I built a Bolger Elegant Punt once with four Lexan windows in the bottom, each about 14" x 6". I used it mostly in NE US waters -- i.e. not crystal clear -- and we found that you'd only get a good view of the undersea world when light conditions were just right. If bright sun was directly overhead, it didn't work. It had to slant in at an angle low enough to illuminate the water
, but leave the window in shadow of the boat's side. Just like with a viewing bucket. And of course you had to be in water four feet deep or less, otherwise you wouldn't really see the bottom anyway.
I'm sure it would have been better in clear tropical water, but for our use, it was a bit disappointing overall.
I've often been tempted to cut a viewing port into the hull
of our 31' Cormorant, down below where it would always be shaded . . . but for some reason can't bring myself to do it. . . .