I should have been more clear. I understood the damage and the way it was modeled, it was the fact that my props were about 10 feet out of the water spinning in the air.
I had been hit by a bomb dropped from a plane which caused some massive damage to the conning tower and torp room. I was able to fix the bulkhead which prevented me from completely losing it, but was then stuck nose down with no protection from the air.
I was unable to find any way to stay below the surface (and sinking like a rock) unless I was set on emergency back. (I would have loved to find that sweet spot like you did until I could get the torp room pumped out). I spent a good hour or so playing around with this trying to pump out the fore torp room, but no luck. I got it to about 1/3rd flooding when the next set of planes appeared. I cut the engines for a second to start my freefall descent, and when I came back up they were still circling and flooded my aft torpedo room. Needless to say, no amount of damage control and ballast could keep me from the 2000m drop.
And my recent thread about the savegame issues only made this worse as the whole mission was a waste (I had a game saved about 20min earlier).