I was on the same conversion course (from Shackleton to Nimrod in 1970 ) as the pilot who ditched the Moray Forth Nimrod 25 years later.On the course we were shown film of Nimrod model ditching trials .
The model, which was of scale strength, and fitted with g recorders, was projected into a large water tank at diferent pitch attitudes, yaw angles, and with different "sea states" It showed that at a reasonable angle and sea state the ditching would be survivable. It also showed that the fuselage would break at a point in line with the trailing edge.
The day after the ditching there on the front page of the papers was an aerial photo of the Nimrod afloat, and broken exactly as predicted.
As I recall (long time ago now) there was also film of other military model ditching trials. The Beverley looked like a duck taking to water.
It makes sense to do such trials for a maritime aircraft, and perhaps for other military aircraft, but I am not aware that civilian aircraft are similarly tested.