Nimitz carrier doing a hard turn

[Sea Skimmer]

Considering the USN found the PHM's a total faliure, I doubt they where twice as fast as a high end torpedo.

As for your method of measuring speed, just what exactly where you using and what speed where you getting? I cant recall if you said so.

Yeah, I didn't think the PHMs where that fast either. From what I heard they were a maintenance nightmare because of the foils and the water jet. I also heard that they only worked well on relatively calm seas. At one time there was supposedly a plan for a ship to carry the PHMs so they could be deployed in places like the Persion Gulf but I've never seen anything other than a sketch.

I can't remember the name of the system I was looking at but it did a lot of things. It had a nice color map display which could be zoomed in and out and the TAO usually had a large projection screen version of it in front of him. On that system what I did was to display a history of our course. The course was broken down into legs. Because the two end points of the legs were documented at specific times this system would give you speed reading based on the time it took to cover the specific distance in the leg.

I didn't say any specific speeds from that system. I just said that I saw a lot that were well over the posted top end of the Nimitz class. I should also say that there were a couple that we so far over that I wasn't buying them which is why I am willing to sugest that what I feel a Nimitz class is capable of may be because I misinterpreted data or don't know the limitations of the system. Heck, I don't know if we were going with the wind, with the current etc... IIRC this system tracked everything by sattelite so it's going to be looking purely at the distance covered and what amount of time.

Still, I feel fairly confident that despite what that article says the Nimtz class is faster than the Forrestal class.

Okay then. You just have hazy memoires, Skimmers goes with logic and information he has no reason to distrust.

Getting a few knots overworking everything might be possibul, depends on just how fast everything is going at what's normally flank. However you not going to get any 5-20 knot jump.

As for which is faster, if we used the giant mile long blimp proposed as a transport a few months back to drop them both from 10,000 feet, the Nimitz should hit the surface first.

[KhyronTheBackstabber]

Captin We've ran out of columbian coffee.

[Hyperion]

I had a friend on the Carl Vinson, a nuke tech, he knew the engines and what the ship could do, he did tell me that if they go for a "one-way ride" with everything at redline that the ship can do at least double or more the publicised speed, though he could not tell me precisely.

That seems theoretically feesible to me. If the posted top end is 33-35knots then redlining at 66-70 doesn't sound too far fetched. I've served on a Nimitz class carrier and I know they can go faster than posted because I've seen quite a bit of evidence for it. The main one is a computerized chart that displays the ships course. When you click on segments it will tell you how fast the ship must have been going to cover that distance in the amount of time it did. Some do seem a bit extreme but plenty of them are at least 35 knots.

The Navy does make some efforts to conceal the top speed. The ACDS system that nearly everyone in CDC uses to monitor radars won't display the ship's speed beyond the posted max. It just sits there pegging at the max. The cool thing is that you can click on other ships/planes on your screen and see how fast they are going. I heard from one of our escort cruisers that they had us doing 55 knots one time.

By the way, as for some of the escort ships I always heard that the limting factor for the Ticonderoga and Spruance ships is the sonar dome. Without it they are supposed to be able to do at least in the high 40 knot range but with it they can damage it if they go all out.

Again giving me reasons to join the Navy, all the cool equipment.

[Hyperion]

One thing we need to take into account is that outside of anyone who actually has worked on the propulsion and control systems on a Nimitz class, we have no clue what is really under the water line. However I do know what most of my Navy friends have told me about the Nimitz class carriers and what they can do, and I can assure you that if they're only exaggerating a little bit, those ships can do a hell of a lot more than 30-some knots.

[Warspite]

One thing we need to take into account is that outside of anyone who actually has worked on the propulsion and control systems on a Nimitz class, we have no clue what is really under the water line. However I do know what most of my Navy friends have told me about the Nimitz class carriers and what they can do, and I can assure you that if they're only exaggerating a little bit, those ships can do a hell of a lot more than 30-some knots.

Bellow the WL?
Well, let's see...
Fuel, Oil, Fresh Water, Water Ballast and Sludge Bunks.
AvGas, Ammunition, and all the asorted parafernalia Stores.
Pumps and miles of piping.
Crew compartments.
Main engine room, Helm machinery room, Nuclear Reactor Room.
Auxiliary machinery and stations.
Tons and tons of structural steel.

That's all I can think of right now.

So, with the exception of the military stores and the nuclear reactor, below the waterline the Nimitz is similar to 99% of all other steel vessels.


It does 30+ knots and that's it, the ship can't go any faster beyond a certain speed due to resistance. Water is a dense medium, and so, it creates a certain amount of resistance to movement. That resistance comes from hull form, hull friction and propeller.
The propeller is designed for a best rpm point, where it can deliver it's full power to achieve a designed speed. More RPM can lead to cavitation, causing propeller damage and shaft vibration, which is very bad, less RPM, and the propeller isn't deliverging it's full power, operating bellow optimum conditions.
The hull needs to meet certain parameters in order to fulfill it's mission with a certain amount of stability in operating conditions and habitability for the persons working onboard, that being, a certain hull form of a certain ship may not be valid for another ship, it's a very elaborate process and still a matter of research.
Hull friction is caused not only by the friction from the hull with the water, minimized by aplying self-polishing paints, but also by material irregularites (usually microscopic and inavoidable), the welds performed during the construction and all the necessary openings.

Taking all this into acount, a ship has always a maximum speed imposed on it, and usually acheiving this maximum speed is detrimental for all the equipment aboard, starting with the main engine, propeller and bearings.
Also, I would like to point out that acheiving 30 knots is already a feat for a ship that size, when normal cruise speed for 99% of ships is between 15-25 knots, and it would be only met during it's life time in exceptional circunstances, not in normal operations (about 90% of it's time).

[Hyperion]

I had meant the screws, drive shafts, hull shape, etc. We really have no clue what the underside of the ship looks like.

As for your comment that 30 knots is the best, I do think that the number of Navy personnel that have told me and others that the Nimitz class can do a hell of a lot more than 30 knots says you are most likely wrong, I'll take thier word over yours any day.

[Warspite]

Hull shape is not a secret you can keep out of everyone else! From bellow the WL, the carrier is similar to any other 90,000 ton ship, with the exception of the 4 propellers, but that doesn't make any difference.

A ship's hull shape is dictated by hydrodynamics, it has been (and still is) studied all over the world for over a hundred years in hydrodynamics laboratories. A ship can attain the same performance with several hull shapes, and usually the chosen is for the best crompromise between stability, internal space, projected speed and mission.
The same performeance the Nimitz is credited with, could be achieved by a similar hull shape, created by a different design team in a different country. It's no big deal what's going on bellow the water.

As for your friends... Fine with me, you stick with sailor stories, I'll stick with a marine engineering degree and published papers dealing with resistance and propulsion.

[Colonel Olrik]

As for your friends... Fine with me, you stick with sailor stories, I'll stick with a marine engineering degree and published papers dealing with resistance and propulsion.

Precious..

[Admiral Piett]

Mr Warspite is,of course, correct.
The link leading to this has already been posted but still

Posted by Stuart Slade on April 29, 1999 at 23:12:50:

One of the prevailing myths of the modern fleet is that the US Navy's nuclear-powered aircraft carriers are capable of extraordinary maximum speeds. As is quite common with Urban Myths, these keep growing with each retelling of the basic story. It started with speeds of "over 40 knots" being alleged. This has risen by stages to 45 knots then to its current level of 50 knots. The story invariably ends with an officer turning off the speed readout for "security reasons." Sadly the truth is much more prosaic.

The official listing of the carrier speeds is "in excess of 30 knots". The actual speed of the CVNs is classified; much as the maximum speed of the SSNs in the 1960s through 1980s was restricted information. However, the design speed of the Forrestal, Kitty Hawk and JFK class carriers is public domain. The JFK was designed for 33.5 knots, the Kitty Hawks 33.6, the Forrestal 32.0 and the other CVs of that class were designed for 33.0. All had powertrain installations designed to provide 280,000 shp except Forrestal which had 260,000 shp. In all cases, the power was delivered via four shafts.

So, the question is, how does the performance of the CVNs compare with that of the CVs? To determine this we have to look at the power train itself. The nuclear powerplant does not drive the ship directly; it generates steam which powers turbines which drive the screws. The power rating of the ship is the output of her turbines, not the steam generating capacity of the reactor. The turbines installed on the CVNs are identical to those on the CVs; they generate 280,000 shp over four shafts. Even if the nuclear reactor component did generate huge amounts of additional steam, there would be nowhere to put it. On these grounds alone, it seems extremely unlikely that a CVN would be any faster than a CV.

Unofficial figures for the Enterprise confirm this; they suggest the ship was designed for 33.0 knots and it has been unofficially suggested that she reached 33.6 knots while running machinery trials after her latest refit. It has been suggested that this figure was "leaked" in order to counter suggestions that she was worn out. In passing, although Enterprise has an eight-reactor power train, only six of the reactors are on line at any one time (the reactors being rotated so that all are used regularly). The reason is quite simple; after recoring, only six reactors are needed to provide all the steam the tubines can handle.

The Nimitz class carriers were originally designed to have 260,000 shp, the reduction being due to a steam deficiency caused by a shift to the use of a pair of large reactors. In fact, they have now all been recored and are rated at the same 280,000 shp as the other carriers. It might be expected that they would, therefore, have speeds in the same 33 knot range as the other carriers.

In fact, this is not correct. The dimensions of the Nimitz class were set by building dock and other industrial and infrastructure considerations. Their hull is the largest practical design without massive investment in base and construction infrastructure. This placed grave pressure on internal volume and forced the adoption of some unusual designs solutions and the use of a significantly fuller hull form. This translated directly into loss of speed. Although the official figures are classified, it is unofficially reported that the design speed of the Nimitz was 31.5 knots on 260,000 shp. This would fit the reduced power and less advantageous hull form. Quite independently, the US Navy has suggested that the "Nimitz Class" have achieved trials speeds of 31.5 knots - this seems to be intended as an average for all the ships in this class rather than specific to any representative ship of that class.

Later ships of the Nimitz class are substantially larger than the earlier members but do have the uprated, 280,000 shp plants. Its unlikely that the extra power fully compensates for the extra size and it has been rumored that the latest ship, CVN-75 USS Harry S Truman, was hard put to reach 31.0 knots on trials.

There is a caveat here. The CVNs effectively have no concerns about running out of fuel. They can be optimized for running at high speed continuously (that is, their hull form can be selected for maximum efficiency at maximum speed). In contrast, a conventionally-powered carrier has to be optimized for optimum performance at cruising speed - 20 knots. Their hulls become progressively less efficient as the ship speed increases. This means that the sustained speed of a CVN over long duration is close to the ships maximum speed (say 30 knots) while the sustained speed of a CV over long duration is the ship's cruising speed (20 knots). So, while there is no significant difference in maximum speed of the two ships, the CVN will have a much higher transit speed. It is quite possible that it is that difference in transit speed that gets misapplied to maximum speed and is the core of the "40 Knot Myth."

I must stress that all the figures in this note are unclassified and are obtained from public domain sources (even if somewhat obscure ones!)



--------------------------------------------------------------------------------

After this was originally published in April 1999, the USN publicly released the speed of the nuclear carriers in June 1999:
Enterprise 33.6 knots after last refit
Nimitz 31.5 knots
Theodore Roosevelt 31.3 knots
Harry S Truman 30.9 knots


--------------------------------------------------------------------------------

[phongn]

Actually, I think Mr. Slade knows the true hull form of the supercarriers, and he has also hinted rather strongly that said information is classified.

[Malecoda]

I had a friend on the Carl Vinson, a nuke tech, he knew the engines and what the ship could do, he did tell me that if they go for a "one-way ride" with everything at redline that the ship can do at least double or more the publicised speed, though he could not tell me precisely.

That is SUCH a navy-instructor line. And the poster is just an ad. We clocked the Hercules gg 53, and that was a hydrofoil. The Wisconsin's gone faster than published top speed (which was 33+) but, though I forgot to bring my accelerometer and microscope that day, it was pbly 35, 36 max. Although, 30 knots does feel like you're gg 60--that, I bet, is the source of many sailors thinking they were gg faster...

[Sea Skimmer]

I had a friend on the Carl Vinson, a nuke tech, he knew the engines and what the ship could do, he did tell me that if they go for a "one-way ride" with everything at redline that the ship can do at least double or more the publicised speed, though he could not tell me precisely.

That is SUCH a navy-instructor line. And the poster is just an ad. We clocked the Hercules gg 53, and that was a hydrofoil. The Wisconsin's gone faster than published top speed (which was 33+) but, though I forgot to bring my accelerometer and microscope that day, it was pbly 35, 36 max. Although, 30 knots does feel like you're gg 60--that, I bet, is the source of many sailors thinking they were gg faster...

With the Iowa class it makes sense. They ran their trials in very shallow water, which makes ships, move slower. In deep water they should go noticeably faster. They where known to reach 35 knots in service, 34 in ths 1980's IIRC. I've near heard 36, but mabey with a light fuel load they might reach it.

[Defiant]

Regardless of top speed, that's still pretty impressive. I've heard that supercarriers actually have rockets that allow them to make even sharper emergency maneuvers.

[Ted]

Regardless of top speed, that's still pretty impressive. I've heard that supercarriers actually have rockets that allow them to make even sharper emergency maneuvers.

Nah, they use aircraft motors if they need to, anchor the planes, then fire 'em up.

They did that in japan.

[Einhander Sn0m4n]

Regardless of top speed, that's still pretty impressive. I've heard that supercarriers actually have rockets that allow them to make even sharper emergency maneuvers.

ROTFLMMFGDQQAO!!!!

ROCKETS?! On an Aircraft Carrier?

[Shinova]

Remember that these are still officially "fleet carriers". We have yet to design a "super carrier".


When we (US) do, we can finally declare a step toward Manji-ism in naval design

[Pu-239]

What about supercavitating propellers that we don't know about, since they are below the waterline? Of course they only work at high speeds.

Isn't the next gen carrier supposed to run windows? Oh the horror. I hate Lockheed Martin even if they didn't pick windows anyways. Boing should have won JSF, the YF-23 should have won instead of YF-22. At least it'll be running Win2k, the least evil M$ O$.

[Ted]

Actually, they tested windows on a Tico a few years ago.

Someone entered a 0 at the wrong time, system crashed.

Ship was left wallowing for hours before the system was rebooted up.

[The Dark]

Isn't the next gen carrier supposed to run windows? Oh the horror. I hate Lockheed Martin even if they didn't pick windows anyways. Boing should have won JSF, the YF-23 should have won instead of YF-22. At least it'll be running Win2k, the least evil M$ O$.

You hit on the joke name for Boeing, probably by accident, but it's still funny. And YF-22/23 weren't JSF. They were ATF. JSF was X-32/35. The YF-23 was a decent design, but while it was more stealthy than the Raptor, it was inferior on most other respects. The X-32, based on its looks and what little I know of aerospace design, was not very stealthy. The F-35 appears to be superior in that regard, and while I haven't read the reports of Boeing's test pilots, I know Lockhead Martian's Harrier pilots were quite impressed with the Mini-Raptor. Far more stable than the AV-8, capable of higher speeds, more extreme maneuvers, and heavier payloads. I don't know what the military saw that they liked better, but either way both companies are still involved, since Congress is requiring Lockheed Martin to allow Boeing to work on both the ATF and JSF production vehicles.

[SirNitram]

Regardless of top speed, that's still pretty impressive. I've heard that supercarriers actually have rockets that allow them to make even sharper emergency maneuvers.

DEPLOY THE ROCKET BOATS!

But there are no rocket boats...

Aren't there? Aren't there? Allow me to display this evidence, which you'll find very convincing...

BOATDOKEN!

[Warspite]

What about supercavitating propellers that we don't know about, since they are below the waterline? Of course they only work at high speeds.

[Snip dreaded nightmare]

Supercavitating propellers are designed to operate constantly at high speed profiles (30-40 knots), not the kind of cruise speed for a carrier (usually in the 20-25 knot), also these propellers are much smaller than those installed on the vessels. A proppeler takes an enormous amount of time to be manufactured and is usually very expensive (being one of the most important elements for the carrier speed). Designing and building a supercavitating propeller (or better, 4) for a ship that doesn't operate in 85% of it's time on speeds above 30 knots is a complete waste of resources.

Supercavitating propellers have a wedge aerofoil profile (since most of the groundwork theory comes from fluid dynamics, the same equations are used for aircraft wing profiles), and are found on small fast sports boats, fast ferries (in the jet duct) and possibly in hydrofoils. All vessels with speed profiles that require to mantain a high speed for a large amount of time (let's say 75% of it's lifetime). To properly generate the low pressure sheet (induced by the cavitation) they need to be small, and have a high RPM in order to perform as required. For the regular propellers, the oposite is true, they are large bladed and the lower the RPM the better torque is transformed into linear motion. Special case are the submarine propellers, mostly scimitar shaped and with 6-8 blades (normal are 3-4), but they have a more important constraint: sound.

And, besides an vast amount of literature that can be found about the carriers propellers (I even have a news clip about a propeller being replaced on a carrier in San Francisco I think, way back in the 80's), the design is mostly performed by state-sponsored and university hydrodynamic laboratories and researchers usually publish most of their work in journals of the area. A secret like that couldn't be kept since '75.
I might add the carriers performance, mission and wake shape created when running can be used to infer it's main characteristics, and they are NOT supercavitating.

Once again, there are no secrets outside a hull of a carrier, besides the four shafts (necessary to deliver the required power), the ship is pretty much similar to most commercial steel ships! The vessels that can easily have an aproximate hull shape are the container ships, since they operate in the same speed range (20-25 knots).



(on the note of rockets mounted on the carrier, has anyone ever watched the "Bridges of Toko-Ri", with William Holden? They used the parked prop planes to assist in the docking procedures, when the carreir arrives in Japan.)

[Malecoda]

With the Iowa class it makes sense. They ran their trials in very shallow water, which makes ships, move slower. In deep water they should go noticeably faster. They where known to reach 35 knots in service, 34 in ths 1980's IIRC. I've near heard 36, but mabey with a light fuel load they might reach it.

I was just waiting for someone to go "Red herring, that's a BB! Concession accepted!" But 212,000/55,000 is bigger than 280,000/100,000, so it's a good comparison.

To counter the "we don't have a clue what they look like underwater" poster, of course we do. It's published--the Navy makes math books too, btw; but also, it would be very similar to a BB, or if you prefer something more concrete, I'm sure there's a pic of a carrier in drydock somewhere... If all else fails, get a scale model.

[ad_pellaeon]

While the Nimitz class is not necessarily the fastest ship in the fleet, the Enterprise certanely is. In the book Carrier, written by Tom Clancy, he describes the Enterprise as being designed with eight nuclear reactors inside, the same number of oil boilers in earlier Kitty Hawk carriers. He then goes on to say that when the Enterprise was first comissioned in the '60's, the ship was so overpowered that its hull could not take the strain of a full-power run and therefore one was never attempted. However, during testing the ship off the Virginia capes that the Enterprise went over 40 knots (even though the numbers are still classified), and that she was able to easily outrun her escorting ships. All this and she never fully tapped her entire hull, as it would have broken up.
Even though speeds like 45 knots seem ridiculous, it would probably be safe to assume that the ship made over 36 knots. Therefore, such a speed is possible to attain.

[Sea Skimmer]

While the Nimitz class is not necessarily the fastest ship in the fleet, the Enterprise certanely is. In the book Carrier, written by Tom Clancy, he describes the Enterprise as being designed with eight nuclear reactors inside, the same number of oil boilers in earlier Kitty Hawk carriers. He then goes on to say that when the Enterprise was first comissioned in the '60's, the ship was so overpowered that its hull could not take the strain of a full-power run and therefore one was never attempted. However, during testing the ship off the Virginia capes that the Enterprise went over 40 knots (even though the numbers are still classified), and that she was able to easily outrun her escorting ships. All this and she never fully tapped her entire hull, as it would have broken up.
Even though speeds like 45 knots seem ridiculous, it would probably be safe to assume that the ship made over 36 knots. Therefore, such a speed is possible to attain.

[1]Clancy's books are not reliable sources
[2] That series of books is written by a team of researchers, Clancy does very little on them
[3] the book specially says that the 40 knot figure is just rumored.

[Sea Skimmer]

With the Iowa class it makes sense. They ran their trials in very shallow water, which makes ships, move slower. In deep water they should go noticeably faster. They where known to reach 35 knots in service, 34 in ths 1980's IIRC. I've near heard 36, but mabey with a light fuel load they might reach it.

I was just waiting for someone to go "Red herring, that's a BB! Concession accepted!" But 212,000/55,000 is bigger than 280,000/100,000, so it's a good comparison.

To counter the "we don't have a clue what they look like underwater" poster, of course we do. It's published--the Navy makes math books too, btw; but also, it would be very similar to a BB, or if you prefer something more concrete, I'm sure there's a pic of a carrier in drydock somewhere... If all else fails, get a scale model.

Actually, Slade address the accuracy of models, http://pub82.ezboard.com/fhistorypoliti ... c&index=12

And the USN tightly controls the filming of its ships in dry dock.