3-shaft propulsion

Discussions about the history of the ship, technical details, etc.

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dunmunro
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Re: Battleship Bismarck: A Design and Operational History

Post by dunmunro » Fri Aug 02, 2019 8:51 pm

marcelo_malara wrote:
Fri Aug 02, 2019 4:08 am
Thanks, I will give a look to that book.

Anyway, consumption numbers do not look good either. According to a table on Koop´s, page 28 of the English edition, Bismarck at 138000 hp, 265 rpm, attained 29 knots with a consumption of 325 g/hp/hr, that would be 44.85 metric t per hour. USS Massachusetts, in an article in WI I have already mentioned, says that "sustained fuel usage for 24 hours was 935.75 t at full power". Full power was 130000 hp at 185 rpm and 27 knots. If the 935.75 t were US tons, they would be 35.36 metric t per hourl, 272 g/hp/hr. If they were imperial tons, they would be 39.65 metric t per hour, 305 g/hp/hr. In any case, the higher pressure does not bring better consumption.

Two more comments. Massachusetts had double gearing. Most BB had a shaft speed of around 180 rpm at max power. Don´t know why the Germans went to 270 rpm for max power.
The USN used long (imperial) tons. You can see actual fuel consumption data here:

https://www.ibiblio.org/hyperwar/USN/re ... el-BB.html

At full power KGV class specific fuel consumption was almost identical to Massachusetts, but Massachusetts had superior economy at cruising speeds.

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Re: 3-shaft propulsion

Post by marcelo_malara » Fri Aug 02, 2019 10:26 pm

Can you post those numbers from KGV?

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Re: 3-shaft propulsion

Post by pgollin » Sat Aug 03, 2019 11:19 am

.

One has to be careful with speed and range quotes as they depend on the state of the hull (fouling).

Trials info TENDED to be with reasonably clean hulls, whereas the RN standard figures usually were quoted with the hull 6 months since cleaning in temperate waters. (The RN also noted the effect of streaming Paravanes.)

.

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Re: Battleship Bismarck: A Design and Operational History

Post by Herr Nilsson » Sat Aug 03, 2019 1:31 pm

Alberto Virtuani wrote:
Tue Jul 30, 2019 4:51 pm
Hello everybody,
Marcelo Malara wrote: "Garzke gives 2863 t for Scharnhorst (125000 hp at 52 kg/cm2) and 2756 t for Bismarck (135000 hp at 58 kg/cm2)."
What was improved in Bismarck's boilers/machinery vs Scharnhorst's ?
Wasn't the Bismarck propulsion plant (including the boilers) basically the same as Scharnhorst's ?
Whitley mentions a pressure of 58 kg/cm2 @ 450° for Scharnhorst too...


Bye, Alberto
It seems to me, that there is some confusion in secondary sources. 58 atü (kg/cm^2) was the working pressure at 450° on Bismarck and Tirpitz and obviously the same on Scharnhorst and Gneisenau. For 125000 SHP Scharnhorst needed 12 boilers at 42 atü and for more than 160000 SHP 12 boilers at 56 atü.
SH.jpg
SH.jpg (42.02 KiB) Viewed 297 times
SH working pressure.jpg
SH working pressure.jpg (12.88 KiB) Viewed 297 times
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Marc

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Re: 3-shaft propulsion

Post by Byron Angel » Sat Aug 03, 2019 2:54 pm

pgollin wrote:
Fri Aug 02, 2019 9:58 am
The RN looked at double reduction gearing and wasn't impressed - at that time the efficiency savings weren't great and the costs and maintenance increase weren't thought to be worth it. Post-war reports basically stated the same with the big regret being lack of reliable high pressure boilers.

The low rotational speed of the Parsons type turbine meant that double reduction gearing would have been of little value. The value of double reduction gearing to the US lay in the fact that it permitted use of the smaller, lighter, simpler, very reliable and robust high speed (about 2x the rotational speed) turbine type that had been developed for use in US electrical power generating plants. The US high speed turbine was also more amenable to high temperature steam in that (from what I have read) its shorter casing of specially alloyed steel proved less prone to warping.

Interesting side note - the US design turbine employed one-piece forged rotors featuring one-tenth the number of blades compared to the Parsons type turbine.

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Re: Battleship Bismarck: A Design and Operational History

Post by marcelo_malara » Sat Aug 03, 2019 5:10 pm

Herr Nilsson wrote:
Sat Aug 03, 2019 1:31 pm

It seems to me, that there is some confusion in secondary sources. 58 atü (kg/cm^2) was the working pressure at 450° on Bismarck and Tirpitz and obviously the same on Scharnhorst and Gneisenau. For 125000 SHP Scharnhorst needed 12 boilers at 42 atü and for more than 160000 SHP 12 boilers at 56 atü.
SH.jpg
SH working pressure.jpg

So what is the maximum normal power of these ships?

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Re: 3-shaft propulsion

Post by Bill Jurens » Sat Aug 03, 2019 5:53 pm

The comparative evaluation of machinery plant design and installation, which is what I think is being attempted here, is a difficult -- and perhaps essentially intractable -- one.

The literature directly comparing two or four shaft vs three shaft propulsion arrangements is rather meager -- there were relatively few three shaft arrangements completed -- and often inconclusive. A fair amount revolves around the physical placement and size of the propellers and how they interact with the hull, the surrounding water, and themselves. It appears to have been somewhat difficult to balance three-shaft arrangements with regard to hydrodynamic considerations insofar as the center shaft is typically operating behind a main skeg whereas the wing propellers are not. The propellers behave differently in that regard, insofar as the flow to the center propeller is usually somewhat disturbed by the wing propellers, which are usually somewhat farther forward, and because the center propeller is aft of a vertical skeg, which can lead to vibration problems as the blades cut across the flow lines. The net result is that the center propeller can often take quite a hydrodynamic beating in sharp high-speed turns. Because the center propeller is working in a different flow field, it is (or at least was) common to make its pitch, diameter, or rpm different from that of the wing propellers in order to maximize efficiency and reduce problems with vibrations, etc. This was true even in four shaft arrangements, where variations in pitch etc. from the inboard set of screws to the outboard set was not uncommon at all.
Bismarck appears to have been somewhat unusual insofar as -- at least to my knowledge -- all three of her propellers appear to have been essentially identical.

Overall, it appears that if the design is done properly, there is relatively little to differentiate a good three shaft from a good two or four shaft arrangement.

So far as machinery weight and horsepower issues are concerned, the main problems, as others have noted earlier, revolves around the precise definition of exactly what items -- or, if the analysis is volumetric, what spaces -- should be assigned to the group 'machinery'. Our discussions on this thread seem to have only included boiler rooms and turbine rooms, but there are quite a few spaces other than that that might be legitimately be included as 'machinery spaces' as well. This is true of many ships where often the only thing one has to go by are the labels (names) assigned to various compartments. Also, there is often a good deal of ambiguity associated with exactly how the noted horsepower was actually measured, or whether it included overload or 'hotel' factors as well. Plant output and Shaft Horsepower are not necessarily the same thing. A small adjustment to propeller geometry can have quite an effect on exactly how much horsepower can actually be delivered into the water, whilst changing the machinery weight hardly at all. A small change in water temperature, which affects condenser efficiency, can have similar effects as well.

Unfortunately, most figures quoted tend to come from secondary sources, who tend to try to compress the results of perhaps a hundred pages of measurement data into a couple of lines in a table. While they can be considered rough guidelines, it's difficult to compare them across international lines in other than a fairly general manner.

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Re: Battleship Bismarck: A Design and Operational History

Post by Herr Nilsson » Sun Aug 04, 2019 12:06 pm

marcelo_malara wrote:
Sat Aug 03, 2019 5:10 pm
Herr Nilsson wrote:
Sat Aug 03, 2019 1:31 pm

It seems to me, that there is some confusion in secondary sources. 58 atü (kg/cm^2) was the working pressure at 450° on Bismarck and Tirpitz and obviously the same on Scharnhorst and Gneisenau. For 125000 SHP Scharnhorst needed 12 boilers at 42 atü and for more than 160000 SHP 12 boilers at 56 atü.
SH.jpg
SH working pressure.jpg

So what is the maximum normal power of these ships?
Officially? It depends on the source:

Scharnhorst: 125,000 SHP normal (160,000 SHP max)

Bismarck: 115,000 SHP normal (138,000 SHP max) or 138,000 SHP normal (150,000 SHP max)
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Marc

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Re: 3-shaft propulsion

Post by marcelo_malara » Sun Aug 04, 2019 6:03 pm

The comparative evaluation of machinery plant design and installation, which is what I think is being attempted here, is a difficult -- and perhaps essentially intractable -- one.
I agree with you, but in the long term there is a reduction in weight and volumes, for example Hood´s machinery weighted 5400 t for 144000 hp. Still I think that the high German steam pressure must manifest itself in some place, be it less weight, less volume or less consumption.
Officially? It depends on the source:

Scharnhorst: 125,000 SHP normal (160,000 SHP max)

Bismarck: 115,000 SHP normal (138,000 SHP max) or 138,000 SHP normal (150,000 SHP max)
Thanks! Can you post in full those graphics?

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Re: 3-shaft propulsion

Post by Bill Jurens » Sun Aug 04, 2019 7:08 pm

Manufacturing and maintenance issues aside, there is always at least a theoretical increase in efficiency as the difference in temperatures between the working fluid, in this case steam, and the thermal sink, in this case seawater, gets greater. The general equation for theoretical efficiency -- basically the so-called "Carnot Efficiency" takes the form

E = 100 (1-(Tc/Th)

So the only way to increase the theoretical efficiency -- with emphasis on the word 'theoretical' here -- is to either increase the temperature of the working fluid, or decrease the temperature of the thermal sump. So higher steam temperatures tend to be more efficient.

In terms of propeller design is concerned, overall efficiency tends to go up as one moves towards fewer and larger propellers with larger numbers of blades rotating at slower speeds.

I would tend to think that one of the reasons that Bismarck adopted a three shaft arrangement stemmed from a desire on the part of the designers to create a number of incrementally-sized 'package' plants. This allows some economies in manufacture and also allows the maximum interchageability of spare parts. One 50,000 horsepower stock 'package' might power a destroyer, two might be used on a cruiser, and three or more on larger vessels such as battleships. I haven't confirmed this with reference to primary sources, though, although the information is here somewhere, probably in one of the NavTechMisEu series.

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Re: 3-shaft propulsion

Post by marcelo_malara » Sun Aug 04, 2019 8:41 pm

In terms of propeller design is concerned, overall efficiency tends to go up as one moves towards fewer and larger propellers with larger numbers of blades rotating at slower speeds.
That is another question I have, and already mentioned, why did they go to 270 rpm propellers when other naval powers stayed at 180 rpm?

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Re: 3-shaft propulsion

Post by Thorsten Wahl » Mon Aug 05, 2019 8:44 am

according to the knowledge of the time 3 screw propulsion had a better propulsionefficiency compared to a 4 screw system.

older german transcription from "the Engineer" 1914
3 Welleneffiziens5.jpg
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Prior to WW2 the Germans said, that a 3 screw ship requires about six percent less propulsionpower for the same speed
3 Welleneffiziens1.jpg
3 Welleneffiziens1.jpg (20.58 KiB) Viewed 210 times
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Re: Battleship Bismarck: A Design and Operational History

Post by Thorsten Wahl » Mon Aug 05, 2019 1:32 pm

pasoleati wrote:
Thu Aug 01, 2019 10:10 pm
Folks, the Richelieu's machinery gave 155,000 shp on 4 shafts and the machinery weighed 2875 tons (=53 shp/ton). Steam conditions were 27 kg/cm2 and 350 deg C.
Bismarcks powerplant weights about 3,300 tons therof about 2,800 tons machinery and about 500 tons feedwater and fuel oil in piping.

Despite having 4 shafts the french powerplant consists of only two independend main units.
the german design had -according K-Amt(wich checked the French design) -more built in redundancy and appears less vulnerable and it was the first german naval powerplant with "sufficient engineering space")( Comparision Richelieu Bismarck 1941)
Last edited by Thorsten Wahl on Mon Aug 05, 2019 2:47 pm, edited 5 times in total.
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Re: Battleship Bismarck: A Design and Operational History

Post by Thorsten Wahl » Mon Aug 05, 2019 1:45 pm

Alberto Virtuani wrote:
Tue Jul 30, 2019 4:51 pm
Hello everybody,

What was improved in Bismarck's boilers/machinery vs Scharnhorst's ?
Wasn't the Bismarck propulsion plant (including the boilers) basically the same as Scharnhorst's ?
Whitley mentions a pressure of 58 kg/cm2 @ 450° for Scharnhorst too...


Bye, Alberto
Bismarcks machinery was more sturdy, the complete steam piping was much better shock protected. Even the heavy underwater mine detonations from the X-crafts does not cause rupture of the steamlines. The War diary of
Tirpitz doesnt show the same "notorious unreliability"(my emphasing)of machinery compared with Scharnhorst, the heavy cruisers and destroyers.
Last edited by Thorsten Wahl on Mon Aug 05, 2019 2:44 pm, edited 2 times in total.
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Re: 3-shaft propulsion

Post by Thorsten Wahl » Mon Aug 05, 2019 2:08 pm

marcelo_malara wrote:
Sun Aug 04, 2019 8:41 pm
In terms of propeller design is concerned, overall efficiency tends to go up as one moves towards fewer and larger propellers with larger numbers of blades rotating at slower speeds.
That is another question I have, and already mentioned, why did they go to 270 rpm propellers when other naval powers stayed at 180 rpm?

Regards
calculated screw slippage
Bismarck class (12-13 %) based on 118 RPM at 15 knots and ~265-270 RPM at ~30 knots (Fahrtabellen and MeilenfahrtBismarck )compares well with the same figure of
Iowa class(12,5%) based on 87 RPM at 15 knots and 196 RPM at 30 knots (FTP 218 war Service fuel consumption of U.S. Naval Suface vessels BB 61 class) these numbers differ a bit from the "First of Class Standardisation Trials)
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

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