lower the ballast casting in place with a small crane or chain hoist. Be sure the casting is as far forward as it can go. Keep some tension on the eyebolt with the crane or hoist to hold the casting in position until the resin cures. Once the resin cures, remove the eyebolt and fill the eyebolt hole with thickened resin. Fill the void aft of the ballast casting with low density filler. This is a good time to fill the keel void aft of bulkhead C to form the aft bilge sump. Glass over the top of the ballast and filler material as shown on dwg no 06-C3, Construction Details, Detail A-4. Step 19- Install the keel floors and transverse frames Keel floors and transverse frames need to be installed at stations 6, 7, and 8 as shown on the Framing Plan and Construction Sections drawings. The dimensions on the Construction Sections drawing are to the foam former. The floor / frame laminate is in addition to the foam former dimensions. Note that the foam former is not structural and can be made out of just about anything. (Sheer stresses are in the stiffener webs and tensile / compressive stresses are primarily in the hull shell and stiffener flange. This is why holes should never be drilled in stiffener flanges for mounting wire hangers or joinery.) Scrap pieces of the deck core material can be used to build the foam formers. The formers may be pieced together in any fashion, as long as the final dimensions are in accordance with the Construction Sections drawing. 10
The foam formers should be glued in place with low density filler. Use the low density filler to create a 6 mm fillet where the foam former material meets the hull skin. Fabricate the floor / frame laminate as shown on the Construction Details drawing, Details A-7 and C-5. Note the laminate is lapped at the top of the foam former. Step 20 - Install the partial bulkheads at stations 3 and 4 The partial bulkheads at stations 3 and 4 are located as shown on the Framing Plan and bonded as shown on the Construction Details drawing, Detail C-7. The bonding at station 4 must be watertight. The process of installing the partial bulkheads is similar to that of Step 16. The 38 mm x 19 mm cleats used to fasten the bunk top to bulkhead A, bulkhead B and the partial bulkheads need to be installed at this time, before the buoyancy foam is poured. Step 21 - Pour the buoyancy foam The K-28 is designed with single compartment subdivision. That is, the boat is divided into watertight compartments and will stay afloat when a single watertight compartment is damaged and flooded. Furthermore, the boat will meet the damage stability requirements of the Maritime and Coastguard Agency Large Commercial Yacht Code. The MCA damage stability criteria are intended for large yachts over 24 meters long, but it was used as a standard for the K-28 because there are no similar criteria for small yachts. It is not enough to remain afloat when flooded, it is important to have adequate stability and freeboard in the damaged condition as well. I have documented the results of intact and damage stability calculations in the K-28 Stability Report which can be found at http://www.pkboatplans.com/NA_Notebook.html. A buoyancy tank located forward under the bunk top is needed to meet the MCA damage stability requirements. This buoyancy tank is filled with foam as indicated on the construction drawings. The buoyancy foam is a two part U.S. Coast Guard approved flotation foam with a density of no more than 32 kg/m^3 (2 lb/ft^3). This is the only type of foam to be used for this purpose. An example is AreoMarine Polyurethane Pour Foam. Enough foam mixture to yield at least 0.25 m^3 (8.50 ft^3) is required. Filling the buoyancy tank with pour foam should be done in several small pours of about 1 to 2 quarts for each pour. The foam mixture is to be poured between bulkhead A and the partial bulkhead at station 3, and between the partial bulkhead at station 3 and the partial bulkhead at station 4. Ultimately, about 2 1/2 gallons, or five to ten pours is required. The foam will expand up over the top of the partial bulkheads and will need to be leveled off flush with the tops of the partial bulkheads. This is a messy job, so it is best to mask off the hull and bulkhead A in the vicinity of the buoyancy tank. A temporary dam at station 4 will help keep the foam from overflowing aft out of the buoyancy tank. Step 22 - Install the bunk top, seats, and cabin sole The bunk top should already be cut out and coated with epoxy resin from Step 3. The bunk top is to be glued and screwed to the 38 mm x 19 mm cleats on the bulkheads and partial bulkheads. Then it is to be bonded to the hull in accordance with Detail B-2 on the Construction Details drawing.
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The cabin sole cleats can be glued to bulkhead B and the keel floors at stations 6, 7, and 8. The cabin sole pieces need to be securely fastened to the cleats, yet removable for access to the bilge. The seats between bulkhead B and station 6 are sized as shown on dwg no 06-B3, Joiner Sections, Station 6. The seats are to be bonded to the hull, bulkhead B, and the frame at station 6 with a thickened epoxy resin fillet. All non-faying surfaces of the plywood seats should be coated with epoxy resin before installation. Step 23 - Paint the hull interior The inside of the hull and the bulkhead bonding between Bulkhead A and Bulkhead D can now be painted. Mask off the area at the rudder tube location to allow bonding of the rudder tube and plywood gussets to the hull. Also mask the part of the keel floor at station 7 where the partial bulkhead will be bonded. Follow the paint manufacturer's instructions for preparation and priming of the surface to be painted. Gel coat is an acceptable coating for the inside of the hull. The plywood surfaces that have been coated with epoxy are not to be painted. Note the reason to paint the interior of the boat is to protect the hull and deck laminate from UV rays that will come in through the deck hatches. The resin used to laminate the hull and deck will degrade over time if exposed to UV rays. Step 24 - Install the interior access hatches, batteries, and cockpit drain thru-hulls Install the access plates on bulkheads A and D, and the access hatch on the bunk top between station 4 and bulkhead B. The batteries and battery boxes may be secured to the cabin sole between station 7 and station 8 at this time. Cover the battery boxes with plastic to protect them from glue, dust, and paint. Install the cockpit drain thru-hull fittings and seacocks. See drawing 06-E1, Piping Plan, Section C-7 for the location of the cockpit drain thru-hulls, and Detail C-2 for the installation. Step 25 - Order the spars, rigging, and sails to be delivered before the boat is launched By now a sparmaker should have been chosen. Basic parameters and dimensions for the mast, boom, and rigging are on dwg no 06-D1, Sail Plan. Location of the vang and mainsheet lugs on the boom are dimensioned on dwg no 06-B2, Deck Plan, Elevation C4. Details of connections and fittings are left to the sparmaker. The sparmaker should be given copies of the Sail Plan, Deck Plan, and dwg 06-D2, Chainplates. The sailmaker will need copies of the Sail Plan and Deck Plan to build the sails. Spars, rigging and sails should be ordered with enough lead time to be delivered before the boat is ready for launch. It is a good idea to independently verify the dimensions of the mast, boom, sails, and rigging lengths with the sparmaker and sailmaker before the spars and sails are made to make sure everything fits properly. Step 26 - Glue and bond the deck part to the hull and bulkheads 12
The deck part should be "dry-fit" to the hull to check the sheer clamp bevel and bulkhead clearances. Make corrections to the sheer clamp and bulkheads at this time. Once a proper fit of the deck part is obtained, glue the deck part in place in accordance with Detail A-5 on the Construction Details drawing. Use screws to hold the deck part in place while the adhesive cures. Be sure to wipe off the excess adhesive on the inside and outside of the hull to deck joint. After the adhesive is cured, the screws can be pulled and the holes filled with thickened resin. Add the (2) x 2408 E-LTM hull to deck bonding as shown on Detail A-5 and the Construction Sections drawing. Step 27 - Bond the bulkheads to the deck and cockpit Bond the deck part to bulkheads A and D as shown on the Framing Plan, Detail B-8. Bond the deck part to bulkheads B and C as shown on the Construction Details drawing, Detail C-7. Step 28 - Install the partial bulkhead at station 7 Cut out and fit the partial bulkhead at station 7 to the dimensions shown on dwg no 06C2, Construction Sections, Station 7. Bond the partial bulkhead to the keel floor and underside of cockpit in accordance with Detail C-7 on the Construction Details drawing. Step 29 - Fair the hull to deck joint This is a critical step. Unlike fairing the topsides to an "8" out of "10" suggested in Step 12, the hull to deck bonding at the sheerline should be faired to a "9 1/2" or a "10". The sheerline needs to be a continuous fair curve. The deck edge needs to be a constant radius throughout. This will make or break the look of the boat. If the sheer is perfect, it won't matter if the topsides are less than perfect with a semi-gloss finish. If the sheer has the slightest wave or bump, the boat will not look professionally built no matter how fair and shiny the topsides are. Use the same fairing materials that were used in Step 12. Step 30 - Fair the deck and cockpit The deck and cockpit are the least critical areas to be faired. Focus on the hatch flat corners and cockpit side / deck corner. The large flat deck area will be covered with nonskid, so it does not need to be perfectly fair. The goal should be to use as little fairing compound as possible and add as little weight to the deck as possible. Once the deck and cockpit are faired, the deck, cockpit, and hull to deck bond can be coated with epoxy primer. Step 31 - Install the rudder tube, rudder bearings, and plywood gussets Carefully locate the rudder stock centerline in accordance with the dimensions given in dwg no 06-A3, Keel and Rudder Details. Cut holes in the hull bottom and aft hatch flat for the rudder tube. Seal the plywood core edge grain in the hatch flat with epoxy resin. Create a fillet around the tube at the hull and deck with thickened resin. Bond the rudder tube in place with (2) x E-LTM 1808. Fit two plywood gussets to the hull as shown in Section B-6 on the Framing Plan. Glue the plywood gussets to the hull and rudder tube with thickened epoxy resin. The gussets should be coated with epoxy resin. 13
The remaining exposed hull surface and bonding in the interior should be painted at this time. Install the rudder bearings in accordance with the bearing manufacturer's instructions. Use a 1 1/2" OD tube dummy shaft to ensure proper alignment of the rudder bearings until the bearing adhesive has cured. Step 32 - Paint the hull and deck exterior I suggest painting the hull and deck exterior with a single semi-gloss light color such white, gray, or very light blue. No stripes or graphics on this minimalist sailboat. Paint can be anything from traditional brushed-on alkyd based yacht enamel to a two part polyurethane applied with an airless sprayer. Using a polyurethane will require a flattening agent to get a semi-gloss finish. This will make matching the finish difficult later for repairs or touch up. The enamel can be semi-gloss right out of the can. The hull bottom, keel, and rudder are painted with anti fouling bottom paint. The boot top (top of the bottom paint) should be a level line 50 mm above the 1200 DWL. Whatever paint scheme is used, the manufacturer's procedures must be followed. Step 33 - Dry-fit the chainplates, and deck hardware Locating and installing the deck hardware is a time consuming job. All of the deck hardware, fittings, and chainplates are to be located as shown on dwg no 06-B2, Deck Plan. As each piece of deck hardware is located, mark and drill the holes for the fasteners. Temporarily fasten (dry-fit) the hardware and fittings to the deck. Lightly torque the fasteners; do not crush the deck core. Be sure to drill holes at the bow and stern pulpit bases for the navigation light and VHF antenna wiring. Coat the exposed core at the wiring holes with resin. Now is the time to install the helicoil (or equal) threaded inserts for the fittings to be installed using fastener Detail C-10 on the Deck Plan drawing. The toe rails should be permanently installed at this time. Step 34 - Apply the deck and cockpit sole non-skid With the deck hardware still in place, mask 3/4" (19 mm) around each piece of hardware. Remove the deck hardware. Mask off the cockpit sole and hatch flat just ahead of the mast for non-skid. Mask the toe rails. The non-skid itself should be something like Awlgrip Griptex or Interlux Intergrip nonskid paint additive. The non-skid particles can be added to the topcoat paint or applied to tacky paint with the "broadcast" method. Whichever method is used, I strongly recommend making a test sample and follow the manufacturers procedures. Step 35 - Install the deck hardware The deck and cockpit sole foam core needs to be prepped for fasteners in accordance with Detail C-14 from the Deck Plan drawing. Fasten each piece of hardware to the deck as indicated in Details C-10, C-12, and C-14 on the Deck Plan drawing. Fasten the shroud chainplates to the hull as shown on Detail A-13 on the Deck Plan drawing. 14
Step 36 - Install the bilge pumps, bilge pump piping, and cockpit drain piping The generalized locations of the bilge pumps, overboards, and strumboxes is shown on dwg no 06-E1, Piping Plan. The bilge pumps are to be installed with the thru-deck fittings in the cockpit sides (not the deck). Refer to the Piping Plan General Notes for more installation information. Step 37 - Install the 12 VDC electrical system The electrical components for the K-28 are called out on dwg no 06-E2, 12 VDC Wiring Diagram. Install the electrical components on the partial bulkhead at station 7, the cockpit sides, and on bulkhead B. The cabin light may be fastened to the underside of the hatch flat. The navigation lights are installed on the bow and stern pulpits. Do not fasten any equipment on the hull, deck, or frames. Wiring is to be run through the wireway openings in the bulkheads near the deck edge. Do not drill any additional holes in the bulkheads for wiring. Use adhesive cable tie mounts to secure wiring to the deck or hull. Do not drill holes in the deck, hull or frames to secure wiring. Step 38 - Install the rudder, shaft collar, and tiller head at the launch site This is a simple installation. However, the boat needs to be raised to allow enough room to get the rudder under the boat. This is best done at the launch site, so the rudder is one of the last things to be installed. Step 39 - Step the mast at the launch site. Install the boom vang and mainsheet. Install the VHF whip antenna The final commissioning items can now be completed. Step the mast and attach the rigging to the chainplates. Adjust the rigging for proper tension and mast rake. Install the boom, boom vang, and mainsheet. I suggest using a whip antenna such as the Shakespeare Mariner 8300 for the VHF radio. The antenna should be mounted on the stern pulpit with a nylon rail mount. The antenna cable should be lead through the stern pulpit. Install the lifelines and lifeline cushions. Add safety gear and personal items, but do not overload the boat. The K-28 is not designed to carry any extraneous weight. Estimated minimum allowable freeboards when the boat is fully loaded without people on board are: Minimum freeboard at extreme bow
640 mm
Minimum freeboard at extreme stern
590 mm
Loading conditions that result in freeboards less than the above minimums may be unsafe. Step 40 - Launch 15