Indian Navy News & Discussion - 15 Dec 2016

[Singha]

its range and payload would be too weak given its small size.

we really need 2 x 12ton helis like SH60/NH90 size on all principal vessels...numbers of serviceable sea kings are so short now, many are carrying out patrols with 1 or 0 helis per reports and scarce numbers are rotated from ship to ship. not a great place to be in. ideally all ships should have allocated helis and some on land for training and reserve.

we also need to think of putting some unmanned rotorcraft or drones on carriers and LPD ships.

having a harpoon armed SH60 gives even a small corvette a strike range of 250+100=350km with a couple of missiles and good protection against swarm attacks by FACs.

[tsarkar]

Ka-226 is ideal for IN, given the long pedigree and history of Kamov helicopters in naval service.

Not quite, the Kamov is noisy and can be heard afar and detectable by submarine sonars, short ranged and maintenance intensive (two sets of rotors). The only USP was Ka-28 & Ka-31 were the only ASW & AEW assets in the post Pokhran years. With the HAL LUH just around the corner, Ka-226 is avoidable.

For IN, the broad level requirements are -

Medium ASW/ASuW helicopters to replace Seaking Mk42B/Ka-28 - for which MH-60R class helicopter is optimally suited.

Medium Transport helicopters to replace Seaking Mk42C/UH-3H on Jalashwa - for which MH-60S class helicopter is optimally suited.

Armed Utility Helicopters to replace MMG armed Chetaks - for which WSI DHruv with EO sight, rockets, 20 mm stabilized gun & folding rotors are a significant improvement.

Chetak Replacement Utility Helicopters - for which Dhruvs with folding rotors can suffice.

Training Helicopters - for which HAL LUH is well suited.

I'm not a aviation person, so I would request member Chetak who is from that branch to explain to us as to what are the constraints for Dhruv to atleast fulfill the Utility / Training / Armed Helicopter role.

Also, to the best of my knowledge, automatic folding blade technology is available commercially, so it isnt an insurmountable barrier.

[Manish_P]

Ka-226 is ideal for IN, given the long pedigree and history of Kamov helicopters in naval service.

Not quite, the Kamov is noisy and can be heard afar and detectable by submarine sonars

Tsarkar Ji, the bear is also very noisy for ASW ops, correct ?

[Karthik S]

It is. Because of the contra-rotating propellers.

[Rakesh]

Where are the new subs going to come from this year? Expect just another Scorpene that's all,unless we're going in for leasing more subs from Russia.Any deal signed o this year will see (from the west) subs appearing post 2020.

Yes only Russia can save the day!

Kalvari is due for commissioning by March 2017 as per the article below...

Indian Navy gears up to induct more submarines, warships in 2017
http://www.asianage.com/metros/mumbai/0 ... -2017.html

According to naval sources, submarine INS Khanderi will be set afloat this month. Khanderi is the second submarine of the Scorpene Class submarines, which are being constructed at the Mazagaon Dock Shipbuilders Ltd (MDL).

Further, the first Scorpene Class submarine INS Kalvari is also likely to get commissioned in March this year.

[Austin]

Brazilian Scorpene Submarine Under Construction: Photos

http://www.defesaaereanaval.com.br/pros ... no-brasil/

[John]

^ Brazilian scorpene deal is mess as well reports of corruption have hampered the nuclear plans. But as always French have managed to make out like bandits 10 bill for 4 subs + SSN tech which is in limbo.

[shiv]

Not quite, the Kamov is noisy and can be heard afar and detectable by submarine sonars,

I have never read any references to the effect that helicopters in the air can be heard by submarines that are completely submerged with no snooping devices sticking out of the surface. The Kamov may be loud but the presence of a tail rotor spinning fast in other helos produces a completely different noise profile that the Kamov cannot produce. This is not a pitch for Russian helos but a request for more information that sound energy can impact the surface of water and not get dissipated but continue as coherent sound waves detectable underwater by submarines.. I doubt it but I am willing to be educated.

The little physics that I know suggests that sound energy from the atmosphere will dissipate itself on the water surface and not get transmitted as recognizable sound patterns for long distances in water. Helicopters are dangerous precisely because they can dunk sonar without themselves being heard

[Surya]

http://civilianplanespotters.blogspot.c ... siest.html

some reference to the Bears noisy props being detected by SONAR -

[Singha]

sound travels better and faster in water than air I believe. subs computers would be loaded with profiles of airborne noise from tests carried out in friendly conditions using blue force LRMP planes.

[tsarkar]

Tsarkar Ji, the bear is also very noisy for ASW ops, correct ?

The Tu-142 like any other MPA works differently, it flies stably at high altitudes, and uses MAD and sonobuoys. I'm not sure of its detectability by submarine sonar.

I have never read any references to the effect that helicopters in the air can be heard by submarines that are completely submerged with no snooping devices sticking out of the surface.

My point of view is empirical but here is a paper on Helicopter Radiated Noise http://www.dtic.mil/dtic/tr/fulltext/u2/a145993.pdf
The graphs Page 10 onward show underwater measurements.

Dipping Sonars are designed to reject helicopter noise https://www.thalesgroup.com/sites/defau ... SONICS.pdf Page 2

Given that in WW1, 2 & Cold War, the US & UK understood the submarine threat, the Seaking has much lesser noise levels unlike the Kamov or Chetak.

The clattering of the Kamov would wake up even bone tired off watch sleepers.

[tsarkar]

My point of view is empirical...
...the Seaking has much lesser noise levels unlike the Kamov or Chetak.

And that is not by accident but by lots of research.

Here is a 1958 paper http://www.dtic.mil/dtic/tr/fulltext/u2/303629.pdf
Page 22

From the data obtained from the noise measurements, the noise radiated by the helicopter into the water was known to be very high.

There are further details on noise reduction efforts in the same page

Since the aircraft described here - Sikorsky S-56 is an older product compared to Seaking S-61, I would believe further noise reduction efforts would've taken place.

[tsarkar]

This is the Moldavian company that manufactures sonobuoys http://raut.md/istoric/?lang=en

The Soviet Union truly believed in National Integration. BDL manufactures torpedoes at Vizag but if we went the Soviet way, we would be manufacturing them in Rajasthan

[vina]

sound travels better and faster in water than air I believe. subs computers would be loaded with profiles of airborne noise from tests carried out in friendly conditions using blue force LRMP planes.

The impedance (exactly like the electrical analogue) difference between air and water is so high that for most practical purposes, the air water separation medium is like a perfect reflecting surface. Sound energy cannot appreciably penetrate the air water medium ,as it will get fully reflected from the surface ,and for all practical purposes a sub underwater cannot hear a hovering helicopter or an LRMP (even if flying very low). So all this talk about a sub underwater hearing a Kamov or Bear because of "contra rotating screws" is bunkum. At best some very high frequency sound might penetrate out of the spectrum and even that will be nowhere like what we hear on the surface.

Also analogously, if a fish underwater cannot see beyond a narrow cone vision for things above water (there will be total internal reflection and the area outside the cone on the surface will be massive blind spots). Similar things will operate even if the sub would put out an optical search underwater.

Fish Eye (World above water as seen by a fish)

[tsarkar]

Sound energy cannot appreciably penetrate the air water medium ,as it will get fully reflected from the surface ,and for all practical purposes a sub underwater cannot hear a hovering helicopter or an LRMP (even if flying very low). So all this talk about a sub underwater hearing a Kamov or Bear because of "contra rotating screws" is bunkum.

http://www.dtic.mil/dtic/tr/fulltext/u2/303629.pdf

LOW FREQUENCY AIRBORNE SONAR SYSTEMS
Airborne Sonar Branch
Sound Division
October 31, 1958
U. S. NAVAL RESEARCH LABORATORY
Washinqton. D.C.

Tests were performed to determine the spectral level and radiation pattern of noise radiated into the water by a Sikorsky HR2S helicopter. These tests, though incomplete, do indicate a high noise operating back-ground...

Table I
New London Noise-Measurement Results Using the HR2S Helicopter

Helicopter Hovering Altitude (ft) Transducer Depth (ft)

50 120
50
25 120
50

Page 9 of 35 shows the noise pattern radiated underwater

Page 13 of 35

However, these results do indicate a very high noise level from an HR2S, which seriously limits the expected sonar range.

Page 22 of 35

Next, a test was performed to see if the noise was transmitted down the cable and picked up by the transducer...This
showed that the noise generated by the helicopter was picked up by the transducer and was not generated by vibrations down the cable.

Page 25 of 35

...the high spectral level of the radiated noise of the HR2S is much higher than sea-state 2 noise,

Page 32 of 35

In one experiment to reduce the noise coupled to the water, fire-fighting foam was spread over the surface of the water. A loudspeaker was suspended about 12 in. above the water and a hydrophone was placed about 12 in. below the surface. A 2.5-kc signal was fed into the speaker to give an indication on the monitored hydrophone output at least 20 db above the ambient noise level. The addition of about 2 in. of foam reduced the hydrophone output to the ambient level....
...However, in an experiment conducted at NRL, a helicopter hovering over the foam blew it away from the surface immediately below the helicopter

http://www.dtic.mil/dtic/tr/fulltext/u2/a145993.pdf

NAVAL UNDERWATER SYSTEMS CENTER
NEW LONDON LABORATORY
NEW LONDON, CONNECTICUT 06320

DETECTION, CLASSIFICATION, AND EXTRACTION OF HELICOPTER-RADIATED NOISE

Date: 25 July 1984

Page 3 of 14

Surface ships operating in conjunction with supporting helicopters may experience sonar performance degradation due to the accompanying interference from helicopter-radiated noise.

Page 6 of 14

For the under water data the 11 Hz fundamental from the main rotor is the first peak in the top graph. The corresponding harmonics from the main rotor are seen as multiples of the fundamental. The tail rotor's fundamental frequency is at 55 Hz and its corresponding harmonics are at 55 Hz multiples.

The conclusions reached by the statistical analyses of the in-air and underwater helicopter-radiated noise measurements are as follows:
1. Helicopter (UH-1) radiated noise can be detected in the frequency domain by its narrowband components up to 400 Hz.

Page 9 onwards has underwater noise measurement data

https://www.thalesgroup.com/sites/defau ... SONICS.pdf

Submersible Unit key features...Rejects helicopter generated noise

While these studies were conducted to improve ship & airborne dipping sonar performance, a submarine sonar just needs to listen to helicopter radiated noise. The farther a submarine can detect helicopter radiated noise, the more time it gets to escape into a thermocline or slowly slink away.

Readers can discern between real scientific research data and fish & whale analogies and scientifically figure out what...

...is bunkum.

[Philip]

In the emerging scenario with the advent of long endurance UUVs, a contact of a sub will be made more likely by a warship,LRMP aircraft or friendly sub/UUV. The sub than has to be classified if friendly or hostile, located and then if possible tracked. ASW helos will then be despatched to scour the area and usually sensor data from at least 3 diff. sources will be able to home in on the sub's location for an attack to be made. Active and passive sonobuoys will be dropped by aircraft and helos. When an ASW helo uses its dipping sonar,it becomes more vulnerable to detection by the sub.If the sub is able to detect the presence of a helo,then it can-as in the Kilo class and supposedly on some western subs, use its SAMs to down it.The Germans have IDAS,the French MICA and the Russkies have Strela/Igla.This is a very crude description of the cat and mouse game that ASW warfare is all about.During CW times,the hunt could go on for days.

[vina]

http://www.dtic.mil/dtic/tr/fulltext/u2/303629.pdf

Page 3 of 14

Surface ships operating in conjunction with supporting helicopters may experience sonar performance degradation due to the accompanying interference from helicopter-radiated noise.

Page 6 of 14


1. Helicopter (UH-1) radiated noise can be detected in the frequency domain by its narrowband components up to 400 Hz.

Submersible Unit key features...Rejects helicopter generated noise

Do you even read what other people write, or do you just google up some random articles to justify your pre conceived ideas and fit them into what you imagine , even if what the article and research is about actually is different? And NO, I didn't read the papers you posted, coz, I don't need to . I know what they are referring to.

Now let us examine what it is.

While these studies were conducted to improve ship & airborne dipping sonar performance, a submarine sonar just needs to listen to helicopter radiated noise. The farther a submarine can detect helicopter radiated noise, the more time it gets to escape into a thermocline or slowly slink away.

Out of this

While these studies were conducted to improve ship & airborne dipping sonar performance

Now, this is ABSOLUTELY correct. The signal to noise ratio of your sonar will degrade if you have a noisy source close by (hovering helicopter for eg. Water transmit leak some (a little) sound energy while reflecting the overwhelming bulk (like 95%). No surface is 100% reflective or 100% transmitive. (Similar principle of your car's rear view mirror, when you flip the tab into night mode to prevent you from being blinded by the headlights of the vehicle behind you, so what happens, is because of this, due to some total internal reflection and at the glass to air surface, the 2nd faint image is formed (iirc at 45deg) and that is the image that you want in the night so that you are not blinded, and what you see when you flip the mirror) . So what you WOULD do in that circumstance is to make efforts to improve your sensor's signal to noise ratio and do signal processing and filtering techniques to sample the noise and filter it out (like in the Thales sonobuoy). Sure. This much is actually true .
,

a submarine sonar just needs to listen to helicopter radiated noise. The farther a submarine can detect helicopter radiated noise, the more time it gets to escape into a thermocline or slowly slink away.

This part is YOUR spin to claim what is actually signal to noise reduction efforts on a dunking sonar says actually what you claim to be true. In fact, yes, the air /water boundary is REFLECTIVE to sound , and there is no way any submarine can actually listen in practice like you want detect that noise from afar and even detect the helicopter and make tactical use of it. Sure, if the helicopter is right over head and the sub is some 5 to 10 ms below the surface, you will have some disemboweled sound filtering in (and no it wont sound remotely like what you hear about the chopper's rotor in the air), very few freqencies of the spectrum would get in and that too with huge phase shifts.. And NO, that sound (follows the square law in terms of energy loss) will dissipate very quickly (esp higher freq) and it cannot be detected at long ranges (which will be low to ultra low freq) and needs to be in SOFAR channels to really propagate far.

[shiv]

tsarkarji Your references do not answer the questions "Can the submarine hear a helicopter?", and if so "from what range?"

You references are all out dated and are from the days when they were still discovering how helicopter sounds interfere with sonar not how submarines can hear helicopters. Modern low frequency sonars are not disturbed by helicopter noise and can detect submarines at very long ranges.

You are completely wrong about Helicopters and dunking sonar. Your biggest error is in assuming that the helicopter needs to be silent. In fact the sonar is used as a sound generator that listens for echoes. You know that is what an active sonar is. Helicopters are better than ships because ships in the water generate a lot more noise in water than helicopters in the air. Within a broad area the sonar generated sound - moving faster in water than in the air will produce echoes that are picked up by ships, buoys and the helo to be analysed. The sub can do nothing. It has to remain silent while it is being bombarded by sound waves.

Here is one paper

More from Global security
http://www.globalsecurity.org/military/ ... ry-asw.htm

In an attempt to make helicopters more proficient in the role of a submarine hunter, a project began in April 1944 to equip them with a "dipping sonar" similar to what blimps carried. The major concern was the noise transmitted to the water by the wash from the helicopter's rotors. Working off the Cobb, it was found that the noise level was insignificant and did not interfere with equipment operation.

also

Beginning in the 1950s, the carrier-based air ASW community was one of the driving forces behind helicopter development, and within the HUK groups, HS squadrons deploying active, dipping sonars became a key new addition to the combined arms ASW team. HS squadrons gave the HUK group an active sonar platform with the speed and mobility of an aircraft. The original attraction of an airborne dipping sonar was in cooperative operations with radar-equipped aircraft in operations against snorkelers. The latter would often detect a snorkel, but the submarine would submerge and be lost when it went on battery because no destroyers were within range to hold the contact with active sonar. The ASW helicopter with a dipping sonar filled this gap by holding the contact until destroyers with the endurance to hold the submarine down until its batteries were exhausted arrived.

and

Dipping sonar allows the helicopter to listen for and transmit underwater electronic signals while in a "hover" or stationary mode. The aircraft typically hovers at an altitude of 50 to 300 feet above sea level and lowers the transducer into the water using a powered reel system similar to a fishing reel. The transducer can be lowered to depths ranging from the water's surface to 2,500 ft. Once lowered to the selected depth, the transducer is activated, generating sound signals and receiving echoes from submerged objects. These echoes can then be processed to identify and locate potential underwater threats.

[Viv S]

Not to take this off-topic but does anyone know how this panned out. Did we go through with it?

India to develop torpedo testing centre in Kyrgyzstan - Sep 2011

India is planning to develop a facility in Kyrgyzstan to produce state of the art torpedoes in order to strengthen its under water attack capabilities.

The Torpedo Testing Centre located at Issyk Kul lake in Karakul province, 250 km away from the capital Bishkek, is considered one of the best locations to launch and recover torpedoes fired during test trials.

“The facility was visited by Defence Minister A.K. Antony a few months ago. An Indian delegation would be visiting Kyrgyzstan soon to make an assessment of investment needed for the project and the terms and conditions for co-developing it,” DRDO Chief Controller William Selvamurthy told PTI.

To develop existing infrastructure at the centre, India has proposed to engage local companies with available know how in torpedo technology to co-develop the facility.

“India is willing to develop the Centre to test all kinds of torpedoes such as heavy weight torpedoes and those having thermal navigation system,” Mr. Selvamurthy said.

The centre has a network of sensors which can monitor the speed, velocity, homing in and direction of the torpedo once it is fired. This enables scientists to make necessary modifications in the navigation system to make the missiles more accurate and fool proof.

The torpedoes fired in the lake are also recoverable enabling the scientists to make physical verification of its structure for further study.

A torpedo is a self-propelled explosive projectile weapons, launched above or below the water surface, propelled under water towards a target.

India is also planning to use the facility to test the Autonomous Underwater Vehicle Developed by Naval Scientific and Technological Laboratory (NSTL).

Developed during the Soviet era, the facility was used by the Russian military as a testing site for torpedo propulsion and guidance systems, and Karakol was home to a sizable population of military personnel and their families.

[tsarkar]

My first response is, "because I know". However, as a student of science, that response is inappropriate.

Noise travels across mediums. And it travels quite a distance.

This is the reason why stealth ships like INS Kamorta mount machinery on rafts to minimise vibrations and noise.

http://www.business-standard.com/articl ... 011_1.html

The major reason for the delay: the Indian Navy has stipulated such unprecedented standards of stealth for every piece of equipment on board that suppliers have struggled to develop engines, transmission, air-conditioning and power-generating systems that work silently enough to meet those requirements. Furthermore, the navy mandated that Indian suppliers would provide much of that equipment.

Earlier this year, DCNS of France supplied the Raft Mounted Gearbox, which almost completely suppresses noise from the power pack. But Wartsila India is still struggling to reduce vibration in the four diesel alternators that will power the corvette’s electronics.

The engine, gearbox, air-conditioning are not in contact with water, yet the noise (NOT sound) generated in air will radiate underwater and travel quite a distance underwater.

Before someone cites the hull will conduct the noise to water, then it's is not the case. The US experiments cited above conclusively proved that dipping sonar cables did not transmit noise.

In fact the Japanese go as far as to suppress noise generated from fluorescent light in their submarines that radiates into water

http://www.japantimes.co.jp/news/2015/0 ... -sub-deal/

Retired Vice Admiral Masao Kobayashi commanded Japan’s submarine fleet from 2007 to 2009. In a recent interview in Tokyo with The Japan Times, when asked to explain one of the country’s most tightly guarded military secrets, he seemed reflective.

Kobayashi pointed to the ceiling lights in the quiet interview room and said: “Take those fluorescent lights, for example. Any fluorescent light generates sound.”

Other than our voices, there were no other sounds in the room.

“Fluorescent lights generate extremely small vibrations. We take anti-vibration measures for every single light in a submarine,” he said .

The noise from fluorescent light transmits via air via water to enemy submarine sonar.

Aircraft noise detection by submarine sonar is known for ages.

http://asa.scitation.org/doi/abs/10.1121/1.1913206

The Journal of the Accoustical Society of America

Noise Signature of an Aircraft in Level Flight over a Hydrophone in the Sea

ABSTRACT

An aircraft flying over a hydrophone in the sea produces a noise signature whose magnitude and duration depend on such parameters as hydrophone depth, water depth, and flight altitude. This signature represents sound reaching the hydrophone in four different ways: via a direct refracted path, via one or more bottom reflections, via the so‐called lateral wave, and via sea scattering. Of these, the refracted path is the most important and easiest to evaluate. Generalized contours for the nearfield of this component are given; in the farfield it is shown that the source in air can be replaced by an equivalent in‐water source having a cosine‐squared directivity pattern and a source level 7 dB less than that of the real source. In a field experiment, a Navy P3 Orion turboprop aircraft flew over hydrophones at two depths in deep water. The brief noise signature, lasting but a few seconds, was found to be accounted for statisfactorily by the refracted sound field. However, under conditions not existing in the field experiment, such as in shallow water, in rough seas, or at very shallow depths, it is conceivable that the other contributors to the total underwater sound field may become important.

I'll respond to points raised in Vina & Shiv's posts later when I'm off work

[Sid]

Tsarkar ji, if that's the case then why not just create sound proof ship cabins? Why spend money on making sure equipment itself does not make the noise?

Sound proofing walls is much easier (and cheaper) then making an sound proof power generator.

[shiv]

My first response is, "because I know". However, as a student of science, that response is inappropriate.

Noise travels across mediums. And it travels quite a distance.

Sir. Active sonar produces noise and listens for echoes. It will selectively listen for echoes of the frequencies it produces and ignore others. It does not matter one whit if the submarine can hear the rotor. the sub can surely hear the ping from the sonar.

The noise from the Ka 226 is irrelevant as long as the dunked sonar is an active sonar that is pinging and listening for echoes. You are wrong.

[hnair]

interesting discussion

The noise from fluorescent light transmits via air via water to enemy submarine sonar.

So a raft mounted gearbox or prop shaft bearings can almost completely smother sound, but a flourescent lamp's minimal hum from magnetostriction cannot be smothered after bouncing around the walls of a craft made for absorbing all sorts of noise? l suspect that Japanese capt is giving out "hollywood sound bites" for impressing the writer and readers.

The lamp's hum can travel towards surrounding sea water a) through its socket b) through the air. a) is probably what is causing this issue, since it is solid-solid-water transmission, rather than air-solid-water.

I dont think that is a great example anyways, since the sub, when underwater, provides only limited space for the sound waves to dissipate, unlike a hovering copter over a sea surface, which has like, half the known universe to disperse the acoustic waves.

[shiv]

An ultrasound scan bounces sound off body organs and creates an image of what is inside. For this the scanner generates sound that travels through the body, bounces off something and returns. Bats do pretty much the same thing. Bats and ultrasound scanners are unaffected by external noises like people talking and other animals. Other sounds are ignored

Active dunking sonars also create images in the same way. They too ignore sounds like rotor sounds

Here is an ultrasound image of an unborn baby


Sonar image of a Sea floor wreck that is world phamous in Amreeka

[LokeshC]

interesting discussion

The noise from fluorescent light transmits via air via water to enemy submarine sonar.

So a raft mounted gearbox or prop shaft bearings can almost completely smother sound, but a flourescent lamp's minimal hum from magnetostriction cannot be smothered after bouncing around the walls of a craft made for absorbing all sorts of noise? l suspect that Japanese capt is giving out "hollywood sound bites" for impressing the writer and readers.

Also the acoustic spectrum of a florescent light is predominant at a much higher than the audible range. Which means any object small enough to be the size of its wavelength will disperse and absorb the sound energy. Every nut bolt, pipe, and surface irregularity will kill off that noise.

The real issue is at low frequency and high energy. For example engine noise and vibrations that have wavelengths comparable to the size of the sub. They cannot be absorbed by the structures in the sub that easily. So need to be damped at the source. If not they will transmit through the hull.

[brar_w]

Slightly different but an interesting read none the less -

Acoustic detection and localization of a turboprop aircraft by an array of hydrophones towed below the sea surface ;IEEE Journal of Oceanic Engineering

[tsarkar]

So a raft mounted gearbox or prop shaft bearings can almost completely smother sound

It minimises but does not almost completely smother noise (not sound).

The lamp's hum can travel towards surrounding sea water a) through its socket b) through the air. a) is probably what is causing this issue, since it is solid-solid-water transmission, rather than air-solid-water.

Despite the losses caused by whichever the medium, modern sonars are sensetive enough to discern. And multi-path and multiple medium transmissions are detectable.

that Japanese capt

Retired Vice Admiral Masao Kobayashi commanded Japan’s submarine fleet from 2007 to 2009.

Irrespective of whatever he said and with whatever intent he said, please refer him with his proper designation. Please respect his role and what he's earned.

Sir. Active sonar produces noise and listens for echoes. It will selectively listen for echoes of the frequencies it produces and ignore others. It does not matter one whit if the submarine can hear the rotor. the sub can surely hear the ping from the sonar.

The noise from the Ka 226 is irrelevant as long as the dunked sonar is an active sonar that is pinging and listening for echoes. You are wrong.

Coming to your basic premise, do you know what percentage of operations does a naval sonar spend in the active mode, irrespective of whether it's ship, submarine or helicopter mounted? And why?

[Singha]

I will go behind tsarkar on this. a sub might not be able to triangulate and generate a SAM solution on a wandering heli but should be able to pickup something is there, perhaps even using a tethered sound detector variable depth buoy towed behind it. unlike the limitations of a airborne platform subs have no lack of antenna space, processing or power budget ... the sonar is the key equipment onboard.

[shiv]

Coming to your basic premise, do you know what percentage of operations does a naval sonar spend in the active mode, irrespective of whether it's ship, submarine or helicopter mounted? And why?

You are moving the goalpost sir. Dunking sonar will be active and so it does not matter whether the sub hears the helo or not so your Kamov helicopter noise argument was wrong. That said in these days of advanced acoustics - it should be possible to cancel out the helicopter noise or ignore those frequencies and listen for the frequencies produced by active sources on ships or buoys.

I would have thought that a sub captain would be foolhardy if he did not go all quiet when he knows that his sub is being pinged. Once he goes quiet the only way to detect him is by active sonar. This much is common sense and general information.

[shiv]

a sub might not be able to triangulate and generate a SAM solution on a wandering heli but should be able to pickup something is there, perhaps even using a tethered sound detector variable depth buoy towed behind it. unlike the limitations of a airborne platform subs have no lack of antenna space, processing or power budget ... the sonar is the key equipment onboard.

Yes but when it picks up something it cannot run away at 1000 kmph. All it can do is go as silent as possible and wait for the helo or ship to start sending out pings and hope that the subs own stealth features prevent it from being picked up. So the helo crew need not care two hoots whether the sub can hear then or not. They dunk their sonar and start pinging away to glory while all the ships and buoys within tens of km listen for the echoes, drawing an image of the echoes returned by the pings

[tsarkar]

Coming to your basic premise, do you know what percentage of operations does a naval sonar spend in the active mode, irrespective of whether it's ship, submarine or helicopter mounted? And why?

You are moving the goalpost sir. Dunking sonar will be active and so it does not matter whether the sub hears the helo or not so your Kamov helicopter noise argument was wrong. That said in these days of advanced acoustics - it should be possible to cancel out the helicopter noise or ignore those frequencies and listen for the frequencies produced by active sources on ships or buoys.

I would have thought that a sub captain would be foolhardy if he did not go all quiet when he knows that his sub is being pinged. Once he goes quiet the only way to detect him is by active sonar. This much is common sense and general information.

No, the goalpost is the same.

How do you conclude dunking sonar will be active all the time?

How do you think helicopters hunt submarines? Fly out to the middle of the sea and start pinging at full volume on dunking sonar in active mode?

In fact if active sonar is such a wonderful panacea, why take so much effort for lowering acoustic observability and radiated noise in Kamorta and Shivalik class ships? Just go full volume on active sonar the moment the ship leaves harbour. Why don't ships do so?

The answer to this question is the answer to the original question - and goalpost - why helicopter radiated noise should be low.

[Rakesh]

AFAIK, Pakistan or China does not have something similar to the link below in their arsenal...so what can actually happen to an Indian helo crew looking for a Pak or Chinese sub?

https://en.wikipedia.org/wiki/IDAS_(missile)

[ShauryaT]

My understanding is active sonar is used only intermittently as the source can be tracked.

tsarkar: Are there qualifications of depth of the sub and frequencies to the sound from air and also height of sound emission, decibel levels if loudness is the issue? Cannot think there are no mitigating factors that IN would not be using all these years.

[ramana]

Service experience beats book knowledge often times.

Japanese admiral does not need to impress anyone.

He is telling facts of life.

The high frequency of fluorescent lamps magnetic ballast (~ 2KHz) is the problem as it travels far.

Even electronic ballast has >20Khz and can be detected.

Also hydrophones and attached computer processing (FFT) are very sensitive.

Why are we getting so argumentative?

[shiv]

How do you conclude dunking sonar will be active all the time?

How do you think helicopters hunt submarines? Fly out to the middle of the sea and start pinging at full volume on dunking sonar in active mode?

In fact if active sonar is such a wonderful panacea, why take so much effort for lowering acoustic observability and radiated noise in Kamorta and Shivalik class ships? Just go full volume on active sonar the moment the ship leaves harbour. Why don't ships do so?

The answer to this question is the answer to the original question - and goalpost - why helicopter radiated noise should be low.

Sir you are fudging now. There is no such thing as a silent helicopter. Once a helo dips its sonar it is not going to hear any submarine noises.

But it can still listen for pings. Pings can be produced by the helicopter sonar itself or an external sonar - on a ship or a buoy. If the helo produces the ping it will be in active mode. If the helo is listening for pings produced by some other source it will be in passive mode. In every case the echoes will be of known frequency. The submarine sonar will hear everything but there is precious little the sub can do other than sit silent and hope it is not detected.

Secondly the expected frequency of noises from a moving submarine are in a low frequency range different from the sea state 2 noise made by helicopter downwash. Those latter noises will be ignored or in fact actively cancelled. So this business of silent helicopter is a bogey. I certainly do not agree with what you have claimed. You have failed to produce any papers to support your claim and have simply chosen to sidestep your subject of more noisy-less noisy helos by asking goalpost moving questions

[tsarkar]

How do you conclude dunking sonar will be active all the time?

How do you think helicopters hunt submarines? Fly out to the middle of the sea and start pinging at full volume on dunking sonar in active mode?

In fact if active sonar is such a wonderful panacea, why take so much effort for lowering acoustic observability and radiated noise in Kamorta and Shivalik class ships? Just go full volume on active sonar the moment the ship leaves harbour. Why don't ships do so?

The answer to this question is the answer to the original question - and goalpost - why helicopter radiated noise should be low.

Sir you are fudging now. There is no such thing as a silent helicopter. Once a helo dips its sonar it is not going to hear any submarine noises.

But it can still listen for pings. Pings can be produced by the helicopter sonar itself or an external sonar - on a ship or a buoy. If the helo produces the ping it will be in active mode. If the helo is listening for pings produced by some other source it will be in passive mode. In every case the echoes will be of known frequency. The submarine sonar will hear everything but there is precious little the sub can do other than sit silent and hope it is not detected.

Secondly the expected frequency of noises from a moving submarine are in a low frequency range different from the sea state 2 noise made by helicopter downwash. Those latter noises will be ignored or in fact actively cancelled. So this business of silent helicopter is a bogey. I certainly do not agree with what you have claimed. You have failed to produce any papers to support your claim and have simply chosen to sidestep your subject of more noisy-less noisy helos by asking goalpost moving questions

I'll start by answering my own questions first.

When an active sonar sends a transmission, the range at which a discernable reflected echo is received is less than the range to which the original transmission will go. So more than detecting something, active sonar advertises your presence. An enemy submarine might receive an active ping from the dipping sonar of helicopter at ranges where the return echo might be too faint for the dipping sonar to receive and process. The submarine might fire a Harpoon or Klub at the bearing of the active transmission and take out the ship hosting the helicopter.

Which is why all sonars passively listen 99.99% of the time. Its about finding the other chap before he finds you. Which is why so much accoustic shielding is done for ships and submarines with machinery mounted on rafts to dampen vibrations. Which is why pains are taken to measure radiated noise in the first place, and on discovering discernable noise from fluorescent lighting, efforts are taken to dampen them. So that you hear the other chap before he hears you.

How do helicopters hunt submarines? Comparing the size of seas bordering our coast and the area of an active dipping sonar or sonobuoys, thousands of helicopter sorties and lakhs of sonobuoys would be required.

Submarines go by the credo of run silent run deep. So much is the paranoia for silence that during action stations, men hold their urine because of the noise made by the liquid on ceramic/metal pan, and the noise made by liquid running inside the pipes, the noise of flushing.

They hide between layers of thermocline, hence run deep.

Submarines are detected at a high level by their electronic transmissions. Both PNS Ghazi and PNS Hangor were detected and tracked by their radio communications with HQ.

Submarines are also detected by seabed sonar arrays or low frequency arrays towed by ships. Given the length of arrays, ships deploying such arrays would not at their max speed, because the flow noise might impede the arrays.

Needless to say, towed array detection range is more than ship sonar detection range. Once a contact has been discerned on TAS, Maritime Patrol Aircraft are called in or own helicopter launched.

When helicopter launches dipping sonar, the intent is to passively listen. Because one hears at longer ranges than the range one might get its own transmission reflections.

Only when a rough fix is estimated, then active sonar is used to provide accurate cueing for launching helicopter torpedo. In case of ship, it will use its shipbourne active sonar to provide cueing for shipbourne torpedoes or rockets. Active sonars are used less than 1% of the time.

A submarine with alerted crew moving on batteries is impossible to detect. So the enemy submarine should not suspect anything. It will be moving on diesels making discernable noise. It will go silent at the slightest of threat.

Which is why a helicopter with higher radiated noise has a higher chance of alerting the enemy submarine when it is transiting to/from probable locations where submarine has been discerned by ship's low frequency arrays.

INS Kukhri was sunk because she was at low speeds trying to detect PNS Hangor using Lt. Jain's sonar. However, PNS Hangor detected INS Kukhri first, stayed silent, and plotted Kukhri's course.

Now, Ramana, I need you to decide who is being argumentative here. The sequence of posts is there for everyone to read.

Shiv is accusing me of fudging. Is there truth in his allegation? Do I have the right to respond?

Shiv's original post was -

I have never read any references to the effect that helicopters in the air can be heard by submarines that are completely submerged with no snooping devices sticking out of the surface......a request for more information that sound energy can impact the surface of water and not get dissipated but continue as coherent sound waves detectable underwater by submarines.. I doubt it but I am willing to be educated......The little physics that I know suggests that sound energy from the atmosphere will dissipate itself on the water surface and not get transmitted as recognizable sound patterns for long distances in water.

I responded with research data on helicopter radiated noise. The post is there for everyone to read. There are graphs on helicopter radiated noise measurements.

Vina makes the following post with no scientific basis, comes up with his favourite fish analogies, and calls the reseach data bunkum. I ask moderators how Vina gets away by calling authentic reseach data bunkum?

...Sound energy cannot appreciably penetrate the air water medium ,as it will get fully reflected from the surface ,and for all practical purposes a sub underwater cannot hear a hovering helicopter or an LRMP (even if flying very low)...

Vina then makes a personal attack on me with no facts. What do moderators do about this? Nothing. Maybe he could've posted data to substantiate his point of view. But no, Vina being moderator's friends, can do what he wants.

This part is YOUR spin to claim what is actually signal to noise reduction efforts on a dunking sonar says actually what you claim to be true. In fact, yes, the air /water boundary is REFLECTIVE to sound , and there is no way any submarine can actually listen in practice like you want detect that noise from afar and even detect the helicopter and make tactical use of it. Sure, if the helicopter is right over head and the sub is some 5 to 10 ms below the surface, you will have some disemboweled sound filtering in (and no it wont sound remotely like what you hear about the chopper's rotor in the air), very few freqencies of the spectrum would get in and that too with huge phase shifts.. And NO, that sound (follows the square law in terms of energy loss) will dissipate very quickly (esp higher freq) and it cannot be detected at long ranges (which will be low to ultra low freq) and needs to be in SOFAR channels to really propagate far.

Shiv then responds without facts as well.

You references are all out dated and are from the days when they were still discovering how helicopter sounds interfere with sonar not how submarines can hear helicopters.

Shiv conveniently ignores that one of the papers was published in 1984 and much after discovering how helicopter sounds interfere with sonar.

He does not get any scientific explanation as to why submarines cannot hear helicopter radiated noise, especially if its in the same frequency range that interferes with dipping sonar transmission and reception.

By his convoluted logic, dipping sonar transmissions can travel and its reflections can return, but helicopter radiated noise in the same frequency range cannot travel.

I ignore their personal attacks and respond with more research data

http://asa.scitation.org/doi/abs/10.1121/1.1913206
Noise Signature of an Aircraft in Level Flight over a Hydrophone in the Sea
An aircraft flying over a hydrophone in the sea produces a noise signature whose magnitude and duration depend on such parameters as hydrophone depth, water depth, and flight altitude. This signature represents sound reaching the hydrophone in four different ways: via a direct refracted path, via one or more bottom reflections, via the so‐called lateral wave, and via sea scattering..........In a field experiment, a Navy P3 Orion turboprop aircraft flew over hydrophones at two depths in deep water. The brief noise signature, lasting but a few seconds, was found to be accounted for statisfactorily by the refracted sound field.

Brar_w posts more research data on detection of aircraft noise underwater.

Shiv ignores the research data and keeps making personal attacks

Dunking sonar will be active and so it does not matter whether the sub hears the helo or not

Shiv assumes the submarine will be within dunking sonar reflection range. Does Shiv pause to consider if the submarine is beyond the range at which dunking sonar will receive a discernable reflection, but submarine can receive the original transmission? This is the case most of the time in the big wide sea.

And finally Shiv makes more personal attacks

Sir you are fudging now. There is no such thing as a silent helicopter.

There is no fudging, the posts are there for everyone to read. And it was never about silent helicopters, it was about helicopter radiated noise

I certainly do not agree with what you have claimed. You have failed to produce any papers to support your claim and have simply chosen to sidestep your subject of more noisy-less noisy helos by asking goalpost moving questions

All papers on helicopter radiated noise, P3 detected by hydrophones in deep water, further research as posted by brar_w is there for everyone to read.

Now, coming to a larger issue, coteries are there everwhere. Some COAS have Rajput Regiment coterie, some COAS have Gurkha Regiment coterie. There is NDA coterie, there is IMA coterie, there is OTA coterie. In the corporate world, there is IIT coterie, there is IIM coterie, there is REC/NIT coterie, there is Ivy League coterie too. Coteries are the biggest enemies of meritocracy but exist everywhere.

So I'm not surprised coteries exist on BR and shiv & vina being pally with moderators get away with pages after pages of irrelevant whale analogies.

Vina denigrates respected naval officers on page 105 of the previous Naval Thread and no moderator does anything.

See the trouble with throwing names like this and appealing to "Admiral Hiranandani" is disregarding the possibility that the other guy might actually have greater background, experience and knowledge than the good Admiral in these particular matters (after all, Admiral was a Deck Officer otherwise he couldnt have become Chief) . Coming to the point is there even a possibility , nay a plausibility (however remote) that I might actually know better than the Admiral on these limited points (not on overall naval warfare and stuff etc).

Admiral Hiranandani was VCNS and wrote 3 volumes of Indian Navy's history. Had Vina bothered to read, then the chapter on INS Shivalik construction quoted the Cdr (now Rear Adm) Vaidyanathan, who was project director.

https://www.indiannavy.nic.in/sites/def ... 7Apr16.pdf

Yet Mr. Pompous Vina thinks he knows better than the project director but no action is taken against Vina.

Not just that, Vina makes dishonest remarks on ACM Raha

Let me also point out a few things more than Arup Raha Harrumphed about recently as "improvements "

Asked for provision of growth for AESA. Asked for higher fuel load and range, asked for airborne refuelling,asked for IR tracker, asked for internal SPJ (they had already done the Bison upgrade by then, they knew that an SPJ was needed), asked for higher thrust engine. IF they had done that at the start of FSED phase, the LCA that would have come out would have the mould line of the proposed MKII right from the beginning and NOT the current Mk1 version! There would have been a fuselage stretch for extra room for equipment and fuel, aero refinements to match that ask and you could have fielded a version with a normal radar like the MK1 but with an airframe that incorporated the stuff you wanted , you have got a right sized airframe and not come and Harrumph and try to derail the program at the last minute saying oh, I want an INTERNAL SPJ! Where the hell were you guys at FSED stage , when the plane is basically getting re-engineered?

What remedies do moderators offer for members saying outright lies and dishonest statements?

For me, I come to read and absorb, and share what I have to share. I respond to personal attacks with facts, and let reader's decide what is wheat and what is chaff.

But if there exists a coterie on BR that makes dishonest statements and personal attacks, and gets away with it, then wouldn't this coterie turn BR into a frog in a well that thinks nothing is bigger than the well?

http://www.swamivivekanandaquotes.org/2 ... story.html

[tsarkar]

tsarkar: Are there qualifications of depth of the sub and frequencies to the sound from air and also height of sound emission, decibel levels if loudness is the issue? Cannot think there are no mitigating factors that IN would not be using all these years.

For undersea warfare, a whole variables are scientifically measured and addressed.

This is where Survey Ships and Acoustic Research Ships like INS Sagardhwani come to play. Survey ships patiently measure the depth of thermoclines in different seasons in different parts of the seas.

This research helps 1. hunt enemy submarine better and 2. own submarine to operate effectively.

http://timesofindia.indiatimes.com/city ... 167573.cms

The most striking features of the vessel are the eight scientific laboratories in different disciplines

[Cain Marko]

I will go behind tsarkar on this. a sub might not be able to triangulate and generate a SAM solution on a wandering heli but should be able to pickup something is there, perhaps even using a tethered sound detector variable depth buoy towed behind it. unlike the limitations of a airborne platform subs have no lack of antenna space, processing or power budget ... the sonar is the key equipment onboard.

Ya, I think I remember something to this effect in the hunt for red October

But this link suggests that it is nearly impossible for sound made above water to be heard below....although sensitive machines could potentially do so...pg. 65

https://books.google.com/books?id=roIk6 ... er&f=false

[sudeepj]

Can the slap of the rotors be heard under water? IMVVHO, probably yes. Consider that sufficient air is being slapped down to hold up the 12 tonne chopper! This is a lot of energy being transmitted to the air mass and thence to water. In fact, in this picture, you can see the rhythmic harmonics on the ocean surface, not very different from a tabla/drum struck hard!

Does a twin main rotor chopper such as the Kamovs produce a bigger rotor slap on the water? Again, possible because the air flow from the rotors would be over a smaller area compared to the single rotor.. But I am not sure.

Lastly, variations in amplitude up to a few dbs are not much as far as detectability goes.. the gain can be increased using many widely known signal processing techniques. Further more, just as the sound signature of ships are known, I am sure the signature of choppers beating down on the water is also widely known (or could be estimated from known parameters of the chopper). This knowledge of whether the main frequency is 100Hz, 200Hz etc. makes it easy to improve the (theoretical) detection capability of the sub. The first set of improvements a competent electronics engineer will do to a system detecting a sub hunting chopper from a sub will render the few dbs difference in the 'under water radiated sound' irrelevant. Just my opinion.

[Singha]

the americans also use the CH53 to drag a floating mine trawl - which no doubt has its own noises.

I have heard they also experimented with flying a heli low over the water behind a carrier and ahead of a wake homing dummy torpedo to make the water turbulent and slowly mislead the torpedo onto another course while the carrier shuts its engines...no idea if that was a trial or a combat strategy since the carriers have their own torpedo decoys and some variation of the prairie masker system https://en.wikipedia.org/wiki/Prairie-Masker