Originally Posted by jfdubu
Just out of coureosity, has anyone thought of or used the styrofoam insulation panels rather than plywood or balsa? My guess is it would be as strong as balsa, not so much with plywood. But it would never absorb any more water and would be much easier to form to the cavity.
I've made plug molds with it using west system epoxy so the chemicals shouldn't dissolve the panel.
Better than balsa, plywood or styrofoam (which has little strength in compression, and would therefore be a disaster), a friend of mine runs a company that produces MacroCore. This is the core material used by the US Navy for their new destroyer. It is a lightweight, epoxy based, high strength, closed cell syntactic foam which bonds well with epoxy based resins. Because it is epoxy based, MacroCore would not be affected by moisture. I used some in a small core repair that I did around a chainplate.
To learn more, see this link; MacroCore
They are not in the market for small boat repair, but if you contact me, I will make an inquiry on your behalf.
DISCLAIMER: I have no financial interest in this company or product. Merely passing on information about a little known option.