[locusjag]

Speaking of the INS Arihant, here's an analysis by a 2 decade experienced retired US submariner -

https://youtu.be/stoYRQKhKtQ

He also alludes to the similarity of the Arihant's hull and the Kilo's hull.

[V.Narayan]

@ads11 and @locusjag, thank you for sharing your posts, videos and charts. Some observations -

1. In terms of our nuclear strategy we seem to be following, and in my opinion rightly so, the minimum credible deterrent approach like France. A nation with 400 nuclear warheads is probably only 1% safer than a nation with 20. So if we have one boat out at any point in time with 3 SLBMs and 3 SRBMs on board that's all we need to stay credible.
2. Whether we took the Kilo as a starting point I don't know. In any case when a ship's hull is designed you first build a scale model and test it in a tank and then scale it up to a real life dimension of say 20X to build a Kilo or 25X to build an SSBN. All pure tear drop hull bows look identical. Photo of USS Ohio below.
3. The 15-metre beam seems to match the typical 10-metre beam of the single hull USN/Royal Navy SSBNs adjusted for the double hull. So I would think the inner dimensions of both pressure hulls {Arihant and HMS Resolution class} are similar.
4. INS Arighat should be commissioning this year after completing her sea trials and the next two will be slightly longer to accommodate 8 large tubes instead of the 4 on Arihant.

Photo Source - US Navy, Wendy Hallmark

[ads11]

Originally Posted by locusjag

Speaking of the INS Arihant, here's an analysis by a 2 decade experienced retired US submariner

I think by now everyone should have bookmarked JiveTurkey (Aaron Amick's) Youtube channel and twitter. Along with HI Sutton (of Covert Shores fame and the man behind all those great cutaway schematics) and AncientSubHunter (Kevin Noonan) you have 3 subsurface leading lights to follow in the social media space to keep abreast of the latest goings on.

Originally Posted by V.Narayan

@ads11 and @locusjag, thank you for sharing your posts, videos and charts. Some observations -

1. In terms of our nuclear strategy we seem to be following, and in my opinion rightly so, the minimum credible deterrent approach like France. A nation with 400 nuclear warheads is probably only 1% safer than a nation with 20. So if we have one boat out at any point in time with 3 SLBMs and 3 SRBMs on board that's all we need to stay credible.
2. Whether we took the Kilo as a starting point I don't know. In any case when a ship's hull is designed you first build a scale model and test it in a tank and then scale it up to a real life dimension of say 20X to build a Kilo or 25X to build an SSBN. All pure tear drop hull bows look identical. Photo of USS Ohio below.
3. The 15-metre beam seems to match the typical 10-metre beam of the single hull USN/Royal Navy SSBNs adjusted for the double hull. So I would think the inner dimensions of both pressure hulls {Arihant and HMS Resolution class} are similar.
4. INS Arighat should be commissioning this year after completing her sea trials and the next two will be slightly longer to accommodate 8 large tubes instead of the 4 on Arihant.

I can't argue with this. I'm no total denuclearisation advocate (though it would be nice to have a world where this is possible) but I will admit I've been disheartened by recent tensions and collapse of control treaties leading to Russia, USA and now Britain(*) to announce an increase in warhead count for the first time in decades. I truly find it absurd that military leadership would resort to this when each of these countries already possess well beyond the necessary stockpile to achieve their second strike deterrence needs (*I will admit in Britain's case that increase in numbers could just be from the overlap period for bringing in the Trident replacement missiles but Boris could've explicitly said so).

The Russians don't really have a pure tear drop hull do they? Or at least not the smooth elongate cigar shapes the Americans favour. I'm only saying because the Kilo class, which if the basis for the Arihant, doesn't have that same shape.

Good spot on the relative beam size!

Wasn't sure if there was to be a B-spec to the Arihant class but again it doesn't surprise me in the slightest given the incremental build history of the IN. Might as well take the decades worth of new knowhow and feedback on the first in class boats and the Arighat and incorporate that on later builds.

Found it interesting in JiveTurkey's video above that he at some point thought the Arihant might be an SSN or SSGN even. I guess all of us will truly find out the similarities whenever the Indian nuclear attack boat breaks cover.

[V.Narayan]

Originally Posted by ads11

The Russians don't really have a pure tear drop hull do they? Or at least not the smooth elongate cigar shapes the Americans favour. I'm only saying because the Kilo class, which if the basis for the Arihant, doesn't have that same shape.

The only true true tear drop shaped hulls were the USS Albacore, the first tear drop and its immediate operational successors the three Barbel class USN boats. Among squadron subs the Dutch Zwaardvis and the Japanese Uzushio were pure or almost pure tear drop shapes. After that to ease construction and improve internal volumes all navies went for the cigar shape more or less with tear drop only at the fore and aft. This gives immense practicality in construction and hull strength for only a tiny degradation in hydrodynamic efficiency and drag factor. The Kilo is actually closer to a pure tear drop shape than say a Los Angles. But for all practical purposes all submarines designed and built today are fundamentally tear drop hulls.

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Originally Posted by V.Narayan

The only true true tear drop shaped hulls were the USS Albacore, the first tear drop and its immediate operational successors the three Barbel class USN boats. Among squadron subs the Dutch Zwaardvis and the Japanese Uzushio were pure or almost pure tear drop shapes. After that to ease construction and improve internal volumes all navies went for the cigar shape more or less with tear drop only at the fore and aft. This gives immense practicality in construction and hull strength for only a tiny degradation in hydrodynamic efficiency and drag factor. The Kilo is actually closer to a pure tear drop shape than say a Los Angles. But for all practical purposes all submarines designed and built today are fundamentally tear drop hulls.

Gotcha, that makes sense now. The Barbel, Zwaardvis and Uzushio classes almost look organic when you see them side on - like a seal. It's always interesting to me to see how different the Royal Navy hull forms are compared to the USN boats or even the French ones.

[V.Narayan]

Originally Posted by ads11

Gotcha, that makes sense now. The Barbel, Zwaardvis and Uzushio classes almost look organic when you see them side on - like a seal. It's always interesting to me to see how different the Royal Navy hull forms are compared to the USN boats or even the French ones.

The Royal Navy stretched the parallel piece of the hull to its hydrodynamic limit thereby increasing the volume aft. Which is why when on the surface they seem more bulbous or raised aft. They also modified the fore or the 'cone' to a more angular one to better fit the sonar arrays (upper) & tubes. (lower). So each Navy worked out some variation that suited their philosophy or equipment suite best. The French did not receive tear drop design mathematics or blue prints from the USN. French boats got tear drop shapes only from their Rubis class SSNs onwards to best of my limited knowledge. I could be wrong.

Of course the biggest jump in submarine hull design and propulsion since tear drops and nuclear steam is the ducted propeller with pumpjet like propulsion which not only increase thrust significantly but also shrouds the noise of a cavitating screw. Some say the thrust at slow speeds goes up by 25%. I don't have the facts but even half the number would be mind numbing. Photo below on a model of HMS Trafalgar

[Jeroen]

The ducted propellor is not something unique to submarines, although I am sure they must have their own design and research.

The fundamental research was carried out in the 1930s! In the merchant marine ducted propellers, or nozzles as they are sometime referred to tend to be used on vessels that need to produce a lot of thrust at low speeds. E.g tugs, trawlers and such.

In fact all of the ocean going tugs and anchor handling vessels I sailed on had ducted propellers. Cavitation is of a somewhat less concern in the merchant navy, at least for noise components, which is really import for the navy. Obviously, cavitation will always cause corrosion of the propellor, hull, rudders.

I am not sure when a duct propellor becomes a pumpjet? A duct propellor is a pumpjet, but a pumpjet is not necessarily a duct propellor

I was wondering, do submarines make use of variable pitch propellers? One would think so as they need to operate at a quite a broad speed bandth. A variabele propellor would help dealing with the cavitation at different speeds as well.

Somehow, but I might be totally wrong, I have the impression submarine have fixed propellers?


Edit: just found this paper. https://s3-ap-southeast-2.amazonaws....aper/Final.pdf

Make for a fascinating read. One thing I learned, nuclear submarines might benefit from an inefficient propellor system. They need to burn off power, so the propellor acts essentially as a heat sink!

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Originally Posted by Jeroen

I am not sure when a duct propellor becomes a pumpjet?
I was wondering, do submarines make use of variable pitch propellers?
Somehow, but I might be totally wrong, I have the impression submarine have fixed propellers?
One thing I learned, nuclear submarines might benefit from an inefficient propellor system. They need to burn off power, so the propellor acts essentially as a heat sink!

Really interesting point about the propeller on a nuclear boat being used as a heat sink!

On the topic of the pump jets I remembered a great video JiveTurkey did (remember what I said about him being an incredible resource?):

https://youtu.be/mv0RjBfs-7c

Linked article too.

Coming back to the topic of when a pumpjet isn't a ducted propeller or not, I remembered this article about the system on German boats, dubbed propulsors. More specifically the Propeller Boss Vortex Diffuser or PBVD. You can find pictures and more info below: https://www.thedrive.com/the-war-zon...stic-signature

I will say I agree with you - I think submarines have fixed propellers, and by that I'm guessing you mean the blades themselves right?

[V.Narayan]

Originally Posted by Jeroen

I am not sure when a duct propellor becomes a pumpjet? A duct propellor is a pumpjet, but a pumpjet is not necessarily a duct propellor

Yes I agree that kort nozzles or ducted propellers have been around since the 1930s mainly on slow moving high torque vessels like tugs or trawlers and I am aware that this is not a traditional pump jet of a speed boat. But let’s not get caught in nomenclature. As Shakespeare wrote, “what’s in a name….”

These shrouded props of the submarines are I believe something different even though they are commonly referred to by their navies as pump jet propulsers. The name it self might be a deliberate tactic to throw nosy bodies like us off the scent.

These shrouded props clearly not only add to thrust significantly but reduce cavitation noise and I presume they are good for the top speeds of a nuclear SSN say 30+ knots or 35+ knots which itself makes it different from a kort nozzle even though both belong to the broad family of a shrouded prop. Have a look at these two photos of a Kilo class being fitted, on a trial basis, with a shrouded prop. Have a look at that prop or maybe it is one of two or three on an axis. Compare that with a traditional six or seven blade submarine prop.





Similarly the Germans in one of their latest U212 class boats fitted this device at the hub of the propeller . The cylindrical Propeller Boss Vortex Diffuser or PBVD system sits over the hub of traditional submarine propellers. It's specially machined core works to greatly decrease turbulence and cavitation they say cutting down on the propeller's audible signature and improving propulsion efficiency. How it works I don’t know. Merchant ships have had simpler variants of this on their prop hubs but this seems custom designed for a diesel electric sub.

[Jeroen]

Thanks, very interesting images. Had not seen so much detail before. Definitely different from your typical Kort Nozzles. It almost look like there is also some sort of stator (with fixed vanes) build in next to the propellor rotating.

From the little video (Borei class) I also understand something along similar lines

I will need to look into this some more, see what is available in the public domain.

Jeroen

[V.Narayan]

Govt of India approves the issue of tender for 6 conventional submarines.

https://www.indiatoday.in/india/stor...796-2021-06-04

The Govt has approved the issue of a tender by the Indian Navy for 6 diesel electric boats to be built in India in collaboration with an Indian partner. The two Indian partners are Larsen & Toubro and Mazagon Docks. The tender is likely to be in the Rs 50,000 crore range {~US$ 6.8 bn}. The submarine specs are expected to include provision for a mix of 12 land attack cruise missiles and anti-ship sea skimming missiles. I assume AIP will be specified.

I wonder if to save time and cost would it not make sense to develop a Kalvari Mk II with the French and build 6 more of them while we wait for a few or more years this historically long process to be completed.

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Originally Posted by V.Narayan

Govt of India approves the issue of tender for 6 conventional submarines.

I wonder if to save time and cost would it not make sense to develop a Kalvari Mk II with the French and build 6 more of them while we wait for a few or more years this historically long process to be completed.

This makes no sense. If they're going through the effort of retrofitting a domestic AIP module by cutting the hull of existing Kalvari class boats (no small feat mind you), why not just build more of them under license but with the AIP module included from the start just like you said? Call it the Mk2 or give it a new classification for all I care. God, our procurement really is taxing on your sanity..

The current Kalvaris can only launch the Exocet through their torpedo tubes right? I'm guessing they aren't rated for any other cruise missiles (as yet?). I'm trying to envision the thinking behind a new clean sheet design and it only makes sense to me if they were planning on going with a VLS approach for the cruise missiles, in which case, borrowing the modular playbook, you could essentially borrow from the Arihant missile module. Again, none of this is as easy as just going with the Kalvari design and just working out how to launch the cruise missiles through the torpedo tubes but I suppose someone must be thinking of the former layout for this new tender.

[locusjag]

Vishnu Som over at NDTV has reported today that our leased SSN INS Chakra is well on its way back to Vladivostok where Indian Navy is legally bound to return her, since her 10 year lease with the Indian Navy is up.

https://www.ndtv.com/india-news/navy...ed%20by%202025.

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Originally Posted by locusjag

Vishnu Som over at NDTV has reported today that our leased SSN INS Chakra is well on its way back to Vladivostok where Indian Navy is legally bound to return her, since her 10 year lease with the Indian Navy is up.

https://www.ndtv.com/india-news/navy...ed%20by%202025.

Just came across a post on ET Defence's Instagram page confirming this as well. They go on to say that as a consequence the IN won't have a SSN for a 5 year period.

I take it this means 2025-2026 is the timeline for the indigenous SSN derived from the Arihant class to become operational? Or is there another lease deal in place with Russia?

I mean the timing of the new 6 subs is hardly surprising now in context of this lease ending. Should only emphasise the importance of having more hulls to task towards tailing any adversary boats in the IOR.

[ads11]

Some rather interesting news from the Korean peninsula. Seems South Korea has joined the exclusive domestic SLBM club.

Not much known beyond the fact that the ROKN tested the SLBM from a submerged pontoon - pretty much the same way in which India proceeded as well before tests on the SSBN platform (INS Arihant). The South Koreans plan to use an entirely domestically designed AIP conventional boat with 6 VLS cells for their SLBM. They already have cruise missile equipped boats. One can't help but think, like the author does, that the signs point towards South Korea going the nuclear route, either with their boats, and eventually the SLBMs themselves. Otherwise it's a curious capability considering their primary adversary is the North (who btw have their own vintage spec ballistic missile boats), and I suppose to a lesser extent the PLAN and JMSDF.

I find it interesting in the synergy & divergence of the Indian and South Korean pathways.
India went the whole hog in terms of having a domestic SSBN with its own native SLBM capability (adapting the knowhow from land based ballistic missile programmes). South Korea it seems is building a stop gap for now, but very much leaving the door open to go nuclear later both with their propulsion and their warheads.

Speaking of the new IN submarine tender, wonder if the South Koreans will submit any bids.