INS Arihant (ATV) News and Discussion -2

[member_23370]

Nothing wrong if its severodvinsk hull design as long as we can make many more. Chinese and pakis will be shitting bricks at this news.

[Manish_Sharma]

No no I didn't mean having design from Severodvinsk was bad, in fact I like it as its russia's latest and best. Apologies if gave that impression.





http://defenceradar.com/wp-content/uplo ... -sub-3.jpg

[Singha]

had never imagine the Operation Behemoth thing...super impressive.

[negi]

I think as Bharat Karnad as usual at times gets a bit too far with speculation. The hump on a SSBN is because of the height of the VL tubes for the SLBMs those who have managed to build short stubby long range BMs obviously manage with subs with little or no hump. There is no hydrodynamic advantage of having a slight hump over not having a hump else SSNs and other subs would have sported one which he implies by saying "the so-called “one and a half hulls””– that permits the boat to slice through water, performing diving and other actions more efficiently. It is a design aspect, along with several other design features, taken from the Russian Severodvinsk and Borei class nuclear subs."

One thing to bear in mind is a SSBN's primary role is to carry SLBMs iow former is designed around latter a cursory look at Russia's SSBNs is a testimony to this their SSBNs have now become leaner with less pronounced hump as they moved away from old bigger liquid fueled SLBMs to new Bulava . At height of cold war making sure you had a bigger missile capable of lobbing bigger and more nukes was a priority sonar technology was not at today's level so hydrodynamic noise was not high on priority list in any case Russians back then were still using those wide blade propellers they only moved to scimitar prop design when they got hold of high precision milling machines from Japan so noise due to a fat hump was secondary.

[vsunder]

Also the channel into Vizag is 20m deep, as per many sources. In fact they need to dredge it often.
I am not sure where Karnad gets 100m. That figure when I saw it looked suspicious. No port in India has an approach channel that is 100 metres deep. In fact no port in India has an approach channel that is 100 feet deep.

http://www.appcpir.com/visakhapatnamport.html

Also as I pointed out before, if the conning tower has crimping then how come no crimping is visible on the ledge where the gents are resting their hand. It looks the same as the hull.

[NRao]

Also as I pointed out before, if the conning tower has crimping then how come no crimping is visible on the ledge where the gents are resting their hand. It looks the same as the hull.

Eye-ball-test: The color of the hull and the ledge seem to be the same. Is it possible that both made of the same metal?

[vic]

It may just be anti-reflective paint or radar stealth coating.

[Gagan]

I think the sub has not been out of Vizag Harbor.
They have done harbour trials, letting the sub go underwater and sit on the bottom of the harbour, probably in the confines of the sub pen.
What one can say from the discoloration from plankton around the exhaust vanes is that the sub was underwater for quite some time.
Maybe the navy has dredged the 'pond' around Arihant's enclosure so that for the time being it is deep enough for submersing, maybe like 20-40meters in a very small area.
If someone says, that they kept the sub underwater for like a week, with the crew inside, in the harbour, to test its environmental systems, power generation, comms, I will believe it. But there are no crush depth trials if the sub never left the harbor

Saying that the sub reached crush depth is IMHO trying to pull a fast one out of one's musharraf.
This sub is too big, and the Vizag channel and harbour too shallow and narrow for them to take her out unobserved, period.

[Gagan]

This sub is a big enough vessel to probably need harbour tugs to escort it out of the harbour. The sub has to be surfaced for that to be done safely. The IN is not going to take a sub even partially submerged out of vizag harbor.

[Gagan]

If anything the color difference between the conning tower (Fresh and shining black) vs the hull (showing signs of algae growth) indicates that the sub went underwater ONLY to the level of the hull. The conning tower was always over the waterline.

So this sub only underwent Harbour trials, and that too was only submerged to the level of the hull, the conning tower has not tasted salt water yet

[Gagan]

tsarkar-ji, this is exactly as you described. Many thanks for your guidance that day - I had a lot of fun drawing those diagrams. It was like the blind man of HIndoostan (Me) trying to draw the sub from your directions.
Many Thanks for your directions !!!

I had made several versions of the design, one of them had EXACTLY the same contours as the Arihant, will post it

[Manish_Sharma]

True Gagan ji, your and Tsarkar ji's joint venture is a masterpiece:



Profound Pranams

[negi]

Pretty accurate , may be torpedo tubes might need to be re-positioned for we might have a Sonar array there.

[Manish_Sharma]

Why Yasen uses up whole of nose for the sonar? While we use just a small part of upper nose for sonar? Is it due to advancements by Shri AJ Paulraj that we've equally capable sonar in smaller size?

http://cdn.wonderfulengineering.com/wp- ... insk-5.jpg

[vina]

Countries with mathematical expertise and ocean going traditions have developed far better understanding of cavitation and know how to control it even at high rpm and thereby know how to build proper propellers which run silently whatever that means

Cavitation is pretty well understood. Obviously you don't want super cavitating wedge shaped blades like in a high speed boat's outboard motors where the blades are designed so that the cavitation bubbles pop well behind the blades and dont damage it.

In a sub, the trick is to have a large slow spinning prop, so that the local pressure of the water at any point does not drop below the vapor pressure at that depth. So a deeply submerged sub , it is sort of mitigated, especially when it is running slow (10m water approx 1 atm). The trouble is really when running close to the surface at high speeds.

The answer is really to increase the expanded area ration (EAR) of the blade (ie % of the blade area out of the total disc) , so that the the loading of the blade per unit area is reduced. So sub prop blades will have more blades than usual (7 to 8 blades, while even a 100,000 dwt ship will have a single 4 bladed prop) and highly twisted blades , scimitar shaped , so that there is less shock loading on the blade as it enters the water and probably highly optimized airfoil profiles (if not lifted from a standard NACA profile) from 3d inviscid flow programs.

Pump jet propulsors

Read above para. Normally there is a max on the size of the prop you can have. So either you need to go multiple props (which is more expensive, but more optimal),but if you want the ideal streamlined under water shape, either you put props one behind the other , contra-rotating like in a torpedo (or like the TU-142 airplane's or the Alizes that operated out of the Vikrant). Or if you want to have multiple stages (like in a pump), because one small sized prop cant absorb all the power, you will need to enclose it in a duct (just like your submerged bore well pump, the pumpjet propulsor is exactly that, a submerged borewell pump that sends water backwards instead of upwards).

Trouble is, as the Yakherder from UlanBator will tell you, the highest propulsive efficiency is with a single large propeller (the Betz propeller model ), not to mention complexity and weight and costs as well. Adding all the stages and the enclosed ducting (like in a borewell pump) decreases efficiency. So, if you can make things work with a single large prop without cavitation in 95% of regimes, it is the best solution. The rest is all bakwaas. Think of it. You do that in a borewell, because of the limited dia of the bore onree..

That said, in stuff like tugs, you DO want a ducted propeller because the duct is shaped like an airfoil and generates thrust and increases the bollard pull of the tug (highest pull generated at zero speed), but that is done for specialized applications, but not very good for long range open water cruising where it increases drag and adds weight.

[Indranil]

^^^ Excellent! Now that is a post. I learned a few things. No opinions. No hyperboles. Only shudh desi gyan.

[negi]

Why Yasen uses up whole of nose for the sonar? While we use just a small part of upper nose for sonar? Is it due to advancements by Shri AJ Paulraj that we've equally capable sonar in smaller size?

There is no replacement for displacement

[Cybaru]

Doesn't the first pic that India Today put out in 2-3 years ago also had the same wavy form on the conning tower ?/ If that is indicative of deep dives, then perhaps it has been deeply dippy before..

Hate linking livefist.. but this is what I could find. Admins please substitute if you can with another link.

http://www.livefistdefence.com/2009/08/arihant.html

[Manish_Sharma]

Here is one link where the collage of different images of Arihant has been put together

https://imageshack.com/i/kqcrcGauj

[Austin]

Why Yasen uses up whole of nose for the sonar? While we use just a small part of upper nose for sonar? Is it due to advancements by Shri AJ Paulraj that we've equally capable sonar in smaller size?

http://cdn.wonderfulengineering.com/wp- ... insk-5.jpg

Yasen like LA and Virginia uses Large Active/Passive Spherical Sonar that covers the entire nose and hence TT has to move backward ,Something like this
http://fas.org/man/dod-101/sys/ship/ssn21-array.jpg

Arihant like Akula or even UK Astute uses Active/Passive Cylindrical Bow Arrary (Sonar) that covers Top ( like Arihant/Kilo ) and Lower part of the sub nose below TT and the middle/top area has TT.

Something like this of Akula http://31262.tumblr.com/post/7624510396 ... onar-array

[Singha]

the spherical bow sonar probably has the biggest size and widest FOV. right from the LA class khan has gone that route. Russia has introduced it into Yasen class. so that looks like the f22 soln. rest are all compromises to various degrees to due tech lags, volume constraints....

thats why I say the virginia must be masterpiece of pkging. massive weapons loads, sonars hanging out of every place, sealed for-life reactors, yada yada.

[Manish_Sharma]

Here is a story of Sonar posted by Austin saar before also:

FIRST HAND | How Shrimp Nearly Wrecked India's First Brush With A Nuke Sub

By Vice Admiral (Retd) R.N. Ganesh

As always, the submarine left harbour in the small hours, while the city slept. A huge, ominous shadow in the dark, she moved silently but for the faint hiss of the water against her sides. At five thousand tons, she was the largest warship in the Indian Navy after the carriers. The young Captain on the bridge had done this dozens of times, but taking this formidable vessel out through the narrow channel was still exciting, with a potential surprise lurking at every bend.

Slowly the submarine made its way out of the harbour and set course for the diving area. Today they were leaving on an extended surveillance patrol of the Bay islands under simulated war conditions, as part of the essential and never-ending process of maintaining presence in one’s own waters.

Before that, however, there was a game to be played. Units of the Fleet were returning from deployment in the south, and Headquarters had decided that the submarine would intercept them in a staged encounter and carry out a mock attack before detaching to proceed on her main mission. The ships would be closer in to the shore and the submarine further out, listening out for them against the backdrop of shallow water noises. The interception area was some miles to seaward of an estuary, and recent rains would have made the seawater density variable, causing trimming problems. Not ideal waters for a large nuke, thought the Captain, but therein lay the challenge. In addition, his crew would enjoy the thrill of the hunt.

“Bridge - twenty minutes to diving area!” came the report from the charthouse. “Right - inform the Commander, please”. The order was still being relayed when the Captain reached the control room, just as the Commander ordered “diving stations.” The Engineer Officer was already there.


“We’ll catch a quick trim, then we need to crack on some speed; our initial position is about twenty miles south of here.” The first dive after leaving harbour was always a ‘trim’ dive - a slow, deliberate dive done in stages to make any adjustments necessary to the Engineer Officer’s calculated trim.

“Diving stations correct, sir,” reported the Commander. The Captain nodded at the Engineer Officer. They had worked together as a close-knit team for a year now, and there was no need for unnecessary words. Flood end groups” ordered the Engineer Officer. The diving panel operator switched the end group ballast tank main vents to “open”. There was a muffled roar as hundreds of tons of seawater flooded the end groups of tanks. The submarine sank perceptibly beneath their feet; she now rode on the buoyancy of the centre group tanks alone. While the Commander ordered “Inspect compartments” and received the reports from them, the Captain studied the trim and depth gauges and the inclinometer, looking for the first pointers to any major problems in the trim. There were none. “Submarine inspected and correct - ready to go down.” reported the Commander. “Permission to flood the centre group, sir” asked the Engineer Officer This time the roar of the water flooding the tanks was louder since the tanks were around the hull right outside the control room.

“Trim her at 40 meters for four knots - we’ll be doing a lot of listening.” The Engineer Officer nodded. The trimming operation was over soon, and as planned, they increased speed to fifteen knots. It felt good to be able to order higher speeds and not worry about the battery, thought the Captain. “We may expect contact with the ‘enemy’ between an hour and two hours from now,” reported the NO. The Captain left the control room leaving instructions to carry out a sonar search of the area and call him when anything was heard.

They reached their designated position twenty minutes early. An hour passed, and then there was a knock at
his cabin door. It was the Sonar Officer. “There’s a small problem, sir”, he said; Pilot says they should be within twenty miles of us to the south, but the sonar is unable to hear anything.”

“Unable to hear?” repeated the Captain.

“The entire southern sector - that’s where NO says they’ll probably come from - is blanked with noise. We
can’t hear anything through it.”

This was bad news. If the sonar malfunctioned, it could take hours to locate and rectify the fault. Even the main mission could be in jeopardy if dockyard help became necessary. “Get the Commander and the electrical Officer to the charthouse. We need to discuss this. Who’s on the sonar?”

“Master Chief Attar, sir” was the answer. The Captain was reassured. Attar was the best sonar Chief in the submarine arm, as far as he was concerned. He went across to the ‘sound room’, which was just abaft the control room. The Sonar Chief wished him ‘Jai Hind”, and silently handed him the headphones. The Captain had spent many an hour in the sound room getting his ears tuned to the sounds of ships’ propellers - called ‘hydrophone effect’ or ‘HE’ for short. On this occasion all he heard was the noise - it was a continuous crackling, with an occasional popping sound as made by a fire of dry, resinous wood. The noise blanked the entire southern sector - it would be impossible to hear anything through that racket, even if the ships passed close by.

They held a council in the charthouse. “No problems during the pre-patrol checks yesterday?” asked the Captain, though he knew that all sensors had been reported checked and correct. The Electrical Officer
confirmed this.

“Can you say whether the noise is external or a system fault?”

“I would say external” interposed the Commander. We made two ninety-degree turns after initially hearing the noise, but the true bearing of sector didn’t change.” The Captain nodded in agreement.

Time was ticking away. The submarine would never live it down if the fleet ships sailed past undetected. Many years earlier, the Fleet Commander, a bluff, laconic man with a sardonic sense of humour, had been the Captain’s Divisional Officer in Kharakvasla. He would have a thing or two to say about the marvellous capabilities of nuclear submarines when they next met, thought the Captain wryly.

He went back to the sound room. The Chief Sonar operator handed him the headphones and said with conviction: “It’s bio-noise, sir.” The Captain agreed. Landsmen, he mused, thought of the ocean depths as dark and silent. In fact, there was a cacophony of noise down there that could drive submarine sonarmen to distraction - whales with their long, soulful moans, dolphins with their clicking and whistling, and a host of other noisy creatures, not to mention the ambient noise of the sea itself. They had a whole taped reel of

these sounds but he had never heard this kind of noise before - certainly never anything near this loudness.

“Can’t we go around” asked the Sonar Officer.

“No - we can’t leave the area. Maybe the noise will stop after some time.”

“Sir....” The Sonar Chief hesitated. “We can try one high power transmission in that sector. It may have some effect.”

“Good idea!” The Captain got up, slapped the Sonar Chief on the shoulder, and left for the control room, visibly excited.

Although the submarine had a powerful active sonar, a transmission could compromise its stealth and was only used after carefully weighing the balance of tactical advantage. However, on this occasion there was nothing to lose. And if it worked it was well worth the tactical ‘risk’.

Soon the order came from the control room. “Sound Room, Control - standby single pulse, high power, centre bearing 200.”

“Sound room roger, stand by single pulse, high power, centre bearing 200.”

The Captain went back to the sound room, the Electrical Officer close on his heels. ‘Let’s hear it, Master Sa’ab”. One of the sonarmen switched on the loudspeaker for them. The noise was as loud as before. Sound room ready for single pulse, high power, centre bearing 200” reported the Sonar Chief. “Transmit” came the order. The second operator flipped up the guard cover and pressed the red button. They could hear the pulse as it left the ship.

More than a minute passed. And suddenly it was as if somebody had turned off a switch. One moment there was that overpowering crackling noise, and the next - total silence. The Captain shook the Sonar Chief’s hand and said “Well done, Master Sa’ab!”, and went back to the control room. Hardly had he sat in his

Captain’s chair that the report came in, the deliberately expressionless voice of the Sonar Chief:

“Control room - group HE on bearing 175, classified warships.”

The atmosphere in the control room was electrified. The Commander took the mike in hand: “D’ye hear there! This is the Commander. The sonar team has detected ‘enemy’ ships in sector south. A big shabash to them. Action stations - torpedo attack!”

“Game on!” said the navigator, as he bent over the attack plot.

We never pumped our fists in those days.

Post Script: This story is based on a real experience in INS Chakra in 1988. The noise was generated by the denizens of large shrimp beds in the general area of Kakinada. From later reading I learned that the culprit was the snapping shrimp, which thrives in tropical waters near the coast. A one and a half-inch crustacean almost foiled a 5000-ton nuclear submarine!
http://www.livefistdefence.com/2012/01/ ... ecked.html

[negi]

Arihant like Akula or even UK Astute uses Active/Passive Cylindrical Bow Arrary (Sonar) that covers Top ( like Arihant/Kilo ) and Lower part of the sub nose below TT and the middle/top area has TT.

We will be able to make a guess if we get to see position of Arihant's torpedo tubes.

[Austin]

the spherical bow sonar probably has the biggest size and widest FOV. right from the LA class khan has gone that route. Russia has introduced it into Yasen class. so that looks like the f22 soln. rest are all compromises to various degrees to due tech lags, volume constraints....

The Brits have similar solution as Akula/Arihant and they say their Astute sonar is the most capable out there , so I am not entirely convinced Spherical Sonar is the only way forward.

thats why I say the virginia must be masterpiece of pkging. massive weapons loads, sonars hanging out of every place, sealed for-life reactors, yada yada.

In an exercise between Virginia and Astute some where near US coast Astute managed to do well.

Check this http://www.freerepublic.com/focus/news/2855290/posts

[Austin]

Arihant like Akula or even UK Astute uses Active/Passive Cylindrical Bow Arrary (Sonar) that covers Top ( like Arihant/Kilo ) and Lower part of the sub nose below TT and the middle/top area has TT.

We will be able to make a guess if we get to see position of Arihant's torpedo tubes.

Agree Sir but if I have to bet my money I would say its TT is similar to Kilo.

Arihant does seem to have sonar on the top of bow too similar to Kilo.

[Singha]

only bartania keeps on loudly claiming the astute is the best
almost trying to justify its existence as a running-dog of the big gorilla.
khan baba as the incumbent big dog lets its hulking 'presence' and natgeo/discovery speak for themselves.

[jcrocks]

[quote="Dhananjay"]Here is a story of Sonar posted by Austin saar before also:

[quote]
Thanks for the interesting post, sir.
Hi all, can anyone suggest some books (fiction or true stories) based on Navy/Warships/Submarines etc. Fascinated by the challenging life of a sailor in blue waters and want to know more.
Thanks for the help.
jc

[rkhanna]

Hi all, can anyone suggest some books (fiction or true stories) based on Navy/Warships/Submarines etc. Fascinated by the challenging life of a sailor in blue waters and want to know more

If you can get invited for a few drinks at the US Club in Navy Nagar, Mumbai..

[ravip]

tsarkar-ji, this is exactly as you described. Many thanks for your guidance that day - I had a lot of fun drawing those diagrams. It was like the blind man of HIndoostan (Me) trying to draw the sub from your directions.
Many Thanks for your directions !!!

I had made several versions of the design, one of them had EXACTLY the same contours as the Arihant, will post it

I appreciate your effort sir, but this image by ndtv is the first one which let the cat out of the bag, as a matter of fact even they might have obtained it from NDB. .

[negi]

only bartania keeps on loudly claiming the astute is the best
almost trying to justify its existence as a running-dog of the big gorilla.
khan baba as the incumbent big dog lets its hulking 'presence' and natgeo/discovery speak for themselves.

I still remember in other paki foras and even keypublishing , Astute was spoken about in very high regards no one knew about it's capabilities but since it was latest from Bartania sarkar there were rumours about it being better than the Seawolf and capable of detecting chime of bells being rung in some distant church until it ran aground off isle of sky .

[Gagan]

No this was the picture that I drew with tsarkar-ji
But even this is imperfect, the tail fin is different, the curvature around the conning tower and the height of the hump need some changes. Also the water intakes and vents need to be edited. Surely there are other things on the hull under the waterline that need to be added here. But this is it !

Another image


And this for a follow on Boomer:

[tsarkar]

Gagan, when you see a photo of Arihant in the same view as your second drawing, you'll realize how close you are.

I just realized the top rudder tailplane in your drawing has greater height than the lower ruddertailplane. If you decrease the height and make them equal, then it'll be closer to the real one.

The sonar is USHUS, so you'll get reference size from Defexpo/Aero India pictures.

[tsarkar]

Ravi P, NDTV either copied or commissioned Gagan's work

[Singha]

so it would seem the arihant class is not a perfect round cylinder but more ovoid due to the hump ... which shape is dare I say like the HMS Astute herself

https://i0.wp.com/i.dailymail.co.uk/i/p ... 34x421.jpg

[tsarkar]

http://bharatkarnad.com/2014/08/21/arih ... ng-depths/

The most obvious thing that has not been commented on is the humpback on the hull — the so-called “one and a half hulls””– that permits the boat to slice through water, performing diving and other actions more efficiently. It is a design aspect, along with several other design features, taken from the Russian Severodvinsk and Borei class nuclear subs.

Mr. Karnad is horribly mistaken in -
1. His flawed understanding of “one and a half hulls”
2. Equating the hump to “one and a half hulls”
3. Incorrectly stating the benefits of the hump as "permits the boat to slice through water, performing diving and other actions more efficiently"

The correct explanation of double hull, single hull & "one and a half hulls" as well as benefits of each is accurately described here http://rbth.com/defence/2014/06/17/russ ... 37483.html

It was decided that Yasen-class submarines would not make use of the double-hull structure that all Soviet submarines had at the time. However, neither did it become a single-hull submarine, like its U.S. equivalents. Two hulls ensure a submarine's reliability and buoyancy, while a single hull means noiselessness and invisibility. Yasen became something in between, having the so-called "one and a half hull" architecture, with a light hull covering only part of the submarine's pressure hull. Another traditional feature of Soviet submarine design that was not implemented in the Yasen-class submarine was the location of its torpedo tubes in the bow. That was where the submarine's powerful sonar system Irtysh was based, so there was simply no space left for torpedoes. Consequently, the torpedo tubes were placed in the middle section of the submarine at an angle to the centreline, borrowing a construction solution widely used in the U.S.

The "performing diving and other actions more efficiently" statement is hilarious, because diving is a function of ballast tanks and hydroplanes and tailplanes. Not hull type.

The Arihant may benefit from a revolver-like contraption firing ballistic and cruise missiles; so the SSBN may carry more than just 4 K-4s/K-15s.

Revolver mechanisms require horizontal space beside the firing mechanism to store the rest of the revolver mechanism and reloads as shown here http://upload.wikimedia.org/wikipedia/c ... ighted.jpg

Unfortunately Arihant has no such horizontal width to store revolver mechanism or reloads.

Our strategic analyst is writing things without any scientific or engineering basis.

[ravip]

Ravi P, NDTV either copied or commissioned Gagan's work

May be that might be the case sir but however there are two propositions that prompted me to assume otherwise

1. The colour in the picture for different parts like underwater or the tower or the body is exactly the same as used by NDB, one can see the pictures released by NDB of submarines in NDB section of navy website or the pictures of Kolkata class ship, shivalik class etc.

2. I don't know for what reason DRDO highly prefers Mr.pallav bagla of ndtv to have first access to many historic events as it was evident during the launch of agni5, nirbhay or the k-15 video or RCI building inauguration etc. He always gets the Footage first and exclusive.

[Philip]

New naval base coming up near Visakhapatnam
http://www.business-standard.com/articl ... 458_1.html

Bay of Bengal base will house nuclear submarines and aircraft carrier
Ajai Shukla | Visakhapatnam
August 26, 2014 Last Updated at 23:25 IST

The navy has lifted the shroud of secrecy over a major new sea base being built on India's eastern coast, which will be home to the first indigenous aircraft carrier, INS Vikrant, and an armada of warships under the Eastern Naval Command.

The new base, on the Bay of Bengal, will also house India's nuclear ballistic missile submarine (SSBN) force. Current plans involve building six SSBNs, to form the underwater leg of the country's nuclear triad. The first, INS Arihant, will soon be operational; the second and the third are currently being built.

For years, the ministry of defence (MoD) has refused to acknowledge the existence of the base, which will come up around the coastal hamlet of Rambilli, 50 km south-west of Visakhapatnam. The plan is code-named 'Project Varsha'.

Divulging that the new base will house conventional as well as nuclear warships, Vice-Admiral Satish Soni, head of Eastern Naval Command, told Business Standard, "We don't talk about it much for obvious reasons. There are plans for a new base, and we hope to see one in a matter of seven-eight years."

India's eastern seaboard on the Bay of Bengal, with deep water and harbours with over 10 m depth, is far better suited as a nuclear submarine and aircraft carrier base than the western seaboard, where the shallower Arabian Sea is barely four metre deep along the coast.

Like China's massive nuclear submarine base at Hainan Island, the depth of water at Rambilli will allow submarines to enter and leave the base without being detected by satellites. This secrecy is crucial for SSBNs, which must remain undetected when they leave for months-long patrols, carrying nuclear tipped ballistic missiles.

China's rapid naval build-up, and its belligerent handling of maritime disputes with smaller neighbours in the South China Sea and East China Sea, has caused New Delhi to focus keenly on enhancing the operational posture of the eastern fleet, which must counter any threat from China.

The same concerns had, in 2001, led to the creation of the tri-service Andaman & Nicobar Command (ANC), 1,225 kilometres from Visakhapatnam in the Bay of Bengal. The ANC dominates the Malacca Strait, and the shipping routes between West Asia and south-east Asia.

Visakhapatnam is home to the eastern fleet, India's biggest, with 50 warships. The new base at Rambilli will decongest Visakhapatnam - also a major commercial hub - and provide a secure base that is removed from population centres.

Western Naval Command already has such a base, INS Kadamba, built in 2005 to decongest Mumbai. Located at Karwar, near Goa, it is home to the aircraft carrier INS Vikramaditya, and much of the western fleet. Being built in several phases, that project is code named 'Project Seabird'.

With INS Vikrant harboured in Rambilli after the aircraft carrier is commissioned in 2018, the naval air base at Visakhapatnam - INS Dega - is being expanded to house the Vikrant's MiG-29K and Tejas fighters and its helicopters when the carrier is not at sea.

Soni says the government has approved Rs 200 crore for infrastructure at INS Dega for the Vikrant's MiG-29K fighters; and another Rs 200 crore for the navy's Hawk trainers that will be based at Visakhapatnam.

Visakhapatnam's importance as a naval aviation centre has been boosted by the recent identification of a secondary airfield, to which aircraft can be diverted in case of emergencies or bad weather at Visakhapatnam. Soni says land acquisition has begun, and the state government has provided clearance to the navy.

"We are looking at Bobilli, a disused, World War II airfield about 45 nautical miles from here (Visakhapatnam). We will have fighters flying from here, so we will need an alternative base, to which flights can be diverted. Bobilli is north-west of Visakhapatnam, towards Vijayawada", said Soni.

Currently, the diversionary airfields around Visakhapatnam are: Vijayawada (157 nautical miles); Bhubaneswar (212 nautical miles); and Shamshabad (279 nautical miles).

[ramana]

Bobilli is a historical place in Andhra Pradesh history. Good choice.

[member_28108]

Bobilli is a historical place in Andhra Pradesh history. Good choice.

Bobilli is indeed a historical place but how would that be relevant to selection as a submarine harbour ?
Prasanna

[merlin]

So here are my questions on the INS Arihant

1. What are the dimensions? Length - 111 m (or 112 m?), Beam - 11 m (or 15m?), Draft - 10 m (or 11m?)
2. Surface displacement is 6000 tonnes. What is the dived displacement?
3. 83 MWt translates to how many SHP?