Bharat Rakshak

imo a small lean nuke sub made if titanium is best for that role...like a new alfa class with a light water reactor....the oscar would have a tough time in areas of east asia under green water belt

Any news, on when the second sub is getting delivered to us?

going by certain fire accidents with russkie subs, I expect us to focus on fire proof silicone rubbers for those smooth joints, bushings, washers, mounts, vibration control and other sound proof requirements.

^ If you are referring to the recent fire in Murmansk, it's the workers from the yard that are at times careless. While yards have good safety practices, it is not unusual amongst thousands of workers some to be careless and be a cause for a fire. It would not be an operational sub they would be working in a dry dock. Power would be from the yard, Multiple gangs doing hot and cold steel work on the hull and tanks..safety coordination in such matters is quite dependent on the yard than on the operational and safety features built into the sub.

^^^ harbans,

I agree with you 400%.

I also think we must keep in mind that the hulls of these subs are clad in rubber, actually an engineered form (I mean chemically and morphologically engineered) form of rubber that holds flowing pockets of water against the metal hull of the sub. The outter surface is essentially smooth, and it wouldn't take more than one hot, flying spark to ignite that, particularly if it were a little greasy too and there was a steady wind blowing across the point of contact. Once such a fire gets going, depending on the kind of rubber, it may leach oils while burning, making the fire impossible to extinguish with water. This means chemical fire fighting materials must be used, but those loose a lot of pressure when used in cold environments.

Folks, I know it looks bad, but current military technologies are very demanding. The average observer looks at something like this and immediately thinks of careless smoking (which happens everywhere) and wonders why they couldn't be more competent in a military shipyard. Well, there's more to it than that......

........ there always is.

Wait for the official report.

I am thinking if we can build a line of smallish N-boats like the Alfa class 3200t submerged with a single small reactor (max submerged speed can be 30knots rather than a record breaking figure to keep the reactor and steam gear smaller) that could be a nice improvement to the AIP proposal.

essentially the same crew and armament as a kilo and able to visit the yellow sea and south china sea where big clumsy 7500t SSNs have difficulty

http://en.wikipedia.org/wiki/Alfa_class_submarine

They may not have the endurance needed for an N-sub in that case sir.

Doesn't a low submerged speed have more to do with reduced turbulence and stealth?

Yes it does but modern submarine like US Virginia , Akula-3 ,SeaWolf maintain something called as silent tactical speed where the submarine is fast enough yet it can maintain a good stealth and sonar working at those speed. That was actually one of the key innovation of US Sea Wolf class SSN which credited for fast search rates at high tactical speed maintaining stealth.

Just as an example older nuclear submarine for eg you really had to do 4-5 knots to get those stealth capbility while Sea Wolf was credited to achieve the same stealth at 18-20 knots and Akula-2/3 at 12 knots.

high sprint speed is useful to relocate after firing shots and then drift or escaping from hostile torpedoes. obviously silence is not a concern there.

Correct me if I am wrong, after firing of torpedoes or in case of a SSBN, its nuclear tipped missiles, dont the subs run as silent as possible, so as to remain undetected. And running silent implies running slowly. One would not want to create a ruckus while escape, and the best way to do is via slow speed.

The other point is who tells the truth about max depth reachable and max speeds?

the wiki entry for Alfa class (42 knot top speed) claims the appearance of this class the likelihood of similar follow on classes made the western allies develop faster torpedoes like mk48cap and spearfish, and asroc type missiles. ofcourse the ussr discarded the idea later and went for quietness over speed in victor and akula class...but still the retained the 35knot top speed .... perhaps to be better escape torpedoes in the water and so on...if not to run away after firing a salvo.

The high speed of these Subs, i.e. Alfa, was so that they could do a quick sprint out of their harbors to neutralize any ships/submarines lying outside soviet ports. Due to the nature of naval aviation, the US CBG, had to approach close to soviet ports to enforce a blockade. Alfa were primarily meant to neutralize such threats. Consider Alfa's armaments, less than 150 km range nuclear missiles or torpedoes. These submarines were not meant to serve as SSBN.

Alfa primarily made a choice of speed over silence. Unless we plan to factor in a war with USN, we will not face any threat which will attempt to blockade our ports using naval aviation or naval surface ships. At least not until this decade is over. What we need right now is not speed. But quietness. And off course bigger displacement and bigger reactor.

In which case the faster speeds are for reaching someplace fast, instead of escaping from some place fast.

NOBODY

Even today USN official statement is that the N subs do excess of some 12 - 15 knots !!!!!!

K

Australians

Possible. For their Collins the max speed is 0.84365 knots and max depth reachable is 6526.0983 mm

K

Just a few thoughts - with no real information. A submerged speed of 8 knots translates to about 15 kmph or 360 km in 24 hours. Not great for going places - the sub would have to travel a week to find itself in foreign waters 2000 km away - but it would be virtually undetected.

Even twice that speed (16 knots) is hardly a sprint. Sailboats of yore could probably better 16 knots.

It strikes me if I pull out high school physics from the recesses of my mind that boats can be speeded up if you reduce their area of contact with water by cheating - as in hydrofoil boats, or by sheer raw power. I suspect (with no proof) that at speeds below 30 knots a ship that weighs 5000 tons and a sub that weighs 5000 tons would have a roughly similar surface area in contact with water. So if the ship can do 25 kts on the surface it should be able to do the same underwater given the same amount of power.

So I wonder if low underwater speeds have everything to do with stealth. Apart from engine/gear noise - the ship will surely set off turbulence that is detectable. Also I am guessing that no matter how high tech and stealthy you make the propeller/screw the faster you turn it the more likely it is to be noisy. That means that stealthy subs cannot turn on full power in one go and "burn rubber" as it were by letting the screw go whirrrrrrrrrr "Avast! Full speed ahead!!" as the ship accelerates. Even the acceleration must be slow to avoid turbulence and noise. That means the propeller is gradually accelerated from whoooooosh-whoooooosh to whooosh-whooosh-whooosh to whoosh-whoosh-whoosh-whoosh.

If India goes for type 216/U-216 sub, it could incorporate a NR in a local version of it.
I guess this is why the second line is delayed.

http://www.navyrecognition.com/index.ph ... iew&id=264

well if a torpedo is coming at you, stealth is moot - you need to escape and accelerate as fast as possible.

the layer of water in contact with the props actually 'boils as steam' iirc under pressure of the blades...maybe the 7 blade thing turns slower and minimizes this

Most modern cargo ships cruise at around 15 knots around most economical speed, a trade off between fuel consumption and number of trips you can made. This is a function of fuel price. Before 1970, ships traveled at 22 knots + , after fuel crisis , speeds dropped to 15 knots. Today, it is only "high speed" ferries and some container ships that go to 22knots and beyond



Some basic YinJin Ear Ring here. There are two components to a ship's resistance. They are 1) The wave making resistance, you make waves, you lose energy. Waves are made because of the air water boundary on the surface.. this is measured by the Froude Number (google for it) and 2) The skin friction resistance, which you alluded to, that is a function of the Reynold's Number (google for it).

Coming to ships and submarines. Now unlike a surface ship , a submarine has NO , repeat NO, Zilch, Nada, Zero, Cipher, Shoonya wave making resistance, because it is fully submerged and there is no air/water boundary to make waves.

So, your point that a ship with a given wetted surface area is going at 25 knots, a sub with the exact wetted surface area has to go at the same speed is not true. The sub in fact will be going substantially faster (assuming that both the ship and sub are hydro dynamically efficient and "ship shape" and have similar powering).

Google for the United States "Guppy" program and why it came about and why modern submarines have a "tear drop " hull shape, compared to WW-II subs which have a shape like a "surface boat", with the top sides fully closed.


There is a tactical speed beyond which your sensors will become "blind" with your own noise (though modern signal processing probably obviates some of this.. think Bose active noise cancelling headsets) and passive sensors will get lost in all the noise and you might have to start using active sonar . And yes, true about the propeller/screw, but with good and careful design, you can make sure that it is well manageable within the design speeds.



There is such great inertia in the system and ship machinery, that in any case, it is not a "quantized jump" from say 200 rpm to 500 rpm like in a motor boat with an outboard engine in a juffy. More than the prop, usually in ships/subs much of the source of vibration is not the props per se, but other rotating machinery, in fact the drive shafts (long rods, prone to vibration) are notorious, and hence efforts to isolate all machinery on mountings so that they cant transmit vibrations and other stuff. Subs with the motor in the aft and small short shafts and single screw will have mercifully less of such a problem. Put the engine amidships and long drive shafts driving props in the rear like most surface combatants and older WWII types...yeah, big problem.

In fact, even flushing to toilet in a submarine has to be extremely quiet. If you take the "parryware" toilet or even the TFTA "American Standard" or Uber TFTA Japanese "TOTO" and install it on a sub and if a sailor takes a dump and flushes, the "woosh" can be picked up if not isolated.

the bulbous whale nose shape is the most efficient underwater shape for a large vessel....whales have evolved into it and some of them swim 100+km a day. the swordfish & tuna family (tuna, swordfish, sailfish, marlin) can swim faster but obviously internal volume is not ideal.

the shape of a modern N-boat is almost like a killer whale.

How that "cavitation" works is like this. As the prop spins, the local pressure drops and the dissolved air in the water trends to escape by forming bubbles (aka boiling, just like water boils at lower temperatures at altitude it takes literally forever to cook rice/daal in hills and Bangalore compared to the plains as well, unless you use a pressure cooker).

What can be done is to make the props spin slower (ie bigger props, spinning slower, far more efficient), but then you run into practical limits on how big you can given the draft /clearance etc and you cant have the props get exposed when running on surface (props hitting water after going through air.slap..slapp is sure fire way of getting the thing to pieces by shock under high loading) and also increase the "Area Ratio" (ie amount of surface area of the prop in actuality, compared to what it would be if it were a solid disc.. less area more efficient, due to less loss due to surface friction.. more area, (accomplished by increasing number of blades and or increaseing the area per blade, so that a greater part of the full disc is blade and not empty) less loaded prop (ie thrust per area)and hence local pressures remain elevated preventing bubbles from forming) . One more trick that is used on surface ships is to be okay with the bubbles forming, but make sure that the bubbles collapse a bit downstream of the blades so that they are not damaged, but that cant work in a sub , where you really want to prevent any cavitation.

Shivji ... your analysis is not true.

The coefficient of friction between air and the ship is very different (much lower) than the ship and the air. So much so that there is an entire branch of hydrodynamics which deals with how to handle the layer of ship where the transition happens from water to air.


Also water being a much more denser fluid has a much higher drag. In lay mans terms think of this if you are trying to push a sub through fluid, then you have to displace the fluid in front of it. The heavier the fluid, the more effort you have to make. For vacuum it will be zero, for air it will be higher, for water it will be even higher, even higher through quicksand and so on.

Hence any sub at full power will be much faster when at the surface than when completely submerged.

P.S. Did not see Vina's answers ... he has explained things in detail.

True for WW2 era design sub that was more of boat shape and spent more time above water then under.

But the more modern design of Tear Drop Hull( Kilo ) or Albacore type ( Virginia ) are much faster under water then when surfaced.

^^^ I stand corrected.

Most of the energy is wasted in cavitation around the screw and by generating the bow wave and wakes. Tear drop-shaped hulls generate huge waves and wide wakes and lose a lot of energy when surfaced. This is not a problem when submerged. Also beyond a particular depth, the higher pressure of the water causes the screw to be more efficient by reducing cavitation and improving the linear flow of water.

Both these cause increased propulsion energy to be utilized to move the sub forward rather than waste it by creating turbulence in the water.

If you mean "laminar" flow, well, foggedabout it. Other than the front part of the bow (I distinctly remember a very nice pic of a US N boat, Virginia class? running on the surface with such flow clearly visible) the rest of the flow will be partially or fully turbulent, more so towards the rear as the flow is decelerating and tends to separate out.

Great way to identify laminar flow btw. If it is "transparent" and you can see through the water, it has to be laminar..sort of like looking through a glass tank, coz the layers aren't mixing.

Jumping from all this technical discussion to something more strategic, if the babus are serious about poking around in the S.China Sea, a 2nd Akula would be of great use, not to mention them backfires. Otherwise, best stay put and dhoti shiver in waters closer to home!

Modern torpedoes travel beteeen 50 and 100 knots so no sub would seriously be able to outrun a torpedo coming at it except under exceptional circumstances - provided the sub has sensors to detect the incoming torpedo. Anti- torp weapons may be an idea but I don't know of any

Every sub would have sensor to detect an incoming torpedo - a passive sonar. Something traveling at 60+ knots should be noisy and detectable no?

Most torpedoes are said to have speeds of 45-55 knots. The closer one is to a torpedo, the lesser the chance of escaping. If lucky and at a distance then the best way is to run away from it at maximum speed. This will give more time to release lots of countermeasures with the only hope of the torpedo selecting the countermeasure instead of the sub.

Merlin most torpedoes today have variable speed pump jet propulsion , so they can attain silent slow speed or top sprint speed during terminal attack , generally they are guided by fire optic cable and can attack the target approaching the target from different direction/speed making it difficult to get to its source which is the submarine stretching across many km , the onboard sonar on the torpedo ( and/or submarine sonar ) will give all the needed information on the target and the operator can control it till its very close and then cut loose the FO/Wire and let the Torpedo attack at full speed either passively or using topredo own active sonar , giving the target very little time to react , you just need a small hole on the sub pressure hull , the depth and pressure will do the rest.

A good example is British Spearfish HWT
http://baesystems.com/ProductsServices/ ... 91715.html

These seems to be the basics of Torpedo evasion for a sub
http://www.scribd.com/doc/49609458/101/Torpedo-Evasion

Ok so sounds a bit more difficult to detect a torpedo if its running ultra quiet. Wonder if it would be more easy to detect the launching sub and fire an anti-sub missile/rocket to force it to cut of the torpedo and evade the incoming.

Also torpedo, once its guidance cable is cut, should be amenable to full jamming via noisemakers right?

No. It's more like chaff and flares used by aircraft when chased by a missile. Something similar but here it takes place in slow motion. The chances of the torpedo choosing the sub over the countermeasure exits. and the number of torpedoes that can be fired against a sub is much higher.
Each and every platform varies in it's torpedo evading game. Subs can dive deep, can run silent. Surface platforms don't have that luxury but they do have capabilities like helicopters that help to detect subs using active sonar techniques. Subs always prefer to be in silent mode or passive sonar mode listening to whatever is in their surrounding. Once a surface ship detects a contact, it will use rockets to target that area. This may be followed by Torpedo launch followed by launch of a helicopter to detect that sub. Once spotted by a surface combatant and if the sub is not attacking, then the chances of its survival is almost nil. The only thing the sub can do is go so slow and keep diving to the maximum depth and move away from the possible searching area of the surface combatant. Almost impossible.

The ultra quiet torps are the new inventions. It makes evading torpedoes much more difficult. So subs must try to get undetected in the first place (Nowadays it's much more important than earlier times, earlier there was a second chance. Today it may not be there).

http://www.bharat-rakshak.com/MONITOR/I ... oseph.html
Austin, is that written by you? Needs update on India's latest torpedoes Varunastra, LWT training torpedoes etc.
http://livefist.blogspot.com/2011/05/in ... ready.html Is there something called Takshak Torpedo?
India's torpedoes
http://livefist.blogspot.com/2011/01/in ... -2011.html

Yes its almost been a decade , its times to rewrite considering there is so much of development happening around , may be after DexExpo we might see more information on Indian Torpedo development coming out and would re-write it.

I remember reading a long time back we were working with Kazak on Wake Homer Torpedo but nothing after that , hopefully we have worked and quietly inducted it.