It’s done in a ‘‘sag mold.’’ A polycarbonate sheet is heated, and allowed to sag into the mold cavity. A mold for each side, top and bottom, the parts are then assembled in a ‘‘clam shell’’ fashion, at the perimeter. Some single piece aircraft canopies are formed in a similar way. Heat and gravity.
Once it comes down to building molds then vacuum infusion becomes reasonably straightforward. Female molds for both sides, hit it with mold release, lay the dry cloth >> peel ply >> infusion media >> vacuum bag. The shell comes out finished. The hardest part would be how to lay the peel ply and bagging material cleanly on the “core” side of the shell so you don’t get wrinkles or bridging. I guess that’s where the ultra stretchy bagging film comes into play.
I think it would be easier to just use an existing board (sans fins) as a male mold, hit that with ton of mold release and simply do a hand lam past the apex of the rail for each half.
That got the wheels turning GDaddy…
hmmmmmmmmmmmm
did a quick search and found this, to illustrate the point