I noticed this also when I had the realistic sinking time setting checked. Not sure why, but once I removed that setting I started getting a lot more variety in the way ships sink. A little off topic, but try using the deck gun with armor piercing ammo. Aim just below the waterline of the ship and start pounding away. If you do it along the length of the ship you should be able to produce some good capsizing scenes. At any rate, it's fun to watch the ship start to list after a while in the direction of where it's taken the hits.
