"Old Nick" wrote in message
...

My feelings:

As has been saidKevlar would be a difficult material to use to make
ribs as you suggest. Try epoxy/glass.

I cannot see any troubles. Although the foam is softer than wood, the
glass (kevlar) skin is what makes a foam/glass frame stiff, and stiff
it would be. Make the "walls" heavier than the "roof (inner) and
"floor" (outer) skins. make the floor heavoer than the roof.

I think this is where people often mistake stiffness versus strength.
Plain vanilla fiberglass is about the same stiffness as wood. In
other words, make a 1 inch by one inch by 12 inch stick of wood,
clamp it onto your workbench, and put a five pound weight on the
end. It bends about what, a half inch? Make a 1 inch by one
inch by 12 inch stick of fiberglass, put the same five pound weight
on the end, and it will bend about a half inch as well.

Now the fiberglass will support more weight before it breaks, but
it's also about three times heavier. Give me three times more
wood to use, and if I can make the beam a one by three, then I can
approach the load strength of the glass. Wood is good stuff for
resisting bending. I call it a naturally occuring unidirectional
carbon fiber reinforcement ;=)

I could go further into the engineering analysis and try to come
up with some numbers for equivalent stiffness of glass or
kevlar cored stringers. They'll either need to be larger in section
or solid glass. But in the end it sure seems like it's going
to be a lot of extra labor to build it that way, when the time could
be used to find some decent regional straight grained boatbuilding
lumber.

Just MHO.

Assuming that decent boatbuilding wood really is too difficult to
find, then I do like your idear of cutting kerfs on the wood stringers,
framing and skinning the boat, then filling the kerfs with epoxy/wood
dust and covering the kerfed face with glass.

Matt