Building the Ultimate Expedition Kayak
Building the Coaming
I had intended to build a wooden cockpit coaming, but at the last second, I decided to make the coaming lip out of carbon fiber instead. I had already built the vertical rise of the coaming, so all that was needed was to trim it to the proper height and form a mold for the lip. I made the mold using foam pipe insulation. After cutting the foam lengthwise into thick, long strips, I wrapped the foam around the coaming and masking taped it into place to build the flat surface the lip would sit on. By adjusting the tension of the tape, the angle at which I attached the tape to the deck, and the thickness of the foam, I could control the shape and angle of the coaming lip all the way around the cockpit. The only drawback (which I did not realize until later) was that the soft foam would allow the carbon fiber to warp and shift if too much pressure was applied during the wet-out process. Fortunately, I took care to be gentle with the lip anyway, so I ended up with a fairly fair cockpit rim, even if it was not so perfectly flat as a commercially-built kayak's cockpit.
I used narrow strips of fiberglass and carbon fiber to make it easier to turn the radius of the cockpit as I went around. The lay-up sequence was one layer of 5 oz. glass, one layer of 5 oz. carbon-fiber, three layers of 5 oz. glass, one layer of 5 oz. carbon fiber, one layer of 5 oz. glass, one layer of 5 oz. carbon fiber (laid very carefully to make it cosmetically attractive), and one last layer of 5 oz. fiberglass (to protect the cosmetic layer of carbon fiber from scratches). The result was a very stiff, very attractive coaming. I should also mention, perhaps, that I used wide strips of carbon fiber for the cosmetic layer (as wide as was practical) to reduce the number of visible seams. When all was said and done, I used five strips to cover the entire cosmetic layer, resulting in five subtle-but-visible seams around the cockpit. Because the wider strips don't like to stay tight against the cockpit radius, you'll need to exercise a little diligence and watch carefully to make sure the carbon fiber does not pull away from the rim before the epoxy sets fairly thoroughly. I watched over my finished lay-up for about an hour afterward and used gentle pressure with gloved fingers to keep everything tightly in place.
Because I had covered the cockpit in Saran Wrap before laying up the coaming, my carbon-fiber coaming was not permanently bonded to the rim. I pried it off the cockpit, removed the Saran Wrap, foam, and masking tape, and then glued it back into place with a thick mixture of epoxy and sawdust (known to many builders as "dookie schmutz"). A day later, the coaming was thoroughly bonded to the deck. To ensure that it stayed that way, I sanded the coaming thoroughly and laid one last layer of 5 oz. fiberglass over the whole coaming, purposely wrapping it down under the deck to effectively seal everything permanently in place. Afterward, I used a block plane around the outside of the coaming lip to plane the lip down to the approximate width I desired.
Joining the Shearline
The process of joining the deck to the hull is fairly well documented by a lot of builders on other sites, so I won't go into great detail here. The one thing I will say is that this step requires quite a lot of patience. I gave the shearline one last sanding along the deck and along the hull to ensure everything was flat and smooth for joining.
To make sure the inside seam of fiberglass would be perfectly centered over the shearline, I attached dry 6 oz. fiberglass tape along the length of the deck and spot tacked it in place every foot or so with a small dot of hot glue. Half the thickness of the tape was allowed to hang over so that it would overlap with the hull. Once this was finished, I placed the deck on top of the hull and tucked the fiberglass tape inside from bow to stern. Then I taped the deck and the hull together as tightly and as closely aligned as possible. I used fiber-reinforced packing tape because I was afraid duct tape or masking tape would tear or stretch and allow the shearline to shift out of position. When I was satisfied everything was as well aligned as I could get it, I mixed up some epoxy, attached a paint brush to the end of a three-foot stick (to help reach up into the ends of the kayak), and started wetting out the tape inside from bow to stern.
The whole process took about two hours and the tape was a bit stubborn to wet out. I also had my fair share of runs on the inside of the kayak. To save sanding later, I tried to blot as many of them as I could, but in the end I still ended up with a bit of a mess. Regardless, the tape wet out successfully. I allowed it to cure for two days, and then I repeated this process on the outside of the kayak, except that I used two layers of 6 oz. fiberglass tape on each side. A day later, after the epoxy had cured, I spent a lot of time sanding to feather the thickness of the tape so that it would blend with the deck. Not wishing to weaken the shearline joint, I purposely under-sanded, leaving a noticeable, but small and not unattractive ridge running the full length of the kayak. At long last, the kayak was starting to look like a kayak.
The process of installing bulkheads is, in my opinion anyway, an exercise in "rough science." It may be true that some builders will be able simply to copy the station forms which correspond with the approximate positioning of their bulkheads, but in my case, because I had altered the shearline, I had to test fit and approximate the shape for each bulkheadtrimming and trimming and trimming until the piece finally fit into place with minimal gap. Different builders will have different standards of course, but I decided that any gap of about 1/8" or less was tolerable. My thinking was that even large gaps could be filled with epoxy and sawdust if necessary. In fact, I decided it was much more important to make sure the bulkheads did not fit so tightly that they might distort the hull or deck shape when wedged into place. For this reason, I erred on the side of a slightly loose fit, though snug enough to stay put while fiberglassing. Alternatively, I suppose one might cut a loose bulkhead and then hot glue it into place long enough to fiberglass it in permanently.
For bulkhead material, I used 1/4" thick Luaan plywood. After cutting each of the three bulkheads (one in the front; two in the rear to provide for my day-hatch compartment), and achieving a reasonably good fit, I fiberglassed both sides to seal them permanently from water penetration. Then, a day later, I installed each bulkhead by forcing it into place, sealing around its edges with "dookie schmutz" (a mixture of epoxy and sawdust mixed to peanut-butter consistency), and then glassing it into position all the way around with 3-inch wide, 6 oz. fiberglass tape. Because of the effects of gravity, I chose to glass in the bottoms of the three bulkheads first, and then flip the boat over about 7 hours later to glass in the tops. This way the fiberglass tape was sure to stay put while the epoxy cured.
All in all, it was a tedious, messy process, but the final results were quite good. For the sake of convenience, I only glassed one side of each bulkhead, but then later I sealed the back of each bulkhead with industrial-grade silicone sealant to safeguard against the possibility of leaks. Although I had expected it, I was still amazed to see how much the addition of bulkheads stiffened the deck. Now the whole kayak feels rock-solid!
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Copyright © 2004, Wesley Kisting