Fortunately, I've never had a long encounter with a destroyer. Anytime I have ever tangled with them I have been able to lose them with little effort. I don't understand why this has been such an issue for so long. I've browsed many a threads about "uber" destroyers and the like, all stating the extreme difficulty of shaking the would be death dealers. Perhaps I have a bug in my install? I always tend to stay in water over 1000 meters, but I have attacked harbors and convoys in shallower water before as well. Sometimes, in foul weather, I will wait until an escort is within a 1000 meters distance before diving when attacking convoys while still evading them. I always dive deep from the get go as well. Say, 150 meters to start. Then deeper if charges are getting too close. I would say no more than a half hour of game time has been the longest I've had to dance with an escort.
Maybe, I'm just a superb u-boat commander! (just kidding)
Jazer