Take regular depth soundings from your sonar man. A lot of relatively shallow waters, especially in the North Sea! The enemy cannot hear your ping so there's no excuse.
Depending on how damaged your hull is can change how deep you can successfully dive, however, even if your hull integrity is in question it won't stop you diving - you'll just increase damage/flooding and eventually there will be no way back to the surface, you'll just die a horrible death. But it's only a game
