For what it's worth, if I have no damage I have no hesitation in going to the crush depth (red needle) and a bit more if necessary with no detrimental effects. Depth is your friend particularly if you can get a couple of thermal layers above you. Again, patience is the key. Always try to minimize your profile to the 'hunter' (difficult when you have a pack of them on your butt!).
I try to use the depth charge explosions as cover and increase speed during all that noise and cut back to 1/3rd when I think the depth charges are done. That's a pure judgement call as the Captain. If I know a destroyer has got my number on a run I'll hit the gas as he's coming in, noise be damned!
Keep changing course but remember at 1/3 speed course changes take time and pick a general direction away from the convoy etc to try and increase the gap as much as possible.
Above all, patience, patience, patience and try to stay deep and quiet.
