I wondered if they are seeing your periscope - night/day attack? - instead of the torpedos wake...
Either way I use Webster's Ship Maneuvering Fix for v1.4 and v1.5
http://www.subsim.com/radioroom/down...do=file&id=942
And as vanjast suggested - it will definitely help with the jackrabbit starts and 20 yard stopping power.
Good luck and happy hunting!