Sorry to have to disagree, but I also would really like more acurate depth charts, and not for the reason you seem to assume above.
You are absolutely correct that trying to go possum on the bottom when active sonar is pinging away is not a reasonable tactic. No argument there.
However, and here is my beef. I've just successfully put two into an Ammo Ship, 2 into a large tanker, and 2 (rear) into a medium merchant. I am running silent, in the middle of the convoy, parrallelling their path, heading for 100m, where I intend to go all stop and wait for the convoy to pass overhead to the horizon (its early in the war, I'm in my 2nd flotilla IXb, and the escorts still haven't got onto active pinging yet (why not?)). All of a sudden, at 85 m there's a sound louder than 2 whales humping as I bottom out, do some moderate damage, and alert every escort within 10k as to my location! Not happy, Jan!
So, yes. A man's got to know his limitations.