: First, I can't get a grip on your concept without some kind of visual and a
: statement about what you are trying to accomplish would help, too.
: I have read many discussions on building paddleboats with glass on plywood
: and glass on marine foam but never anything that combined the two. But
: there is nothing impossible about it.
: In general, I would say you will play hell trying to make something even
: close to a top-drawer plastic fishing kayak. Fishing kayaks are the domain
: of rotomolded polyethylene. The shape of and the accoutrements of a
: fishing kayak, both on top and on bottom,are relatively simple to do in
: rotomolding. A mold is quite expensive but it's potential for complex
: shapes is unparalleled. They can make hull shapes that are near impossible
: in any technique based on plywood and/or foam.
: Next, foam core may have a few design advantages but one of them isn't light
: weight. Glass on foam suffers from lack of resistance to penetration and
: the only way to get that is to use sufficient glass and a lot more epoxy
: which increases weight quickly. Epoxy is about 9¼ lb. per gallon. Thats
: more than the weight of water. Also, marine foam is very expensive and the
: rule of thumb is a foam cored hull will cost about twice as much as it's
: glass and plywood counterpart.
: If you are thinking about using houshold insulation to cut cost be advised it
: has already been done but has never caught on. I think it's because the
: stuff crumbles if subjected to a lot of flexing.
: If you want to build your design by all means go for it. But don't expect to
: build anything that competes head to head with what can be bought,
: currently. The pros have designers that are conversant with the mysteries
: of hydrodynamics. They have the know-how and the technology that can make
: a big stabile fishing kayak paddle fairly well for it's width so you can
: go way out there and tussle with very big fish and not end up in the water
: yourself.

Good answer

Bill H.