Cool idea! :|\
I can only give experiences I've had with extremely slow sinking ships, and I can say that on three different occasions, I've waited at least eight game hours in various locations watching over a sinking merchant and waiting for it to sink (this has usually been in a Type IIA and I'm out of torpedos!)....
Even though the effects are nice, the lapping of water into (and onto) the ships, it seems to me that the sinking ships (and also my U-Boat) never really moved in regards to ocean movement....also, my position, as far as I know, never changed on the map (I like to look often at the TDC map screen to get a better idea of what things look like, even though I play at 100% realism, and I still don't see too much...I simply like the close up protractor).
Hope this helps,
-Jeff