If I dive to 200m+, ahead 1/3 and set planes to surface my boat kind of skims along without sinking deeper. Above 200m DD's can hear me. Thermocline maybe?
Passive phones on ASW vessels I appreciate but they always seem to be making far too much noise for their soundman to stand a chance of hearing me creaking/RFSR at 25m? ASW trawlers I always find parked between Gib and Tangiers but the real McCoy(Tribal/BlackSwan/J&K)never seem to stop and listen....
Rich