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#21 Bingo

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Posted 06 January 2015 - 03:02 PM

What about these on the Titanic?

Three propellers and the two one the right are the same, but here you also have a rudder into the mix.

Sparky, do you know?

 

Titanic%27s_propellers.jpg


Edited by Bingo, 06 January 2015 - 03:04 PM.


#22 VicHockeyFan

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Posted 06 January 2015 - 03:04 PM

Some kind of anti-vibration thing?


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#23 Bingo

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Posted 06 January 2015 - 03:07 PM

Some kind of anti-vibration thing?

Do you mean turbulence?



#24 VicHockeyFan

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Posted 06 January 2015 - 03:09 PM

Do you mean turbulence?

 

No, some kind of resonance vibration that wrecks the bearings when the shafts are in sync.


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#25 LJ

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Posted 06 January 2015 - 07:42 PM

Bingo, on 06 Jan 2015 - 4:02 PM, said:

What about these on the Titanic?

Three propellers and the two one the right are the same, but here you also have a rudder into the mix.

Sparky, do you know?

 

Titanic%27s_propellers.jpg

Well bingo you have just re-written history. Up until now there has never been a picture of the Titanic with her props in place. She was fitted with a three bladed center prop according to all known documentation. This was probably the Olympic.

 

The most efficient prop is a one bladed however it produces too much vibration, for each increase in blades there is a reduction in vibration but also in efficiency, Most ships use three or four bladed props.


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#26 Bingo

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Posted 06 January 2015 - 09:56 PM

MGY_Cutaway2.JPG

http://www.titanic-w...MGY_Cutaway.htm

 

The heading at the top of the cutaway states, "White Star Line Tripple Screw Royal Mail Steamship Titanic"

 

Machinery

Engine Builder: Harland & Wolff Ltd, Belfast

Engine Type: 2 X triple expansion inverted vertical direct acting surface condensing, 1 X low pressure turbine

Cylinders: 2 X 54; 2 X 84; 4 X 97 inches

Stroke: 75 inches

Nominal Horse Power: 6,906

Boilers

Description: Cylindrical multi-tubular

Number: 24 double & 5 single ended

Iron or Steel: Steel

Pressure when loaded: 215 lbs

Screw: Triple

Speed: 21 knots

Signal Letters: H. V. M. P.

 



#27 Bingo

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Posted 06 January 2015 - 10:11 PM

Here is the explanation.

 

Rotation

Right-hand propellers rotate clockwise to provide forward thrust.
Left-hand propellers rotate counter-clockwise to provide forward thrust.
Note: Left-Hand Propellers are primarily used on twin engine boats to cancel the steering torque

that would be caused if both propellers spun in the same direction.

 

The direction a prop rotates when viewed from the stern facing forward.

 

how_rotation.jpg

 

http://www.hhprop.co...-props-work.php

 

 



#28 VicHockeyFan

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Posted 07 January 2015 - 06:46 AM

Well bingo you have just re-written history. Up until now there has never been a picture of the Titanic with her props in place. She was fitted with a three bladed center prop according to all known documentation. This was probably the Olympic.

 

 

 

What LJ meant, Bingo, is that your photo shows a four bladed center prop, wile the Titanic only had a three bladed one, in the center of it's three props.


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#29 lanforod

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Posted 07 January 2015 - 07:26 AM

That is partly why Titanic was faster than Olympic.
I did some googling yeaterday wondering if a triple screw design has lots of torque but I guess it's no more than a single screw. As for the rudder, very useful at high speed.

#30 VicHockeyFan

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Posted 07 January 2015 - 07:44 AM

Let's be clear.  The Titanic had three screws.  So did the Olympic.

 

Blades on each prop:

 

Titanic:  three - three- three

Olympic:  three - four - three (like the photo in this thread)


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#31 Bingo

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Posted 07 January 2015 - 08:06 AM

What LJ meant, Bingo, is that your photo shows a four bladed center prop, wile the Titanic only had a three bladed one, in the center of it's three props.

 

Okay, that was the Olympic, probably named after our mountains near Port Angeles. I did use the wrong photograph, as it seems there are no known photos of the Titanics middle propeller installed, which was supposed to be a three bladed prop. Even the wreck does not show the propeller configuration as it is buried into the sea bottom. I do expect that once Robert Ballard reads this he will be going down to the wreck to have another look.

 

The Olympic experimented with number of blades, diameters and pitch of her propellers and perhaps Titanic would have done the same had she survived.

 

more info; http://www.encyclope...-propeller.html



#32 Bingo

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Posted 10 January 2015 - 05:27 PM

Waiting for the cruise ships

IMG_6404.jpg

 



#33 Sparky

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Posted 10 January 2015 - 05:37 PM

 it seems there are no known photos of the Titanics middle propeller installed

 

 

Titanic resized.jpeg

 

http://www.theguardi...pton-exhibition



#34 LJ

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Posted 10 January 2015 - 07:13 PM

Apparently The Guardian has similar reporting skills as the TC. 

 

http://www.encyclope...-propeller.html


Edited by LJ, 10 January 2015 - 07:17 PM.

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#35 Chef-eth

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Posted 07 February 2015 - 04:17 AM

Jason is correct, contra - rotating propellers cancel out "prop walk". (It's the same with aircraft engines on multi engine aircraft). Otherwise the tendency would be for the stern to move in a direction opposite to the direction of rotation. In the case of a stern drive, (inboard outboard leg), a rudder is not required as the leg moves the propeller's line of thrust and it has a small rudder in the form of a protective skeg under the prop.

 

Asymmetric power settings (one engine running faster than the other) will also cause the craft to turn. The larger the thrust difference, the faster the rate of turn. When docking, one engine can be placed in reverse, the other remains in forward thrust to assist in pivoting the craft. (Bow thrusters in combination with this technique are a most helpful device!).


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