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Old 06-13-2020, 04:45 PM   #1
stellaferox
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Default ASDIC modelling in game

Hi,

I was wondering how ASDIC has been modelled in the game. i noticed that even at periscope depth the escorts can ping you from distance. Historically the ASDIC signal couldn't get a ping shallower than 40 deg to the surface. Anyone with that information?
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Old 06-14-2020, 11:46 AM   #2
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Destroyers in game usually make a visual or hydrophones detection, and commence an attack-run pinging in case you dive. That they are pinging doesn't mean they've made an asdic detection. If you don't dive, (and they'll assume you havn't if they make no asdic detection, then you'll get hammered near the surface. If you do dive, them of course that'll make it easier for them to make an Asdic contact, at which point only considerable depth will give you the time to evade whilst the DC's come down.
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Old 06-14-2020, 12:54 PM   #3
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Maybe the real life effective angle was 40 degrees with that type of ASDIC. But it could have been that the uboat would still hear some of it above that. Just not enough to reflect a solid detectable ping back to the escort. Every microphone or speaker has a certain fall-off directional emission pattern. The edges of the cone are usually defined where the intensity is halved (-3 dB) with reference to the maximum level. So with enough amplification it might still be heard outside of the angle.

Also, with hindsight as they didn't know this yet at the time, if the sun has warmed up the upper layer of water the sound rays keep curving back to the surface and bounce down shallow again. Creating what is known as a surface layer. That would make the escort been heard by the uboat at longer distances than the escort would be able to effectively detect it.

But I doubt this is modelled to real life in the game at the moment. Devs have made it clear that the finer touches on the game will be made later.
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Old 06-14-2020, 01:50 PM   #4
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Thank you. I am aware of this. But even if I lie completely still for a longer time at periscope depth they are able to home in on me using ASDIC. That doesn't seem right.
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Old 06-15-2020, 07:12 AM   #5
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If you are at PD and an escort or merchant comes close your scope will be spotted. Also, even with the engines off, active sonar will pick you up if you come within range of a searching escort.
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Old 06-15-2020, 02:25 PM   #6
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Quote:
Originally Posted by stellaferox View Post
Thank you. I am aware of this. But even if I lie completely still for a longer time at periscope depth they are able to home in on me using ASDIC. That doesn't seem right.
Lying still only means you are not producing engine,prop or waterflow noise. You could still emit ambient noise inside the boat that the escort hydrophone may be able to pick up. And being motionless does nothing to limit your ability to reflect active pings. Is your depth allowing you to be in the ASDIC vertical baffle zone? Well, apparently that is not modeled as such. Or it is shallower than you thought/history.
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Old 06-15-2020, 03:26 PM   #7
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Yes, I thought as much. It is clearly homing in on ASDIC and nothing else. Well, have to take that into account. Something for the devs to put on the wishlist. Realism for ASDIC....
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Old 06-16-2020, 11:16 AM   #8
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I'm not sure if thermal layer are modelled either.



And about sea floor, in my last mission I was 3-5m over the sea floor at 240m of depth. And the still managed to ping me, I repeated, move the uboat to another location and I stopped again pretty close to the floor. Again pinged. 4-5 attemps later I desisted. They shoud have problems pinging me at the sea floor, right?
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Old 06-16-2020, 03:59 PM   #9
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Actually lying ON the seafloor gives some protection as I noticed. As long as it is the range of 150 - 200m
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Old 06-18-2020, 07:54 AM   #10
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First, i have to admit i still have not played, but i will
As far as i read and followed the development, thermal layers have not been modelled yet.

Regarding ASDIC, from witness reports to what i read over decades i have some doubts about the accuracy and general effectiveness of ASDIC, at least until very late in the war. It is right that the systems got better over time, but most of escorts had an early type 141 or earlier on board, if at all. A lot of escorts did not have installed any.

Also it is unlikely to find a boat via ASDIC at periscope depth, for the same reason it could not be detected by it when surfaced. The ASDIC's detection cone for shallow swimming objects only works in very "special" environments, and mostly not even in completely calm seas. In most of the 50ies books about submarine detection this is still described as a big problem.
When waves are reflected from the ocean floor at shallow depths it is more likely, also a thermal layer can reflect upwards to meet a U-boat hull, and then being reflected back by already becoming inaccurate.
So even if the DE is lucky and gets a reflection from a certain direction, the real depth and distance are impossible to measure. If you think of atlantic waves and the general disturbance in the upper water column the chances for detection are small, to say at least. This has been modelled in some of the real old simulations.


If a boat still had been detected by active ASDIC at low depth, the contact would be gone by a distance of appx. 400 meters, from then on the DE would have to race to the last point of detection, guess where the boat turned to and at what speed, and also guess its depth.
Listening devices and ASDIC would also not work at higher speeds of course (which is why hedgehog and squid had been developed).
The DE also had to be quick to not become a victim of its own depth charge explosions.

The tactics and methods can be read quite accurately in C.S. Forester's "The good shepherd", though even this is highly optimistic for the time it is supposed to happen.

To make it short i doubt a boat at perisope depth could be detected by ASDIC in most circumstances . If anyone finds a good report on that, i would like to read it.
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Old 06-19-2020, 04:32 AM   #11
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@Catfish

You are right. They couldn't detect U-boats on the surface or at periscope depth. That is how Kretschmer got detected. One of the crewmembers shouted ALARM and the U-Boat crashdived from the surface whilst on attack on a near convoy. That way the destroyers could find him. There is good material on that on YT.

It is not modelled well in the game, same as layers. At that time that knowledge wasn't widely used though. I am still waiting for some significant updates on the game. The last one being september last year. Since then there was only a login update (which we cannot notice) and the addition of morse, which nobody uses. They have been announcing Scapa Flow missions, chartupdates and more challenging gameplay since september 2019 but there is complete silence on the weekly updates from the DEV-team. Not a good sign for an Alpha game. UBOAT has been developing much faster and is really attractive nowadays. It is a pity as I like this game very much.

I fear for the further development of the game
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Old 07-01-2020, 11:20 AM   #12
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I'd hesitate to ease to ease the risk of asdic detection, as in some ways this compels more realistic behaviour. For a start maintaining PD was not always easy, and so keeping to PD in daylight when hunted was a tactic with it's own risks. Firstly that part of the boat my accidently broach and be spotted, after which it was in for a very rough time, or, the much faster manoeuvering destroyers presented a risk of being rammed.
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Old 07-19-2020, 11:13 AM   #13
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Quote:
Originally Posted by stellaferox View Post
Historically the ASDIC signal couldn't get a ping shallower than 40 deg to the surface.
Where are you getting that from?



See also page 16 here:

https://acoustics.ac.uk/wp-content/u...nn_History.pdf

Last edited by AKD; 07-20-2020 at 05:06 PM.
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Old 07-26-2020, 03:13 PM   #14
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Thanks for this post. I don't know if this was the case in the beginning after the war. Anyway if you read up on how Scheppke could be sunk and Kretschmer was invisible on the surface until the dive alarm was (falsely) given. Then he showed up on ASDIC. Read the numbers in there somewhere.
Anyway ASDIC didn't work on surfaced U-boats of at periscope depth.
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Old 07-27-2020, 03:33 PM   #15
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ASDIC (searchlight type developed before war) could detect subs at periscope depth. It could also detect surface ships in particular conditions, although a surfaced U-Boat would be a small target, especially if bow-on.

ASDIC maximum range was against a submarine at periscope depth, typically given as 2,000-2,500 yards (in ideal conditions, perhaps out to 3,000-4,000 yards), although average detection range during the war was more like 1,300 yards. For a periscope depth target, contact could be maintained down to 250 yards or so, depending on signal-echo merge. Contact on deeper submarines would be lost at greater distances, which was countered with additional mid- to late-war tech like "Q" and "Sword" in illustration above that allowed ASDIC operators to maintain contact with deep subs down to the signal merge. However, ocean conditions could alter detection ranges based on depth significantly.

For the anecdote given, ASDIC performance varied hugely depending on ocean conditions and operator skill. Conditions can also alter radically during the course of a engagement due to depth charges and wakes.

Last edited by AKD; 07-27-2020 at 04:54 PM.
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