: Bill - yes I confronted this problem in the model. I attached the chines to
: the hulls individually, but the hulls picked up some curvature from my
: not-very-flat dining table. Lack of inner chines (the model has ply inner
: faces) meant there was no opposing chine tension to hold the hulls
: straight, so they were also kind of floppy. To solve this, I clamped the
: two hulls together and added diagonal braces (bamboo skewers) while
: clamped straight. The result was pretty amazing, dead straight hulls with
: very little flex. They look and feel like fat model airplane wings.

: I like your idea of gussets, and they may be enough stiffening to avoid using
: the diagonal bracing. If I could find resin-impregnated paper tubes like
: we used to make airplane fuselages when I was a kid, I think they would
: make good braces, but gussets would be better. I think it will help to
: have at least one chine on the inner wall to help balance the outer
: chines, and ply walls will add little flex resistance in the lateral
: direction unless they have a good vertical camber - seems like this will
: take a great deal of work the first time through, but may be the best in
: the long run.

: For building the prototype, I plan to jig the hulls together as in photos 34
: and 40 at the link below. Even though the inner hulls on the full-size
: boat are not flat, I'll use spacers to hold the bulkheads a couple of
: inches apart for the build - this will allow the outer chines of the two
: hulls to oppose each other until the frame is pegged and glued. It should
: be almost like building a regular boat, plus the bulkheads will definitely
: be at the same location, you can use your eye to judge symmetry, etc.

: BTW - I forgot to ask - I was going to buy 1/2" marine ply for the
: bulkheads, does that make sense to you, or should I just get birch ply?
: Thanks, Carl

Hi Carl,

That's a good solution, should have thought about that, just sticking the hulls together back to back to build them

I've added an inner chine roughly in the middle from the deck to the keel, also this will support the fabric on the flat inner hull side. My hulls are designed to be 15" from the deck to the keel, that's alot of unsupported fabric and without some support I suspect the inner hull shape in the water would be concave, probably not the ideal.

On my first Yost kayak, I used birch ply for the frames, will likely use it on the prototype, okoume would certainly be lighter, but it's fairly pricy for a prototype. I'd suggest looking carefully at who you buy the ply from, I got my first panel from Home Depot and it looked great with no visible voids, but delaminated really bad so had to scrap that set of frames. The second set I got from a smaller local yard and it was excellent. Luckily these frames are tiny so even with birch they don't add much weight. Might even get the entire set of frames out of one sheet of "real" baltic birch, but since those sheets are only 50" x 50" would probably require more.

Bill H.