The Triple Screws

[Stephen Stanger]

I was just thinking though, most propellers would not have been solid moulds in the 30's especially on the Queen Mary.
I doubt Cunard/White Star would have crafted solid moulds for her considering what they thought her screw revolution/speed was going to be. Also any damage to a screw from any type of flotsam would require complete replacement of the whole thing which is why they started attach blades to the central key instead of solid molding them, and that is as far back as Titanic.
SOD THAAT for replacing 35 tons of screw, it don't make sense that they would be solid.

Anybody?
Stephen.

 

[Kyrila Scully]

Stephen! I've been trying to contact you by phone at the Titanic exhibition. Jim Trembowski told me I should get in touch with you. I tried your e-mail shown in your profile, but it didn't work.
Kyrila Scully
[email protected]

 

[Daryl Dobbs]

I have just been to a very entertaining talk at the Gloucester and District Model Boat Club on a recent tourist dive by the Russians on the stern section.

One picture we were showed was very interesting, it depicted one of the screws projecting above the sediment. It must have been forced up by the impact on the sea bed. One aspect of the picture interested me is that the conical cover on the end of the keyway the blades are bolted on to is missing.

Is is possible that;

A/ It sheared off when it hit the bottom.
B/ Someone salvaged it.
C/ They were never fitted when the Titanic had to leave dry dock to make room for the Olympic.

If C what happened to them? If they were fitted to one of the other two Olympic class ships what happened to the ones destined for them or did the White Star line carry spares?

Many Thanks
Daryl

 

[Adam Leet]

I'm pretty sure they were installed before the ship left Belfast. As for whether they were sheared off or salvaged, I would assume they came off on impact. I haven't heard a word regarding that piece in any salvage, and the first photos of the props show them missing.


Adam

 

[David G. Brown]

Assume nothing regarding the propeller fairings. I can think of at least one reason why they would not have been installed for the maiden voyage. That reason's name is J. Bruce Ismay. There may be other reasons, such as lack of time or the failure of the shop to have completed the pieces. Until we have proof...photo or eyewitness...one way or the other, it is too dangerous to make an assumption.

-- David G. Brown

 

[Daryl Dobbs]

I have just received a very kind e-mail letting me know the correct name for them along with a good explanation. It appears that they were made of thin metal and hollow inside as the air pressure increased with the depth the assembly imploded.

A good explanation which I did not think of as I thought they were a more solid casting. It has surprised me that no one has thought of salvageing them. I know it is going off track but has any of the bells been located. I heard that a French expidition tried to get the one in the crows nest but dropped it when the crows nest fell apart.

Regards
Daryl

 

[Daryl Dobbs]

Do any of the work records exist at Harland and Wolf as to what work was carried out on the screws. Would it have been possible that it sailed without the fairwaters.

How much would they weigh?

Regards
Daryl

 

[Roy Currie]

I unfortunately am not privy to all the info you guy's have but regarding the "prop fairings". would they not be some type of retaining cone rather than a piece of hollow metal for streamlining? Roy Currie

 

[Scott R. Andrews]

Roy,

The cone, also called a "fairing" or "fairwater", placed over the end of the each propeller, was a relatively thin, lightweight casting. It's basic purpose was to provide a hydrodynamically "clean" surface, reducing turbulence as the water was forced aft of the screws. They had a secondary purpose in preventing or reducing corrosion of the shaft, keyway and key within the propeller hub. The cone was sealed to the hub of the propeller with one of a variety of substances in use at the time, creating a watertight enclosure around the lock nut holding the propeller hub onto the tailshaft. The opposite end of the propeller hub was also fitted with a sealing device. The gap between the shaft bossings on the hull and the leading edge of the propeller hub was then nearly closed up by a metal band which was fastened in place.

The actual lock nut on each shaft is visible in some of the dry-dock photos of the Olympic, and is readily visible in the photo of Titanic's starboard tailshaft being fitted prior to launch. It is located on the very end of the tailshaft. The type of nut H&W used on these ships was not the more familiar-looking hex type. Look for the large barrel-like protrusion having a series of holes bored into the periphery perpendicular to the centerline of the shaft at the end of the shaft. I would guess that the nuts were installed on the shafts and left in place during the launch and, afterwards, during fitting out, to protect the threads on the end of the tailshafts from damage.

This type of nut is both tightened and broken loose with a large forged crescent-shaped spanner having a tooth at the outer end which locks into one of the holes on the periphery of the nut. These spanner wrenches are often unique to the specific ship, and because of this are sometime carried aboard the ship so that they are available for use in dry-dock in locations away from the builder's yard. Titanic carried hers lashed to the after outboard bulkheads of the after well deck - one having a smaller radius for the lock nut on the center screw, and one having a larger radius to accommodate the lock nuts on the wing screws. Photos taken 1912 and later of the Olympic show these propeller spanners stowed aboard her in similar fashion and in the same location.

Regards,

Scott Andrews

 

[Daryl Dobbs]

Which direction did the screws rotate. I have heard that the port and centre screws rotated clockwise and the starboard rotated anti-clockwise.

How did the rudder compensate for two screws roatating one way and the third roatating the other, I would have thought that the ship would tend to want to steer to one side without constant corrections.

I have read the answer somewere but I cannot find the thred.

Thanks
Daryl

 

[Daryl Dobbs]

Any experts care to answer the question above?

 

[David G. Brown]

Looking at the ship from the stern -- starboard prop rotates clockwise, or in nautical terms is "right handed." Port prop rotates anti-clockwise and is "left handed."

I would love to say that the center prop rotated "the other way." Of course, there are only left or right handed propellers. So, the center prop was right handed.

Titanic's rudder did not "compensate" for the right hand rotation of the center screw. There is a rudder design, used on Liberty ships in WWII, that does compensate for the rotation of the propeller, but this had not been invented in 1912.

There is a side pressure generated by a rotating propeller. On small boats this can be quite a problem and is known as "propwalk." The two outboard props on Titanic cancelled themselves out. The center prop gave no more problem in forward than any single screw ship (like Californian) would have encountered.

Reverse is when side pressure becomes more apparent. However, the turbine powering the center prop did not have reverse gear. Without reverse power, the center prop had no effect on backing.

--David G. Brown

 

[Daryl Dobbs]

Thanks for answering my question

Regards
Daryl

 

[Philippe Delaunoy]

Dear all,

Just one question from a Titanic novice. Sorry, if the question was already asked on another thread :

In J. Cameron's movie, when the Titanic is leaving Southampton's harbor, you can see the 3 propellers starting simultaneously.

Question 1 : knowing that the Parsons' turbine took the exhaust steam from the reciprocating engines, is it correct to show 3 propellers moving at the same moment?

Question 2 : is (or was) it custom to leave port with the turbine started?

Your enlightened comments are welcome!

Warm regards.

Phil

 

[Mark Chirnside]

According to Olympic's Engineers, the turbine was only started when the main engines were at 'half ahead' (50 r.p.m.).

'Slow ahead' was used when leaving port, 30 r.p.m. without the turbine. So it would be wrong for them to start simulataneously; 50 r.p.m. would be needed to start the turbine.