Cavitation and Acoustics in SH3

[Pillar]

Do the propellers of these old WW2 boats always cavitate, even at low speed? The graphic always shows bubbles coming off them, it looks like they are always cavitating.


Is there any modeling of the thermal layer? If so, where is it normally approx?


I'm trying to learn a bit about the acoustics as I'm not having much luck surviving destroyers in 1944. The usual pattern is that once they locate me for the first time, I can never "shake" them. I can usually do pretty good to avoid being hit by depth charges, but it will go on forever.

I've tried just sneaking away at silent running and slow speed after a depth charge run, and they always pick me up on active sonar. I've tried sprinting, but that really never helps. I don't know if they are just hearing my prop or are picking me up on active still. I've also tried brief sprints while the charges are booming, with course changes opposite to the direction the destroyer turns after his run -- nadda. Even bottoming the boat and cutting the engine didn't work out, because they pounded me with active. (Depth was about 150m)

One time I got lucky in an XXI (cheating, I know). I used 1/3 (one bell faster than slow) and must have got out of his active sonar range while still remaining quiet enough for his passive sonar not to hear me. However, I found "Slow" didn't get me far enough away from the Destroyer before he pounded me with active again, even in the XXI.

If anyone has any advice and can help me understand how the acoustics work I would most appreciate it.