3-shaft propulsion

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marcelo_malara
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Re: 3-shaft propulsion

Post by marcelo_malara » Tue Aug 06, 2019 9:06 pm

dunmunro wrote:
Tue Aug 06, 2019 7:09 pm
marcelo_malara wrote:
Tue Aug 06, 2019 6:47 pm
Thorsten Wahl wrote:
Tue Aug 06, 2019 6:46 am
Howe_endurance1.jpg
What book is this from?

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British Battleships of World War two, by Raven and Roberts.
Thanks! Raven´s British cruisers don´t have info like that!

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Re: 3-shaft propulsion

Post by marcelo_malara » Tue Aug 06, 2019 11:54 pm

I compiled the following data:

................Steam pressure...HP turbine......Shaft ..........Consumption
Hood...............235 psi..........1500 rpm......210 rpm
Massachusetts.....600 psi.........6052 rpm......185 rpm.....304 gm/hp/hr
Sumner/Gearing..565 psi.........5676 rpm......350 rpm.....290 gm/hp/hr
Bismarck...........825 psi...…....2880 rpm......270 rpm.....325 gm/hp/hr

I think that as the steam pressure increases, so does the HP turbine rpm. The higher pressure gives a higher speed to the steam flow, so the turbine turns faster to match it, if not a lower efficiency would have to be accepted, as it was before reduction gearing was introduced. On the other side, to work efficiently the propeller has to turn at low rpm.

My idea is that the high pressure Bismarck steam must have needed an even higher turbine rpm than the Massachusetts, but the lack of double reduction would have made the propeller turn at an imposible speed. So the Germans accepted lower efficiency in the turbine, making it to turn at less that half the optimum speed, and lower effciency at the propeller, making it to turn at 150% the optimum speed for a BB.

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Re: 3-shaft propulsion

Post by Byron Angel » Wed Aug 07, 2019 1:35 am

See DK Brown's "Design and Construction of British Warships" regarding fuel consumption and endurance. There could be dramatic differences between trials values and actual wartime service values.

B

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Re: 3-shaft propulsion

Post by Bill Jurens » Wed Aug 07, 2019 2:05 am

Mr. Malara is dancing around some of the key parts of the problem, namely figuring out some way to reduce the speed of the turbines, which are happiest at high speed, to suit the propellers, which tend to be happiest as the speed goes down. The Germans and the British used only single reduction gearing in their big battleship plants, and the highest practical reduction there is typically around 12:1. The Americans were able to manufacture double reduction gears, which -- as one might expect -- brought possible reduction ratios to something like 24:1 instead. A big advantage.

One also must keep in mind that shaft horsepower (SHP) is only that, i.e. the power delivered to the shaft. A lot -- one might say the most important parts of the operation -- goes on aft of that, involving issues surrounding how well the propellers are able to transfer useful thrust into the water, i.e. is reflected in what is commonly known as THP or Thrust Horsepower. A high SHP with inefficient propellers and poor flow to the driving disks is likely to produce less actual useful horsepower than a plant with a relatively low SHP driving efficient propellers well-placed, and suited to the situation at hand (A propeller nominalized for good high-speed performance is likely to be less efficient at low speeds, and vice-versa.)

In the case of Bismarck, I suspect that some of the choices which led to the adoption of a three-screw arrangement revolved around the design and layout of the engineering spaces themselves; there was enough space to fit two turbine rooms side by side near midships, but this couldn't be continued very far aft, especially if there was a desire -- or requirement -- to keep all of the layouts physically nearly identical. In Bismarck as built, the turbine rooms are very similar in size and shape and the arrangement of the main machinery seems to have been kept quite similar, though perhaps swapped left-to-right-hand. This undoubtedly saved money and engineering effort, and if three 50000 SHP plants would do the job, there would seem to be little incentive to design, and attempt to install, four 37,500 SHP plants instead.

One must, I think, be careful to avoid convincing oneself that for various and sundry reasons one engineering plant arrangement was in some way notably ‘better’ than another. All involved the applications, and although ‘better’ and ‘worse’ do apply under somewhat restrictive conditions, as engineering skill – and to a somewhat lesser extent industrial capacity -- were similar, the plant arrangements as seen might best be evaluated as being simply ‘different’ instead of being superior or inferior overall.

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Re: 3-shaft propulsion

Post by marcelo_malara » Wed Aug 07, 2019 2:59 am

Looking for info on this, in the book "Power of the great liners" I came to the fact that in 1919 Cunard ordered five liners of the Scythia class, which used double reduction, albeit the power of the machinery was in the low side at around 12.000 hp. Gear ratios gave 2660 rpm in the HP and 1783 rpm in the LP turbines to 92 rpm on the shaft.

A high SHP with inefficient propellers and poor flow to the driving disks is likely to produce less actual useful horsepower than a plant with a relatively low SHP driving efficient propellers
Yes, that is the propulsive efficiency. The ratio of EHP/SHP, where:

EHP = resistance * speed
SHP = torque * rotation speed

Strange that nobody (at least to my knowledge) has calculated the resistance of Bismarck´s hull nowadays that CFD is common.

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Re: 3-shaft propulsion

Post by Bill Jurens » Wed Aug 07, 2019 4:35 am

No need to compute Bismarck hull resistance from scratch. The towing tank test results have survived. I'm not at liberty to post them, though, and I'm not entirely sure it would be productive to do so.

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Re: 3-shaft propulsion

Post by Herr Nilsson » Wed Aug 07, 2019 7:40 am

Thorsten Wahl wrote:
Tue Aug 06, 2019 7:39 pm
Herr Nilsson wrote:
Tue Aug 06, 2019 12:33 pm

Scharnhorst's and Tirpitz' turbines were of similar design, but Bismarck's was very different.
According their manuals Scharnhorst and Tirpitz had a very similar (almost identical) steam consumption per SHP
You meant the consumption drawings in Kriegserfahrungen...Oberbaurat Krux?

Power RPM ....steam consumption t/h


3 × 1.880 95..........30
3 × 4.660 122 .......57
3 × 10.050 160 ......108
3 × 16.000 190 ......165
3 × 25.800 220........ 255
3 × 32.000 235 .......321
3 × 42.100 253 .......417
3 × 48.000 270 ........492

R* 3 × 16.000 190 ...375
One boiler produces maximal 50 t steam per hour
Required fuel at this output 3,950 kg per hour.
No, I meant the original Brown, Boveri & Cie operating instructions for Scharnhorst's turbines and two pages from another manual which are from the BBC instructions for Tirpitz. The steam consumption you've posted is the sum of all three turbines. In the original operating instructions the values are for just one turbine (but at 3-turbine operation).
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Marc

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Re: 3-shaft propulsion

Post by Thorsten Wahl » Wed Aug 07, 2019 9:53 am

@Herr Nilsson, the 270 RPM value for Bismarck/Tirpitz refers -coincidentally- to a speed of about 30,2 kn of the Bismarck Meilenfahrt? is this correct?

additional edit:
according to MDV 371 or the Oberbaurat Krux Memo the Marine Wagner Boiler consumes 3,950 kg fuel oil (at äußerste Last) to produce 50 t of steam per hour at 58 atm.
therfore maximal fuel oil consumptin of twelve boilers was in theory 47,400 kg fuel oil per hour

this value seems in considerable contradiction to the "korrigierte Tabelle über den Fahrbereich Tirpitz ...für normalen Betriebsdruck"

the Range for 7717 m³ fuel oil (= about 7331 t(~0,95 density)) for 30,8 kn is given with 3354 sm. Fuelconsumption therfor about 60,7 t/h (calorific value about 8800 kcal/l)

does it mean the boilers could be overloaded over "äußerste Last" by about 28 percent? at normal operational pressure?.
Last edited by Thorsten Wahl on Wed Aug 07, 2019 10:39 am, edited 4 times in total.
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Re: 3-shaft propulsion

Post by Herr Nilsson » Wed Aug 07, 2019 10:28 am

@ Thorsten

Almost, BS 30.05 kn and TP 30.15 kn.
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Marc

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Re: 3-shaft propulsion

Post by pasoleati » Wed Aug 07, 2019 1:39 pm

Bill Jurens wrote:
Wed Aug 07, 2019 4:35 am
No need to compute Bismarck hull resistance from scratch. The towing tank test results have survived. I'm not at liberty to post them, though, and I'm not entirely sure it would be productive to do so.

Bill Jurens
A bit strange statement for how could someone have any legal reason to prevent anyone publishing such data for I doubt the data is any longer secret...And if someone wishes to keep the data secret just because, that someone belongs to 6' under.

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Re: 3-shaft propulsion

Post by Thorsten Wahl » Wed Aug 07, 2019 1:41 pm

many thanks,
difference appears negligible to me
additionally the power output of the turbines and the power output of M1-machinery for different RPM comparing Fahrtabellen and turbinedata is seemingly in very good agreement.
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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Re: 3-shaft propulsion

Post by Alberto Virtuani » Wed Aug 07, 2019 1:49 pm

Hello everybody,
Herrr Nilsson wrote: "What are you looking for exactly?"
Maximum (design, extrapower and actual) power for all 4 German battleships and their corresponding maximum speed, based on their power plant differences (if any relevant to these data).

AFAIK (looking for confirmation):
for both Scharnhorst and Gneisenau the design max power was 53.360 shp per shaft, thus 160.080 shp in total, the extra-power was 166.500 shp.
At trials GU developed only 153.900 shp for 30.7 knots (while hunting HMS Glorious, she registered 32 knots, thus developing, at least, the same extra-power under war-operative displacement conditions)
SH, at trials, developed 166.500 shp for 32 knots.
Bismarck ?
Tirpitz ?


Bye, Alberto
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Re: 3-shaft propulsion

Post by marcelo_malara » Wed Aug 07, 2019 3:55 pm

Bill Jurens wrote:
Wed Aug 07, 2019 4:35 am
No need to compute Bismarck hull resistance from scratch. The towing tank test results have survived. I'm not at liberty to post them, though, and I'm not entirely sure it would be productive to do so.

Bill Jurens
Productive...? May be, not because they are from Bismarck, but for us the enthusiasts as an example of all calculations needed in the design of a warship. Hope some day you can publish them!

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Re: 3-shaft propulsion

Post by Bill Jurens » Wed Aug 07, 2019 5:20 pm

Pasoleoti wrote:

"A bit strange statement for how could someone have any legal reason to prevent anyone publishing such data for I doubt the data is any longer secret...And if someone wishes to keep the data secret just because, that someone belongs to 6' under."

Well, the death penalty for this sort of thing does seem a bit over-the-top to me, but you are welcome to your opinion on the subject.

Actually, there are quite a few legitimate reasons to restrict the circulation of primary source information.

a) The original documentation may lie in a private collection, not in an archive. If that is the case, than like it or not, the choice to circulate it or not does (or should) normally remain with the owner. In such cases, it's not uncommon for material to be provided on a 'not for further circulation without my permission' basis.

b) Many archives actually DO provide copies with the proviso attached that the information not be further circulated. Many archives (legitimately) use the sale of information as a source of funds to 'keep the lights on', and might have to cease operations or cull collections. If you want to retain good relations with the archives and the archivists, it's usually not a good idea to break this rule.

c) Sometimes the data involved is voluminous and difficult to copy.

d) Quite often the data is not of much use when taken in isolation, e.g. it might be easily subject to misinterpretation, if not accompanied by other data. Often the necessary accompanying data to properly interpret the 'mother load' either no longer exists, or is not readily available. In such cases, a general summary of the information is probably just as useful -- perhaps more useful -- than a a pile of raw paperwork. Preparing such a summary can be time-consuming.

e) NEEDING the data and WANTING the data are two different things.

f) Once data is posted to the internet it is, in effect, 'out there' to more-or-less all readers everywhere, always. Such 'broadband' circulation is not always productive, and can sometimes be technically and historically damaging. Much of this sort of primary source material was originally produced on a 'secret' or 'confidential' basis for good reason, and although many of these initial reasons may have disappeared -- or at least heavily dissipated -- that does not necessarily mean that it is therefore a good idea to circulate them for all to see on the internet. Basically, releasing information of any sort usually requires some level of 'qualifying the customer' to determine if release is appropriate appropriate and required. When the 'customer' is essentially everyone, everywhere, always, (e.g. the internet), it's actually often historically more responsible to withhold.

It is not, overall, in good taste to choose to withhold information being presented in support of an argument, e.g. to proceed along lines such as "I have this information which supports my argument, but I'm choosing not to release it." In this particular case, because I HAVE no particular argument, I was just making information available, i.e. that the towing tank tests have survived. This revelation does not, and should not, obligate me to release that information helter-skelter on the internet. Knowing it exists means that serious researchers can usually find it on their own.

Several issues in the above list apply in the tank test data issue. If the recipient is easily identifiable (individuals known only by internet pseudonyms, such as "gangaman" or 'mrbarf' exclude themselves automatically), can demonstrate a legitimate need for the data other than idle curiosity, and appears to have the necessary skill set to interpret and utilize the data in a responsible manner afterwards, then usually some sort of transfer can be arranged.

This is, of course, more difficult if the holder is '6' under'.

Bill Jurens

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Re: 3-shaft propulsion

Post by pasoleati » Wed Aug 07, 2019 7:20 pm

Mr. Jurens's response flies against everything that solod historiography is. For example, the very basic foundation of the reference noting system in serious academic works is that every source must be open to checking by anyone so willing. I don't think any doctoral thesis could pass the bar if the aspirant kept his sources secret.

If there are archives that actually stipulate that any 3rd Reich era German material cannot be publicized, such archives should be closed down as what they do is stealing. I am quite certain that such archives/persons have not either conducted those tank tests or originally paid for them, so they have no genuine intellectual rights to them. In other words, they are making money on someone else's intellectual property. And that is stealing.

As for the claim that materials should be "interpreted properly" before giving access to it to all is akin to anti-gun gun grabbers who want to dictate who can bear arms and who cannot. In a free democratic society such attitude is unacceptable. Especially when the material concerned is something that presents absolutely no danger to anyone's security or privacy.

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