maybe you all got 98% damage above the waterline, so that the ship is ruined but not sinks
try to distroy the hull below the waterline
I battered the bottom of the powerboat on the bulge of a big ship. You could see the massive holes at the bottom, but it didn't sink, and the damage showed as 0%.
I've also made holes in the bottom of ships with the damage showing in terms of appearances and %, but they didn't sink either. This is very frustrating.
It seems to me that no one has sunk yet, but it's still early days. In real life, if you crashed a powerboat into a solid wall at top speed, the powerboat would get crushed and it'd blow up. In SS08, the front of the boat will be crushed a bit, and you'd get about 14% damage, and that's it.
Still, the visible damage is a step up from SS06.