Boat Building Forum

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Material: Composite sandwich with foam?

In the various plans and technique books that I've seen, I notice that all the composites are either wood covered in fiberglass, or non-cored 'glass & resin layups. Is there a good reason not to use a foam core? I'm looking at some of the stitch & glue plans, and seeing that it would be very easy to replace the plywood with 1/8" or even 1/4" Divinycell foam, then laying over a layer of kevlar, and layer of s-glass, then a couple of layers of s-glass and some strategic carbon for reinforcement. Would this not make a lighter-weight boat compared to the S&G? It would also be stiffer than a plain 'glass & resin layup. I understand there would be a price impact, but other than cost what are problems with this technique?