General ship propulsion

Wolverine

Banned Idiot
Re: PLAN ship propulsion thread

Is it worth the effort? Is the rest of a carrier's propulsion quiet enough, or potentially quiet enough, to make such reactors worth while? We are talking four shafts and speeds that are dictated more by wind over the deck considerations than outright stealth. It is up to her escorts to sprint and drift, and to listen intently while drifting. Would not a sprinting escort give the game away too?

Did I mention anything about stealth? China does not have a shipbased nuclear powerplant and I was wondering out loud about whether its sub-based nuclear reactors could be used in lieu of a reactor designed specifically for ships.
 

Ambivalent

Junior Member
Re: PLAN ship propulsion thread

Did I mention anything about stealth? China does not have a shipbased nuclear powerplant and I was wondering out loud about whether its sub-based nuclear reactors could be used in lieu of a reactor designed specifically for ships.
I'm thinking out loud too. :) Submarine reactors are designed with quietness in mind. This is probably not such a priority for a big aircraft carrier's propulsion. What is the shaft horespower of China's most powerful submarine? I can't find any open source figure. Could we assume it is close to the 30,000 Kw of France's SSBN's? Assume for the sake of argument you could achieve 40,000 or so horsepower per shaft? Is that reasonable to you?
I have seen several power plants attributed to the Kuznetsov, some claiming it is powered by a pair of 50,000 horsepower turbines through four shafts ( two turbines into four shafts, hmm, how does that work? ) . One source claims the powerplant is gas turbines, which is not believable since the class has known boiler problems. The best claim I have seen is eight boilers, eight turbines and four shafts, for 200,000 shp total. That sounds an awful lot like two powerplants from an old Berkut or newer Sovremenny ( same hull and machinery from the same shipyard ) which seems more reasonable. All three classes are plagued by boiler problems too. How many submarine reactors will you need to build the 200,000 shp one would need to move a Kuznetsov sized hull at tactical speeds? I'm thinking there will have to be some major scaling up from a submarine powerplant. It wouldn't be a direct swap.
 
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montyp165

Senior Member
Re: PLAN ship propulsion thread

The Enterprise uses 8 reactors for 4 shafts, so even using 2 20,000 KW reactors per shaft wouldn't be an issue in itself.
 

Ambivalent

Junior Member
Re: PLAN ship propulsion thread

The Enterprise uses 8 reactors for 4 shafts, so even using 2 20,000 KW reactors per shaft wouldn't be an issue in itself.
Yes, but this implies China would have to develop a different turbine set than used in it's submarines. The turbines are what generate the shaft horsepower, the reactors or boilers simply supply the steam. Instead of one reactor driving both high and low pressure turbines on a single shaft, you will have two reactors feeding steam to a heat exchanger that develops steam for a larger, more powerful set of gear turbines. Since nuclear propulsion runs at lower temperatures and pressures than the superheated dry steam ( lower pressure wet steam ) typical of modern high pressure oil fired steam plants, the turbines will have to be very different from those in a Kuznetsov.
 

Pointblank

Senior Member
Re: PLAN ship propulsion thread

The Enterprise uses 8 reactors for 4 shafts, so even using 2 20,000 KW reactors per shaft wouldn't be an issue in itself.

Ah, but the original intent of having 8 reactors for the USS Enterprise was because they were very conservative as to the estimated power requirements. If the Enterprise was an conventional carrier, she would have had 8 boilers in the place of the reactors. Along with her cruiser-styled hull, the Enterprise has a surprising ability to quickly build up steam and accelerate, which was only matched by the gas-turbine powered ships in the late 1970's. The Nimitz-class carriers used a 2 reactor design because of the expense required to build, fuel, and maintain a carrier with 8 reactors.
 

Ambivalent

Junior Member
Re: PLAN ship propulsion thread

Ah, but the original intent of having 8 reactors for the USS Enterprise was because they were very conservative as to the estimated power requirements. If the Enterprise was an conventional carrier, she would have had 8 boilers in the place of the reactors. Along with her cruiser-styled hull, the Enterprise has a surprising ability to quickly build up steam and accelerate, which was only matched by the gas-turbine powered ships in the late 1970's. The Nimitz-class carriers used a 2 reactor design because of the expense required to build, fuel, and maintain a carrier with 8 reactors.

They are using bomb grade high enriched uranium in the Nimitz reactors, the reason why they can go so long between refuelings compared to Enterprise and earlier nuclear powered ships. Those refuelings are incredibly costly and time consuming, requiring a lot of the ship to be opened up.
 

Pointblank

Senior Member
Re: PLAN ship propulsion thread

They are using bomb grade high enriched uranium in the Nimitz reactors, the reason why they can go so long between refuelings compared to Enterprise and earlier nuclear powered ships. Those refuelings are incredibly costly and time consuming, requiring a lot of the ship to be opened up.

I should also mention that the USN is facing a personnel crunch, especially in the nuclear technician trades... this is part of the reason why the CGN's were retired early despite a refit only a few years earlier.
 

duskylim

Junior Member
VIP Professional
Re: PLAN ship propulsion thread

Dear Sirs:

The primary reason the Enterprise used 8 A2W reactors is that AT the TIME (late 1950's to early 1960's), those were the only proven designs available. By the time the Nimitz was designed (late 1960's to early 1970's) civilian and shipboard nuclear reactors had been scaled up to the point where only 2 were required instead of the original 8.

Another problem with the choice of the particular reactor design (PWR's - pressurized water reactors) is that it limited the conditions in the steam generators to below the critical temperature of water, thus limiting thermal efficiency and power that could be extracted.

That problem has plagued pressurized- and boiling-water reactors ever since, though there have been proposals to provide special channel within GE's boiling-water reactors (BWR's) for superheating steam, no commercial system has yet been fielded.

For China to have successfully built its own 2nd or 3rd? generation, naval propulsion reactors (for the 093 and 094 class submarines), means that it has probably achieved the technical level of the US in the 1970's or 1980's (using a lot of what they learned from the commercial power reactors they have been building).

As to the PLAN's indigenous Naval Gas Turbines, the progress made (or claimed) has been encouraging although no new-build designs use them.

In comparison, China builds many sea-going vessels using commercial diesel designs made in China.

Those vessels bring us back to Crobato's CODAD vs CODAG situation.

We can sum up the PLAN's situation like this, for extended cruising its vessels will probably need medium or high-speed diesels as the primary propulsion units, and (when this becomes possible) use gas turbines for higher power needs.

As they have not yet done this on their latest and fastest building new vessel (the 054A frigate, which given its limited displacement really needs a light power plant), we are forced to conclude that a suitable gas turbine power plant is not yet ready.
 

Ambivalent

Junior Member
Re: PLAN ship propulsion thread

I should also mention that the USN is facing a personnel crunch, especially in the nuclear technician trades... this is part of the reason why the CGN's were retired early despite a refit only a few years earlier.
Well, I'm not sure that is the whole story. The USN decommissioned anything that did not have VLS and Aegis. Converting the CGN's to ship VLS and AEGIS was proposed, but not worth the cost.
Meanwhile, the House Armed Services Committee and the Navy consider a law that all new combat ships be nuclear powered, and that would include destroyers and amphibs.
 

Skywatcher

Captain
Re: PLAN ship propulsion thread

Well, I'm not sure that is the whole story. The USN decommissioned anything that did not have VLS and Aegis. Converting the CGN's to ship VLS and AEGIS was proposed, but not worth the cost.
Meanwhile, the House Armed Services Committee and the Navy consider a law that all new combat ships be nuclear powered, and that would include destroyers and amphibs.

Than what's going to happen to Bath Iron Works and Ingalls?
 
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