Yuan Class AIP & Kilo Submarine Thread

[FairAndUnbiased]

Based on what I heard from my sources, they definitely do have noise and completely isolating those noise against low frequency sonar in deep water is not a given.

Yes, hybrid cars are quiet, but the engine in question would be a lot larger and deep sea water transmits sound really well.

I don't see why you would want to keep Stirling AIP when there are clearly better technology available now.

Your source does not say Stirling engines are noisy. It says that Stirling combustion noise is small compared to the machinery noise - transmission noise. Hybrid cars are quiet - but that's not solely due to engine size. Motorcycles are loud with a much smaller engine. Regular cars are still louder despite equal engine. Hybrids are quiet because they can run the engine cycle quietly, and that's despite having a complicated transmission.

The purpose of Stirling is that diesel fuel has far higher energy density than battery, it isn't even close. even if you halve it to account for having to bring LOX, it is still far better than pure battery. It can remain submerged with no snorkeling much longer.

The purpose of pure lithium battery subs is if you have safe waters to snorkel in - waters free of enemy ASW planes - you can charge the batteries quickly on 1 snorkel. Otherwise, ASW planes can find the radar return of the snorkel or use an onboard gas sampler to find diesel fumes. It has to be ASW planes, because otherwise ships are limited by the radar horizon in looking for snorkels.

Japan has that luxury, since the only real opposing ASW planes are PLAN, and PLAN has to get air superiority first to deploy ASW planes. But PLAN itself does not enjoy ASW plane coverage out to the 2nd island chain, only in local waters. In this situation, PLAN conventional subs have to stay submerged as long as possible and only surface when 100% absolutely safe.

Note that at the end of your source, it says that lithium battery + AIP is a great combination and SK is working on that. I have no doubt that PLAN is working on that too and is upgrading old 039As by removing lead acid batteries and replacing them with LFP.

Now fuel cell is better than Stirling for noise alone but there's some weaknesses: you need a second fuel tank to run the fuel cell since its difficult to run fuel cells off diesel directly. German Type 212 keeps the fuel cell fuel in tanks outside the pressure hull. This makes for a larger submarine diameter for equal sized pressure hull and requires hull feedthroughs for the fuel lines, creating weak spots. Fuel cells also have high nominal efficiency, but only for H2. H2 is has low energy density, so you need either pressure (costly) or a chemical hydrogen generator from ammonia or methanol. This makes fuel cells somewhat inefficient at the end.

 

[Andy1974]

Your source does not say Stirling engines are noisy. It says that Stirling combustion noise is small compared to the machinery noise - transmission noise. Hybrid cars are quiet - but that's not solely due to engine size. Motorcycles are loud with a much smaller engine. Regular cars are still louder despite equal engine. Hybrids are quiet because they can run the engine cycle quietly, and that's despite having a complicated transmission.

The purpose of Stirling is that diesel fuel has far higher energy density than battery, it isn't even close. even if you halve it to account for having to bring LOX, it is still far better than pure battery. It can remain submerged with no snorkeling much longer.

The purpose of pure lithium battery subs is if you have safe waters to snorkel in - waters free of enemy ASW planes - you can charge the batteries quickly on 1 snorkel. Otherwise, ASW planes can find the radar return of the snorkel or use an onboard gas sampler to find diesel fumes. It has to be ASW planes, because otherwise ships are limited by the radar horizon in looking for snorkels.

Japan has that luxury, since the only real opposing ASW planes are PLAN, and PLAN has to get air superiority first to deploy ASW planes. But PLAN itself does not enjoy ASW plane coverage out to the 2nd island chain, only in local waters. In this situation, PLAN conventional subs have to stay submerged as long as possible and only surface when 100% absolutely safe.

Note that at the end of your source, it says that lithium battery + AIP is a great combination and SK is working on that. I have no doubt that PLAN is working on that too and is upgrading old 039As by removing lead acid batteries and replacing them with LFP.

Now fuel cell is better than Stirling for noise alone but there's some weaknesses: you need a second fuel tank to run the fuel cell since its difficult to run fuel cells off diesel directly. German Type 212 keeps the fuel cell fuel in tanks outside the pressure hull. This makes for a larger submarine diameter for equal sized pressure hull and requires hull feedthroughs for the fuel lines, creating weak spots. Fuel cells also have high nominal efficiency, but only for H2. H2 is has low energy density, so you need either pressure (costly) or a chemical hydrogen generator from ammonia or methanol. This makes fuel cells somewhat inefficient at the end.

As soon as the snorkel goes up it’s going to be detected by satellites, if not now then in the very near future, which is fine if they can’t attack you I suppose but I wouldn’t rely on this in an emergency. Hell, soon the sub will be detected by satellite laser if it comes up to a certain depth, if not already.

What is the problem with just making a very long submarine, that has enough battery for missions lasting 3 months with decent speed, and the ability to sprint to very high speed if required?. Surely, with todays technology they can just add more batteries until the requirements are met? What am I missing here?

 

[tphuang]

China is at the forefront of electric motor and battery technology right now. LFP battery is very safe and quiet and can be recharged quickly over and over again. It has very little degradation. You don't really need much of a enclosure for it, since there is no risk of damage or fire. Or you can go with Lithium SSB. Much higher density, but you have to design the enclosure around it to keep safe. We've seen the technology here repeatedly improving. Yes, it's density will never come close to diesel or nuclear, but it also does not require additional machineries/raft and housing. On balance, if you can have 500t battery with today's LFP technology or 400t battery with today's semi-solid state battery, you could have 75 to 80 MWh of battery power.

From what I was told, it is very hard to completely isolate the sound from AIP installation. I think that's why the Japanese went away from it eventually. Also, you always want redundancy on a sub. If 2 Stirling engines generate 300 kw power and then 1 one of them ceases to operate, then you barely have enough power for even hotel load. Stirling engine produces roughly 200 to 300 kw of power to keep boat moving at 4 knots. with 75 to 80 MWh of battery power, that could last 2 weeks. If China develops a larger boat to succeed Yuan in a few years, you could see this number jump to 120 or even 150 MWh of battery power. The technology just keeps improving. Over the next few years, you could get 3 weeks of power with Lithium ion batteries alone.

The other question is about frequency of snorkel. Even with AIP, there is need for submarine to come to periscope depth and ventilate by stick out it's snorkel. This is to clear out the CO and CO2 in the submarine.

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Diesel-electric submarines snorkel frequently, to clear the exhaust from running their diesel generators to charge their batteries.

The difference with non-AIP subs is that they need many hours to fully recharge the batteries. Ventilation can be done in 30 min to an hour. If LIB charging is fast, you maybe able to do frequent 30 min to an hour surfacing in order to charge your batteries. Maybe the thought process behind the radar reflecting sail is that it will be almost as hard for MPAs to detect that type of sail vs a snorkel.

Given that China will almost assuredly have air superiority in any conflict where it will win (since it has clear underwater inferiority), Chinese submarines can count some level of protection from enemy MPAs and helicopters. As such, MPAs may not be able to detect surfaced sail from far out if PLA can provide air cover during that time. Remember, China has aircraft carriers now to protect its MPAs and to chase away enemy MPAs.

So in my mind, Stirling AIP is not optimum solution long term. There is too much speed constraint, space usage and noise concerns as far as I'm concerned. I'd much rather see if I can add as much battery pack in there as possible without affecting the speed and buoyancy of the submarine.

 

[FairAndUnbiased]

As soon as the snorkel goes up it’s going to be detected by satellites, if not now then in the very near future, which is fine if they can’t attack you I suppose but I wouldn’t rely on this in an emergency. Hell, soon the sub will be detected by satellite laser if it comes up to a certain depth, if not already.

What is the problem with just making a very long submarine, that has enough battery for missions lasting 3 months with decent speed, and the ability to sprint to very high speed if required?. Surely, with todays technology they can just add more batteries until the requirements are met? What am I missing here?

Japanese subs can use snorkel. Chinese ones can't. That's the point.

If you keep making a sub longer you have 3 problems: not cheap, not mechanically stable and not suited for littoral operations.

Cheap: it takes a ton of money to build pressure hulls with an elongated aspect ratio.

Mechanical stability: a high aspect ratio for a conventional sub means higher lateral force from currents without corresponding increase in propeller power, and you have to turn very slowly because during a turn with the planes the viscosity of the water exerts an inertial shear force on the other sides of the submarine.

Littoral operations: China's main seas are the Yellow Sea, East China Sea and South China Sea.

South China Sea is the deepest, with 5000+ meters at the deep end. This is OK for sub operations.

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In fact,

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0. Most of China's water is littoral. Chinese subs have to be good here.

1. If your sub is longer across than the water is deep (i.e. 100 m long in 80 m water) then it can't maneuver well, because it can't pitch down and dive fast without crashing.

2. There's

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, thermal layers which reflect sound are complicated because of high heating gradient relative to the water depth and discharge of freshwater from river mouths. A large, long sub creates distinctive acoustic effects here.

So for a littoral sub - which is what China needs for conventional subs - being small is very important. A littoral sub has a completely different design philosophy - except for being quiet - than an ocean sub. That's why even North Korean midget subs can sink ASW frigates in the Yellow Sea, as proven by the sinking of Cheonan.

 

[Andy1974]

Japanese subs can use snorkel. Chinese ones can't. That's the point.

If you keep making a sub longer you have 3 problems: not cheap, not mechanically stable and not suited for littoral operations.

Cheap: it takes a ton of money to build pressure hulls with an elongated aspect ratio.

Mechanical stability: a high aspect ratio for a conventional sub means higher lateral force from currents without corresponding increase in propeller power, and you have to turn very slowly because during a turn with the planes the viscosity of the water exerts an inertial shear force on the other sides of the submarine.

Littoral operations: China's main seas are the Yellow Sea, East China Sea and South China Sea.

South China Sea is the deepest, with 5000+ meters at the deep end. This is OK for sub operations.

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In fact,

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0. Most of China's water is littoral. Chinese subs have to be good here.

1. If your sub is longer across than the water is deep (i.e. 100 m long in 80 m water) then it can't maneuver well, because it can't pitch down and dive fast without crashing.

2. There's

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, thermal layers which reflect sound are complicated because of high heating gradient relative to the water depth and discharge of freshwater from river mouths. A large, long sub creates distinctive acoustic effects here.

So for a littoral sub - which is what China needs for conventional subs - being small is very important. A littoral sub has a completely different design philosophy - except for being quiet - than an ocean sub. That's why even North Korean midget subs can sink ASW frigates in the Yellow Sea, as proven by the sinking of Cheonan.

Thanks. I suppose this just confirms my belief that recharging has to be used.

 

[FairAndUnbiased]

China is at the forefront of electric motor and battery technology right now. LFP battery is very safe and quiet and can be recharged quickly over and over again. It has very little degradation. You don't really need much of a enclosure for it, since there is no risk of damage or fire. Or you can go with Lithium SSB. Much higher density, but you have to design the enclosure around it to keep safe. We've seen the technology here repeatedly improving. Yes, it's density will never come close to diesel or nuclear, but it also does not require additional machineries/raft and housing. On balance, if you can have 500t battery with today's LFP technology or 400t battery with today's semi-solid state battery, you could have 75 to 80 MWh of battery power.

From what I was told, it is very hard to completely isolate the sound from AIP installation. I think that's why the Japanese went away from it eventually. Also, you always want redundancy on a sub. If 2 Stirling engines generate 300 kw power and then 1 one of them ceases to operate, then you barely have enough power for even hotel load. Stirling engine produces roughly 200 to 300 kw of power to keep boat moving at 4 knots. with 75 to 80 MWh of battery power, that could last 2 weeks. If China develops a larger boat to succeed Yuan in a few years, you could see this number jump to 120 or even 150 MWh of battery power. The technology just keeps improving. Over the next few years, you could get 3 weeks of power with Lithium ion batteries alone.

The other question is about frequency of snorkel. Even with AIP, there is need for submarine to come to periscope depth and ventilate by stick out it's snorkel. This is to clear out the CO and CO2 in the submarine.

Please, Log in or Register to view URLs content!

The difference with non-AIP subs is that they need many hours to fully recharge the batteries. Ventilation can be done in 30 min to an hour. If LIB charging is fast, you maybe able to do frequent 30 min to an hour surfacing in order to charge your batteries. Maybe the thought process behind the radar reflecting sail is that it will be almost as hard for MPAs to detect that type of sail vs a snorkel.

Given that China will almost assuredly have air superiority in any conflict where it will win (since it has clear underwater inferiority), Chinese submarines can count some level of protection from enemy MPAs and helicopters. As such, MPAs may not be able to detect surfaced sail from far out if PLA can provide air cover during that time. Remember, China has aircraft carriers now to protect its MPAs and to chase away enemy MPAs.

So in my mind, Stirling AIP is not optimum solution long term. There is too much speed constraint, space usage and noise concerns as far as I'm concerned. I'd much rather see if I can add as much battery pack in there as possible without affecting the speed and buoyancy of the submarine.

Stirling AIP does not have speed constraints when used solely as a generator in combination with LFP. Nobody says you have to keep inferior lead batteries just because you use Stirling AIP. Stirling AIP is used to run a generator which doesn't care what particular battery is on the other end. It had speed constraints on the Gotland class because Kochums made the Stirling AIPs in the 1980's when everyone used lead batteries. You can always speed up with LFP as long as you don't care too much about endurance. There's no way around the energy density of diesel vs. LFP in terms of pure storage.

Conventional subs that are too big are not good, see my above post re: littorals. The entire Yellow Sea is only 44 m deep on average and 152 m deep at the most. A Soryu sub stuck vertically reaches as tall as a 5 story building above the water in the Yellow Sea. East China Sea is 3/4 < 200 m deep. The smaller the conventional sub, the more it resists active sonar pings (assuming equal shaping and anechoic tiles) and avoids weird multi-reflection waveguide effects with either the surface or the ocean bottom. That means denser the better.

The mission of PLAN conventional attack subs is to sink enemy shit in shallow waters. Shallow waters, in China's case, is almost all water within 700 km of China. AIP helps this mission. Just because US or Japan does something doesn't mean it's good for China's situation. Japan has Sea of Japan and NorPac missions against Russian subs after all. How come Sweden never reconsidered AIP for the Baltic Sea and North Sea, which is very similar to China's situation?

 

[Andy1974]

Stirling AIP does not have speed constraints when used solely as a generator in combination with LFP. Nobody says you have to keep inferior lead batteries just because you use Stirling AIP. Stirling AIP is used to run a generator which doesn't care what particular battery is on the other end. It had speed constraints on the Gotland class because Kochums made the Stirling AIPs in the 1980's when everyone used lead batteries. You can always speed up with LFP as long as you don't care too much about endurance. There's no way around the energy density of diesel vs. LFP in terms of pure storage.

Conventional subs that are too big are not good, see my above post re: littorals. The entire Yellow Sea is only 44 m deep on average and 152 m deep at the most. A Soryu sub stuck vertically reaches as tall as a 5 story building above the water in the Yellow Sea. East China Sea is 3/4 < 200 m deep. The smaller the conventional sub, the more it resists active sonar pings (assuming equal shaping and anechoic tiles) and avoids weird multi-reflection waveguide effects with either the surface or the ocean bottom. That means denser the better.

The mission of PLAN conventional attack subs is to sink enemy shit in shallow waters. Shallow waters, in China's case, is almost all water within 700 km of China. AIP helps this mission. Just because US or Japan does something doesn't mean it's good for China's situation. Japan has Sea of Japan and NorPac missions against Russian subs after all. How come Sweden never reconsidered AIP for the Baltic Sea and North Sea, which is very similar to China's situation?

If burning diesel (and supporting systems) causes enough noise to be detected by your enemies, it doesn’t matter how energy dense it is. I hope China goes for the quietest solution possible which I believe is just plain electric. There are some range issues right now, but new batteries will have more power in the future and can be swapped out.

A battery sub that can patrol the Yellow Sea today can maybe patrol much further after a battery upgrade during a MLU for example. The energy density of diesel is not getting better, but battery’s are.

Ultimately, China needs battery boats that operate in the middle of the pacific.

 

[tphuang]

Stirling AIP does not have speed constraints when used solely as a generator in combination with LFP. Nobody says you have to keep inferior lead batteries just because you use Stirling AIP. Stirling AIP is used to run a generator which doesn't care what particular battery is on the other end. It had speed constraints on the Gotland class because Kochums made the Stirling AIPs in the 1980's when everyone used lead batteries. You can always speed up with LFP as long as you don't care too much about endurance. There's no way around the energy density of diesel vs. LFP in terms of pure storage.

Again, Stirling AIP installation produces noise. The great thing with battery electric is that they don't require additional generators, so are very quiet. Using Stirling + LFP to achieve a certain speed doesn't make sense when you can get to that speed with LFP alone.

If you can get 10 to 15 days of endurance with LIB, I don't really see why you want the additional complexity of AIP. Again, let's say in 5 years, we get to 400 wh/kg Lithium SSB and 250 wh/kg LFP battery in production (they are already close to that right now). If you build a large sub that can hold 600t of LFP battery or 450t of SSB battery, then you could get 150 to 180 MWh of battery. That's enough for 500 to 600 hours of endurance at 300 kw. Why would you not remove AIP?

And given their very advanced fuel cell industry, I'd explore putting fuel cell (with no Diesel engines) into conventional subs also. Maybe the technology isn't there right now to power the sub to move at greater than 10 knots, but it will continue to improve over time. They'd need to come back to the port to get refueled. But if you can get a month of endurance from that, it seems well worth it.

The goal should be how to make the sub quietest possible.

Conventional subs that are too big are not good, see my above post re: littorals. The entire Yellow Sea is only 44 m deep on average and 152 m deep at the most. A Soryu sub stuck vertically reaches as tall as a 5 story building above the water in the Yellow Sea. East China Sea is 3/4 < 200 m deep. The smaller the conventional sub, the more it resists active sonar pings (assuming equal shaping and anechoic tiles) and avoids weird multi-reflection waveguide effects with either the surface or the ocean bottom. That means denser the better.

The mission of PLAN conventional attack subs is to sink enemy shit in shallow waters. Shallow waters, in China's case, is almost all water within 700 km of China. AIP helps this mission. Just because US or Japan does something doesn't mean it's good for China's situation. Japan has Sea of Japan and NorPac missions against Russian subs after all. How come Sweden never reconsidered AIP for the Baltic Sea and North Sea, which is very similar to China's situation?

China has a new littoral class submarine. You know, that new single hull sub we saw recently. They are perfect for littoral waters. And with LIB, they can have many days of endurance. They can do that job much better than Song class.

China needs a large conventional sub to operate in the deep waters of SCS and Philippines Sea. You don't put those long range LF flanker array sonars on Yuan unless you want them to detect surface ships from really far out in deep water. They don't have the same operating environment as the Swedes and Germans.

Keep in mind that with the TAS they installed on 039C, Yuan subs will also be better at detecting quiet subs in deeper water. All of this extends the territories where 094s can operate.

Japanese subs can use snorkel. Chinese ones can't. That's the point.

why? Chinese subs already snorkel as I discussed above. Having AIP does not provide enough power for systems that remove CO2 and CO from a sub. You still need to ventilate.

If China does not have local air superiority, then it's really in trouble. All those missiles are to ensure that they can prevent the other side from taking off from carriers or air bases.

 

[Strangelove]

 

[FairAndUnbiased]

Thanks. I suppose this just confirms my belief that recharging has to be used.

well that's actually a pretty interesting idea, a wireless charging infrastructure buried in the shallow littorals. wireless charging has already been proven to work through several meters of water.

if I were a PLAN sub designer, I'd design next gen "Type 043" subs as a littoral specialized sub that dominates the shallow water within the 1st island chain with the following characteristics and infrastructure:

Infrastructure:

1. fund offshore wind turbines at random places.

2. use cables connected to both offshore wind turbines and the on-shore grid to secret seabed recharge points located remotely

Actual sub:

1.

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for both AIP and surface engine, no mechanical hydrocarbon engine at all. This eliminates 3 detection routes: 1. detection through exhaust gas samplers 2. detection through engine noise 3. detection through transmission noise

2. LFP batteries with wireless charging capabilities for fast sprinting, fast recharge and very high endurance in littorals.

3. Littoral specialized equipment and nonacoustic sensing: LIDAR and refractive index (wake) sensors on photonic mast, fiber optics guided UUVs, mines and torpedos

Again, Stirling AIP installation produces noise. The great thing with battery electric is that they don't require additional generators, so are very quiet. Using Stirling + LFP to achieve a certain speed doesn't make sense when you can get to that speed with LFP alone.

If you can get 10 to 15 days of endurance with LIB, I don't really see why you want the additional complexity of AIP. Again, let's say in 5 years, we get to 400 wh/kg Lithium SSB and 250 wh/kg LFP battery in production (they are already close to that right now). If you build a large sub that can hold 600t of LFP battery or 450t of SSB battery, then you could get 150 to 180 MWh of battery. That's enough for 500 to 600 hours of endurance at 300 kw. Why would you not remove AIP?

And given their very advanced fuel cell industry, I'd explore putting fuel cell (with no Diesel engines) into conventional subs also. Maybe the technology isn't there right now to power the sub to move at greater than 10 knots, but it will continue to improve over time. They'd need to come back to the port to get refueled. But if you can get a month of endurance from that, it seems well worth it.

The goal should be how to make the sub quietest possible.


China has a new littoral class submarine. You know, that new single hull sub we saw recently. They are perfect for littoral waters. And with LIB, they can have many days of endurance. They can do that job much better than Song class.

China needs a large conventional sub to operate in the deep waters of SCS and Philippines Sea. You don't put those long range LF flanker array sonars on Yuan unless you want them to detect surface ships from really far out in deep water. They don't have the same operating environment as the Swedes and Germans.

Keep in mind that with the TAS they installed on 039C, Yuan subs will also be better at detecting quiet subs in deeper water. All of this extends the territories where 094s can operate.


why? Chinese subs already snorkel as I discussed above. Having AIP does not provide enough power for systems that remove CO2 and CO from a sub. You still need to ventilate.

If China does not have local air superiority, then it's really in trouble. All those missiles are to ensure that they can prevent the other side from taking off from carriers or air bases.

My assumption for littoral would be snorkeling possible very occasionally, but almost no snorkeling possible past Okinawa.

If PLAN is deploying a dedicated new class of littoral midget sub then I think that would be a better choice.

For future tech, I think China could go, like you said, with 100% fuel cell, no mechanical engine at all, once fuel cell tech matures. I believe ammonia fuel cell will be the best choice, and it has matured sufficiently for at least testing on marine cargo transport. In addition, key advantages of ammonia fuel cell is that you don't need to urgently get rid of exhaust (scrub NOX, main exhaust is just H2O and N2) and ammonia fuel cells are inherently AIP if you add a LOX tank, no need for separate drive.

A 100% ammonia fuel cell sub would be extremely deadly: 0 engine noise, 0 transmission noise, 0 hydrocarbon fumes. The only remaining route of detection is magnetic or looking for the snorkel which pops up only 20-30 minutes every day.