Given white waters ability to turn whatever you have made into chunks I second Davids comment about ensuring that the design has designated weak points for your safety. I would lean more towards a thin ply core 3mm with heavier and specific layups. With cost no object thin kevlar and s-glass would be a pricey construction, otherwise lots of multiple layers of 4oz and a layer of polyester cloth wood make for a sturdy and impact resistant laminate. You might consider vacuum bagging to keep the synthetics from soaking up too much but for the life of me can't imagine the setup. Consider foam pillars as needed. Carbon fiber is so much different than plywood in its characteristics that I can't see it's use unless it's everywhere in the boat, I mean wood is pretty stiff,carbon is ultra stiff so the wood fails easily at the bond. Make a bunch of panels and bang them around. keep us posted-lee