Actually on the hook you will prefer the hatch to open to the windward forward position. When it's hot you really want the breeze. You can't sail with a hatch open as the sheets
can catch it no matter what. I really don't see waves causing the hatch to lift
. Our last boat had home made hatches about 24 inches square. There were 5 of them. The hinges were external and one end screwed to the deck
and the other to a 1 by 2 teak
frame. The top was 1/2 inch lexan
screwed every 3 inches around the top. They were quite strong and you could jump up and down on them. There was a raised edge on the deck
did not creep under the hatch as the frame did not sit flush to the deck. You do have to watch out with hatch frames as you will get water
between the parts
so it needs to drain out. It's almost impossible to make the hatch totally water tight so you need to design it so it easily drains (hopefully out of the boat).
The forward edges of the hatches has hand wheel
screw down dogs on the interior
so you could lock the hatch down. Even in pounding waves we never had a trouble with the hatch over the V berth dripping.
If you make the edge around the deck raised so the inside of the lexan
top hits the top of the ridge you could put a seal there so water can't come under, up, over and down. Two inches worked on ours and we had really no rubber seal just wood on lexan. The hatches were made in 1989 and even today the the new owner has no problems with them other than a little crazing. Don't make the hatches too tight around the sides of the lip so water can drain out as it will get under the edges. If it gets trapped in there even teak
. The lips around our hatches were of two varieties one hatch had a teak raised edge and the rest had molded ridges from when they laid the glass for the deck. The latter is of course better. If you dog the hatch from the inside no wave can lift
the hatch. Even a pry bar would be difficult though possible. I may have some pictures if it's something you have interest in.