Here's a picture on the avoiding thing:
If you manage to shake them off for an instance, in GWX I remember sometimes being able to just keep a steady silent course with no changes to the course. In NYGM that wouldn't work, at least to my knowledge. Of course the 90 meters depth might make that impossible.
And what the picture doesn't take into account is the fact there is a 3rd escort that you also need to avoid. It is probably making DC runs against you as well, so probably the spotter is the one that you need to avoid most.
The depth charge attackers lose contact momentarily after every run. They can't ASDIC to their stern. The spotter who keeps listening to you might have a contact on you all the time. He's the biggest threat, but he is also slow, as he needs to be almost dead in water in order to hear you.
Use your speed bursts to gain distance to the one who is listening. The speed bursts are not only for the purpose of avoiding the explosions.
One thing more. You probably know it already, but some others might not know that the sound of explosions in SH3 don't hinder the escorts from listening to you. In the good old days with Aces in the Deep, you almost welcomed a good DC'ing because the ruckus enabled one to cruise away at flank speed until it was quiet again.