Escape hatch reinforcement

I'd frame it

I'd frame it, as in wood construction, and glass over the frame. I'd core the frame with something like high density grass reinforced urethane foam, often called Penske board after a brand that was sold to Airex. Airex renamed the product to something forgettable. I'd also use a Baier all aluminum hatch used on commercial boats. Too many of these alleged 'safety' hatches have broken in a seaway, at great risk to the boat and crew. Go2Marine.com sells Baier hatches. -See http://bigcatcatamarans.com for some unusually seaworthy and user friendly designs. TD