Ask An Expert- Battleships

[desertswo]

That beings up a question I have had on my mind for some time. How could the Iowas be fitted with the same screws as the Essex carriers? The Essex class had 150,000 shp and the Iowas had 212,000. How could the same set of screws absord so much more power? Did the Iowas turn them at higher RPM?

In a word, yes. The Iowa's displaced roughly 20K more tons than an Essex-class CV. Still, the engineering plants were very similar, but the propulsion power required to move those extra 20K tons at the same speed as the carriers that they were tasked with escorting (hint: there's a reason why they used to be referred to as "fast battleships" as compared to earlier designs) must logically be greater, ergo the boilers, while operating at the same pressure as those in Essex, generate a greater volume of steam, and the impulse and reaction turbines that make up the HP-MP-LP Turbine/Main Reduction Gear combination (hereafter referred to as "main engine") were engineered to extract the greatest amount of enthalpy from that increased volume.

All that said, the screws are not the point of emphasis with regard to absorbing the increased torque and thrust generated by operating those screws at higher RPM. It's not about the screws; it's all about the installed Kingsbury Thrust Bearings found on pages 96 and 97 at the link here. Rather than me explain it, it's an easy read. Take a look and then come back with whatever questions you have and I'll help you out, but basically it comes down to the greater the shaft horse power generated by the main engines found on those two ship classes, the stouter must the main thrust bearings be.

[SteveDaPirate]

As far as I know, I'm probably the only one here who has even had shots fired in anger at himself while at sea.

Is this something you have expounded on previously? It has certainly piqued my interest!

[desertswo]

Is this something you have expounded on previously? It has certainly piqued my interest!

Earnest Will and some counterdrug ops in the Caribbean. Stuff happens.

[RustyBattleship]

That beings up a question I have had on my mind for some time. How could the Iowas be fitted with the same screws as the Essex carriers? The Essex class had 150,000 shp and the Iowas had 212,000. How could the same set of screws absord so much more power? Did the Iowas turn them at higher RPM?

Probably. But I'm a structural and armor engineering type, not mechanical. However, on the speed trials I have been on with both the New Jersey and Missouri. we start off at about 80 rpm. We hold that speed for 10 minutes while bearing temperatures and vibrations (if any) are measured. Then we kick it up to another 10 rpm to 90 for 10 minutes for the same readings. Then 100 rpm. Then 110 rpm. Well it doesn't get too exciting until around 160 rpm when the turbulence of the water under the fantail evacuates all of Chief Quaters aft due to vibration JUST FROM WATER. At 180 rpm we are putting up a rooster tail. One of our escort Destroyers had to pull out for another one to replace it that had a full fuel load.

We usually leveled off at 200 rpm though they are capable of more. But we are already doing 32 knots plus so we just keep them up to 200 rpm for the next 8 HOURS. Then while still at 200 rpm we do our high speed turns. Now THAT can be fun if you don't have a full load and are riding a bit high in the water. The Big J heeled quite a bit but the Mo with a heavier load of fuel and ammo was barely noticable. But no worry, they are designed to take up to a 40 to 45 degree roll (or so our Scientific Section in the Design Division told me) and not capsize (though the 01 level might get a bit wet). I wouldn't want to be on one though in a 45 degree heel. I prefer walking on the deck, not the bulkheads.

The next advantage is the shape of the hull. When I first visited the USS Wisconsin (BB-64) in 1952 her Welcome Aboard pamphlet described the hull of the ship is actually an large Cruiser hull designed for high speed and not just a bulky floating fortress. Combine that with perhaps improved reduction gear design you have a heavily gunned and heavily armored ship that could sh*t and git.

[Thoddy]

We usually leveled off at 200 rpm though they are capable of more. But we are already doing 32 knots

Wow this 32 kn is remarkably better then the FTP 218 figures may indicate for 200 rpm and also significantly better then the results of the standardisation trail published in a215701 First of Class Trials on USS IOWA (BB 61) Class - Past and Present. Does you have steam consumption values on this speed?

[RustyBattleship]

Wow this 32 kn is remarkably better then the FTP 218 figures may indicate for 200 rpm and also significantly better then the results of the standardisation trail published in a215701 First of Class Trials on USS IOWA (BB 61) Class - Past and Present. Does you have steam consumption values on this speed?

Sorry, I do not. Note my post above yours in that my "expertise" is "restricted" to Hull design (plating, stiffeners, rivets and/or welds), compartmentation, displacement, stability, masts, antenna platforms, access routes, replenishment-at-sea structures, refueling-at-sea structures, cargo handling, bulkheads, decks, doors (water tight and non-watertight), hatches, scuttles, anchoring systems, mooring systems and armor, armor, armor and just a tad more armor.

[Tom]

... those four Essex class propellers ...

IIRC, Essex-class had four-blade; Iowa-class, five. I'll have an answer shortly.

[Tom]

Well, that's a bad start: Iowa-class had five-blade inboard, four-blade outboard. I cannot find my "Intrepid" book, so I'll hold off on a definitive answer for now. I doubt they were the same, though; a 40% difference in power is huge. The Iowas typically were good for 235 - 240k shp. The Essex' generally stayed closer to design. I think Shangr-La was one of the best at 158 - 161K shp.

[Tom]

Without researching it, I think 200 rpm is a bit low, but a good round figure. I would agree with 200 - 205 rpm for 31 kts., but not 32.

[Michigan_Guy]

I've seen this said so many times that the Iowa class battleships are capable of 32 knots, but have any one of the four actually reached that speed?

[85 gt kid]

I believe Rusty was on a run with one when they reached that. Said they verified by GPS and revolutions.

[RustyBattleship]

I've seen this said so many times that the Iowa class battleships are capable of 32 knots, but have any one of the four actually reached that speed?

Yup. I was on both the New Jersey and Missouri during their sea trials. As soon as they hit that speed it was announced on the 1 MC. But we didn't hold that speed for the full 8 hours of full flank straight ahead after reaching it, it was not necessary. So we let her (them) cut back to 30 knots (or maybe a tad less) which allowed our escort Destroyers and/or Frigates keep up without using too much Navy Distilate (that all non-nuclear ships run on today).

Hitting 32 was always the goal of each ship even for just a few minutes. But this was during trials and the Captains didn't want to go over 200 rpm on the props (though our head Mechanical Engineering Supervisor on board said that 210 would have been a piece of cake). After all, these were only TRIALS, not responding to an emergency that would take a toll (however small) on the machinery.

Sort of like if you can do a Wheelie on a motorcycle. Great. But for how long? Would you want to ride from San Diego to Boston on only one wheel of a motorcycle built in my home town? You do it for a short distance just to show it can be done. But you do not do it continuously unless it is absolutely necessary. The Hog can take it, but you would be ready for a Chiropractor (and/or a Psychiaratrist) by the time you got to Phoenix.

[Thoddy]

the ships propellers of Iowa class and Essex class also had different diameters and different pitch. So they werent strictly comparable.
Iowa class
propellers No.blades Diameter Pitch
2 inboard. ....5 ...........17'0" 18'41/2"
2 outboard ....4 ...........18'3" 19'01/2"

Essex class
propellers No.blades Diameter Pitch
2 Inboard ....4 ...........14'7" 15'31/2" at 2/3R
2 Outboard ....4 ...........14'7" 15'31/2" at 2/3R

[RustyBattleship]

the ships propellers of Iowa class and Essex class also had different diameters and different pitch. So they werent strictly comparable.
Iowa class
propellers No.blades Diameter Pitch
2 inboard. ....5 ...........17'0" 18'41/2"
2 outboard ....4 ...........18'3" 19'01/2"

Essex class
propellers No.blades Diameter Pitch
2 Inboard ....4 ...........14'7" 15'31/2" at 2/3R
2 Outboard ....4 ...........14'7" 15'31/2" at 2/3R

It sort of puzzles me that (according to your research) that the Essex class Carriers did not have any five bladed propellers on them. Back in 1985 I was walking past our propeller balancing shop and the new propellers for the Missouri were sitting on some pallets waiting their tests. I wrote down their sizes, number of blades, weight and which shaft they would be attached to.

I also wrote down their serial numbers. Propeller 3, the 5 bladed inboard for the port twin keel, had a surprisingly different serial number (18570) whereas the other three had nearly consectutive numbers (5232, 5235 & 5237). But the 5-bladed prop also had the name ESSEX engraved in it.

So, if the Battleships had 5-bladed ESSEX class propellers, why didn't the Essex class Carriers also have them?

[Michigan_Guy]

Yup. I was on both the New Jersey and Missouri during their sea trials. As soon as they hit that speed it was announced on the 1 MC. But we didn't hold that speed for the full 8 hours of full flank straight ahead after reaching it, it was not necessary. So we let her (them) cut back to 30 knots (or maybe a tad less) which allowed our escort Destroyers and/or Frigates keep up without using too much Navy Distilate (that all non-nuclear ships run on today).

Hitting 32 was always the goal of each ship even for just a few minutes. But this was during trials and the Captains didn't want to go over 200 rpm on the props (though our head Mechanical Engineering Supervisor on board said that 210 would have been a piece of cake). After all, these were only TRIALS, not responding to an emergency that would take a toll (however small) on the machinery.

Sort of like if you can do a Wheelie on a motorcycle. Great. But for how long? Would you want to ride from San Diego to Boston on only one wheel of a motorcycle built in my home town? You do it for a short distance just to show it can be done. But you do not do it continuously unless it is absolutely necessary. The Hog can take it, but you would be ready for a Chiropractor (and/or a Psychiaratrist) by the time you got to Phoenix.

Impressive :) I was always curious if they ever actually tried to run them that hard, even for a short time.