LuftWolf and Amizaur's Realism Mod Poll #11: Nuke Speeds

[Amizaur]

Originally Posted by FERdeBOER

I'm not correcting, I'm just asking: are not the nuclear carriers bigger than conventional ones?
If so, the engine power of the nuclear reactor should be bigger than conventional to move them at same speed.

I was talking about the case when they were same or very similar type of carrier, older units with conventional and newer ones with nuclear (was that te case?). People tend think (after reading Clancy's books) that nuclear carriers are capable of much higher speeds, some people claim 37 some even over 40kts "in emergency". But they all forget that those carriers shared the same steam turbines and all other machinery, only the steam generators were different (conventional or nuclear). The turbines had the same maximum power output so max speed was in fact the same.... Nuclear not faster than conventional ones...
But what was true that nuclear ones can accelerate much faster from low to high speed (leaving all other conventional ships in group behind, that could make false impression that they are much faster - even though fast conventional ships eventually speeded up and could even overtake the carrier at max) and can keep those max speed for long periods without worring for fuel efficiency.

Where was am reading about this... :hmm: same site as "russian post-wwII torpedos" page... NavWeaps... O here it is:

http://www.navweaps.com/index_tech/index_tech.htm

search for 'Speed Thrills III - Max speed of nuclear-powered aircraft carriers"



P.S. I have read that again and indeed - seems that some CVNs are little bigger than older CVs and actually - yes, slower, with the same power output. So you are right

Enterprise 33.6 knots (actual after last refit)
JFK 33.5 (design speed)
Kitty Hawks 33.6 (design speed)
Forrestal 32.0 knots (design speed, lower because of only 260k HP compared to 280k for above)

Nimitz 31.5 knots (actual)
Theodore Roosevelt 31.3 knots (actual)
Harry S Truman 30.9 knots (actual)

[FERdeBOER]

I also red once on an spanish defence magazine that the other "problem" with the nuclear powered carriers is the escort.
While the engine endurance is "unlimited", the carrier needs to be resuplied with food and water. And the escorts need also fuel.
And there's other thing about non-superfast nuclear carriers: some escorts could not follow it so, where's the need of developing a faster carrier? That only will be a waste of time and money (and probably reactor safety) for having a 40knot carrier wich could never use that speed.

That magazine also compared the time spent on deploying nuclear and non nuclear carrier groups from its bases... and the difference was very few...

[LoBlo]

[quote=Amizaur]

Originally Posted by LoBlo

About Seawolf speed - yes, it can have much more powerfull reactor, but it is also much bigger than LA. And correct me if I'm wrong, it's not reactor that counts, it's first the steam turbines limit (this is reason that nuclear carriers had same max speed as conventional - they had different steam generators, one conventional, second nuclear, but the turbines were the same and had same output power...) and secondly how much power the propeller can transfer to the water... (but yes, IIRC the LA is rather reactor-limited, all other parts of chain being more capable).

yep, In fact, I'm almost 100% certain that that's the origins of both the SW's quieting and its improved poweroutput of its S6W reactor over the older S6G reactor of the LA, I'ld garantee that the S6W has supplemented a traditional coolant loop cycle (like the S6G) with an additional natural circulation cooling loop providing a "silent" (i.e. no coolant pump needed) mode to 20 knots with activation of its traditional coolant pumps for full power. The combination of the two is what neccessitated the larger diameter hull and would also provided increased peak turbine flow (with the maximum flow volume of the steam turbine cycle dictated by the maxmum steam -> water cooling rate of the sub). The addition of a NC cycle, provides a "quiet mode" and boost the maximum steam flow rates at the same time.

At least that's my completely and utterly amateur theory anyway.

The SW, when compared to the Akula II, is smaller, lighter, has a more advanced propulsor, larger "powerplant" spacing, and I believe a improved peak output power. A 4-6 knot speed advantage is reasonable to me. (33 knots for the Akula II vs 38knots for the SW, or 35knots for the AkulaII vs 40knots for the SW).

btw, I'm not an expert by any means, but I did do some elementary fluid dynamics training in college. I could share some of the simple and basic stuff I remember if it would help and if anyones interested. Don't remember enough to give any hard calculations though.