I have difficulty in accessing and so maintaining the rear end of my engine and beyond. Serious maintenance of prop shaft etc.. would require the engine out at present
I am considering a cockpit sole hatch or hatches in a small but very sea worthy GRP yacht, circa 1973,with generous sole thickness.
I want the hatches to be very strong and watertight and of the highest quality, yet fairly quick and easy to open for access.
What suggestions please?

Several ways to achieve it. One is a commercial hatch, but it will protrude and be difficult to walk over, so you might have to make a grating to give a level floor to the cockpit.
Or you could see if there are any flush hatches - I have seen white rectangular hatches at Force 4 with recessed handles.
Final option is to source some bolts and nuts and make it yourself. You will need to cut the outline very carefully, then use the cut-out piece as the hatch. Add a flange below the cockpit sole, made from epoxy-coated ply, plenty of area because of the weight it will have to bear. Then make a seal using closed-cell neoprene rubber foam, and bolt the hatch down - not quick release, though!

I had this problem and solved it by fitting a proprietery inspection hatch. They will not stand walking over, so amended the teak grating so as to cover the hatch and provide support. Works well.

Thanks Simon,Alan.
Iv'e seen some excellent DIY hatches but although my skills are sound, my time is limited so quality hatches would be a way to solve this in shorter time possibly. Alan, what make/type of hatch did you use?
Scotty.