To start gotta clear up a common misunderstanding about "crash depth";
In the CFG file for the sub "crash depth" is the depth that the crew will level off at when you hit C to order a crash dive. In the ZON file it's "The maximum depth this ship survives", I think they really meant CRUSH depth but somebody translated it wrong.
While poking around in surface ship ZON files I found they actually have a "crash" (crush) depth too;
So lemmee see if I got this straight, a submarine designed to go underwater can survive down to 150 meters and start taking damage lower than that, but a light cruiser can dive to 300 meters with no problems?
That would explain this;
Dead in the water and sunk up to the smokestacks yet still firing at every US ship passing by. Tankers are even sillier;
This one has been hanging at that depth with two holes in him for over an hour, doesn't count as destroyed yet.
After some experimenting with a KONGO, I found the "crash depth" is not keel depth but depth below normal surface draft for surface ships. With a 990 foot deep crash depth before it starts taking hit points I can't figure out why they bothered, but I set originally for 30, no effect, then 10, then 5 4 3 2 etc. 2 or 3 is too shallow, normal wave action will sink a light cruiser in about half an hour or so, so I set the minimum at 4 for cruisers, 5 for CVs and BBs and 6 for Yamato. So far that works okay, no more half sunk battleships steaming off into the rising sun with 4 holes in the bottom and down by the bow with the number 1 turret completely submerged. Main thing it needs now is tweaking and testing, so a BB with so much flotation gone it's settled 20 feet deeper doesn't run off like there's nothing wrong, but we don't want one taking damage from settling 5-10 feet either.