Bismarck's propulsion damage

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Nedwille
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Bismarck's propulsion damage

Post by Nedwille »

From many report it is mentioned that Bismarck's center propeller and starbord rudder broke into each other and port rudder stuck ina certain degree. However i wonder why they did not use the side propellers in different thrust powers to compansate the rudder effect or try to advance in astern condition. Ithough that also the starboard propeller dislocated in line so only port propeller was in contact condition. But in the videos, Bismarck turning constantly to port so if the starbord propeller was out of action she should be turning to starboard. Can anyone explain the contradicting situation?
Steve Crandell
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Re: Bismarck's propulsion damage

Post by Steve Crandell »

This is from my memory, so beware. :)

I believe Bismarck's shafts converged slightly, and that in tests the ship was unable to steer with the props only, even with the rudders amidships. After the torpedo hit her captain tried a lot of different combinations and was unable to change course for France. The best he could do was to get the ship on a more or less stable heading in the hope that gunnery wouldn't be impaired too much by her erratic course.
Bill Jurens
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Re: Bismarck's propulsion damage

Post by Bill Jurens »

It is generally impossible (or nearly so) to steer a large multi-screw ship by propellers alone, especially in any sort of wind or sea state. The yawing motion created by the propellers is not really due to fore-and-aft thrust differences -- those these of course occur -- but the distance between the shafts and the divergence or convergence of the shaft lines is usually of minimal (if any) consequence. The main side-thrusts from reversing propellers primarily results from pressure differences on each side of the 'deadwood' which separates the propellers themselves. Basically, the ahead propeller creates a relatively low-pressure region on one side, while the astern propeller generates a relatively high-pressure region on the other. Most of these effects are minimized at any significant speed.

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Nedwille
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Re: Bismarck's propulsion damage

Post by Nedwille »

Thank you for your responses. Your explanations seem legit but Vittorio Veneto took a very similar damage in the battle of cape matapan and she could escape by using only starboard shafts. Also in my previous question i tried to say that once ship came to a heading to west, could not Bismarck cruise full estern to east. In astern cruising rudder effect would be insignificant. Ok, in rough sea, inevitably, contolling the yaw motion would be impossible but at least she could adnavce in a direction range of northeast to southeast and may enter the earial support region.
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Re: Bismarck's propulsion damage

Post by Bill Jurens »

I would not agree that the Cape Matapan torpedo damage to V.V. was in any way 'very similar' to that sustained by Bismarck. If I'm reading my drawings correctly, the V.V. hit actually took place about about 40 meters forward of the main rudder, and damaged only what might be best-described as an 'auxiliary rudder' forward. This suggests that rudder control remained reasonably intact, i.e. that V.V. ended up running with with starboard shafts ahead, no shafts astern, and a rather large imposition of starboard rudder.

The problem with steering with engines is that although one can sometimes obtain a fairly significant twisting motion while the ship is nearly stationary, this is because one can generate large transverse moments by running one set of propellers astern while the other set goes ahead. This can't be maintained at speed, because the net force of the propellers pushing forward on (say) the starboard side, is compensated by the net force of the propellers pushing aft on the port side. If one shuts down the astern shafts to gain forward speed, then steering is lost. If one doesn't shut down the astern shafts, one can't really proceed at any meaningful speed in a forward direction -- net steerageway is residual in nature, i.e. relatively small.

Bill Jurens
Steve Crandell
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Re: Bismarck's propulsion damage

Post by Steve Crandell »

I can remember being on a rather long diesel submarine trying to get out of a tight dock into a channel so we could get out of a harbor. Fortunately there was no wind or it would have been impossible without a tug. We moved out into the channel and turned using the screws, but it took IIRC 10 to 15 minutes to turn about 90 degrees. Awkward, but all we could do at the time because there were no tugs available.
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wadinga
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Re: Bismarck's propulsion damage

Post by wadinga »

Hi All,

Steve's point about windage is very important and often neglected. Ships operate on the boundary of two powerful fluids which may be in rapid motion relative to one another. They are also designed to steam efficiently going forwards, not backwards, with prop thrust going clear of the hull, often directly past the rudders to enhance their effectiveness. Any heavy weather coming in from the stern quarters tends to render the rudder less effective and steering is particularly difficult which may result in uncontrollable slewing beam-on or broaching.

In the gale force wind and heavy sea conditions prevailing, wind pressure on Bismarck's hull and superstructure would have been many, many tons, varying in strength and centre of effort depending on the orientation at any one time. The ship was wallowing helplessly with a list so bad some waves were breaking over the deck amidships. The accounts suggest all combinations were tried and they were all ineffectual, and the only stable orientation was the one achieved. Any number of hopefuls have come up with their imaginative concepts with dangled anchors, towed U-boats, sailing home in reverse and Lord-knows-what, but those who were there did their best with their ship and lives at stake, tried for hours and hours and only achieved what they achieved.

In the constantly changing dynamic interplay of turning forces, there was no stability in any vaguely east west orientation, so the only balance was apparently a slow forward motion creating a starboard turn balancing windage which was constantly trying to push the ship's head off to port. Too much power and a helpless uncontrolled circle off to starboard, too little and a helpless drift downwind to port results.

Weather conditions for Vittorio Veneto were nothing like those prevailing for Bismarck, and are thus irrelevant. If the sea had been millpond smooth, and there had been not a catspaw of wind, maybe one of these solutions would have helped a bit, but a slow-moving Bismarck would still have been caught and destroyed by overwhelming force.

All the best

wadinga
"There seems to be something wrong with our bloody ships today!"
paul.mercer
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Re: Bismarck's propulsion damage

Post by paul.mercer »

Gentlemen,
I may be wrong, but I thought that I read somewhere that the 'Nelsons occasionally had problems trying to turn in a strong crosswind.Is this true?
pgollin
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Re: Bismarck's propulsion damage

Post by pgollin »

.

Only a grain of truth in the story.

ABC said in a letter that the rear placement of the "Queen Anne Mansions" led to a certain amount of windage. however that anyone with a knowledge of sailing a dinghy should be able to handle the ships.

The poor handling "story" came about when one went aground in the approaches to a port, HOWEVER, the full story is revealed in the B.R. "The Handling of Ships" which states that at first the grounding was blamed on windage, but more work showed that there had been very little clearance between the ship's bottom and the muddy harbour bottom - this caused a suction effect which over-rode the power of the rudder.

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HMSVF
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Re: Bismarck's propulsion damage

Post by HMSVF »

pgollin wrote: Thu Mar 04, 2021 11:48 am .

Only a grain of truth in the story.

ABC said in a letter that the rear placement of the "Queen Anne Mansions" led to a certain amount of windage. however that anyone with a knowledge of sailing a dinghy should be able to handle the ships.

The poor handling "story" came about when one went aground in the approaches to a port, HOWEVER, the full story is revealed in the B.R. "The Handling of Ships" which states that at first the grounding was blamed on windage, but more work showed that there had been very little clearance between the ship's bottom and the muddy harbour bottom - this caused a suction effect which over-rode the power of the rudder.

.

HMS Nelson on the Hamilton Bank.

https://www.youtube.com/watch?v=urdNCLHHs4o&t=81s


I read somewhere that the Captain had the crew run from side to side in attempt to get her off!
pgollin
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Re: Bismarck's propulsion damage

Post by pgollin »

.

Excellent - I never knew that footage existed.

Thanks.

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