me too, but only in real shallow water. Otherwise, move and try to get in the dd's back. And alway have a torps ready for a quick shot. But you have to be really lucky to hit something.

I managed to escape 4 destroyers and frigates in very shallow water near the canadian coast in stock SH3. The just lost me somewhere after a wild chase.

Basically, yeah :D

As I said, sitting on the bottom makes you pretty much invisible to passive sonar (hydrophones) as it eliminates all mechanical noise, but it doesn't help you much against active sonar (ASDIC).

Sonar fish-finders work pretty much because the sonar signal bounces off the fish's swim bladder (an air sac inside a fish that it uses to control boyancy).

BOLD decoys deployed on u-boats work by releasing a mass of bubbles that creates a return on active sonar that looks like a u-boat.

And an ultrasound imaging machine is basically sonar, just at a different frequency. The image on the screen is basically showing the density of whatever is underneath the transponder.

Just got back from a harrowing mid-'42 IXC patrol to New York. BdU, in its infinite wisdom, sent me to CA28, which is all shallows just east of New York. I managed to sneak in to the square and set myself up guarding the entrance to the bay leading to the harbour, when a Large Cargo crossed my bow. With the sneering command of "Be more aggresive" ringing in my ears I dared not fail to shoot, and sink she did.

What followed was a 15 hour escape in 12-15m deep water with DD's and torpedo boats going ape**** around me. Going silent I managed to evade most of them for quite a while until a Clemson stumbled upon me, and immediately started pinging me. This led to a second DD approaching, and my big, hulking boat, barely concelead beneath the waves seemed doomed. I had six torps remaining tough, and through desperate manouvering and very poor marksmanship I finally nailed the Clemson with the last of the six.

But the other DD was still on me, doing several DC runs. The trick that worked best for me, apart from maintaining a small angle to him, running fast when he was pinging and constantly turning away from his charges was a liberal deployment of BOLDs. Firing off two BOLDs I went flank, turned so that the BOLD formed a barrier between me and the DD and set off at oblique angles in respect to my initial course. After doing this four or five times the DD ended up attacking my latest BOLD drop for several minutes - allowing me to flank off to reach the critical separation I needed to loose him.

So all in all, 1 DD sunk, 1 evaded, survived 3-4 DC runs directly over my position with 100% integrity remaining - still can't beleive my luck :) (GWX 1.03 100% realism btw)

I am playing in 85% (contact updates on,100% in GWX for some reason) I only use the contacts update because its enormously time consuming to manualy plot and very difficult to get an accurate range with the periscope/UZO.. Although, this means no instant id of a target, no AoB, no speed. Just a generic description like destroyer, patrol ship, etc if you get a visual or warship, marchant if you are using your hydrophones. If i wat to shoot i need to enter the time of shoot distance (range), calculate the AoB for each target, Jim's tools (included in stock and GWX) will only help you calculating the AoB if you are aprox 90 of an incoming target.
Then you need to plot, count one minute at least and plot again for a speed value (using the charts). Real life Captains and people who really go 100% still have to plot and calculate AoB based on aspect ratio and whatnot. Its very risky and prone to fail letting a valueable fish go at a 35knots incoming destroyer. I never shoot at escorts or destroyers.
AoB, range and speed may not be important if the destroyer is coming towards you at 0º or 180º but mind the fact torpedos need 300m to arm. And the very shallow chance you have to hit an incoming bow. Maybe magnetic fish would prove better at this, but still very risky and bear the 300m to arm. Do the enemy sub hunters zig zag? I remeber that was a mandatory tactic for any human playing a DD (Destroyer Command) against human U-boats, SH2.
My point is, if you play 100%, in shallow waters, upon detection your only hope is to flank and manover until you can dive deeper.Its often better in my experience to even avoid diving for a couple minutes to gain some more ground, until the splashes in the water hit your watchmen.

The DD's do indeed Zig Zag when going for final approach on a DC run. That is part of the reason I used six torps to sink one DD, the slimy bastard turned in the nick of time, everytime... Grr :)