After realizing I was fooled by Wikipedia (and perhaps some other sources) into thinking Chinese nuclear subs are all turbo-electric, I thought a bit more about explanations for the seeming delay apparent Huludao expansion and Type 09IIIB's construction.
As has already been discussed in this thread, one plausible explanation is that the delay was partially because PLAN wanted to wait a bit longer for better technology. If we look at the timeline of 09IIIB's construction, we see the construction began roughly the same time as Type 039C, if we account for that design approval process and construction should take longer for nuclear submarines. This matched timeline give credence to the theory that 09IIIB and 039C were waiting for some same technology.
In the 039C thread, I explained four new technologies 039C is potentially using
Lithium batteries and fuel cell AIP are irrelevant for nuclear submarine. The 2MW high speed PMSG is mated to diesel engines. So this left us with the 5MW permanent magnet marine propulsion motor. We know from official news reports that this motor was tested onboard of a submarine in Sanya in 2017. This is compatible with 09IIIB's development timeline. But is there a place for a 5MW PMM in a 6,000 - 7,000 ton nuclear submarine?
Well Shilao and crew claimed on multiple episodes of their podcast that 1) The design goal of Type 09V is for it be a state-of-the-art platform, like the J-20 of Chinese nuclear submarines. 2) Type 09V is still years away. 3) Type 09IIIB is a stopgap measure. but 4) nevertheless PLAN is satisfied with Type 09IIIB design and it will be produced in significant number.
We can expect Type 09V to be an IEPS nuclear submarine with pump-jet propulsion. What can be done with the Type 09IIIB to make it a satisfactory stopgap? Well, there's no space for IEPS unless PLAN's ready to accept lower top speed. Even turning the existing propulsion turbines to turbogenerators will probably take additional space, and the space saving from removing the mechanical transmission system is probably not enough. IEPS has its own complex power control system which is not space free either.
Well, what could be a stopgap between mechanical propulsion and IEPS? Hybrid propulsion, of course! All non-turboelectric nuclear submarines are already hybrid in a weak sense. They all have emergency/low speed electric motors. Soviet designs (Victor & Akula) have twin electric motors powering two small propellers. US designs, on the other hand, mount a small induction motor directly on the main shaft. This is where the new 5MW PMM comes in. I don't know what low speed electric motor configuration China uses, but PMMs are overall much smaller in size than induction motors of the same power and torque. I expect it won't take much additional space to replace 09IIIA's old low speed electric motor(s) with the 5MW PMM. Maybe it requires slightly lengthening the hull, or maybe not.
In the hybrid system, the 5MW PMM is mounted directly on the main shaft after the reduction gearbox, i.e. American-style. This is also the configuration of ABB's Permanent Magnet Shaft Generator. The PDF files on ABB's web page explain how it works
To make this work 09IIIB will need less powerful propulsion turbines and more powerful generator turbines. This modification is probably space neutral. And given Chinese industry's advances since Type 09IIIA's turbines were designed, new turbine designs are desirable anyway.
In the new "real hybrid" propulsion system, the 5MW PMM can either assist the propulsion turbines in driving the propeller or drive the propeller on its own once the reduction gears on the main shaft are disengaged to decouple the PMM from the propulsion turbines. My completely unscientific guesstimate is 5MW is enough to drive Type 09IIIB to about 13 knots in this turbo-electric mode.
Oh, with the right control system the PMM can do the regenerative braking thing to help speeding down the propeller and recharge battery at the same time, so the submarine can decelerate faster.
Turbo-electric propulsion mode eliminates noise from propulsion turbines and mechanical transmission (esp. the reduction gears). If 09IIIB features new coolant pumps and turbogenerators that are quieter under low loads (quite possible given China's advances in computing power, electric machines design, material & manufacturing capabilities), 09IIIB can be fairly quiet in turbo-electric mode (still noisier than Type 039C obviously, but it can move faster in electric propulsion mode than 039C can in AIP mode for a much longer period of time).
The hybrid propulsion system I purposed is definitely technologically feasible as ABB is already offering something similar as off-the-shelf commercial product. We already have the 5MW PMM ready for use, all it takes is some power control magic, which is one of the things Ma Weiming's team is very good at. Given that a full electric propulsion system is out of question due to space constrain (unless PLAN is willing to settle for a much lower top speed), a 5MW electric + 15+MW mechanical hybrid propulsion system is a very good compromise between quietness and space. All enabled by the power/torque dense PMM technology and Ma Weiming team's work on IEPS.
In conclusion, if we accept the thesis that the 09IIIB's development timeline reflected PLAN decision to wait a bit longer for a better design, then I think the development in PMM is possibly what PLAN was waiting for. I don't think PLAN would mass produce some slightly tweaked Type 09IIIA in 2020s. I expect substantial improvements. But new reactor design takes a long time to develop and test. Full electric propulsion requires either significantly enlarged hull or significantly reduced top speed. Hybrid propulsion offers quieter performance at lower speed with minimal reduction in top speed, and it uses only publicly reported hardware that we know (or highly certain) to be ready.
Last I want to say a bit on the IEPS possibility. I suppose if PLAN's ready to accept an IEPS submarine with much lower top speed (say 22 knots), I can imagine a configuration where the reactor is connected to one 20MW or two 10MW turbogenerators to power three 5MW PMMs in series. We save space by installing less powerful turbines and removing the entire mechanical transmission and the original low speed electric motor, we then use the saved space to install three PMMs (IEPS's power equipment can be distributed to some other parts of the submarine). Maybe it's doable. Whether it's worth it depends on the reactor's noise curve and how much PLAN values top speed vs quietness at medium speed. The hybrid propulsion system is potentially a significant upgrade in low speed quietness with minimal drawback, the IEPS option involves serious tradeoffs (IEPS's trade-off in top speed could be less or nil if China has pump-jet ready for use, but we have no evidence for Chinese pump-jet).
As has already been discussed in this thread, one plausible explanation is that the delay was partially because PLAN wanted to wait a bit longer for better technology. If we look at the timeline of 09IIIB's construction, we see the construction began roughly the same time as Type 039C, if we account for that design approval process and construction should take longer for nuclear submarines. This matched timeline give credence to the theory that 09IIIB and 039C were waiting for some same technology.
In the 039C thread, I explained four new technologies 039C is potentially using
Yuan Class AIP & Kilo Submarine Thread
Thanks for your analysis. I discussed this with @FairAndUnbiased a while back on the possibility of different motor on 039C. To me, it makes no sense for them to declassify engine/AIP performance on 039B and take 4 more years to develop 039C. A while back, there was speculation that they'd...
www.sinodefenceforum.com
Well Shilao and crew claimed on multiple episodes of their podcast that 1) The design goal of Type 09V is for it be a state-of-the-art platform, like the J-20 of Chinese nuclear submarines. 2) Type 09V is still years away. 3) Type 09IIIB is a stopgap measure. but 4) nevertheless PLAN is satisfied with Type 09IIIB design and it will be produced in significant number.
We can expect Type 09V to be an IEPS nuclear submarine with pump-jet propulsion. What can be done with the Type 09IIIB to make it a satisfactory stopgap? Well, there's no space for IEPS unless PLAN's ready to accept lower top speed. Even turning the existing propulsion turbines to turbogenerators will probably take additional space, and the space saving from removing the mechanical transmission system is probably not enough. IEPS has its own complex power control system which is not space free either.
Well, what could be a stopgap between mechanical propulsion and IEPS? Hybrid propulsion, of course! All non-turboelectric nuclear submarines are already hybrid in a weak sense. They all have emergency/low speed electric motors. Soviet designs (Victor & Akula) have twin electric motors powering two small propellers. US designs, on the other hand, mount a small induction motor directly on the main shaft. This is where the new 5MW PMM comes in. I don't know what low speed electric motor configuration China uses, but PMMs are overall much smaller in size than induction motors of the same power and torque. I expect it won't take much additional space to replace 09IIIA's old low speed electric motor(s) with the 5MW PMM. Maybe it requires slightly lengthening the hull, or maybe not.
In the hybrid system, the 5MW PMM is mounted directly on the main shaft after the reduction gearbox, i.e. American-style. This is also the configuration of ABB's Permanent Magnet Shaft Generator. The PDF files on ABB's web page explain how it works
To make this work 09IIIB will need less powerful propulsion turbines and more powerful generator turbines. This modification is probably space neutral. And given Chinese industry's advances since Type 09IIIA's turbines were designed, new turbine designs are desirable anyway.
In the new "real hybrid" propulsion system, the 5MW PMM can either assist the propulsion turbines in driving the propeller or drive the propeller on its own once the reduction gears on the main shaft are disengaged to decouple the PMM from the propulsion turbines. My completely unscientific guesstimate is 5MW is enough to drive Type 09IIIB to about 13 knots in this turbo-electric mode.
Oh, with the right control system the PMM can do the regenerative braking thing to help speeding down the propeller and recharge battery at the same time, so the submarine can decelerate faster.
Turbo-electric propulsion mode eliminates noise from propulsion turbines and mechanical transmission (esp. the reduction gears). If 09IIIB features new coolant pumps and turbogenerators that are quieter under low loads (quite possible given China's advances in computing power, electric machines design, material & manufacturing capabilities), 09IIIB can be fairly quiet in turbo-electric mode (still noisier than Type 039C obviously, but it can move faster in electric propulsion mode than 039C can in AIP mode for a much longer period of time).
The hybrid propulsion system I purposed is definitely technologically feasible as ABB is already offering something similar as off-the-shelf commercial product. We already have the 5MW PMM ready for use, all it takes is some power control magic, which is one of the things Ma Weiming's team is very good at. Given that a full electric propulsion system is out of question due to space constrain (unless PLAN is willing to settle for a much lower top speed), a 5MW electric + 15+MW mechanical hybrid propulsion system is a very good compromise between quietness and space. All enabled by the power/torque dense PMM technology and Ma Weiming team's work on IEPS.
In conclusion, if we accept the thesis that the 09IIIB's development timeline reflected PLAN decision to wait a bit longer for a better design, then I think the development in PMM is possibly what PLAN was waiting for. I don't think PLAN would mass produce some slightly tweaked Type 09IIIA in 2020s. I expect substantial improvements. But new reactor design takes a long time to develop and test. Full electric propulsion requires either significantly enlarged hull or significantly reduced top speed. Hybrid propulsion offers quieter performance at lower speed with minimal reduction in top speed, and it uses only publicly reported hardware that we know (or highly certain) to be ready.
Last I want to say a bit on the IEPS possibility. I suppose if PLAN's ready to accept an IEPS submarine with much lower top speed (say 22 knots), I can imagine a configuration where the reactor is connected to one 20MW or two 10MW turbogenerators to power three 5MW PMMs in series. We save space by installing less powerful turbines and removing the entire mechanical transmission and the original low speed electric motor, we then use the saved space to install three PMMs (IEPS's power equipment can be distributed to some other parts of the submarine). Maybe it's doable. Whether it's worth it depends on the reactor's noise curve and how much PLAN values top speed vs quietness at medium speed. The hybrid propulsion system is potentially a significant upgrade in low speed quietness with minimal drawback, the IEPS option involves serious tradeoffs (IEPS's trade-off in top speed could be less or nil if China has pump-jet ready for use, but we have no evidence for Chinese pump-jet).
