Boats (Flying boats ) with a high wetted area are prone to a lot of drag. Wave action causes air to get under the hull and reduces it.
Jemima is a Searey and several Searey pilots have experienced what we call a "suction effect" on glassy water While on the plane (up on the step) on glassy water a very slight forward motion of the stick causes more hull area to be in contact and raises the drag enough so that between a high thrust line (above the high wing) relatively high CoG and the low drag line the nose goes down, causing more drag, etc, etc and the aircraft goes base over apex.
This is in addition to the common problem of discerning height in the last few feet of a landing on glassy water. (It can be literally impossible to judge even up to forty or fifty feet.)
One technique in float planes when taking off (as mentioned above,) is to lift a float when you have enough lift to do so reducing the drag to that from one float and allowing a heavily laden aircraft to get a little more airspeed. Flying boats don't have that opportunity.