I brought this up a couple years ago and someone pointed out this web site.
http://www.clcboats.com/shoptips_glassbottom.html

I have another idea. I would think that you could rough up some plexiglass and use it in place of the wood in a section of the bottom of the boat. Make sure that the epoxy will bond to the plexiglass by testing it first. The fiberglass would go on both sides of the plexiglass just as if it were wood. There would be no need to worry about it leaking like a bonded on plate.

The light in fiberglass cloth is scattered as it goes through the glass strands that is why it is white. Once you apply the epoxy the light can shine straight through the fibers making it clear. This is also why window dings on cars can be fixed by injecting them with epoxy making the window clear. For these reasons I believe the epoxy will soak into the roughness of the plexiglass and the light will shine through. If the bottom of the kayak gets scratched, it should be clear once it is in the water.

: While paddling this morning I thought "It would be kind of cool to have
: a window right there between my knees so I could look at the fishes".

: Any ideas on how I could build a window into the bottom of my next Guillemot?
: Is there something liquid that turns clear enough when it hardens? Has
: anyone done something similar already? No sense re-inventing the wheel.

: Dwight