Something which is not simulated in SH3 is that the british depth charges didn't "work" deeper than 600 feet (183 m). In practice, some german commanders went to 800 (244 m) or even 850 (259 m) feet to avoid DC...
... according to this video (at 13:53) :
So, a way to simulate this is to limit the ASDIC range to 183 m, but this is historically wrong...