:: . . . A viewing box works because the window at the bottom reflects the
: dark interior of the box. Your face in the opening cuts most of
: the daylight from getting in, making it very effective.
: So a viewing box might be a fun easy to make solution. The issue
: with a kayak is leaning over the side to look. Maybe a little
: ballast on the bottom, a float collar (pool noodle?) wrapped
: around the outside, and a way to hook it onto the coaming to
: make it work like an outrigger. Be really neat if there was some
: wide angle lens, or maybe a convex mirror so you could see more
: than a narrow angle straight down . . .

It's difficult to get close enough to a horizontal window or viewing box to cut off the reflection of the bright sky in a kayak. What may work is a window in the bottom, between the legs, made so at an angle so you are looking into it more or less at right angles to the glass. Your body will tend to shade it, and you will then be looking in the direction you are going which will probably be more interesting, too. The boat will have to be rather beamier than usual in a kayak to allow space for the legs, of course. It will have to be below the waterline and arranged so air is purged.