Doubts about three shafts stern of Bismarck

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Hartmann10
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Doubts about three shafts stern of Bismarck

Post by Hartmann10 »

hello to all, It´s one of my first posts: I would like to know if the three shaft arrangement of the stern of the Bismarck and another German ships (catastrophic failliures), was less resistant to torpedoes and battle damage, and if it is more ineficient than a more conservative four shaft arrangement. Thanks in advance to all.
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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

Actually, the tail-end failures were overstated, I think. Everyone's ships have failures of all kinds.
It is not a simple matter to change a ship from 3 to 4 screws without extensive redesigns and substantial changes in the navy’s design “philosophy”. The Germans opted for the “pointy end” on their warships and that probably made 4 screws almost impossible. H. Evers in “Kriegsschiffbau”, eds. 1931 and 1943, states some of the reasons for opting for 3-screw propulsion: smaller turning radius, substantial weight reduction in engines and auxiliary machines, driveshafts as well as space and personnel savings. Furthermore, the idea was that the 3-screw setup would have a direct action on single and double rudder steering. Also, they thought that this setup would reduce cavitation. The German navy preferred 3 screws and one rudder for maneuverability (Schleswig-Holstein), but in the larger and faster ships the rudder had to be divided. Even newer design plans such as the H class, have 3 props.

"Seemannschaften" Gladisch and Schulze-Hinrichs, 1943, praises the 3 prop system also and there are handling instructions. But Graf Zeppelin would have had 4 props on the pointy end. I don't know what a marine engineer would think of this arrangement.

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Hartmann10
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Post by Hartmann10 »

A lot a thanks, Ulrich. I supposed this. It´s because in other forum (in Spanish: http://www.elgrancapitan.org/phpbb2/vie ... &start=180 ) it was stated by some members that the three shaft arrangement was a serious flaw in the design (I didn´t think that, but I couldn´t prove it). in other state of things, do you know if the maximal shp usable and transmisible per shaft and axe was something like 60700 shp?. A lot of thanks in advance
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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

As far as I know, the actual full speed and shp of the Bismarck over a measure distance is not known. This was mathematically derived by extrapolating from an appoximate 75% load; it is probably reliable. At these tests, the shaft shp was estimated to be about 38,000 at 250 rpm. BS was designed for a combined shaft hp of 138,000 shp and apparently could have made 150,000 by extrapolation of the data of the speed trials at 75% load. I don't know where you got the 60000 shp from. The table at lower right: Calculation of Full Performance Estimates of the Three-Shaft Turbine Installation based on Test Speed Trials at 43,000 t. (WPS = shp; Kesselzahl = Number of boilers; n = rpm; Kn = knots; Brennstoffverbrauch = fuel consumption) Erich Gröner "Die deutschen Kriegsschiffe 1815 - 1945", 1966.

NB: I hope some expert will answer your posting....... :angel:

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marcelo_malara
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Post by marcelo_malara »

I agree with Hartmann10. There has to be a limit in the power a shaft can transmit without breaking, and it seems to be near 50000 hp, as you have no battleships with 3 shafts and more than 150000 total hp.
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ontheslipway
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Post by ontheslipway »

Modern container ships have over 90,000 BHP on a single shaft.
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Post by marcelo_malara »

Interesting data. May be post-war steel is better than pre-war one. Is the power of those ships diesel or steam?
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ontheslipway
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Post by ontheslipway »

Diesel, but I doubt it has anything to do with the material of the shaft, more a matter of the power you can get on a single propeller or reduction gear.
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Javier L.
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Post by Javier L. »

HOLA!

Tirpitz made over 160,000 hp with 3 shafts. That said, having three-shafts is not a design flaw. Every arrangement has their advantages and inconvenients.
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Matthias
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Post by Matthias »

Indeed, and I would had that, as stated many time, the three shaft arrangement has nothing to do with the torpedo damage...;)
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marcelo_malara
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Post by marcelo_malara »

Diesel, but I doubt it has anything to do with the material of the shaft, more a matter of the power you can get on a single propeller or reduction gear.
So Foeth, be it because of the shaft or the reduction gear, we agree that the total power has something to do with the numbers of shafts, at least in the 1930s.
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ontheslipway
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Post by ontheslipway »

Well, if more power had been installed a 4 shaft arrangement would have been more likely, but it seems the 3 shaft setup was an inheritance of previous experience. The reasons as given above for a lighter and compacter engine rooms are the most important reasons. Hydrodynamically there isn't too much of a difference between 3 or 4 shafts, both being not quite optimal. The entire layout of the ship and hull afterbody changes with an added shaft, it's not a simple matter to add one.

Redundancy with 4 shafts is somewhat better, but you increase the number of parts, maintenance, crew, engine rooms etcetera. Perhaps it is interesting to know why many other navies choose 4 shafts?
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Post by marcelo_malara »

It would be interesting too to know if any navy had thought of a battleship with just two shafts, as I think that according to war experience, two shafts would provide adequate redundancy.
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Post by Matthias »

Zara class heavy cruisers had only two shaft, differently from the previous Trento class, which had four shaft.But I dunno the cause of the changing.Anyway Zara class heavy cruisers remained very fast ships, but I should ask to an expert of the Italian Navy, Erminio bagnasco, he surely knows why.May be Antonio could ask him...;)
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Ulrich Rudofsky
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Post by Ulrich Rudofsky »

foeth wrote:Modern container ships have over 90,000 BHP on a single shaft.
Do variable pitch props have any influence on that? See wild pics at

http://www.spiegel.de/wirtschaft/0,1518,400908,00.html
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