Well i was hit(rammed) in channel by nasty DD and as a result of heavy flooding in stern i hit the bottom(some 40m)....For the next 20-30 mins the DD was buzzing all around me and droped a LOT of DCs but none come near close to make any further dammage to my sub...Eventualy he left me on the bottom to fix my ship and return to port(i was returning anyway)....so i think there is some conections between sitting on the bottom and detection cappabilities of DD...