: . . . The twist is that I'd like to try a 3-piece skin on frame kayak as opposed to
: a wood-core composite; I can't find any evidence of anyone attempting to
: build a skin on frame kayak as a 3-piece, so the engineering hurdles may
: be beyond my capabilities.

It has nothing to do with your engineering skills. All the engineering problems were solved decades ago. The answers will cost you anywhere from $30 to $4500. For the low end, you can buy a set of plans for a wood-framed folding kayak from Clark-Craft. (www.clarkcraft.com) if you want to go with the high end, you can buy a complete Klepper. (www.klepper.com).

I picked up a copy of the Percy Blanford kayak plans (BK12) for his 13 foot by 27" folding kayak several years ago. There is also a plan for a 17 foot by 32" double (BK19) The frames are plywood and the attachments are made from brass or bronze sheet netal. You cut them out according to the pattern that come with the plans, (metal cutting blade on a jig saw) and then twist them a bit to get them into the right shape. If you didn't mind using rust-prone steel, you could find similar pieces already formed at many hardware stores, in the area where they have mending plates and screen-door hardware.

: It SEEMS straight forward enough, but the
: gunwale/chine/keelson connections to the solid bulkheads seem like
: definate weak areas. Reinforcing these areas with gussets or other methods
: might provide enough strength, but its hard to say just using armchair
: engineering.

That is one of the reasons nobody cuts SOF's into pieces. The long stringers which bend around the ribs or frames achieve thier shapes by the actions of the frames (bulkheads if you wish) pushing out on them at certain places. The pieces are in tension as they are bent. If you cut them then then they lose their shape s the tension is destroyed. You could make some very strong brackets to force them back into shape, but why bother.

It is a lot of effort and cost--and for less effort and cost you can make the whole thing fold up or come apart.

If you like Yost's designs, but can't find, or afford aluminum tubing, use wood instead. Yost uses pieces of smaller diameter tubing as internal connectors. You can make ferrules for your wood--just like those which are used on take-apart paddles--and use them as external connectors. You'll be using thinner wood for your stringers and keel thn is used for paddle looms, so your ferrules will be a smaller diameter. They can be round, oval, square, rectangular, or what ever shape your stringers and chine are. Make them from glass fabric and polyester resin. That is available at any Home Depot, or major auto parts store. You can use epoxy resin, but it is 3 times more expensive than polyester. Use ash or maple for your chines/stringers, make them as long as you can get away with, so you'll have fewer joints. A 3/4 inch to 1 inch square chine is going to be strong enough. You could use 1/2 inch wood wrapped with 2 layers of glass cloth, too. Make the bow and stem pieces from plywood instead of a bent piece of aluminum tubing (look at the plywood non-folders on Yost's site) Use stainless bolts and nuts for holding things together.

Hope this helps

PGJ