Hms Queen Elizabeth

[swerve]

Wouldn't have made any difference to the difficulty or otherwise of converting to cat & trap during the build. Still have needed major structural work.

 

Only benefit would have been that we could have fitted old-fashioned catapults of a type the USN is no longer buying.

[Panzermann]

Makes me wonder why the three NATO states looking at new catapults did nit get together to standardize a common EM catapult to lower unit costs?

[DB]

Nuclear steam is pretty crap - core temperature limitations to prevent the softening of fuel rods mean you don't get the highest pressure steam, which means that you also need a separate steam generating plant for the catapults (I suppose alternatives are possible, but I'd imagine they would make the catapult design even more bulky). This is one good reason for moving away from steam catapults. Sure, nuclear-electric power generation isn't as efficient for the same reasons - low quality steam - but it matters much less there.

 

"NATO States looking for new catapults" = US + UK + FR, with the US wanting about 3 times as many as the other two combined, and also putting them on a ship that has about twice the displacement. The chance of getting a collaborative agreement that results in a workable solution for all is, I would wager, negligible.

[Adam_S]

Nuclear steam is pretty crap - core temperature limitations to prevent the softening of fuel rods mean you don't get the highest pressure steam, which means that you also need a separate steam generating plant for the catapults (I suppose alternatives are possible, but I'd imagine they would make the catapult design even more bulky). This is one good reason for moving away from steam catapults. Sure, nuclear-electric power generation isn't as efficient for the same reasons - low quality steam - but it matters much less there.

 

"NATO States looking for new catapults" = US + UK + FR, with the US wanting about 3 times as many as the other two combined, and also putting them on a ship that has about twice the displacement. The chance of getting a collaborative agreement that results in a workable solution for all is, I would wager, negligible.

 

Surely you wouldn't want to feed steam directly from the core to the catapults anyway, what with it being massively radioactive and all. Plus I thought military reactors were pressurized water designs anyway, meaning that there shouldn't be any steam in the reactor at all.

[Sardaukar]

Which I why im surprised we didnt work more closely with the French if this was supposed to be an option, rather than going with the gold plated version from the Americans. I accept the real issue was not designing in enough room into the ship to put them in, but you would have thought we would have alt least talked to them about closer collaboration in the early design stages.

 

RN working closer with French?? You gotta be sh*tting me! That Idea is..dead on water since 15th century.

[swerve]

 

Wouldn't have made any difference to the difficulty or otherwise of converting to cat & trap during the build. Still have needed major structural work.

 

Only benefit would have been that we could have fitted old-fashioned catapults of a type the USN is no longer buying.

 

Did the French develop their own, or did they salvage ones from their previous carriers?

 

When Charles de Gaulle was built, back in the 1990s, the USA was still building carriers with steam catapults. CdGs catapults were new. The French ordered some more for the cancelled (or indefinitely postponed) PA2, but when that was dropped the USN took over the order for spares for its old catapults - thus reducing future orders for spares. AFAIK they were the last US-built steam catapults.

 

US steam catapults will be supported for many years, but there won't be any new ones.

[swerve]

Which I why im surprised we didnt work more closely with the French if this was supposed to be an option, rather than going with the gold plated version from the Americans. I accept the real issue was not designing in enough room into the ship to put them in, but you would have thought we would have alt least talked to them about closer collaboration in the early design stages.

AFAIK there's room - but without it being reserved, it was convenient to use it for other purposes, rather than put them elsewhere. The stuff now there wouldn't be lost if catapults were fitted, but there'd have to be lots of cutting open of compartments, re-routing of utilities, putting in of new bulkheads, etc.

 

We did talk to the French. There was actually a spell in the last decade when the French bought into our design & we were working on it jointly, with the French version (PA2), having US-built steam catapults (see above), but even so . . .

 

I was following it at the time.

 

 

PS. EMALS was too undeveloped for the French to trust it back then, & there was also the commonality with CdG issue.

Edited November 4, 2015 by swerve

[zaarin7]

Well we used plenty of their ships before. I seem to recall listening to the tour guide on HMS Victory that the RN loved French ships because they were well built.

 

They French know how to fight in them, but.....

I've read in more than one place the RN found French prizes to be higher maintenance than English built ships because the timbers were not seasoned enough and the ships were built heavier.

[Colin]

But they were also better designed and sailed better and closer to the wind then their counterparts from my reading.

[sunday]

 

Nuclear steam is pretty crap - core temperature limitations to prevent the softening of fuel rods mean you don't get the highest pressure steam, which means that you also need a separate steam generating plant for the catapults (I suppose alternatives are possible, but I'd imagine they would make the catapult design even more bulky). This is one good reason for moving away from steam catapults. Sure, nuclear-electric power generation isn't as efficient for the same reasons - low quality steam - but it matters much less there.

 

"NATO States looking for new catapults" = US + UK + FR, with the US wanting about 3 times as many as the other two combined, and also putting them on a ship that has about twice the displacement. The chance of getting a collaborative agreement that results in a workable solution for all is, I would wager, negligible.

 

Surely you wouldn't want to feed steam directly from the core to the catapults anyway, what with it being massively radioactive and all. Plus I thought military reactors were pressurized water designs anyway, meaning that there shouldn't be any steam in the reactor at all.

 

 

Well, the boiling water reactors actually feed to turbines steam generated in the core. Pure water does not get radioactive when passing through a reactor core. Only a bit, and that is because impurities.

[Adam_S]

 

Well, the boiling water reactors actually feed to turbines steam generated in the core. Pure water does not get radioactive when passing through a reactor core. Only a bit, and that is because impurities.

 

 

Yes but in a BWR the steam is condensed and fed back into the reactor again in a closed loop.

 

Here's a picture of a steam catapult launch. See how there's steam coming out of the catapult? Now if that was coolant water from out of the core then that flight deck is not going to be a healthy place to be.

 

 

Coolant water can also become radioactive from absorption of neutrons giving things like deuterium or short-lived isotopes of nitrogen.

[sunday]

No modern Rankine-cycle plant works with an open primary loop -like Mississippi paddle-wheelers or steam locomotives- anymore. Anyway, in the matter of coolant activation, is way, way more important the contribution of the rust particles dissolved in the water than the possible activation of hydrogen to give harmless deuterium (quite low cross section), then tritium. And tritium is, after all, a weak beta emitter, so mostly harmless.

 

There could be a possible problem with oxygen activation, but it is very short-term. See this:

 

 

 

In the areas around a pressurized water reactors or boiling water reactors during normal operation, a significant amount of radiation is produced due to the fast neutron activation of coolant water oxygen via a (n,p) reaction. The activated oxygen-16 nucleus emits a proton (hydrogen nucleus), and transmutes to nitrogen-16, which has a very short life before decaying back to oxygen-16.[2]
16
8O + 1
0n → 1
1p + 16
7N (Decays rapidly)
16
7N → γ + e− → 16
8O
This activation of the coolant water requires extra biological shielding around the nuclear reactor plant. It is the high energy gamma ray in the second reaction that causes the major concern. This is why water that has recently been inside a nuclear reactor must be shielded until this radiation subsides. One to two minutes is generally sufficient.

[DB]

I believe that reactors tend to use primary and secondary loops, with a heat exchanger to transfer heat from the primary coolant loop (i.e. the one that cools the core) to the secondary loop. Regardless of whether primary loop coolant is used or not, the issue is that the generated steam temperature is low compared to that possible with superheated boilers.

 

In other words, the argument that a nuclear kettle is somehow better for steam catapults may be a bogus one.

 

tl;dr: I'm arguing with Stuart over something, as usual.

[rmgill]

The super heated plants on the Iowa BB's was a peculiar system. There were a set of fast resupply transports that had the same steam plants and knowledge. I think use of all of those spares was part of the calculus alongside their manning cost that did in the BBs.

[sunday]

Both BWR and PWR send saturated steam to the HP turbine. No superheating -like in the Iowas power plants, for instance- is possible. I know of a naval nuclear plant that tried to use steam superheating, in the first Seawolf nuke attack sub, but the superheater tubes were trouble and difficult to put to work.

[swerve]

I believe that reactors tend to use primary and secondary loops, with a heat exchanger to transfer heat from the primary coolant loop (i.e. the one that cools the core) to the secondary loop. Regardless of whether primary loop coolant is used or not, the issue is that the generated steam temperature is low compared to that possible with superheated boilers.

 

In other words, the argument that a nuclear kettle is somehow better for steam catapults may be a bogus one.

 

I think it's better than diesels, which is the alternative. With diesels, a separate steam generator would be needed, just for the catapults.

 

Of course, there's always all-electric propulsion with electric catapults, no steam anywhere.

Edited November 5, 2015 by swerve

[Mr King]

[Chris Werb]

On a CVN couldn't you use turbines powered by lower pressure steam to generate electricity that would in turn super-heat steam for the cats?

[Simon Tan]

Shhhhhhh......

[RETAC21]

The super heated plants on the Iowa BB's was a peculiar system. There were a set of fast resupply transports that had the same steam plants and knowledge. I think use of all of those spares was part of the calculus alongside their manning cost that did in the BBs.

 

https://en.wikipedia.org/wiki/Sacramento-class_fast_combat_support_ship

 

"The AOEs were also designed to be much faster than previous auxiliaries at 26 knots, giving them the ability to operate in company with a carrier battle group rather than in a separate, slower replenishment group. The speed was obtained by giving each ship one-half of the powerplants removed from the unfinished Iowa-class battleships Illinois and Kentucky."

 

But note that a fifth one was planned, so whose machine would have propelled it?

[Yama]

Well there was plenty of Iowas available for scrapping and recycling the plants...

[RETAC21]

 

I believe that reactors tend to use primary and secondary loops, with a heat exchanger to transfer heat from the primary coolant loop (i.e. the one that cools the core) to the secondary loop. Regardless of whether primary loop coolant is used or not, the issue is that the generated steam temperature is low compared to that possible with superheated boilers.

 

In other words, the argument that a nuclear kettle is somehow better for steam catapults may be a bogus one.

 

I think it's better than diesels, which is the alternative. With diesels, a separate steam generator would be needed, just for the catapults.

 

Of course, there's always all-electric propulsion with electric catapults, no steam anywhere.

 

 

Which is better because electricity can be generated all day long, while eventually steam runs out, plus:

 

"Current steam catapults use about 615 kg/ 1,350 pounds of steam for each aircraft launch, which is usually delivered by piping it from the nuclear reactor. Now add the required hydraulics and oils, the water required to brake the catapult, and associated pumps, motors, and control systems. The result is a large, heavy, maintenance-intensive system that operates without feedback control; and its sudden shocks shorten airframe lifespans for carrier-based aircraft.

To date, it has been the only option available. Hence its use on all full-size carriers.

EMALS (Electro-Magnetic Aircraft Launch System) uses an approach analogous to an electro-magnetic rail gun, in order to accelerate the shuttle that holds the aircraft. That approach provides a smoother launch, while offering up to 30% more launch energy potential to cope with heavier fighters. It also has far lower space and maintenance requirements, because it dispenses with most of the steam catapult’s piping, pumps, motors, control systems, etc. Ancillary benefits include the ability to embed diagnostic systems, for ease of maintenance with fewer personnel on board."

[Ken Estes]

 

The super heated plants on the Iowa BB's was a peculiar system. There were a set of fast resupply transports that had the same steam plants and knowledge. I think use of all of those spares was part of the calculus alongside their manning cost that did in the BBs.

 

https://en.wikipedia.org/wiki/Sacramento-class_fast_combat_support_ship

 

"The AOEs were also designed to be much faster than previous auxiliaries at 26 knots, giving them the ability to operate in company with a carrier battle group rather than in a separate, slower replenishment group. The speed was obtained by giving each ship one-half of the powerplants removed from the unfinished Iowa-class battleships Illinois and Kentucky."

 

But note that a fifth one was planned, so whose machine would have propelled it?

 

 

 

Good point, there was no AOE-5 built and the Supply class continued at AOE-6, four ships using gas turbines for the same mission.

 

I wonder if a set of turbines existed for one of the Montanas or the three more Midways that were never built?

[Jeff]

Has any thought/engineering been given to retrofitting EMALS into the existing CVNs? Not worth the effort?

[Corinthian]

Tour the almost finished QE CV