Thanks for the link.
According to my experience after a torpedo impact the destroyers will stay for less than an hour if they haven't managed to make contact (that is around 40min). If they make contact but lose it for some reason then, it will be certainly an hour. 1944 and onwards they might stay longer but i can't be more exact. I remember a destroyer pinging me for over an hour after i attacked a small convoy. This destroyer was its only defense (!) and was desperate to kill me. I had to go to periscope depth and launch a T IV torpedo.
What troubles me is the behaviour of the armed trawlers (the flower class ones). It stayed long after the destroyers had left and despite the fact that it had no more depth charges it kept pinging me. It wouldn't go! I had to surface the boat and attack with the deck gun. My watch officer was killed.
Question. How many depth charges a destroyer could carry on average?
P.S. Next time i will be ready. I'll have the "Knocking on Heavens Door" by Bob Dylan playing when the "Abandon Career" screen appears!
Keep pinging!