Friend you do need to update your knowledge a bit. 2nd and 3rd generation SSNs had to run around 6 knots because they were pretty noisy back then. After pumpjet propulsion system 4th gen nuke boat doesn't need to care much about a SSk as was the situation against them some time back.
Friend, now you're changing the subject matter from a SSN to a "pump-jet propulsion SSN." Not all SSNs currently operated by every navy have pump-jet propulsion. Does your recently leased Akula use pump-jet? am I correct that your Akula 's quiet mode/tactical speed is still only around 6 knots (even with the OK-300s)??
Yasen class SSN does not have pump-jet, and I thought they are fourth generation nuke sub? If I remember correctly, Yasen tactical speed is well below 15knots. So they definitely patrol or hunt below 15knots.
If you think pumpjet SSN doesn't need to care much about SSK anymore, then you should write to the US naval war college and tell them to revoke their article:
Diesel-Electric Submarines, the U.S. Navy’s Latest Annoyance
https://www.usnwc.edu/getattachment...RIGHT-SUBMARINE-FOR-LURKING-IN-THE-LITTO.aspx
But even if we are only talking about pump-jet SSNs, I still don't believe that they would hunt for SSKs at over 20knots. I know that some US official claim that their Seawolf's tactical speed is 25knots, and then some BAE pr guy said their Astute can atleast match the tactical speed of the best US SSN. But when we're talking about these SSN vs modern SSKs, they won't operate at these kind of speed. (and I think comparing SSN vs SSK is relevant here, since the opponents of Chinese SSNs most likely SSKs from Japan, Vietnam, Taiwan and most likely opponent of Indian SSNs are Pak's SSK).
The reason I said they won't go over 20knots when hunting suspected enemy SSKs is because of the flow/hydrodynamic noise from the hull or the sonar array. Yes, pump-jet decreases cavitational noise and flow noise over traditional propellars dramatically but it can't help much in reducing the flow noise going across the hull and sonar array. This mean the passive sonar from enemy sub has a chance to detect this noise. But more importantly, the noise from water flowing over the array sonar can interfere or reduce its sensitivity. The flow noise from the hull can likewise compromise its hull mounted passive sonar.
Self-noise [SN] comes from the noise from the platform the sonar is on or from the flow of water across the receiving array itself. This self-noise has a minimum value which is present regardless of the speed that the array is traveling through the water, and the self noise will increase due to flow noise and the increase in noise from the platform which carries it. Self noise has a frequency and speed dependence.
Now since the flow noise increases in proportionate to speed, the SSN would need to slow down in order to increase the sensitivity of its sonars. Now, you may be right in saying that american SSNs has powerful sonars, but I highly doubt it can detect modern SSKs when going over 20knots. When modern SSKs are loittering around at under 4knots on batteries/AIP or sitting still in ambush position, they are almost silent. They pratically won't produce any flow noise or any other self-noise. The only sonar can detect them is the active sonar and the SSN would need to slow down to make the most out of it. (I have an article somewhere on my PC which explain how the current sonars that the US have in operation have difficulties in detecting modern SSK and now they are developing UUVs to solve this problem, I can link it when I have time to find it).
And if we consider the environment where enemy SSKs are most likely to operate in (near coast or littoral area), it is extremely hard for SSN to detect them. That article from naval war college explains it well.
So yes, top SSNs with pumpjet propulsion may have tactical speed over 20knots, but this speed only mean the top speed that the SSN can go undetected (supposedly). But to detect enemy SSK, this speed will need to be reduced in order to make the most out of its sonars. So when when enemy sub are suspected to be in the patrol zone or when hunting for them, its speed is decreased. This is what I mean.
And when you are claiming the 20 knots speed for SSK, it will be suicidal run for it as they don't have the required resources for it.
Most modern SSKs like the U214/212 or Scorpene can sustain a speed of 20knots for a few hours if I remember correctly. These are burst speed used in rarely situation only (maybe in a sub on sub fight or manouvre like you mentioned?).
And what do you mean by rarely operating over 20 knots. I don't get it. Regarding ssn vs ssk fight, when I say higher speed, i mean survivability and outmaneuvering.
Meaning its for certain maneuvering in certain situation only, or for transitioning when encounter with enemy subs are not expected. Like I mentioned before, they have different speed for different situation like patrolling during peace time, patrolling in hostile environment or hunting mode, etc (btw, the speeds I gave previously are for PLAN subs that I've read). Different navy may use different speed to due their different SSNs characteristic or doctrine. I suspect the Russian navy will have similar figures but I may be wrong.
A SSN biggest advantage is high speed because due to this only even if a ssk detects it first it can get behind the ssk much easily. And don't forget that even though Ssn is noisy than a ssk but its SoNAr and intelligence gathering is also pretty strong backed by abundent nuke power.
Yes this is true. But I don't agree this is going to be the case when going up against a SSK sitting still in ambush position in a littoral environment (and this is the most likely scenario that a PLAN or Indian SSN can face). But in these cases, PLAN and Indian's SSKs will be deployed to patrol these littoral area, not SSNs. If the SSNs were deployed, they will still be at a disadvantaged like what the article say:
Because of the short distances, high
sustained speed for a submarine is
not as critical a factor as it is in the
open ocean. In shallow water, a fast-
moving sub would have little time to
take corrective action should anything
go wrong. The proximity of the seabed
creates an area of reduced pressure,
called the squat (suction), under the
keel.This can lead to handling difficulties and even grounding.
And I seriously doubt PLAN and Indian's SSN will be challenged in the open ocean (blue water). Maybe the Japanese Soryu SSK with its relatively long endurance.
And why not to run away at faster speed if your position has been compromised. If you stay longer more suicidal it will become.
If you're on a solo patrol, then yes. But a SSN on an escort mission would not just simply run away, especially if the SSK is only targetting the surface fleet and not the SSN itself.
And mind it that was not only Chinese ssk which penetrated surface force screen, there have been multiple encounters and exercises where ssks have scored hit against a carrier. Surface fleet is always at disadvantage against a sub surface fleet. Period.
True.
When on patrols nuke subs are always on high level attention which means even if a ssk detects a ssn, they don't have much chance against it. If those ssks try to coordinate they will give away their position easily. They will lose their most important weapon, their stealth.
What I meant by coordinate was that a SSK would predict the coordinate that a SSN/surface fleet would pass by (with coordination and assistance from airpatrol craft, surface ships, satelite, etc.) and sit still in ambush position or loittering slowing on batteries/AIP. In this situation, the SSN is at an disadvantage in detecting the SSK. And if the SSN/surface fleet enter within the SSK torpedo range, they are in trouble.
But we are getting off topic in this thread. So I'll try say something relevant instead:
A little bird once told me that the PLAN will phase out all of their SSKs in the future. They will only be for the export market. To deal with the littoral/coastal area and where SSKs has an advantage, they're developing UUVs that works in coordination with the SSN. The silent and fast UUVs equiped with sonar will go out and scan for enemy subs or mines. The SSN would play a role of cammand and control center. The US is also developing this. They've already managed to developed battery operated UUV with endurace of over 1 month. The future is UUVs.
U knew what i mean here ... 
