Titanic's Central Propeller


Mar 22, 2003
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The more a propeller has propeller blades, the more its efficiency will decrease. Hence, in terms of perfomance, I don't believe that a three bladed propeller is "going backwards". Nevertheless, it surely does in terms of comfort. Like Mark said in his article, it's all about finding the balance between those two factors. It also depends on what kind of ship you want to build I guess.
Going backwards in technology? Decisions were made for good reasons at the time they were made. Richard simply ignored the fact that we now have primary source evidence of the propeller configuration on Titanic as well as that on Olympic, including the changes made to Olympic's over the years. The Drawing Office notebook, as Mark said, documented the changes made to Olympic. The relevant pages are shown below. On the right is the original spec for Olympic. The pitch value crossed out and replaced was the modification made in Jan 1912. On the left is the changes made in Mar 1913. Nobody seems to question what was documented here, or the fact that Olympic was fitted with a 3-bladed center prop in 1913, but some just seem to ignore it, just like they ignore the what was documented in the H&W engineering notebook that Mark uncovered in 2008.

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Mike Spooner

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Mark or Sam.
I don't question your research into a three bladed centre propeller for Titanic, but rather surprise that nobody took a photo of the propeller installed.
However I have heard that more blades decrease the performance. So what was the theory in using a four bladed over a three bladed for the Olympic ship?
 
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Going backwards in technology? Decisions were made for good reasons at the time they were made. Richard simply ignored the fact that we now have primary source evidence of the propeller configuration on Titanic as well as that on Olympic, including the changes made to Olympic's over the years.
Yes I agree with that, I never said the contrary ! I was simply quoting Mike for the "going backwards in technology" because I don't think that was the case. Like you said, they knew what they were doing.

I'm sorry I probably should have expressed myself better, it led to confusion :).
 
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Cam Houseman

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Mark or Sam.
I don't question your research into a three bladed centre propeller for Titanic, but rather surprise that nobody took a photo of the propeller installed.
However I have heard that more blades decrease the performance. So what was the theory in using a four bladed over a three bladed for the Olympic ship?
Didn't Olympic have a three bladed prop for a short time in 1913?
 
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One question why do think that the Olympic used a four bladed centre propeller and not a three bladed propeller?

In that H&W seem to have been experimenting as to the best configuration, I'm not sure it makes a difference which ship had the four-bladed unit or the three-bladed unit, because they would only have comparable data when both ships were in service.

Nobody seems to question what was documented here, or the fact that Olympic was fitted with a 3-bladed center prop in 1913, but some just seem to ignore it, just like they ignore the what was documented in the H&W engineering notebook that Mark uncovered in 2008.

Exactly so. Those who deny either a 3-bladed centre propeller for Titanic in 1912 or a 3-bladed centre propeller for Olympic in 1913 do so on the basis of deliberate ignorance of the primary source evidence.

By the way, as Bill Sauder states in the video I linked to, he has evidence a 3-bladed centre propeller WAS cast and the weight of the unit is even documented.

Yes she did (until 1919 I think)
We have evidence a 3-bladed centre propeller was fitted in 1913 and then a 4-bladed centre propeller was photographed in 1919 and installed for the 1919-20 refit.

There may have been a further change in between but we do not have evidence of it.

Best wishes


Mark
 
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Mike Spooner

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Perhaps I can give a reason why fit a less efficient four bladed over a three bladed propeller in the first place. That will come from two other ships built before Olympic.
Laurentic and Megantic both are the same size, yet Laurentic has the same combination as the Olympic three engines on a smaller scale. However did they find the three bladed centre propeller produce more vibration that of the two screwed propeller on the Megantic? So to sacrifice some efficient less vibration for passenger comfort, where a four bladed propeller is fitted to Olympic. However I can see the logic fitting a three bladed centre propeller to Titanic for increase efficient. I don't see any complains from Titanic passengers of vibration problems. Yet at of the day the four bladed was more in favour as fitted to Britannic and to Olympic after the WAR years.
 

Thomas Krom

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I don't see any complains from Titanic passengers of vibration problems.
On the 14th of April, when the Titanic was nearing a speed of 22 and a half knots, vibration problems were noted by multiple passengers which either were aft at the time or had their stateroom near the stern (George Rheims near the first class smoking room, Edith Haisman, Mahala Douglass at the after Louis XIV staircase to name a few people).
 

Mike Spooner

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On the 14th of April, when the Titanic was nearing a speed of 22 and a half knots, vibration problems were noted by multiple passengers which either were aft at the time or had their stateroom near the stern (George Rheims near the first class smoking room, Edith Haisman, Mahala Douglass at the after Louis XIV staircase to name a few people).
Would you think that was a feasible reason to change over to a four bladed propeller? Or did Olympic with a four bladed propeller have that problem at 22 knots plus?
 

Cam Houseman

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Yes she did (until 1919 I think)
In that H&W seem to have been experimenting as to the best configuration, I'm not sure it makes a difference which ship had the four-bladed unit or the three-bladed unit, because they would only have comparable data when both ships were in service.



Exactly so. Those who deny either a 3-bladed centre propeller for Titanic in 1912 or a 3-bladed centre propeller for Olympic in 1913 do so on the basis of deliberate ignorance of the primary source evidence.

By the way, as Bill Sauder states in the video I linked to, he has evidence a 3-bladed centre propeller WAS cast and the weight of the unit is even documented.


We have evidence a 3-bladed centre propeller was fitted in 1913 and then a 4-bladed centre propeller was photographed in 1919 and installed for the 1919-20 refit.

There may have been a further change in between but we do not have evidence of it.

Best wishes


Mark
Thanks a ton!
 
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However did they find the three bladed centre propeller produce more vibration that of the two screwed propeller on the Megantic?

I don't think this is a true comparator.

Laurentic and Megantic were sister ships, one with a triple screw arrangement and one with twin.

Best wishes,
 
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Jim Currie

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Two things to think about -
1. When Titanic was felt to vibrate, her engine rpm had not been changed since noon that day. However, anyone who has ever spent much time at sea will tell you that when a ship is in a sea and or swell and out of enclosed waterways, vibrations are not noticed. However, when that same ship enters calm waters, hull and piping vibration becomes very obvious.

2. One-piece big ship ropellers were sand-cast in iron (spare) but usually phosphor bronze. Each one was cast to order. Before the casting took place, a lot of specialized preparations were made. Given this - what do any of you think the lead-time was back in 1912 to place a replacement order for the biggest ship in the world? (think about what Bill Sauder said about WSL cheap-skates.)
 
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Mike Spooner

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I would agree with Marks on his fine research he has found on paper work that the Titanic had a three bladed centre propeller. However since there are no photos and signed document that does not 100% guarantee was fitted to Titanic.
If we can find the manufacture of this propeller and seems there was made for Olympic, that would definitely or near dam it give 100% prove was fitted to Titanic.
Two things to think about -
1. When Titanic was felt to vibrate, her engine rpm had not been changed since noon that day. However, anyone who has ever spent much time at sea will tell you that when a ship is in a sea and or swell and out of enclosed waterways, vibrations are not noticed. However, when that same ship enters calm waters, hull and piping vibration becomes very obvious.

2. One-piece big ship ropellers were sand-cast in iron (spare) but usually phosphor bronze. Each one was cast to order. Before the casting took place, a lot of specialized preparations were made. Given this - what do any of you think the lead-time was back in 1912 to place a replacement order for the biggest ship in the world? (think about what Bill Sauder said about WSL cheap-skates.)
Jim can you highlight what you meant by:
(think about what Bill Sauder said about WSL cheap-skates.)
 
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However since there are no photos and signed document that does not 100% guarantee was fitted to Titanic.

I have no doubt some would even dispute a photo. This was certainly true in a 'discussion' about Mauretania's propeller configuration! (A gentleman argued she was launched without her propellers and, on being shown a photo of her prior to launch with her propellers fitted, simply denied that 'those objects' on 'all four shafts' could be propellers because he already 'knew' they were not.)

The issue here is not assigning percentages, but pursuing an objective analysis of the evidence we have.

From my perspective, the question comes back to human familiarity bias.

Before the H&W evidence to the contrary became available in 2008, everyone assumed Titanic had a 4-bladed centre propeller and this assumption became accepted as fact over decades. Nobody suggested exploring the stern beneath the mudline simply to confirm what they thought they already knew. In the same vein, the only reason people demand a higher standard of proof for the 3-bladed centre propeller configuration is because it conflicts with what they previously thought to be true.
 
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Mike Spooner

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Mark thanks for the reply. You would make a good Solicitor or Lawyer indeed!
I am looking at the time scale to make a one off, one piece special three bladed propeller.
Now the original plan as for Olympic was to make a one off four bladed centre propeller, one would of thought that was the same to follower for the other ships Titanic & Britannic. Not to put you on on the spot here, so when did you think they decided to change the design to a three bladed propeller and why to?
I can see this not a five minute item to manufacture as well!
 
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Not to put you on on the spot here, so when did you think they decided to change the design to a three bladed propeller

We don't know that they did change the design.

The notebook in the Stephen Pigott papers dates to c. summer 1910 and includes a both a 4 and 3 bladed centre propeller unit - one for each ship. The intention apparently being to compare the real performance of the two ships in service. (Titanic's loss meant that they had to obtain data on a 3 bladed unit by using Olympic after she emerged from the 1913 refit.)

Bill Sauder discusses this in some detail in the video link.
 
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Jim Currie

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I would agree with Marks on his fine research he has found on paper work that the Titanic had a three bladed centre propeller. However since there are no photos and signed document that does not 100% guarantee was fitted to Titanic.
If we can find the manufacture of this propeller and seems there was made for Olympic, that would definitely or near dam it give 100% prove was fitted to Titanic.

Jim can you highlight what you meant by:
(think about what Bill Sauder said about WSL cheap-skates.)
I'll try, Mike.
When a new ship was first contemplated, the prospective owner presented the builder with a set of criteria including a budget figure. Thereafter, the designers played about with many ideas based on existing shipbuilding practices and tried to produce a design that best met the needs of the client while remaining within budget.
All ship designers were aware of the pros and cons regarding the number and shape of propeller blades to be fitted to a single shaft. Consequently, there was no need to have a "field" experiment. Three blades = faster but more cavitation therefore more vibration. Four blades = less speed less cavitation = less vibration.

However, before a single propeller was cast for any of the Olympic class vessels, the builders knew the pluses and minuses of speed v comfort. This begs the question as to why (since they knew this) would the WSL go to the considerable expense of experimentation on a new ship? An experiment which, if it failed, might blemish the reputation for comfortable ocean travel which in turn, might hand clients to the competition and consequently a fall in revenue.
In addition, such propellers were custom-made. This would involve a lot of pre-casting and post-casting work, and we know that even today, custom-made items are expensive. Therefore there would have been a considerable lead-time between order and delivery.

Just some thoughts
 
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there was no need to have a "field" experiment.

It sounds like you're unfamiliar with Lusitania and Mauretania.

The 'real life' experiments of both ships with numerous different propeller configurations is well documented, including four bladed units and three bladed units, as well as a mixture of both on the same ship!

The experimentation of Harland & Wolff with different propeller configurations for Olympic, Titanic and Britannic is also well documented.
 
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Mike Spooner

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We don't know that they did change the design.

The notebook in the Stephen Pigott papers dates to c. summer 1910 and includes a both a 4 and 3 bladed centre propeller unit - one for each ship. The intention apparently being to compare the real performance of the two ships in service. (Titanic's loss meant that they had to obtain data on a 3 bladed unit by using Olympic after she emerged from the 1913 refit.)

Bill Sauder discusses this in some detail in the video link.
I do find rather strange if the two ships Olympic & Titanic are ordered by summer 1908, yet haven't sort out the centre propeller design until summer 1910. Where a top line engineer from John Brown Shipyard Stephen Pigott will step in and sort out what propeller to use! Then land up with three and four propeller design. I cant help thinking this should of been sorted out before the 1908 order was place?
 

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