How do they detect you when on the bottom?
 

I just had an end to my first campaign...its was short 10/09/39. After damaging a couple of troop carriers in a medium sized convoy off east England, i noticed an Escort heading my way, so i dived.

Not realising the relative shallow depth of 70m i soon hit the bottom...going to external view to check what the noise was about (im still new to SH5), i found my boat 'Actually' on the bottom (as in not floating 20m above it!) and to the side of a big boulder.

I decided to sit it out with all engines off and crew at silent running to see the result, sure enough the ASDIC pings picked me up and before i knew it, i was to damaged to move....despite letting of decoys, i was a sitting duck and the single relentless destroyer made many passes before finishing me off!!

My question is though, how do they detect you??, if im not moving, then they cant hear me, im not on the surface so they cant use radar, and surely Asdic will detect an object moving in the middle of a body of water, but if im motionless on the bottom, i would have thought it would just bounce of the bottom of the sea bed like it would off any rock or formation under the sea.

How can they tell that its a U-boat on the sea bed???

Sound bounces off metal differently than the sandy bottom?

I believe it has to do with how they hard coded the game. They didnt incorporate hiding on the bottom into it. At least thats how it is for us folks with SH3 Im not sure about 4 and 5 but Im pretty sure itd be the same thing.

If not my guess is he picked you up before hand on hydrophone (if you were making noise) or got lucky and guessed where your torps came from and just started making runs when he hadnt picked you up

it's does matters if you are moving or not moving,the ASDIC will detect you.the sound wave struck a submerged object like submarine and it is reflected back and picked up by the receiver .
you say how they detect me if i am not moving ,the answear is up.

Not necessarily. There are several incidents of submarines successfully hiding on the bottom in shallow water. The bottom absorbs the sound waves, or reflects them in odd directions. Also the sand absorbs the shock waves from the depth charges, enabling the sub to survive several hours of attacks. On the other hand, while we know about the few times this worked, we don't know exactly how many times it failed.

Unfortunately the game models none of this.

you talk here the u-boat attack in 1942-1943 which terorized the Saint Lawrence River(canada).There the u-boat was practically invisible,because was hidding by turbulance water of river,and remains undetected.The destroyers never get a solid contact of u-boat :rock:,u-boat was invisible :salute::arrgh!:.

In shallow waters and clear conditions I think it is possible in real life to occasionally simply see the submarine, especially from the air. Not sure if that would be the case in the Atlantic and 70m sounds pretty deep for this, though. And even if it was possible, I don't believe it's modelled.

Edit: I was thinking something along these lines. Those are in periscope depth, but you get the point.

I agree with Bogdanz. Its ASDIC that detects you. The seafloor is mostly flat, apart from rocky shore areas, reefs or deep ocean mountains which are not the case here. For ASDIC, a laying submarine is a clear obstacle of high density material (low wave absorbtion, high deflection). However, there seem to be a chance to lay in some kind of seaflor ditch or trench and thus make ASDIC detection very hard. In a book about Operation Paukenschlag I read about Hardegen's U-123 succesfully hidden this way once at the East coast of US.

No, I wasn't talking about that at all. I was mainly referring to the adventures of S-38, which attacked the Japanese fleet in the Lingayen Gulf in 1941. She grounded four separate times and survived over 36 hours of on-again-off-again depth-charging.
http://en.wikipedia.org/wiki/USS_S-38_(SS-143)

Hello,
Hardegen also reports being overrun by destroyers numerous times at a depth of some 30 meters, also Topp, also Prien, and some others.

"How do they detect you when on the bottom?"

They don't. In reality ;)

Greetings,
Catfish

There is no way to see the ground 70 meters down as water absorbs all light within 60 meters even under perfect conditions. Being on a plane obviously does not help.

I've seen the wreck of a ww2 corvette at about 35meters in the red sea from just UNDER the surface and you could barely see it even when knowing exactly were it was.

As the red sea is way clearer then the Atlantic/north sea and there was no distortion from the surface I'd say it's impossible to see a u-boat below 30m or so.

Very true MoN. However the issue here does not have anything to do with such an "organic" issue as actually seeing through water with eyeballs. It is simply that the game does not have that many variables programmed into it. Destroyer ping hits sub, sub does not move so contact is not lost, depth charges hit sub. That's it.

However, even if such things as hiding on the bottom were programmed in I think that sitting totally stationary in shallow water launching decoys as the OP said, would be a sure way to die even with the stupidest AI. "Hey! Look at all those obviously man made bubbles that keep coming up from the exact same spot!"

That's it exactly.
And this is unfortunately what has been obviously unchanged since SH3 :shifty:

They find you at the bottom regardless of depth, and they find you at periscope depth. With hydrophones, or with ASDIC/Sonar. Surface noise not modelled, sound channels not modelled, and if the probablity to find you is set to 0,1 (so they find you in 10 percent of the times) they will find you anyway, because after finishing the cycle they search again and will get you surely with the 10th sweep. Guaranteed.

Running silent with additional full stop 4 miles away they hear, ping, see and detect you everytime if they come near to 500 meters. And there is not even 10 meters of leeway, they find you exactly. Leaving the U-mark on you see that they will cruise exactly through that mark, directly above you, not a meter aside.
Maybe in late 1944, and 45, but never in 1939.

According to the reports of the time U-boat captains would run silent at PD with destroyers passing some 100 meter away without being detected, neither by using passive or active detection. They raced ahead, dived, and let themselves be passed by the convoy. Not so in Silent Hunter.
I wonder why they ever built U-boats in reality if it would have been that way. The only advantage you have is you will not be rammed, apart from that you could as well be a surface vessel, your exact position is always known.

I really wonder why one would enhance just of all the AI, if the vanilla one finds you that way already in 1939 ? :-?

But you can adjust the AI level, as i read - will sure do that in 1939.

Greetings,
Catfish

I always thought that behond the thermal layer approx 30m, Sonar waves would be distorted and thus find it harder to detect..thus being motionless on the sea bed at depths below 30m shpuld prove very hard to detect by all but the most experenced crew.

Its a great shame that the 'U-boat' sim does not 'sim' these vital and core gameplay tactics and effects, and also supprising, that no modders have endevoured to solve these core issues!

Lets face it, U-boat warfare leaves little to do apart from hunting / sinking ships, and evading being sunk by them...If this is'nt right.....

Hello Poacher,

this is not necessarily true - thermal layers are modelled in SH5 as far as i know, but you will not know if there is any change in the water around the U-boat, be it density or thermal layers. So sometimes you will not be heard, and sometimes you will - THIS is ok in my book. Thermal layers do occur, but not everywhere, and not at the same dephts. German U-boats did not measure the water to find out layers, thermal and salinity changes. Indeed i think the US boats were the only ones to do that at that time.

From what i read you would be relative safe in anything else than absolute calm waters at periscope depth, because hydrophones will not pick you up when being slow, or even running silent at less than 100 revs per minute due to surface noise.

As well mostly ASDIC will not pick you up there as well, since the upper part of the active ASDIC detection cone is NOT parallel to the water surface. Even if it was, the wave action in anything but zero wave conditions will screw this up. It works better in shallow undisturbed waters because the sound waves are then reflected from the shallow ground, going up at an angle, and thus being able to detect the boat. But where would you find such conditions, in reality ? Even in the baltic it is almost impossible -
There is one possibility of "bent-up" sound waves, if an underwater layer is thick enough to reflect, or even bend the waves in a transition zone thus being able to detect the U-boat. Does not happen very often, and was not so well-known in the early days.

So indeed the deeper you go, the more will enemy active ASDIC/SONAR be able to detect you, BUT THERE WAS NO DEPTH DETECTION UNTIL LATE 1944. They would just detect a 2-D contact, and throw charges at varying depths to hit you by chance.


But until "capturing" the U-570 (later tested as "HMS Graph") the Allies had no idea that a german sub was able to dive deeper than 80 meters, so you would be safe until october 1941 if you go deeper than that - the depth charges would be set to 80 at most before that date. In german transmissions depth was coded as "A", meaning "Achtzig" or "Eighty". 220 meters diving depth would have been 2a+60 meters, in a coded transmission. British submarines were not able to go anywhere near a diving depth of 100+ meters, or 300 feet. This is very seldomly mentioned, even today :dead:

If there is no thermal or other density layer, blue water conditions are perfect for active ASDIC later Sonar down to 160 meters, but not near the bottom, and not at periscope depth. Below 160 meters there is again a change in sound wave transmission, making detection harder again.
Some commanders never went down that far and survived nontheless. Erich Topp says in "Fackeln über dem Atlantik" (would that be "Torches over the Atlantic"?) that he seldomly dived deeper than 30 meters, because at that depth the boat's hydrophones were perfectly able to detect and hear an attack run when it began, making an early evasion possible. An attacking escort at full speed was deaf and blind until going back to slow again - unless there is another destroyer listening. But even then this other one will not hear the boat at full speeed as long as the other D. is at its attack speed. It was not easy to detect U-boats, until late 1943 - even then you needed a well trained crew.

Using hydrophones it depends on how loud you are (obviously). If you are going slow they will not hear you in reality, as well evading depth charges by suddenly going to full speed and then decelearating again after having changed the direction, will confuse them as well.

As soon as there is more than one destroyer and they use the run and listen tactics, you will probably be toast; until you are - by chance - at another depth than the charges are set to. Without depth detection they know roughly where you are, but not how deep (In SH3-5 depth charges explode at your exact depth already in 1939).
When Walker developed his tactics of using one destroyer for listening and ASDIC, and another for the chage run few U-boats escaped, but again: Not every destroyer crew was as well trained as the U-boat hunter groups, and convoy escorts usually did not have the time and training to do that - as well the noise of a whole convoy rendered the hydrophones useless. In the middle of a convoy a boat at PD will be roughly at a depth of the surrounding freighter hulls, and impossible to detect by passive or active systems.

It is a shame that you still cannot copy the original tactics and survive after three iterations of a "developing" sim, at least until 1943.

But it looks nice. ;)

Greetings,
Catfish