Grand old ship...new life?

[Shannow]

Originally Posted By: 440Magnum

I guess "fine" is relative to the diameter, the teeth are still fairly decent sized compared to anything you'd find in a car.

The other thing I find really cool about steam ship plants is that the thrust bearing has its own compartment astern of the bull gear, with its own oil pumps and cooling systems. Think about how many thousands of TONS of forward force there is on each shaft when its working, and the bearing built to absorb all that and couple the propulsion force to the hull is huge and generates a lot of heat.


Hope Google Books Link Works

Some interesting commentary, as back in the day, the different manufacturers specialised in either impulse or reaction blading...Parsons (first to put a steam turbine on a boat IIRC) like reaction, but reaction HP turbines lack efficiency, while impulse rule up that end.

As to thrust bearings, the Tilting pad thrust bearings (aka Michell bearings after the inventor are an amazing piece of kit...they can take staggering loads at near zero speeds, as the pad itself can tilt, and has a centre of hydrodynamic pressure slightly ahead of the pivot point, causing the pad to tilt, creating the closing gap that generates the hydrodynamic pressure.

Dyno testing the turbines can be done in the shop, hooking up to a generator and load...can measure shaft "twist" and RPM and calculate back, or load sensors on the mounts.

(most I ever got out of one of my machines was 998,000hp...couldn't get the last 2,000, even bumping up to 2,357 psi).

 

[440Magnum]

Originally Posted By: Jarlaxle
Originally Posted By: Al
The biggest prooblem they had in building ships during the WWII era was cutting the main (bull)Gear. They just did not have enough gear cutting machines and it was not really solved til late in the way.


That is one reason that the fifty(!) Casablanca-class escort carriers used "jug-jumper" reciprocating steam engines.


Well, that and Henry Kaiser. Those ships were somewhat death traps, but they served a huge purpose in getting airplanes to where they needed to be. They just weren't fit to actually go into combat, which they had to do from time to time due to the fact that a war was on...

 

[KevinP64]

The old passenger liners also hauled a lot of human cargo to the US. I came to US on the QE in 1951 with my parents. Family pic of me being held in a life ring. Saw its hulk sitting in Hong Kong at start of some James Bond movie and sort of made me feel sad. Went on the Mary in Long Beach when I lived there. Lots of talk of war ships and WWII. I left VN on the USS Paul Revere an APA(?) and think it had WWII ribbons on its stack. That was quite a hulk. I lived in LB working evenings and a morning paper said it was decommissioned that day (1979) if I had known in time I would have gone. Wonder if anyone that actually took a 'cruise" on that thing was there! The LPH vessels were almost a five star hotel to me after the APA. LSDs not much better. Thnx for the memories.

 

[Astro14]

In the summer of 1975, my family and I went on vacation (Holiday for you, Kevin...) for a month in the UK.

We left New York on the Cunard Lines' QE2, and traveled across the ocean at a leisurely ( ) 28 knots. She was throttled back due to the spike in oil prices that year. We stopped briefly in Cherbourg, and then went on to Southampton.

We flew back on a British Airways 747. Fast, but lacking all the charm, luxury, and yes, adventure of that sea voyage.

It was my first ocean crossing. But not my last. And I still remember the ship, the sea, and the adventure.

I hope, someday, to repeat the experience. It's a slightly different experience on a nuclear carrier...

You can all imagine the difference in accommodation, but the CVN actually cruises much slower than that grand luxury liner...to save reactor life for wartime exigencies...

 

[Jarlaxle]

Originally Posted By: 440Magnum
Originally Posted By: Jarlaxle
Originally Posted By: Al
The biggest prooblem they had in building ships during the WWII era was cutting the main (bull)Gear. They just did not have enough gear cutting machines and it was not really solved til late in the way.


That is one reason that the fifty(!) Casablanca-class escort carriers used "jug-jumper" reciprocating steam engines.


Well, that and Henry Kaiser. Those ships were somewhat death traps, but they served a huge purpose in getting airplanes to where they needed to be. They just weren't fit to actually go into combat, which they had to do from time to time due to the fact that a war was on...


None of the CVEs were built for combat...they were for convoy escort, submarine hunting, and supporting ground troops. Note that the other classes of CVE all did use turbines (the Bogue and Commencement Bay classes)...only the Casablanca-class used reciprocating engines.

Considering the huge number built, note that only six were lost. (The US Navy lost four fleet carriers and two light carriers in the war.)

 

[Al]

Originally Posted By: Jarlaxle
(The US Navy lost four fleet carriers and two light carriers in the war.)

Not one Essex Class carrier was lost.

 

[Jarlaxle]

Never said it was. Your point?

 

[wrcsixeight]

Originally Posted By: Astro14
In the summer of 1975,....
We left New York on the Cunard Lines' QE2, and traveled across the ocean at a leisurely ( ) 28 knots.


Not sure how many crossings the QE2 did that summer, But I was 3.6 years old and have only some memories leaving NY on the QE2.

Carroll O'Connor was on it. I think my parents made me go up and disturb him. I called him Archie.

I remember the spiral staircases. Some other kid had this one car which would hug the outsides of the spiral staircases.

 

[KevinP64]

I have dreamed of cruising on the QE2. Must have been great. I flew over one of the big boys coming into Subic . I was in a chopper flying out to rejoin a LPH. I just couldn't believe how huge that thing looked. LPH seemed big until then, lol. Guess it was either coming off Yankee station for RR or stopping in on way there. Would have been late 69. Had an apprentice instructor that was a machinist on one and he told me you couldn't even tell that you were at sea when in the shop.

 

[Astro14]

The QE2 was fast, and stable. An aircraft carrier is designed for many requirements. A liner like SS United States, or the QE2, was built for one: speed.

If memory serves - the QE2 had stabilizer planes on the bow that helped control roll...but even with those, we hit some big seas and she rolled quite a bit one day...sending my mom to the cabin for the day while the kids were loving it!

Even though I was young (12), I could tell QE2 was luxurious. The food was excellent. As a kid with an interest, my Dad arranged for me to talk with one of the ship's officers. He explained the propulsion, the roll stabilizers, etc. We talked for half an hour.

I remember his kindness, patience, and depth of knowledge about the ship. Truly a first class operation, represented by this man who was willing to spend all that time with me, a kid, when off watch.

 

[hattaresguy]

Originally Posted By: Astro14


You can all imagine the difference in accommodation, but the CVN actually cruises much slower than that grand luxury liner...to save reactor life for wartime exigencies...


I have quite a few pictures of a CVN doing flight ops with the new F35 off Norfolk. I was heading south not to far off shore, maybe 80 miles. I was having my oatmeal watching the sun rise and she came over the horizon off my starboard bow about 6 miles out, doing a very slow 10 knots. Made a big loop around heading the other way, than decided to have fun with me. Made a hard turn to port came into the wind, poured on the steam to 25 knots at least, and blew past me at under 1k yards.

The guys on the seahawk were having a blast hovering around us waving, we were the only thing around and they were bored.

In the mean time I got a front row seat to launching the F35 and one even buzzed me at mast head height near super sonic.

We were the only thing out their within 100 miles so they were playing with us but it was a fun show.

 

[Astro14]

Carriers operate at whatever speed is needed for flight operations.

They transit long distances at lower, more fuel-efficient, speeds.

To replace the reactor core requires wrapping the ship in an air tight, negative pressure tent to contain any possible contamination, then removing the deck plates for several floors, and then working on the pressure vessel. Exact details are both classified and numerous.

But the process is known as a "Reactor Complex Overhaul" or RCOH and the price tag is over $1 Billion. So, yes, they try to save fuel when they can.

But, if a jet has a problem, and more wind over the deck is needed for a safe landing, or if another ship/submarine threatens the carrier, the carrier can move with astonishing speed.

The limiting factor on her speed is the amount of torque through the gears and shaft. Each propeller shaft is about four feet in diameter. Under high power, the gearbox is applying torque to the shaft, which rotates the screw. The shaft actually gets twisted as it rotates from the tremendous torque.

A 20' screw moving tons of water per second resists turning...and the shaft starts to twist. Over its roughly 300' length, it can twist up to 360 degrees. Picture a shaft at rest. Draw a pencil line down the shaft. Under full load, that line will now be a spiral that goes once around the shaft...that's torque!

 

[OVERKILL]

Originally Posted By: Astro14
Carriers operate at whatever speed is needed for flight operations.

They transit long distances at lower, more fuel-efficient, speeds.

To replace the reactor core requires wrapping the ship in an air tight, negative pressure tent to contain any possible contamination, then removing the deck plates for several floors, and then working on the pressure vessel. Exact details are both classified and numerous.

But the process is known as a "Reactor Complex Overhaul" or RCOH and the price tag is over $1 Billion. So, yes, they try to save fuel when they can.

But, if a jet has a problem, and more wind over the deck is needed for a safe landing, or if another ship/submarine threatens the carrier, the carrier can move with astonishing speed.

The limiting factor on her speed is the amount of torque through the gears and shaft. Each propeller shaft is about four feet in diameter. Under high power, the gearbox is applying torque to the shaft, which rotates the screw. The shaft actually gets twisted as it rotates from the tremendous torque.

A 20' screw moving tons of water per second resists turning...and the shaft starts to twist. Over its roughly 300' length, it can twist up to 360 degrees. Picture a shaft at rest. Draw a pencil line down the shaft. Under full load, that line will now be a spiral that goes once around the shaft...that's torque!


Nukes can makes tons of steam and are generally, at least for the power industry side of things, the most efficient wide-open. Not surprising at that power there but incredible all the same

Perhaps the propulsion nukes are a bit different? My knowledge on the subject is pretty much isolated to nuke power and in particular the CANDU Canadian stuff.

 

[KevinP64]

Originally Posted By: Astro14
Carriers operate at whatever speed is needed for flight operations.

They transit long distances at lower, more fuel-efficient, speeds.

To replace the reactor core requires wrapping the ship in an air tight, negative pressure tent to contain any possible contamination, then removing the deck plates for several floors, and then working on the pressure vessel. Exact details are both classified and numerous.

But the process is known as a "Reactor Complex Overhaul" or RCOH and the price tag is over $1 Billion. So, yes, they try to save fuel when they can.

But, if a jet has a problem, and more wind over the deck is needed for a safe landing, or if another ship/submarine threatens the carrier, the carrier can move with astonishing speed.

The limiting factor on her speed is the amount of torque through the gears and shaft. Each propeller shaft is about four feet in diameter. Under high power, the gearbox is applying torque to the shaft, which rotates the screw. The shaft actually gets twisted as it rotates from the tremendous torque.

A 20' screw moving tons of water per second resists turning...and the shaft starts to twist. Over its roughly 300' length, it can twist up to 360 degrees. Picture a shaft at rest. Draw a pencil line down the shaft. Under full load, that line will now be a spiral that goes once around the shaft...that's torque!

Wow that is some shaft. And 20' props. I put a set of bearings on two 23in dia shafts wearing bevel gears once. Used to turn over BOF vessels at Bethlehem Steel. And I thought they were big. They came in the shop on a rail car in big steel boxes with the gear on top and the shaft hanging down inside. One of them dropped when the wire rope lifting it snapped and knocked big pieces out of the other brand new gear. Bring on the grinders, lol. What a screw up.

 

[supton]

Originally Posted By: Astro14
A 20' screw moving tons of water per second resists turning...and the shaft starts to twist. Over its roughly 300' length, it can twist up to 360 degrees. Picture a shaft at rest. Draw a pencil line down the shaft. Under full load, that line will now be a spiral that goes once around the shaft...that's torque!


Does that twist relax away when not under torque? Or does it take a set and eventually need replacement.

That's some torque...

 

[IndyIan]

Originally Posted By: supton
Originally Posted By: Astro14
A 20' screw moving tons of water per second resists turning...and the shaft starts to twist. Over its roughly 300' length, it can twist up to 360 degrees. Picture a shaft at rest. Draw a pencil line down the shaft. Under full load, that line will now be a spiral that goes once around the shaft...that's torque!


Does that twist relax away when not under torque? Or does it take a set and eventually need replacement.

That's some torque...

http://www.amesweb.info/Torsion/TorsionalStressCalculator.aspx
I get about 26 deg of twist, assumming 100m length, 1m diameter with 3cm wall cold rolled steel, transmitting 200,000hp at 200rpm, or 5,400,000 ft/lbs.

Maybe I've messed up some units some where? It seems to me 5.4 million pounds hanging a foot off at one end would twist it more, but the shaft is 165,000lbs itself.
My gut tells me that side forces of a 360 deg twist, or even the shaft shortening from twist would be hard to control or would require alot of bearings all the way along?

Anyways its still an impressive feat of engineering even if it doesn't twist itself into knots!

I guess if you can get into a situation where the ship can transmit full hp at very low prop rpms(variable pitch props?) Then you can start getting huge(r) torques and wind up that shaft like an elastic. 220,000hp at 15 rpm would give nearly a 330 deg twist, due to 75,000,000 ftlbs of torque...

 

[OVERKILL]

Going by the Wiki:
https://en.wikipedia.org/wiki/Nimitz-class_aircraft_carrier

They are 260,000SHP
Each prop is 25ft in diameter and weigh 66,000lbs (30t)

An interesting post from another board discussing this topic:

Quote:
My son is getting to retire after 20 years on the USS Carl Vinson and USS Eisenhower as a nuclear mechanic, and his response to all the questions is below:

The assumption for a 6' diameter shaft is about right. I've never measured it, but my arms are just shorter than the diameter.

The max rpm we can go is 171. That limit is there to prevent shaft damage. Also, we have limited throttle rates to prevent breaking the shaft.

The horsepower rating is correct. 70k HP per main engine. 2 per plant, 1 per shaft.

It's almost impossible to measure the amount of twist on the shaft, but speaking to some of the 10 pound heads (engineers) that work for RPPY (Reactor Plant Planning Yard), a good estimate is about a full revolution of twist.


From here: http://boards.straightdope.com/sdmb/showthread.php?t=441684

 

[Astro14]

Great question, Supton, I honestly don't know. I do know that the shaft is the limiting factor. The reactor can make far more steam, and the turbines more torque, than the shafts can handle.

The top speed is limited by that torque.

Though, I have to say, I've seen phenomenal acceleration from a Nimitz-class carrier when a simulated torpedo attack took place directly astern during training. The speed difference alone (from before the flare in the wake simulating the attack to final speed) was greater than the top speed to which the Navy admits.

We added nearly 30 knots to our speed in just a few minutes. The prop wash coming from the stern was amazing as well...a huge swell of whitewater. You could feel vibration from the ship itself, which I'm told comes from cavitation of the props. Just think about the torque needed to make props that size cavitate...

 

[Astro14]

I'm not certain of the shaft diameter or even if they are solid steel. They might be hollow...from my vantage point at the time, they certainly looked big, and if the guys who work on them say they're six feet in diameter, I won't argue. There are bearings every fifty feet or so.

 

[IndyIan]

I guess if you scaled it down, 6' diameter, 300' long is like a 25" long 1/2" copper pipe. I don't think you could get much more than 90 deg of twist before it buckled or tore.
Copper isn't steel but I think the naval engineers are having a laugh on us...