If you want to build one with foam core, it will have more twist and wobble than a solid core.
You Can stabilize the foam-core, (cradle) with ply on the flat side and 3oz glass on the airfoil
side ; then use it as you would use a female mold.
Stabilize the airfoil itself with 3oz glass , then make a female mold of That , to do
the lay-up in.
PFP molds are the easiest for testing, but a conventional mold of glass & epoxy , with
an epoxy surface-coat, is the best way to learn mold-making.
You can get Reasonable accuracy with Both these methods.
Seriously, if i was a Despicable Low-life, it would be EASY to mold a (state of the art)
hydrofoil, then build a copy from the mold. I got a cold Beer that says the ONLY
person here that could tell My copy from the real thing, would be the manufacturer
himself. The resolution would be a dead give-away, but i would spray the mold
with a clear-coat First, then do the lay-up and come back and shine the finish to
The point is :
"Ya do NOT need a $20,000 mold, to make Good parts out of" !!