MJH. Apples and oranges. Extruded aluminum is quite light in thickness in comparison to aluminum which a fabricator might use. Cast aluminum is used on commercial fishing
boats and while heavy, extremely strong. I have four and they are about 3/8 to 1/2 inch thick. They open with a tool or a built in bar. Fish
boats, USCG boats, commercial
boats...all trust them for deck
hatches. The drawback is cost. If you can find a good aluminum fabricator, they could TIG weld you hatches which could replace your teak hatches without a lot of glass work on your boat
. You could use plastic or glass lenses. My pilot house windows are laminated bank glass but I don’t lift
them up like a hatch.
I purchased four “ Ocean “ hatches ,top quality... nothing but trouble. The smaller sizes are passable but the 24x24 are just too light. The gaskets shrink, one weld failed and one lense split. You just need more aluminum to give you the rigidity, you need to stop any flex and the force of the sea.
Find someone manatee size and have them jump up and down on your hatch.
If it holds, you can call it seaworthy