Sound detection array (GHG) speed

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Ulrich Rudofsky
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Sound detection array (GHG) speed

Post by Ulrich Rudofsky »

There has been a lot of discussion for years here and elsewhere about how fast a ship could go and still use the GHG or passive sound detection array equipment effectively.

It is quite clear from the Tirpitz war diary, which we are translating now, that the answer is 15 knots for optimal performance, although the instrument worked at 28 knots. When the Tirpitz was overwhelmed by aerial torpedoes (no hits!), GHG could trace a couple of torpedoes, but by the time the screws and evasive maneuvers had churned up the water and the rate of drops had increased, the instrument was ineffective.

There is actually a word for listening speed in the text and it is used quite often for indicating low speed in crossing friendly barriers and sub-infested fjord entrances: "Horchfahrt" (listening speed); (not Hochfahrt/full speed). Listening speed was defined as 15 knots. "Horchfahrt" is not always followed by indicating "15 sm", because it was clearly understood to mean 15 knots.
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Kit-Builder
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Post by Kit-Builder »

That is very interesting thanks for posting.
I’ve got a question about it for you…….
…..when you say that Tirpitz used it for evading torpedoes this, to my mind, infers that it’s a passive/defensive system. Did the Germans never use it for offensive purposes? It sounds as if it could have been handy at night or in other poor visibility situations.
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Post by Matthias »

Kit-Builder wrote:Did the Germans never use it for offensive purposes?
Am I mistaken or this device is a kind of hydrophone, or something like that?
May be similar to is now called "passive sonar"?
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Post by Ulrich Rudofsky »

For example: all U-boats used GHG to indentify their target ships and convoys. Convoys could be detected dozens of miles away, single ships about 20 miles. U-boats had GHG since 1935. And of course, the Prinz Eugen GHG detected approaching ships on portside at 0407 hours before they could be seen and identified.
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Post by Matthias »

So, it's what I thought it is...;)
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Outstanding Work Ulrich and Team

Post by wadinga »

Ulrich,

Once again congratulations to Ulrich and the translation team and website hosts for putting superb work like the Tirpitz war diary on the site for enthusiasts like myself. The GHG information is absolutely fascinating and I will need to study it carefully to revise my impressions of GHG's influence on the Battle of the Denmark Straits.

:clap: :clap: :clap:

All the Best and keep up the good work

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Post by Bgile »

From personal experience, I can say that the slower you go, the better it gets. If you want optimum performance of your sonar, you move just fast enough to control the ship's direction - a few knots in calm water.
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Post by wadinga »

Bgile,
Interested to hear more about your personal experience. An excellent article includes following" The Balcony apparatus
We have learned that noise interference, from both inside and outside the submarine was, and today still is, a limiting factor in the use of listening systems. (Herkovitz, 1996 38-40) It became possible to counter this by reducing the speed to 'Schleichfahrt' or slink speed. The electrically powered underwater boats had to reduce their speed to a few knots only (< 3 knots)."http://www.xs4all.nl/~aobauer/GHG1996.pdf

Horchfahrt is by no means Schleichfahrt and I guess it was the fastest speed at which GHG was any real use at all. Without being pedantic I don't think "optimal speed" is right at all since performance would only improve as vessel speed and noise got slower and lower. It would seem that high revving torpedo noise could be heard at short ranges, even travelling at near full speed.

As for ranges I don't want to argue with Ulrich, but I think could be is the operative phrase in his observations about detection ranges. If GHG could deliver this performance reliably, U Boats would not have searched for targets with the Mk 1 eyeball since GHG would always have outranged it. There are occasional references in U boat operations to GHG being the first contact device, but not that often.

I need to plough through the Tirpitz War Diary to identify successful, verified use of GHG at long ranges, eg spotting joining escorts before they were visually identified.

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Post by Bgile »

My experience was on submarines during the late sixties to mid seventies. I will try to make myself useful, but not sure what info I am able to provide, particularly since the period we are referring to is decades prior to my experience. A few observations:

Surface ships are comparatively poor sonar platforms, especially large surface ships with correspondingly large amounts of self noise. In addition to self noise, they also suffer from a lot of flow noise, waves hitting the ship, and the like. Being right under the surface is also not an ideal location for listening.

In a submarine, we almost always heard a ship before we saw it. Usually a very long time before. There are exceptions, however:

There was an area astern referred to as the “baffles” where detection was very poor. You would make periodic turns to “clear the baffles”.

Own ship speed made a big difference.

Marine life sometimes makes noise and hides everything else on the same bearing, sometimes over a fairly large sector.

If a ship is not moving or moving very slowly it becomes much harder to detect, especially if the ship was designed with that in mind. In WWII that probably only means submarines, although we occasionally came very close to a surface ship sitting dead in the water before detecting it on sonar.

Destroyers could be detected at much greater range than normal if they were pinging on active sonar.

In general, own ship speed and target speed are very important factors.

If a submarine is running it’s diesel engines, it becomes very noisy and the sonar is degraded tremendously. WWII submarines ran on diesels most of the time.

Environmental conditions can sometimes make it possible to detect things at much greater range than normal, and the reverse is true as well.

I’m skeptical about large German ships detecting opposite numbers at great range. I even suspect that PE’s phantom torpedoes at Denmark Strait were in fact some auxiliary equipment starting up on Bismarck or even PE itself. Maybe even a drill or some equipment running wild for a short time after the underwater hit from PoW. An emergency pump. A torpedo sounds something like an electric drill.
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Post by Ulrich Rudofsky »

I’m skeptical about large German ships detecting opposite numbers at great range. I even suspect that PE’s phantom torpedoes at Denmark Strait were in fact some auxiliary equipment starting up on Bismarck or even PE itself.
All I can say is that this passive listening device was probably not a perfect solution and had many problems. The interference from other noises must have been great. PG got briefly confused when the destroyers departed, salinity, temperature, etc. affected the performance,e.g., it barely worked in the Baltic. Also there are repeated references to the fact that the operator was crucial and had to undergo long peroids of training, and operators were in very short supply; during long hours on duty they got extra rations of Schokokola (chocolate spiked with caffein and some methamphetamine or straight Pervitin tablets). I don't know if the interpretations of sounds was just by earphones or if the sounds were analysed on an oscilloscope. However, the Kriegsmarine put a lot of trust into the GHG system and a false alarm was better than no alarm. As to the PG torpedo: I would agree that that might have been a fluke and an optical illusion: sound and an observed bubble track. (Actually, F.O. Busch in his 1943 book says there were 3 torpedo evasions during the battle in the Denmark Strait.)
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Post by Bgile »

Ulrich Rudofsky wrote: ... a false alarm was better than no alarm.
I disagree. The PoW may have been saved by that one, and no British torpedoes were fired during that battle.
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Post by Ulrich Rudofsky »

You are right. It just depends what ship you are on.

When the enemy is in range so are you, someone said.
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Post by Ulrich Rudofsky »

Interesting reference on the development of UT and GHG and S equipment http://www.xs4all.nl/~aobauer/GHG1996.pdf
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Post by wadinga »

Ulrich
Yes it is that's why I referenced it above/below whatever in this very thread!!

All the Best
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Post by Ulrich Rudofsky »

That Bauer website has a lot of information. Thank you very much!
http://www.xs4all.nl/~aobauer/
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