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3-shaft propulsion

Posted: Sat Jul 27, 2019 8:55 pm
by Byron Angel
pasoleati wrote:
Sat Jul 27, 2019 8:03 pm
Does the book discuss why Germans adopted 3-shaft propulsion? In detail discussing pros and cons.
Interesting question ...
A quick peek into Groener ("Die Deutschen Kriegsschiffe 1815-1945") indicates that 3-shaft propulsion was a feature of German capital ship designs starting with the Kaiser Friedrich III class of pre-dreadnoughts dating back to 1895 (laying down of first ship in class). This trend appear to have continued (with the sole exception of Prinzregent Luitpold with 2-shafts) all the way to the Bismarck class. The post-Bismarck design projects (H, J, K, L, M, N) had 3-shaft diesel propulsion, while the later designs (H42, H43, H44) had 4-shafts.

The German WW1 battle-cruisers (all the way through the uncompleted Mackensen and Ersatz Yorck designs) featured 4-shaft propulsion.

The post-WW1 diesel powered "pocket battleships" (Graf Spee, Deutschland) featured two shafts. The WW2 era "light battleships" (Scharnhorst, Gneisenau) and the heavy cruisers (Bluecher, Hipper Prinz Eugen) all featured three shafts.


Byron

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 7:17 am
by Herr Nilsson
IMHO the reason for a 3-shaft propulsion was simply the fact that it was sufficient for the required speed.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 4:05 pm
by RobertsonN
Three shafts weigh less than four. Breyer in Marine Arsenal No. 2, p. 6, gives the weight of the shafts and propellers in Gneisenau as 366 mt. So one shaft with its propeller weighed about 120 mt,

Neil Robertson

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 4:44 pm
by marcelo_malara
Why then cruisers had commonly four shafts when three or two would suffice for the power required?

Regards

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 4:47 pm
by Herr Nilsson
What cruisers?

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 5:31 pm
by marcelo_malara
Brooklyn class for example, 100.000 hp could be achived with two shafts.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 5:55 pm
by Herr Nilsson
But Brooklyn wasn't a German warship. The German battlecruisers in WW I required 4 sets of propellers, shafts and turbines to be fast enough. Due to technological progress the German battleships of WW II required just 3 sets and were even faster.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 6:34 pm
by dunmunro
marcelo_malara wrote:
Mon Jul 29, 2019 5:31 pm
Brooklyn class for example, 100.000 hp could be achived with two shafts.
USS Brooklyn (CL-40) had 4 shafts.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 7:46 pm
by pasoleati
Does Herr Nilsson have primary sources to support his theory? After all, to be logical, Germans should have been world leaders in large warship propulsion engineering which I doubt as e.g. Whitley's books mention plenty of inefficiencies and serious reliability issues with German powerplants.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 8:19 pm
by Herr Nilsson
No, I don't have primary sources to support my theory, but in my experience ship building is always a weight saving issue.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 8:36 pm
by marcelo_malara
I don´t agree, warships have others requirements besides hitting the required HP. As I said, most cruisers in WWII have four shafts for 80.000/100.000 hp, what would suffice with two shafts, but AFAIK the only power to go to two shafts in cruisers was Italy. Redundancy, internal subdivision, etc...was a necessity too.

German power plants were a case of engineering beyond reliability. German destroyers used very high pressure steam plants, 70 km/cm2, when other powers stayed around 40 kg/cm2. That advance came with a cost.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 8:43 pm
by pasoleati
And despite high pressures and temperatures, German powerplants weren't particularly fuel-efficient. Question is why not.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 8:54 pm
by marcelo_malara
pasoleati wrote:
Mon Jul 29, 2019 8:43 pm
And despite high pressures and temperatures, German powerplants weren't particularly fuel-efficient. Question is why not.
I didn´t know that. Do you have consumption numbers?

3-shaft propulsion 2

Posted: Mon Jul 29, 2019 9:13 pm
by pasoleati
No, as I don't have the books with me now. I do recall it being mentioned at least in Whitley that German marine steam plants were relatively inefficient.

Re: Battleship Bismarck: A Design and Operational History

Posted: Mon Jul 29, 2019 10:23 pm
by marcelo_malara
Oh I see it now in mine, German Destroyers, page 216, boiler system:

Wagner Large, design efficiency: 78%
Wagner Small, " : 78%
Benson, " : 77%
RN Admiralty, " : 76%

Don´t know exactly what this mean, I think is some sort of relation of the weight of effectively evaporated water to the theoretically maximum that a quantity of fuel can.

May be a more interesting number is the weight of the machinery, from 790 t to 860 t for 70.000 hp, Friedman quotes 600 t for 44.000 hp in the Tribals, for the same power the Geman machinery would weight about 500 t.