The higher the speed the more water loses its cushioning effect. So an incorrectly performed water landing or landing into choppy water will severely damage a plane as in the Ethiopian saga. In Sully’s case, the water was smooth and he did a perfect landing, so the plane didn’t break up. I have a feeling our Bulgarian friends stalled the plane at some height above the water which is why they were injured. Fortunately those planes are built like brick outhouses 😀 The “hardness” of the water is noticeable in the boat at 30 knots already as it bounces on the waves.