Mark Chirnside
Member
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,
Titanic's Central Propeller
- Thread starter Richard Woolcock
- Start date
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,
Mike Spooner
Member
Are there any records from the company who made the propellers for the Olympic class ships?
Jim Currie
Member
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.)
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.)
Mike Spooner
Member
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.
(think about what Bill Sauder said about WSL cheap-skates.)
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.)
Mark Chirnside
Member
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.
Mike Spooner
Member
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!
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!
Mark Chirnside
Member
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.
Jim Currie
Member
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
Mark Chirnside
Member
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.
Mike Spooner
Member
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?
Jim Currie
Member
You are correct, Mark.
I was asked for my thoughts and based them on simple logic.
However, as a former Builder's Risk surveyor at John Brown's old Yard, Clydebank, and as a serving officer, I am familiar with experimental trials on ships and many other marine craft.
Now back to the subject.
If this change of central propeller was indeed experimental work then we are discussing an experiment on a new ship which had to have been contemplated before there had been enough time to evaluate the performance of her sister - a sister which had only been in service for 3 months before having to return to dock for repairs and had only completed 6 monthsof her live before having to go back to drydock once more. The WSL shareholders and The City must have been having deep thoughts about the future when Olympic arrived back at Belfast in early 1912. Hardly the time to experiment would you say?
Samuel Halpern
Member
Think again. Only so much can be learned during the design stages. Anyone involved in producing a product, a system, or even a network, knows that you have to get it out into the "real world" to see how it actually performs under real world conditions. That's true today as it was back then.
Mark Chirnside
Member
Absolutely.
Samuel Halpern
Member
To shift the subject slightly, it is on record that Titanic was expected to do a little better than Olympic in overall speed performance. By that I mean for a given number of revolutions, Titanic was expected to run a fraction of knot better, perhaps as much as 1/4 to 1/3 knot. Anyone want to guess as to what that would mean to a ship owner, even for such a small amount?
Jim Currie
Member
Truer today than it was back in the 1950s and almost unheard of in shipbuilding.
Then, a change was made to a ship design as a result of adverse reports, change of use, and/or change in owner requirements or an unforeseen problem.
On the other hand, experimentation was done by individuals hence the plethora of industrial revolution inventions
However, in 1912, a 3 blade propeller was hardly an untried, new product being marketed by the producer. The problem was one of speed v. vibration.
There is no way that Harland & Wolff as builders changed the center propeller type without the consent of the customer. Nor was there any way that the builder could precisely know when the new build was going to be ready to fit propellers. Consequently, all arrangements for the casting of propellers were made well ahead of time.
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