Question for glass experts and repairmen

[rhafley]

I need to build a structural panel that's 40" x 18: x 3/4" thick, it will have a heavy load. My question is this:

Would it be stronger to use 3/4" fir marine plywood straight up OR 1/2" fir marine plywood laid up with epoxy and stitched mat and fabric on each side to make up the thickness?

[CastingCall]

I'd opt for 1/2", perhaps with 1/4" "shims" under whatever areas need to achieve 3/4" thickness, then cover with a couple layers of cloth and epoxy resin on each side.
Check out Boat Builder Central - most all of the composite construction boats (plywood/epoxy/cloth) those folks build use 1/2" decks and they have no issues.