I can't take the credit - jimbuna told me about this hunting ground a while ago and I just applied my method to it.

On each patrol I go to periscope depth as I leave the harbour and work out what the detection range of my hydrophones is - it differs with the experience of the radio room crew. Once I have this info I can draw a circle of the right radius and know that I can detect anything inside this circle. It's just part of my shakeout routine at the start of each patrol along with test firing the guns etc.

:()1:

@Wreford-Brown
Drawing various detection circles is part of my tactics also. :yep:
But I usualy do the sound check myself, because I can hear a propeler noise long before my SO does, from about 30km.