Is it possible for ships clearly hit well below the waterline to remain afloat?

[Paul Riley]

Last night I hit a medium cargo in the foresection (one roughly below the stack and a second below the foremast) with 2 impact tips set to 5m.Just over an hour later the vessel began to slowly take on water and slow to a stop,and approx 30mins later began to sink on even keel.I didnt want to expend a third torpedo on it as I am currently in a small IIA and I only have 3 left,so this is the reason I hung around so long to see what happened.I dont really care how long it takes so long as that cargo hits the bottom!.
Would it be safe to say that this was normal for ships that had two gaping holes in their hulls,and is it also possible for ships to even remain afloat and carry on their journey? or,do all ships eventually sink in the end,due to a large hole being in their hull?
NOTE - I have the realistic sinking times on.

Cheers.