Hello,
styro core foils for a cat are a pipedream in my opinion.
Most foils on production cats(NACRA's and Hobies) are foam core. Marstrom carbon foils are foam core (Tornado's are hollow core), Mine are are foam core.
The techniques used to determine the shape and size of the core is very similiar to the techniques used to calculate ribs for aircraft wings, it dates to 1910-1920
You do have to taper the trailing edge
well,
i wrote styro core not foam core. they were talking about hotwiring stro like they do with remote control glider wings for a solcat daggerboard.
regular styro soaks water. extruded styro is very hard to bond to with any longevity.
Most all of the strength would be in the skin so you would have to calculate that thickness and subtract that from the shape of the core. you would end up with a pretty thin core which would leave alot of leaway for the shape to change as the blade got laminated.
the foam that is inside of molded blades is pretty strong and doesn't soak up water. Also it can be difficult to obtian, and use effectively. Maybe that's why some are hollow. hollow blades have to be molded because you wouldn't be able to laminate a foil made of air like you could with wood.
if you are making you own foil in your garage, shaping it in wood as perfect as possible and putting a very thin coating to seal out the water is the way to go.
