I was thinking of making a very thin wood [or foam] core , then a layer of carbon fibre, and a couple of layers of regular 6oz. It will be one big single fin , and mould the base for a box fit .
I’d also like to do a set of foam core keels , then 1 layer of carbon fibre , then 2 layers of regular 6oz , then mould the base [epoxy] for fcs tabs , for my fish…
Lots of high end fin makers for windsurf boards use styro core, two layer carbon, and two layers outer glass for the fins from 13" tall to 24" tall. Stiffness is the reason, they want no flex for fins that are long and chord of 5".
Most use a carbon stringer for the first 8" of the base of the fin, to keep stress fractures from happenning.