I've found that the majority of floatplanes/seaplanes bounce in the air in free flight if you start on the water.

This problem can be overcome by adding around a 1ft increase to the COG in the aircraft.cfg.

The problem arises due to the wave effect on the water and the COG must take the wave height into account, effectively dropping the aircraft onto the water from above the maximum height of the wave.

I tested this by looking at the Previous flight.FLT in the PILOTS folder after exiting the game at the top and bottom of the wave and calculating the difference.

Cheers,

Aussie