In answer to a question about how Elbe & Furie sink, I posted pictures and explained that, in deep water, most ships simply settle, some by the head, some by the stern—usually depending upon where the superstructure is.
In shallow water they may not go completely under, and may list depending upon the bottom contour.
If you want to watch a ship sink completely, do it with a trigger in the mission editor.
It is difficult to do it in free-roam.