Ship noise reduction techniques - why surface ship can’t be made as quiet as submarine?.

If I would have to design a ship with reduced noise production, I would go for a SWATH (Small water plane twin hull) vessel with a waterjet. I don't truley believe that water jets are loud, because the jetstream is broken up in the air and will only produce ''weisses Rauschen'' (can't find any English term for that). Even if there would be a lof of structural noises produced in the pump, this could be compensated by a mecanical decoupling of the pump from the hull. The pump could hang like an outboarder on the rear between the two floats of the Swat. Modern engine mounts in cars demontrate how this could be done.
 
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Admittedly I didn't read through the whole thread, so my apologies if I rehash any arguments already covered so far, but in my understanding a completely submerged body is in a much more homogeneous and noise attenuated environment that surface ships, which operate at the air/water interface with all the messy surface wave and atmospheric interactions which cause turbulence effects and associated sounds.
 
T. A. Gardner said:
I suspect, at some point--and it might already be there--this sort of system could find 'blank' spots in the ocean where there is no noise and determine that's where a very quiet submarine is.
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Honestly, the old "hole in the water" Clancyism is sometimes taken a bit too literally I think. Waterborne noise simply doesn't work this way and you can't look for a "quiet" region. Because of the frequency and wavelength of ambient ocean noise (and the beamwidths of sensors in the band) sound is just going to diffract around a submerged body and you won't have a 'blank' spot at any tactically meaningful range.

martinbayer said:
Admittedly I didn't read through the whole thread, so my apologies if I rehash any arguments already covered so far, but in my understanding a completely submerged body is in a much more homogeneous and noise attenuated environment that surface ships, which operate at the air/water interface with all the messy surface wave and atmospheric interactions which cause turbulence effects and associated sounds.
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Yeah. Silent contacts that are dead in the water can still be detected just by wave slap and a moving surface vessel makes noise just through the hull-water interaction. That boundary is simply something that you can't do much about. I do believe it's still worthwhile to try to make vessels as quiet as possible. You'll obviously never be as quiet as a submarine, but there's definite value in being more difficult to track.

(Like in any shipbuilding venture this has to be compared to other considerations, of course. Throwing "let's make the ship quieter" on top of everything else is the sort of idea that makes shipbuilding efforts fail time and time again.)
 
Nicknick said:
If I would have to design a ship with reduced noise production, I would go for a SWATH (Small water plane twin hull) vessel with a waterjet. I don't truley believe that water jets are loud, because the jetstream is broken up in the air and will only produce ''weisses Rauschen'' (can't find any English term for that). Even if there would be a lof of structural noises produced in the pump, this could be compensated by a mecanical decoupling of the pump from the hull. The pump could hang like an outboarder on the rear between the two floats of the Swat. Modern engine mounts in cars demontrate how this could be done.
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Weisses Rauschen would translate as "White noise."
 
tychosis said:
Honestly, the old "hole in the water" Clancyism is sometimes taken a bit too literally I think. Waterborne noise simply doesn't work this way and you can't look for a "quiet" region. Because of the frequency and wavelength of ambient ocean noise (and the beamwidths of sensors in the band) sound is just going to diffract around a submerged body and you won't have a 'blank' spot at any tactically meaningful range.
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I would generally agree, but it is possible. The topic of sonar when applied to the military is generally one that is largely classified so it gets hard to both discuss it and find information on what's going on with the technology.
tychosis said:
Yeah. Silent contacts that are dead in the water can still be detected just by wave slap and a moving surface vessel makes noise just through the hull-water interaction. That boundary is simply something that you can't do much about. I do believe it's still worthwhile to try to make vessels as quiet as possible. You'll obviously never be as quiet as a submarine, but there's definite value in being more difficult to track.

(Like in any shipbuilding venture this has to be compared to other considerations, of course. Throwing "let's make the ship quieter" on top of everything else is the sort of idea that makes shipbuilding efforts fail time and time again.)
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I think the "rotate and radiate" method is better for surface ships in any case. If a sub already knows you're there, no point trying to hide. Instead, deploy lots of sensors and work on integrating these into a network with processing power to find the sub PDQ.
 
T. A. Gardner said:
I would generally agree, but it is possible. The topic of sonar when applied to the military is generally one that is largely classified so it gets hard to both discuss it and find information on what's going on with the technology.
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This one is actually relatively easy to discuss because it depends only upon the laws of physics.

Having sonar beams that are tight enough to be able to resolve a submarine hull at a decent distance is a challenge (and not one that really offers any other benefits), and diffraction of the background noise around the hull would probably swamp any chance of detection of this "black hole" effect. (Edit: And this is assuming perfect directivity of the receiving sonar, with no sidelobes, which would require an impractically large array.)

So even in theory, the "black hole" idea is questionable, and in practice is irrelevant.
 
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tychosis said:
Honestly, the old "hole in the water" Clancyism is sometimes taken a bit too literally I think.
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I did get an interesting discussion out of mentioning the "put out less energy than a 40watt lightbulb" reference on another forum. Had a dude do the math and said that meant 115db on something of roughly Ohio-class hull surface area. At higher frequencies, so they get absorbed pretty quickly in the ocean.

Years ago, my boat and another Ohio-class were doing some training where we'd each approach a point in the ocean, and once we had enough of a track to shoot we'd shoot a water slug and call out bearing on the direction we were shooting it. I won't say how close they were finding us, but I will say that it made my mind boggle at how close it was. Ships displacing 19000 tons each have no business being so quiet that you'd detect them that close to you!
 
Nicknick said:
If I would have to design a ship with reduced noise production, I would go for a SWATH (Small water plane twin hull) vessel with a waterjet. I don't truley believe that water jets are loud, because the jetstream is broken up in the air and will only produce ''weisses Rauschen'' (can't find any English term for that). Even if there would be a lof of structural noises produced in the pump, this could be compensated by a mecanical decoupling of the pump from the hull. The pump could hang like an outboarder on the rear between the two floats of the Swat. Modern engine mounts in cars demontrate how this could be done.
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Modern naval vessels can and at least some do raft propulsion and auxiliary engines on rafts.

As to water jets, I'm not sure how quiet they would be vs propellers or pump jets, as they have lower propulsive efficiency, relying on less mass flow and higher velocity than a propeller. This would mean more power is needed for the same speed. That jet velocity, itself, is a noise source. If the relationship in water is the same as air, and I expect them to be as they're both Newtonian fluids, jet noise is proportional to something like jet velocity to the eighth power.

I don't have any data for the noise levels of anybody's ASW vessels beyond a comment from a former naval person and USN ASW officer that the Spuances were quieter than the Perrys, and the Perrys were "holes in the water." I'm sure that anyone with real data would not reveal it unless they look forward to visits by humorless people with guns and arrest warrants.
 
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Scott Kenny said:
I won't say how close they were finding us, but I will say that it made my mind boggle at how close it was. Ships displacing 19000 tons each have no business being so quiet that you'd detect them that close to you!
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Yeah. Many people have an understanding of submarine warfare that's primarily influenced by video games or by making (incorrect) assumptions about sonar that are based on how we as humans hear things.

My first few years out of the Navy and into the industry as a nub engineer, I spent a solid few years on sensor tuning and testing. Literally thousands of hours loading what feels like every cut we've ever recorded. I'd venture to say I've probably "listened" to literally every single submarine cut from the past few decades (multiple times) and it's why I bristle a tiny bit when people talk about "loud" boats and "quiet" boats without actually understanding what they're talking about.

I'll admit, even in the field we do use terms like "loud" and "quiet" but we're really talking about a spectrum of potential acoustic vulnerabilities. Everyone's boats are "quiet" when freshly-groomed out of the yard, keeping them that way through a robust maintenance and monitoring program (that isn't too cumbersome and doesn't detract too much from availability) is key because any neglected boat will inevitably start to develop vulnerabilities. This rate of degradation is where the differences in submarine engineering knowledge and experience begin to reveal themselves.
 
1635yankee said:
Modern naval vessels can and at least some do raft propulsion and auxiliary engines on rafts.

As to water jets, I'm not sure how quiet they would be vs propellers or pump jets, as they have lower propulsive efficiency, relying on less mass flow and higher velocity than a propeller. This would mean more power is needed for the same speed. That jet velocity, itself, is a noise source. If the relationship in water is the same as air, and I expect them to be as they're both Newtonian fluids, jet noise is proportional to something like jet velocity to the eighth power.

I don't have any data for the noise levels of anybody's ASW vessels beyond a comment from a former naval person and USN ASW officer that the Spuances were quieter than the Perrys, and the Perrys were "holes in the water." I'm sure that anyone with real data would not reveal it unless they look forward to visits by humorless people with guns and arrest warrants.
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The efficiency depends on the speed, water jets are more efficient at high speeds than propellers. Even commercial ferries are using waterjets for propulsion, which they cleary wouldn't do if they would be unefficient.

View: https://m.youtube.com/watch?v=fNNYUq5M-z4&pp=ygUecmljayBuYXZhbCBhcmNoaXRlY3Qgd2F0ZXIgamV00gcJCSUKAYcqIYzv


The water jet is ejected into the air, not the water which is a findamental difference. There is shurly a lot of noise in the water just after the ejection, but almost no way for transmitting it into the water. The jet breaks up in a big rooster tail before it hits the water. This will surly not produce any sound pattern which might be traceable.
 
Nicknick said:
The efficiency depends on the speed, water jets are more efficient at high speeds than propellers. Even commercial ferries are using waterjets for propulsion, which they cleary wouldn't do if they would be unefficient.

View: https://m.youtube.com/watch?v=fNNYUq5M-z4&pp=ygUecmljayBuYXZhbCBhcmNoaXRlY3Qgd2F0ZXIgamV00gcJCSUKAYcqIYzv


The water jet is ejected into the air, not the water which is a findamental difference. There is shurly a lot of noise in the water just after the ejection, but almost no way for transmitting it into the water. The jet breaks up in a big rooster tail before it hits the water. This will surly not produce any sound pattern which might be traceable.
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If you watch the video carefully, the narrator tells us that waterjets are only efficient in a narrow range of speeds and have to be engineered just right. Warships need to be quiet and efficient over as large a range of speeds as possible.
 
Nicknick said:
The efficiency depends on the speed, water jets are more efficient at high speeds than propellers. Even commercial ferries are using waterjets for propulsion, which they cleary wouldn't do if they would be unefficient.

View: https://m.youtube.com/watch?v=fNNYUq5M-z4&pp=ygUecmljayBuYXZhbCBhcmNoaXRlY3Qgd2F0ZXIgamV00gcJCSUKAYcqIYzv


The water jet is ejected into the air, not the water which is a findamental difference. There is shurly a lot of noise in the water just after the ejection, but almost no way for transmitting it into the water. The jet breaks up in a big rooster tail before it hits the water. This will surly not produce any sound pattern which might be traceable.
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I don't think that is correct.
 
Airbus A340 said:
If you watch the video carefully, the narrator tells us that waterjets are only efficient in a narrow range of speeds and have to be engineered just right. Warships need to be quiet and efficient over as large a range of speeds as possible.
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There are ,many different types of warships, some are big, some are small, some are fast and some are slow. I guess, hunting submarines for coastal defence requires small, fast and nimble vessels, the ideal application for water jets.

There is no Warship which is quit and efficient over a large range of speed exept submarines.

Water jets are more efficient at higher speeds, which is not the same as being efficient only in a narrow range of speed.
 
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Nicknick said:
Which sound pattern will they create which might be traced? The water hitting the surface is completely decoupled from any sound produced in the propulsion system.
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It'd confuse people for a little bit, then all of a sudden there's a couple tons of water hitting the surface every second. And where it's landing is moving different to the direction of seas.
 
Scott Kenny said:
It'd confuse people for a little bit, then all of a sudden there's a couple tons of water hitting the surface every second. And where it's landing is moving different to the direction of seas.
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Its a steady flow of water droplets, very likely producing just white noise which is undetectable as long as the ocean itself is producing a lot more white noise.

I've been on the open stern of a fast ferry with impressive water jets coming out, but I couldn't detect any specific noise of them. Of course, you hear the Diesels running and the general sound of the water flowing around a ship but nothing which sounds any different from any other ship (above the waterline). So I doubt, that water jets produce a considerable amount of noise by the jet itself. Of course, the pump housing will emit noises and the intake will transmit some pump noises in the ocean (sound doesn't like to travel backwards...). The pump housing could be a suspended part under the bottom of the hull, powered by a drive shaft with rubber decoupling's and soft attachment points (like engine mounts in cars).
 
Nicknick said:
Its a steady flow of water droplets, very likely producing just white noise which is undetectable as long as the ocean itself is producing a lot more white noise.
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And that's the key.

Generally, the ocean surface isn't that noisy!
 
Scott Kenny said:
And that's the key.

Generally, the ocean surface isn't that noisy!
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We need a scientific source about the noise which is produced by the jets, I tend to believe this isn't ''much''. Despite that, according to my understanding, sonars are searching for pattern which stick out of the background noises. White noise will be hard to detect, even if it isn't exactly silent. Low frequencies, like thy are produced by propellers, are more critical because they can travel over longer distances.
 
Nicknick said:
We need a scientific source about the noise which is produced by the jets, I tend to believe this isn't ''much''. Despite that, according to my understanding, sonars are searching for pattern which stick out of the background noises. White noise will be hard to detect, even if it isn't exactly silent. Low frequencies, like thy are produced by propellers, are more critical because they can travel over longer distances.
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We could track rainstorms on the BQQ-6 sonar on the Georgia 25 years ago.

I've heard that boiling water (nuclear plants) sounds a lot like rain, and so do the Prairie/Masker systems.
 
I wouldn't be too surprised if the waterjet sounds like rain too, or like a waterfall...
 
Arjen said:
A waterfall travelling at dozens of knots. Should be a clue.
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Doesn't help a lot, when tracing is done by looking for patterns. As long as you aren't really close, it is just white noise in a white noise background.
 
Scott Kenny said:
A contact moving relative to you stands out really sharply on a waterfall display.
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When the nois level is significantly louder than the background, yes. The point is, can you detect it from, lets say 100 km distance? Does a Fourrier analysis show any pattern? I think, the direction of the noise source can be determined by the doppler effect, but for this method I guess you need at least one reference frequency which might be hard to find in a white noise.
 
I'd think that you could handle background noise like radio astronomers do in their field. You have a known set of background noises you simply filter out automatically. In addition, you look for patterns. Random noise is rejected. What gets attention are noises that follow a pattern.

For example, one that is probably looked for is steady noise at 50 and 60 Hz. This would equate to electrical power systems on ships (depending on nation). It would be hard to mask or eliminate these entirely.
 
T. A. Gardner said:
I'd think that you could handle background noise like radio astronomers do in their field. You have a known set of background noises you simply filter out automatically. In addition, you look for patterns. Random noise is rejected. What gets attention are noises that follow a pattern.

For example, one that is probably looked for is steady noise at 50 and 60 Hz. This would equate to electrical power systems on ships (depending on nation). It would be hard to mask or eliminate these entirely.
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That's the point, how to filter a white noise out of a white noise? The filtering is done by a Fourier analysis which shows you the relevant frequencies, but what if there aren't any?
 
Nicknick said:
That's the point, how to filter a white noise out of a white noise? The filtering is done by a Fourier analysis which shows you the relevant frequencies, but what if there aren't any?
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Or you look for frequencies that aren't constant and repetitive and filter those out. You could use the equivalent of a bandpass circuit to narrow the bandwidth, taking out the noise a bit at a time while looking for very specific, known frequencies that things you want to find emit, like the aforementioned electrically generated noise.

During one exercise while I was on the Enterprise, we were ordered to run all the electrical generation for ship's service at 59 Hz and 405 Hz for the aircraft and electronics generation sets. The later was mostly generated by turbine generators that had a propensity to hunt between about 397 and 403-ish Hz anyway so we just left them doing that.

The point is, those sets produce noise on the frequency generated both at the generator and in the electrical system itself. That can be detected, and it's hard or impossible to move off the frequency since it will mess a lot of equipment up.
 
T. A. Gardner said:
Or you look for frequencies that aren't constant and repetitive and filter those out. You could use the equivalent of a bandpass circuit to narrow the bandwidth, taking out the noise a bit at a time while looking for very specific, known frequencies that things you want to find emit, like the aforementioned electrically generated noise.

During one exercise while I was on the Enterprise, we were ordered to run all the electrical generation for ship's service at 59 Hz and 405 Hz for the aircraft and electronics generation sets. The later was mostly generated by turbine generators that had a propensity to hunt between about 397 and 403-ish Hz anyway so we just left them doing that.

The point is, those sets produce noise on the frequency generated both at the generator and in the electrical system itself. That can be detected, and it's hard or impossible to move off the frequency since it will mess a lot of equipment up.
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Shure, but my last postings were soley related to the noise of the waterjet hitting the water surface. A spray of water hitting a water surface will hardly produce any constant frequencies which can be filtered.
 
Nicknick said:
Shure, but my last postings were soley related to the noise of the waterjet hitting the water surface. A spray of water hitting a water surface will hardly produce any constant frequencies which can be filtered.
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Thing is, a rainstorm will move with direction of seas (Technically the rainstorm will be driving the local direction of seas).

And a "rainstorm" moving any other direction will stand out. In addition to 50/60hz noise and whatever your engine noise is.
 
Nicknick said:
Shure, but my last postings were soley related to the noise of the waterjet hitting the water surface. A spray of water hitting a water surface will hardly produce any constant frequencies which can be filtered.
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Waterjet... meh. The ship still has electrical generators aboard along with lots of motors and other electrical equipment all giving of that hum.
 
T. A. Gardner said:
Waterjet... meh. The ship still has electrical generators aboard along with lots of motors and other electrical equipment all giving of that hum.
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The power systems can be as quite as on a sub or even quiter (less space limitations), so this is not the critical point. It is the interference with the surface (can be improved wity SWATH layout) and the propeller noise (cavitation is harder to surpress with low ambient pressure).
 
Scott Kenny said:
Thing is, a rainstorm will move with direction of seas (Technically the rainstorm will be driving the local direction of seas).

And a "rainstorm" moving any other direction will stand out. In addition to 50/60hz noise and whatever your engine noise is.
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In this case, you must be able to identify the noise by beeing louder and not by a frequency analysis, this will be hard to do unless you are very close
 
Scott Kenny said:
You'd be surprised.
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Yeah, there are some misconceptions about how broadband works in this thread (and some general confusion between broadband and narrowband.)

It isn't as easy as "hiding" in the "white noise" of the ocean (which isn't actually white.) The entire purpose of the beamformer is to pull localized sources of energy out of that background, and the beamformer can detect sources at (or even below) ambient levels.

Now, some reports indicate that propulsion noise from waterjets can be 10-20dB lower than props, which isn't nothing--and it can still be worthwhile to push your emissions as close to the floor as you can get in the hopes that detectors and operators overlook you. You also rob the adversary of the ability to get a blade count and speed etc etc.

You aren't "silent" though. Nothing is.
 
tychosis said:
Yeah, there are some misconceptions about how broadband works in this thread (and some general confusion between broadband and narrowband.)

It isn't as easy as "hiding" in the "white noise" of the ocean (which isn't actually white.) The entire purpose of the beamformer is to pull localized sources of energy out of that background, and the beamformer can detect sources at (or even below) ambient levels.

Now, some reports indicate that propulsion noise from waterjets can be 10-20dB lower than props, which isn't nothing--and it can still be worthwhile to push your emissions as close to the floor as you can get in the hopes that detectors and operators overlook you. You also rob the adversary of the ability to get a blade count and speed etc etc.

You aren't "silent" though. Nothing is.
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So indeed, water jets can be really much quiter, 20 dB means 100 times lower noise production.

Now, I would like to know if there is also a confirmation about that idea that a SWATH design will lower noise production too.
 
Nicknick said:
So indeed, water jets can be really much quiter, 20 dB means 100 times lower noise production.
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Well, note that the studies citing 20dB were referencing the use of waterjet propulsion in high-speed general transportation and not necessarily on warships:
https://pubmed.ncbi.nlm.nih.gov/26611054/
10-15dB might be more a more realistic reduction for a warship (which is generally built and groomed to be a bit quieter):
https://www.rivieramm.com/news-cont...ts-contribute-to-quietness-of-corvettes-51332
Bear in mind that with surface craft you're starting with a baseline that's well over ambient, so you're knocking 10-15dB off a source level that is several dozen dB higher than background.

So ultimately yeah they may be quieter... but not exactly "quiet."
 
tychosis said:
Bear in mind that with surface craft you're starting with a baseline that's well over ambient, so you're knocking 10-15dB off a source level that is several dozen dB higher than background.
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The literature I have to hand points out that below cavitation inception speed, the dominant acoustic signature is discrete LF tones related to machinery (prime movers, gearboxes etc.), which are independent of the propulsor choice. Above cavitation inception speed, the ship is going to be making an almighty racket whatever you do, and also probably can't hear anything anyway.
 

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