This is NOT for the faint of heart. Cutting a large hole in your boat is daunting.
At boat shows I took photos of every cockpit hatch I could find.
To begin I used the cockpit drain channel as a guide. I tried to simplify the hatch by keeping the top flat. Once I sketched my cuts on the fiberglass I slowed down. Then I made a mock up of the size of the hatch opening using cardboard. Played with that for a few days waiting for a light bulb to go off - like opps I forgot about XYZ or whatever. After a couple of days all still felt good. I cut. The piece removed would be the hatch lid.
I had some cleaning up to do; filling some holes, adding and rounding edges.
Two of the most difficult parts to this project were the inside piece; the mold that would be glassed to the boat and the glassing of that piece upside down in the boat.
This was the first fiberglass mold I had built. I thought I understood what needed to happen. I was off a bit. I built the mold and sanded it smooth, sanded it with 320 grit. I thought that would be smooth enough. I then used mold release wax. Put it in place and was ready. Once glassed I thought I could simply pop out the mold and someone else might want it. The mold came out in pieces.
Glassing upside down was a mess. We had covered the inside with plenty of drop plastic. We cut glass pieces ahead of time. W/ would wet them out and bring them to me, I would put them in place building layer on layer to the desired thickness. We didn't get the thickness right with what we had cut so we hurriedly made some more and glassed away. This process took us close to 5 hours. We finished at 10 pm under flood lights.
A day later we removed the form. That is where I discovered I needed to sand with finer and finer grit paper before waxing.1200 Grit seems to be where I needed to get to. Fortunately I did remove the mold. Unfortunately it was in pieces.
Then I cleaned up the ragged edges or our glass job and prepared for paint. The final photo shows how it all came out.