BIG AK… the rails are hallow and built up with 1/8” cork strips then shaped. There is also cork between the decks at the fin ‘hardpoints’ and the holes for the fins are drilled oversize then filled with epoxy and re-drilled at the proper diameter.
These hallow boards we’re building are glassed inside and out using 4oz s-glass making them stronger than conventional surf/kiteboards. Haven’t sold one yet… too busy making boards for ourselves or friends while experimenting and refining the build process. They actually go together rather quickly believe it or not. Check out the website… MahaloBoards.com