einhverfr
I'm a little bit qualified to answer that one.
Waves.
1/ Would make a controlled forced landing more gentle. Less friction/time. This is why seaplanes prefer a few ripples for take off. Nose down accident landing, with a nose into a wave face, almost infinite pressure loading on surfaces normal to that wave. Liquids are not compressible. Tail down 'landing' - waves wouldn't do much other than pull the nose down, perhaps violently (wave lengths and heights being just 'right')
2/ On floating bits of the aircraft. Any piece of debris with a Specific Gravity greater than 1, attached to a sufficiently large corresponding part with SG less than 1 will float. Wave action (cylindrical flow aligned normal to the wave peak) will have an effect on the piece. If the piece presents itself in the same direction to each wave (because it's shape vs wind/wave dictates that - a tall bit above the surface will keep that piece facing in the same direction wrt apparent wind angle, and or old wave train direction) then there will be repeated strains in a particular plane. If not, then there will be multiidirectional strains.
3/ If SG of the whole piece is less than 1, really very little damage through wave action.
4/ This applies to clothed bodies too. The heavier part is below the water, the wavelets will continually tug at loose bits thereto attached.
5/ At any angle of approach to water with a significant vertical speed you can treat it as concrete. Nose impacts, wings bend, engines off and tail at the end of the chain.
ps. The usual 45 degree thing applies. Hit anything square on fast enough. Terminal. At 45 degrees you might get away with it. Any less and you should buy a lottery ticket.