How fast can a Nimitz class aircraft carrier go?

[sailor]

This is how things were done in the early 19th century. Note the lack of any scientific calculations and that is was all in the eye of the artist.

Sailing Ship Hull

When the length of a Ship is determined, it is usual to fix her breadth by the dimensions of the midship-beam. On this occasion the shipwrights, for the most part, are conducted by rules founded on their own observation; for having remarked, that some vessels, which by repeated experience have been found to answer all the purposes of navigation, have a certain breadth in proportion to their length, they have interred that it would be improper to depart from this proportion: but as other ships have been constructed with different breadths, which were equally perfect, a variety of different general rules have been adopted by these artists, who are accordingly divided in their opinions about the breadth which ought to be assigned to a ship relatively with her length, while each one produces reasons and experience in support of his own standard.

Those who would diminish the breadth allege, that a narrow vessel meets with less resistance in passing through the water; 2dly, That by increasing the length she will drive less to leeward; 3dly, That according to this principle, the water-lines will be more conveniently formed to divide the fluid; 4thly, That a long and narrow ship will require less sail to advance swiftly; that her masts will be lower, and her rigging lighter; and, by consequence, the seamen less fatigued with managing the sails, &c.

Those, on the contrary, who would enlarge the breadth, pretend, 1st, That this form is better fitted to receive a good battery of guns; 2dly, That there will be more room to work the guns conveniently; 3dly, That by carrying more sail, the, ship will be enabled to run faster; or, that this quality will at least overbalance the advantage which the others have of more easily dividing the fluid; 4thly, That, being broader at the load-water line, or place where the surface of the water describes a line round the bottom, they will admit of being very narrow on the floor, particularly towards the extremities; and, 5thly, That a broad vessel will more readily rise upon the waves than a narrow one.

From such opposite principles has resulted that varicty of standards adopted by different shipwrights; and a servile imitation of these mechanical methods has, to the great reproach of the art, produced all these rules of proportion: for the various models they have adopted indisputably prove their doubt and uncertainty with regard to their proper standard.

[smiling_bandit]

@sailor

It is extremely ignorant to say that in the last 300 years nothing has advanced in the knowledge of how hulss behave in the water. It is just not true. A lot has been learnt and a lot is still to be learnt and my cites prove it.

If this is what you are getting out of my statements, then methinks you ought to go back and read them again, and then maybe take a course in Reading Comprehension, because I did not say that. At all. Which leads to believe you are creating a strawmaqn because you either cannot or will not honestly argue with me.

[YamatoTwinkie]

Sailor isn’t the only one with “reading comprehension” issues then. As a mechanical engineer, my B.S.-o-meter was pinging off the scale when I read your original “300 year old textbooks” post.

[paperbackwriter]

By my reading, sailor’s reading comprehension is fine:

@smiling_bandit

The number is easily calculated, and you can get it much more accurate than better than what was listed. A friend of mine nearly gave the Navy security people a heart attack when he was in the nuclear power program. What happened was that he showed them how to calc it, and that the information was in 300 year-old books.

As said, the exact speed possible for a Nimitz-class is neither “easily calculated” nor is that information in “300 year-old books”.

You’re making it look like you’re trying to weasel you way out of what you said, which I’m sure isn’t your intent. If you want to clarify, I, for one, will be very interested.

[robby]

@smiling_bandit

The number is easily calculated, and you can get it much more accurate than better than what was listed. A friend of mine nearly gave the Navy security people a heart attack when he was in the nuclear power program. What happened was that he showed them how to calc it, and that the information was in 300 year-old books. He also panicked them because he brought in perfectly accurate Elemental Charts from the Atomic Energy Comission. See, in the Navy, that was classified since 1943 or so. Of course, you can get them for a buck each by mail order these days.

I’ll just add that the whole part about the “perfectly accurate Elemental Charts from the Atomic Energy Commission” sounds like a bunch of B.S., too.

I went through the Navy’s Nuclear Power School over 15 years ago. What you are referring to is the well-known Chart of the Nuclides. This chart was developed by the Knolls Atomic Power Laboratory (KAPL), working for Naval Reactors and the Department of Energy (DOE). They have published numerous editions. I have never seen a classified version. They have certainly been freely available for decades, and I seriously doubt any “Navy security personnel” would have had a heart attack regarding any such information released by DOE or the Atomic Energy Commission.

[Snnipe_70E]

@sailor

Cavitation is not “the screw slipping in the water”.
Cavitation hurts prop performance and damages the prop but with or without cavitation props have an optimal design speed and their performance will suffer above that.

Some props have blades which can be rotated to change the attack angle. These are caled “feathering” props. These can perform better in a wider range of RPM but will not perform as well at any one given point.

Prop design is another field which is very complicated and theoretical calculations do not provide the full answers so that extensive testing is needed.

Both hull and prop have a speed at which they perform best.

Just gave a simple definition about cavitation. you are right it is not just slipping in the water. It has to due with the bubbles formed on the back side of the blade decreasing the net thrust produced.

The “feathered” props are variable pitch props. When first introduced they were used on direct drive engines.

I will admit it is a different world out there today then when I was sailing. Now almost all new enginrooms are diesel or gas turbine.

[Snnipe_70E]

With a tag line of Sailor which licience do you hold? Or are you Navy? Shellback or pollywog?

[Yaerius]

I totally agree with most of sailors points and Snipe brings up some good points but there is something just off somewhat at least by my experience…

I was stationed on the USS Nimitz (CVN-68) from late 81 to late 86, I was a Machinist Mate in A Division.

Here is a cool link to a sailor taking a shot off the fantail of the Nimitz during some high speed maneuvering - - YouTube

Caveat Emptor - Memory can be a tricky thing and that’s where I believe a lot of Sea Stories come from so I’m not claiming total facts here…so with that said…

I remember us getting a emergency order from JCOS or the CNO when we had liberty (post sea trials before a Med Deployment) at Gitmo (Leeward Side, I believe) we got underway so fast that we left a little under a hundred from ship company & air wing support on the base. They were flown out at a later time.

Here is a distance calculation from Google Earth - Imgur: The magic of the Internet

That is 4331 miles lets just round that to 4300 miles

We were past the straights of Rhodes at before 4 days…now this is the part that is tricky…i swear that is was 76 hours but that is just plain impossible but I know it was no more than 96 but who knows the truth, well I guess the ship logs would be able to say for sure.

That gives a range of 59 to 45 mph (lol, i never did like knots you guys can convert)

Now back to that video…you could watch the fantail camera in berthing and we where putting out a rooster tail that was as high as the flight deck (more than 50 ft). It was nearly impossible to get any good sleep cause you couldn’t stay in your rack what with all the vibration.

I’m an engineer by trade now so I have difficulties believing that we achieved 59 or even close. I know all the calculations and the enormous amounts of energy required to move 100 kilotonnes. But I also know that the rated energy isn’t the top energy and we needed presidential approval to do some special or non-standard (read not-safe acts by Naval standards) to the reactors to achieve those power levels. That being said we where definitely past this speed shown in this example video and we had to be past 32 knots by some significant margin. I just can’t except anything else. However I am sure the science is right and leans more towards sailors cites so let’s just say I would be utterly amazed if we had been just been at the max speed listed in those other links.

I also have to disagree with those that said an aircraft carrier would never leave its escorts…well that is just wrong…it depends on the situation and what you define as leave means. We left our original escorts behind while we crossed the Atlantic…I sure we picked up some others in the Med but it was much later before most of the ships we (ships company I’m speaking about - sure we didn’t know the whole picture but I had shipmates on some of those other ships) knew about in our original task group caught up to us. A-Division had the luxury of going damn near anywhere in that ship…we had lots of friends in the other divisions…you ever been in the IO without AC or the North Atlantic without (Steam Heat) lol.

Interesting Article for Nuke buffs - Home | Rensselaer at Work

Thanks for listening…I wish I really knew the facts and had the data to know for sure but 31.5 or even 35 knots being the top end…just don’t believe it

[Habeed]

@sailor

Look, I know we’re most just bullshitting here but let us try to keep things at least moderately plausible. There is no way a 300 year old book has anything which can usefully be used to calculate anything reagarding the speed of a carrier. Nothing. Not even 200 year old. Even 100 year old is going to be very severely lacking.

No you don’t. If you know that to exceed a particular number, for a hull shaped a certain way, you will need exponentially more energy (factors of 10, etc), then you know that it is highly unlikely that the ship’s drivetrain can supply that energy.

You don’t need to know anything about the details of the drivetrain, except to know that it uses conventional technology. (which nuclear carriers do)

Now, if the carrier had hydroplane wings on the hull, and/or was injecting nuclear heated steam in front to reduce friction, that’s an entirely different story.

[Ethilrist]

Could the maximum speed be increased if they retrofitted them with some means of inducing supercavitation?

[SpyOne]

@Really_Not_All_That_Bright

If a ship’s speed is limited by hull length, how on earth would a city-sized nuclear carrier outdistance a fast frigate or destroyer? I’m assuming the bows of all warships are more or less the same shape- is that correct?

Bear in mind the length thing was pointed out to be a crude rule of thumb for small sailboats, and not even all that accurate there. So what I’m discussing here is sort of an alternate universe where things work differently from ours.

Let me rephrase your question before I answer it:
If there is a hard limit on the maximum speed of a vessel based upon it’s length (which I will call “maximum physically possible speed”), how can a big vessel be faster than a smaller one?

Well, the answer to that is that length isn’t the only limit.

For carriers to be faster than smaller vessels would only require that the smaller vessels not have nearly enough power to reach their maximum physically possible speed.

And that isn’t too hard to imagine.
I believe I read that drag (in water) increases with the square of speed (or exponentially, at least). The author said that you can easily encounter a point where to make a ship significantly faster you need to make the engine so much bigger that you’d need to make the vessel bigger to hold it (and still hold all the other stuff you wanted it to have), Which would increase drag and therefore result in a negligible gain in speed.

The author’s point was that carriers are huge specifically because they have to go fast, which means they have to have enormous engines. Basically, once the vessel reached a certain size, it made sense to make it even bigger and have it carry lots and lots of planes, because it already had to have pretty huge engines. He was criticizing a lot of science fiction that does “carriers in space” without considering that carriers as we know them exist because of the problems with drag in the water, and the difference between how ships and airplanes work. If you take that away, it makes more sense for “carriers” to be small vessels with a small number of “fighters”.

So carriers have huge engines which allow them to reach a much higher percentage of their maximum physically possible speed, while the smaller vessels don’t invest as much of their space on engines and are slower. Their maximum physically possible speed is much higher than the carrier, but they don’t have enough engine to get close to it.

[SpyOne]

@smiling_bandit

Yeahuh. All that proves is that… you don’t know jack about ship design. Sure, you can shove enough power into the screw propellor to make it go a little faster, but on a practical level, the hull is the same bloody shape ships (sailing, not galleys) have been in since Carthage and Rome went at it, and there are some soft but tough limits that elementary physics puts on it. These principles have been known since Newton walked the earth, at least.

All our advances in shipbuilding knowledge have involved engineering the ship’s power systems and making them tougher. We changed How we build but not What we build. You can model fluid mechanics all you want, but it ain’t going to change the fact that a ship’s length and width fundamentally determine what kind of speeds it can attain at any given power output.

Back when Titanic was a big hit movie, some folks had the idea to cash in on that by building a replica of the Titanic and selling cruises. One of the major problems they encountered was that they’d need to change the design of the hull: by modern standards, the original Titanic hull design created too much drag, and would therefore use too much fuel.
In less than 100 years, we’ve learned enough about fluid dynamics to make older hull designs so uncompetitive, economically, as to make them non-viable.
Modern hulls are not even the same shape as hulls used in World War II, much less the ships of Carthage, except in the very broadest of terms. (“It’s kind of an oval.”

[SpyOne]

@Richard_Pearse

or do they just not want to put an actual figure for security reasons?

I suspect that the US government would prefer that nobody know the exact top speed of our carriers.
Several people have pointed out that the Russians probably have a pretty good idea, but … there is a difference between “we’ve never seen one go faster than X” and “It is impossible for one to go faster than X”.
And a lot of the guys we go up against don’t have nearly the intelligence apparatus that the Russians do, and it would be helpful if our exact capabilities weren’t on wikipedia.

When somebody decides that the moment for their douchebag plan is now, because it would take at least 36 hours for an American carrier to get within striking distance, we want them to be less than 100% sure about that figure.

So, yeah, a lot of the stuff that’s still classified seems kind of silly.
As others have mentioned, a lot of stuff taught in Navy Nukes 101 is publicly known; the facts themselves aren’t classified, but the fact that the Navy teaches them is. Knowing what our nuke guys get taught could give clues about our reactors and stuff.

A friend of mine once did a short stint in the Air Force. He said they’d told him when he got out that he could tell people what planes he had worked on, or he could say what systems he’d worked on, but he had to pick one and stick to it. He said “So, I can tell you I worked on hydraulics. But I can’t tell you what planes I worked on, because that would tell you those planes have hydraulics. Although I am allowed to tell you that I am not aware of any Air Force planes that don’t.” But I don’t think he thought the policy was really stupid, just that the specific application was: there are a lot of systems he might have worked on, and knowing which planes had them could help “the bad guys”. But hydraulics probably wasn’t one of them, and that’s what he had worked on (or at least the one he was willing to say).

[SpyOne]

Oh good lord, it’s a zombie!!

Note to self: ALWAYS READ THE DATES.

Move along, folks, nothing to see here.

[rbroome]

@sailor

Really? You really believe this? Really?

I need to count to 100 before I start a pit thread. I’ll be over here counting…

I’ll join you…
That was a breathtaking statement…

[rbroome]

Oh sigh. I didn’t realize this was a zombie.
I really have to get in the habit of checking dates.

[USNAVY1]

Loose lips sink ships

[Richwood7]

A little more than 30 knots. Insane numbers like 60 to 100mph are not possible with the hull design. There are rules of physics and fluid dynamics that have to be obeyed. Also keep in mind the ship is not powered by the nuclear reactors. All they do is generate the steam needed to run the turbines which run the propellers and which total 280,000 shp. Since fuel is not a problem, CVN’s can travel at max speed without a problem but CV must travel at cruise speed or about 20 knots. Going flat out would consume vast amounts of fuel and a CV cannot afford that. Their hulls are designed to accommodate those speeds. These turbines are the same as were used on non-nuclear carriers.

[Xema]

@Richwood7

There are rules of physics and fluid dynamics that have to be obeyed…

This is much discussed among the zombie posts above.

CV must travel at cruise speed or about 20 knots.

No - when called for - e.g. to launch and recover aircraft - they often go substantially faster.

Going flat out would consume vast amounts of fuel …

Indeed it does. But building a hideously expensive ship and then restricting it to speeds that would not allow it to carry out its mission in the name of saving fuel would be false economy.

[septimus]

Are Navy sailors allowed to have iPhones? Reading this thread it occured to me that sailors could know easily how fast they’re going with GPS. What am I missing?