Interesting.  West Systems has 207 special clear hardener.  I'd make up a test piece.  I can see it being translucent, but not transparent.  Maybe without the fiberglass, but that's sketchy.

Check out Tips for boatbuilders, fitting out, glass bottom Mill Creek on this site.

George K   

Thanks, George. Found it: https://www.clcboats.com/shoptips/fitting_out/glass_bottomed.html

Does anyone have experience with it?

   I think given the times I've patched scratches from oysters, rocks, logs, etc I'm not going to waste time on a plexiglass window under the boat.  I may be more adventurous than some but a boat is to use.

The clear hatches on my power boat get scratched, cloudy and don't show the bildge as good as expected.

https://www.clcboats.com/shoptips/fitting_out/glass_bottomed.html

My thinking on this pretty much parallels what other replies have suggested, besides a bottom 'porthole' being prone to leaks, breakage, etc.

Depending upon your needs and the size of the craft you'll be getting out onto the water in (and the depth and clarity of that said water) you might be better served by purchasing something like one of these thingys for your underwater activity viewing.