Building the Sea Kayak

The boat goes together very quickly once you have the wood parts cut out and butted together. Two comments about the wood: first, I strongly recommend buying a wood parts kit from the designer because their pieces are machined from a master template, not cut and sanded, and you will achieve a much fairer boat this way. Since you're cutting both sides of the deck at once (with the two pieces of plywood stacked under the pattern), any slight waviness to your cut translates to double that amount of unfairness in the finished product. Next time I'll buy the parts kit: it's worth the price. Second, I don't understand why designers are still forcing builders to use butt-blocks, fiberglass butts, or worst of all scarfs. Why not just key the ends of the pieces like a jigsaw puzzle, like this:

This wouldn't be hard to cut with a jigsaw, and if you layered and clamped the three pieces before cutting you wouldn't even have to get it perfect. We used butt-blocks on kayak #1 and I wish I had chamfered the edges before installing them because we fiberglassed the interior of the cockpit and I had to do a lot of awkward sanding and filleting to avoid hard edges on the butt-blocks. On kayak #2 we used two layers of four inch fiberglass tape on the seams but this isn't exceptionally strong until the entire piece is glassed so be careful handling the pieces.

For kayak #1, we stitched the wood together with copper wire. Epoxy doesn't adhere to copper wire very well so it was simple to pull the stitches out. Those that were glued in place came out easily after a few seconds of heat from the soldering gun. Kayak #2 was stitched together with nylon cable ties, and the interior chunks of those ties are still buried in the fillets of the seams. I'm not worried about them ever rearing their little plastic heads, though. Stitching was much easier with the cable ties, and the raw ends poking from holes in the outside were easily sanded. They were strong enough to hold the wood with ease, even at the bow and stern where the wood is very twisted.

The major difference in construction between the two kayaks was that kayak #1 was vacuum-bagged after stitching the interior, while we vacuum-bagged the separate hull and deck sections of kayak #2 on a long table before assembly. The table consisted of three long folding-leg office tables with a plastic drop cloth on them. The jury's still out about which method was easier. It's certainly easier to attain a good seal on the bag when you're dealing with a flat seam on a flat table, but the separate panels required more fairing along the edges. My big mistake in building the first kayak was to run a length of nylon "truck rope" along the keel and underneath the bag. This helped get air from the ends of the kayak to the single vacuum port, but also left a mark along the entire length of the boat, which required endless fairing.

Kayak 2 bow, made of stitched laminated panels.

I read many accounts on the web of how Kevlar is impossible to sand. It's not impossible, just very difficult. When you sand it you remove some material and resin but you soon are left with no more resin and the material beneath simply gets fuzzy. At this point you have to saturate this material with resin or fairing putty, wait for it to cure, and start again. Needless to say it's a tedious process so unless you're really into Kevlar (obviously it does have incredible abrasion resistance) it's not worth the trouble unless you really take a lot of time to do it right. Our second attempt was more successful since I ran the rope along the edge of the table, but the smooth panels were soon corrupted with stitches and fiberglass tape. If I did another kayak from Kevlar (which I probably won't) I would be tempted to use a spray-on epoxy-compatible gelcoat since I ended up covering the entire hull with fairing putty anyway.

I wasn't getting a very good seal on the first boat's bag, since I was trying to laminate the Kevlar fabric on the entire hull at once. I had a strip of bag sealing mastic tape along the hull at the sheer, but epoxy from the fabric was dripping onto it, and when it's wet it's useless. So I ended up wrapping the entire kayak in plastic film sort of like Saran wrap. We had a giant roll left over from my company's move and it worked very well after I applied several layers. The only problem was that it bonded to epoxy so it ruined most of my breather fabric. Breather fabric can generally be reused, if it hasn't absorbed too much resin. However, it will probably leave some kind of impression on the surface from the hard resin in the fabric when you do reuse it. I used a perforated release film on the first boat to limit the amount of resin squeezed from the Kevlar, so my breather/bleeder fabric had small dots of resin all over it. When I reused this fabric on the deck parts, they ended up with small indentations from the resin. So for a perfect surface, use fresh breather/bleeder fabric.

Vacuum bagging.

Incidentally, the Saran-wrap method didn't work at all on the table. I can't figure out why except that it might not bond to itself very well unless it's wrapped over a slightly convex surface. Luckily I was doing a test and not the actual bag at the time, so I was able to go back to plastic sheeting and mastic tape.

The only advantage to bagging on the table was that we could bag two pieces at a time. First we did the hull bottom pieces, then the hull sides. This enabled me to make two fewer 18-foot cuts in the Kevlar fabric. Kevlar is almost impossible to cut and you will go through shears faster than 7-11 goes through sporks. After it's been laminated, though, it cuts relatively easily with a jigsaw.

See the vacuum bagging page for more details.

Overall I think the vacuum bagging was worthwhile because the breather fabric weighed at least 4 pounds when I removed it from the hull. The final kayak weighed 41 pounds before outfitting, which is much lighter than a comparable fiberglass or roto-molded boat, and it would have been 10% heavier without the bagging . I think the combination of marine ply and fiber reinforcement is probably the optimal small boatbuilding material, which is one more reason to build your own instead of buying a factory-made boat.