When SH4 claims to be a simulation it's really not better. Try to repair a damaged pressure hull after it was hit by a 3 od 4inch HE shell. The hole isn't just the same diameter as the shell caliber

The devs made here a very good work making the boat unable to dive after such a hit.
EDIT: I was thinking about the silly situation when u can see inside your boat through the 20inch hole and want to dive even to PD. Not sure if such a damage can be repared in SH4 at all, perhaps its still there because to serious to repair and it isn't simply shown in the repair screen.
but nevermind, I'm to tired right now to discuss it. time to sleep

happy hunting