Evading: when to go flank speed?

[Brag]

The area in which asdic or sonar looses you depends on your depth.

Imagine an inverted cone above your sub that ends at the surface.

If you are at periscope depth the cone will be smaller that the lenght of the U-boat and the escort will not lose contact till on top of you.

As you go deeper, the wider the cone will be at the surface and the further away your escort will loose contact.

When in the baffles, he can´t hear you, nor when depth charges explode.