Sandwich wood core strenght

D'ARTOIS: The plywood/kevlar laminate sounds very tough in deed! But, as I mentioned earlier I see probelms forming plywood in three dimensions (non-devlopable surface). What price would you estimate such a laminate to be per square meter? How many times thicker would a stripplank/glass/epoxy laminate need to be to be equally stiff?

I agree with both of you on the rigid foam issue - it should not be used in boat construction, at least not this kind of boat. I also see that I have missused the term sandwich a bit - I've been thinking of glassed wood as a sandwich composite. I'll use laminate from now on. My mistake, sorry.

My initial idea for the hull construction was to stripplank it using norwegian pine over a mould, or directly onto the frames and glass both sides with epoxy. Then start stripplanking a new skin on the inside of the frames, filling the cavity between the skins with 2-component Polyurethane foram as I go along, and glassing the inside when all the stripplanking was done.
My main concern with this approach was moist getting into the cavity and into the PU foam, as I have seen reports that some of these foams are not closed cell at all, despite them beeing advertised to be.
What I'm trying to figure out is how such a construction would compare strenght/weight to the glass/polyester and glass/vinylester laminates used in commecial high performance boats. Reading your posts I see that the whole foam idea may be best left alone? PU foam may be better suited for this purpose than the PVC kind mentioned by Karsten in an earlier post, it still leaves me without any way of inspecting for delamintion when the boat is taken into service.

 

Also; have a look at the "Saint Barbara", also made by Van Dam Woodcraft.
http://www.vandamwoodcraft.com/frames/currentindexmm.html under "Currently Building"

I may be wrong, but it looks like they have stripplanked the hull over a simple mold, and then applied carbonfibre and epoxy inside and out.
I belive this to be a very strong, light and tough boat indeed, and relatively straight-forward to construct.

 

Go for the "Saint Barbara" method if you don't like foam strip planking. The strips for the "Saint Barbara" are most likely made from Western Red Cedar. That's a common wood used for stripplanking. I wouldn't skin the inside of the frames and then glass over it again. The "sandwich" would be unneccessary thick and as you mentioned water ingress and delamination might become a problem.
I warn you from using kevlar. That material has very good tensile properties but is very bad in compression. Besides that it can "wick" water into the laminate. Stick to glass if you want toughness and use carbon if weight is a problem.