[Dogfish40]

Here's some more stuff to try. If you're being actively pinged, lower your boats profile by steering into or away from the ship that's pinging. This should be easy as you want to get away anyhow, so your course should lower the amount of surface area for the sonar to bounce from. Anytime you start hearing pings and you know the source, steer directly away (or into) the source.
As far as passive sonar, three biggest rules are, Silent Running, Silent Running and if you want to get technical, Silent Running. Keep your Knots very low unless they've found you, then scurry away to port or starboard at Flank then get Silent again. If a certain amount of time goes by and they can't reaquire you they will leave.
All the rest has been said by these other fine Kaluens especially to watch out for the shallows as they are sure death. At some point we all get Decoys and they will help as well.
Good Hunting Herr MidnightRider1818