Two layers of 5" (125mm) polystyrene foam with a plywood web/stringer glued in between. The vee side will be the top, but he bottom will be round. I like amas to shed water quickly when rising out of a wave.
Now all I have to do is cut away everything that doesn't look like an ama.
Unfortunately I have some paying work that needs my attention, so progress will slow down for the next week or so.