Escape hatch reinforcement

[BigCat]

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