I think that is how active sonar works. The ship sends a sound pulse in a direction, and listens for echoes. The devices for sending the sound pulse couldn't be directed downwards, so once you're close enough to the ship he can't ping you.

So, in order to avoid active sonar, being pinged, you must be either far enough for the sonar to not reach you effectively (out of range), or deep enough and close enough, that the sonar beam overshoots you. If neither of these is possible, presenting as small a profile as possible helps lower your echo very much, possibly allowing you to not be detected. The further away you are, the lower your echo. Your speed or sound level doesn't effect the ability of active sonar to find you.

Hydrophones, on the other hand, are passive microphones, and they can detect you from any direction, except from the baffles, where the sound of the ships own engines and screws will mask any other sounds.

The most important thing when avoiding passive hydrophones, is being as quiet as possible. Distance helps too, both downwards and horizontally. Furthermore, a thermal layer may greatly reduce the ability of hydrophones to hear you. Keeping a low profile, which was the most important method of avoiding sonar, does nothing to help avoid being heard by hydrophones (except that keeping your stern pointed towards the listening enemy usually moves you away from it, thus lowering your sound level.)

Whether or not the ASDIC is audible to humans depends on its frequency. Generally, or so ive read, earlier ones had a frequency in the higher spectrum of human hearing, and later in the war there were even higher frequency ones that people couldnt hear, but feel because the boat would vibrate.

Ok... so what if you would back up silently with your nose to the enemy instead of heading away with your stern to the enemy.. Would your own boat's profile mask the sound (blocking it if you are facing the enemy on 0 degrees)?

Your boats profile doesn't mask sound as far as I know, at least not in the game. Perhaps realistically speaking, if you moved in reverse, your hull would be in between the destroyer trying to listen for you and your screws, which generate noise, dampening the noise a bit. Moving in reverse is slower though - the same RPMs would move you a bit faster ahead because of the submarine's shape. So moving ahead is probably a better idea anyway.

In game, your sound level depends only on engine RPMs and silent running status (repairs, loading torpedoes etc. cause noise), as far as I know. Your depth and distance from the ship listening for you determine if this sound will be heard or not. Your aspect or direction of movement do not matter.

But if the listening enemy switches to sonar instead, aspect immediately becomes the most important factor and sound level isn't important anymore. Unless, of course, some other ship is still listening, or the ship using asdic switches back to passive listening.

Thus, moving as silently as possible and maintaining as narrow a profile as possible is always the best plan.

I stand absolutely corrected...

Evasion Advise?
 

Pray they don't have Hedgehogs! :dead:

:)

Are hedgehog and squid launchers modeled in the game for the later war?

Real life? WW2 submarines couldn't stop underwater, and trying to back up while submerged would make the boat extremely difficult to control. You'd probably make it worse if you tried that. Even surface ships are difficult to control in reverse.

Hedgehogs are modeled in the game. :damn:
Squids are not.

Depth is your friend. Late in the war, your best chances of survival are to go as deep in the yellow zone as you can. An undamaged sub can go right to the end of the yellow zone no problem. Once my boat sustains any damage, I no longer go after escorted targets as I can't go deep enough to get away.

Amen to that, although I'm still in the early war, I've started to push the depth limits of my boat once discovered. Yesterday I shook off two destroyers after a convoy attack by submerging to 210 meters in my VIIB. I'm running GWX which I think will let you go a bit deeper than the yellow zone... providing you are undamaged ofcourse.

Each time I get a new boat, I take it down until the crew start's screaming about taking damage. Then I take it back for repairs. That's my shakedown cruise. Then for each patrol I take it down to my prefered escape depth (usally >200m) to make sure it still goes that deep, and then continue on my patrol.

In the VII's I would usually take damage around 230m, while the IX's I've tested recently have pegged the gauge with no problems, so at that point i gave up. So in the VII's i'd evade at about 200m, and the IX's 220 or so. I do have randomize crush depth on, so that's why I test each boat each patrol.

I've never been that brave. It seems to me in SH3 once the hull starts taking damage you're screwed so fast you have no time to recover.

Steve

If you want to test your crush depth, I think it is safe to keep going down untill the glass in your dials break, and bolts start working themselves loose. Once you start to see visual damage to your interior, you can begin to surface at this point and you should be fine.

Yes you can. At least this is my experience with Type 209 Subs