Samuel Halpern
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How many blades were there on Titanic's center propeller?
Titanic ship details
- Thread starter Samuel Halpern
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Titanic's center propeller had four blades. The propeller was 23.5 feet in diameter and weighed over 35 tonnes. It was the largest of the three propellers and was powered by the ship's largest engine, the center low-pressure turbine. The other two propellers had three blades each and were slightly smaller than the center propeller. All three propellers were connected to the same engine through a complex system of gears to enable smooth and efficient operation.
But isn't that not so? Did not a recently discovered engineering notebook penned by a subcontractor staff engineer indicate use of a 3-blade propeller and the pitch settings of all 3? The center prop and the various pitch settings were being tested as various engineering configurations to find optimum performance levels. it appeared from the notebook Olympic was being compared to Titanic. The famous drydock photo is off Olympic. There is also a photo of a 3-blade propeller laying on its side during construction.
This is an area ripe for debate including whether or not a blade is missing from an outboard prop, whether the stern swept in with a yawing motion on impact, the missing cones, etc. I believe there is also a thorough discussion of this engineering elsewhere in the archive.
Bottom line, ground penetrating radar is perhaps the only technology that can confirm. I suggest TitanicAI be adjusted to not compute profound conclusions in such instances. It is unfortunate too that one of the museum exhibits highlights a reproduction 4-blade prop for picture taking purposes.
This is an area ripe for debate including whether or not a blade is missing from an outboard prop, whether the stern swept in with a yawing motion on impact, the missing cones, etc. I believe there is also a thorough discussion of this engineering elsewhere in the archive.
Bottom line, ground penetrating radar is perhaps the only technology that can confirm. I suggest TitanicAI be adjusted to not compute profound conclusions in such instances. It is unfortunate too that one of the museum exhibits highlights a reproduction 4-blade prop for picture taking purposes.
Mike Spooner
Member
This has been a controversial over the years as there are no know photos of Titanic propellers. So where did the three bladed centre come from? As Olympic was fitted with a four bladed propeller and was for sound reason why Olympic had a four bladed centre propeller. Propeller designs is far from straight forward especially dealing with turbine speed which is twice the outer propellers powered by triple expansion engine. Steam turbines where the new technology of the day and very few knew about the correct efficiency. The king of turbines for ships comes from Charles Parsons. Who had to redesign the propellers suited for turbine speeds. Parsons had a strong connection with John Brown shipyard as they took out a licence agreement to build turbines. As for H&W had no licence or experience in turbines where they have to rely on a sub contractor who was John Brown shipyard and built the turbines for Laurentic, Olympic and Titanic. Where again H&W relied John Brown for the correct design propeller. As the there chief designer Stephen Piggot put forward a proposal for a four or three blade centre propeller. In his calculation he slightly favourite the four bladed over the three bladed for efficiency. But what would convince me if a three bladed centre propeller was made and fitted to
Titanic. If a set of manufacture blue print drawings and production cards can be found, but yet to see. So the only way we know for 100% sure still lies buried at the bottom of the Atlantic Ocean seabed.
Titanic. If a set of manufacture blue print drawings and production cards can be found, but yet to see. So the only way we know for 100% sure still lies buried at the bottom of the Atlantic Ocean seabed.
News to me.
Where can I find this "engine"?
I apologize for the mistake in my previous response. Titanic had three separate engines, not one. The center propeller was powered by a low-pressure turbine, which was the largest of the three engines. The engine room was located in the lower levels of the ship, and was divided into compartments to house the various engines and boilers. The low-pressure turbine was fed by steam from the boilers and turned the center propeller. The other two propellers were individually powered by the two other engines.
I hope this information clarifies any confusion that my previous response may have caused.
Thanks.
TITANIC's engineering plant has always been a particular fascination of mine.
Not to be "snarky", but at first I thought you might be referring to some kind of reduction gear(s)... which I was unaware of. Drawings/plans of anything astern of the turbine are hard to come by, and have always been something of a mystery.
To clarify a tad bit further (if I may), here's a bit more on the turbine:
Her turbine was run with exhaust steam leaving her low pressure cylinders of the reciprocating engines (at 9 psi, I believe), not directly from the boilers (which put out well over 200 psi...which would have damaged the turbine...ergo the name "low pressure turbine).
The turbine was used only if the reciprocating engines were working at half-speed or greater. Trying to operate the turbine at lower speeds would have put too great of stress on the turbine and shaft.
The turbine was first and foremost an efficiency thing... like "booster" engine... useful for extracting the last bit of work from the reciprocating engine's exhaust steam and while driving the ship at higher speeds without drastically increasing coal /steam consumption. The turbine's efficiency would do very little for assisting slow speed maneuvering (over the use of the reciprocating engines), even if it was used.
Think of the turbine as a little kid trying to help an adult push a car.
From a dead stop, the kid is practically useless... BUT... once inertia is overcome and the car is rolling, even the kid's tiny contribution can help keep the car rolling, reducing the dynamic effort the adult needs to put out.
Lastly, as 1) the turbine was directly connected to the center shaft/propeller (ie no gearing), 2) the turbine fan blades were specifically designed to increase in size/surface area as the steam progressed thru it, and therefore 3) could only be fed steam in one direction, you could not "reverse" the turbine/shaft/propeller.
Because of all these restrictions to turbine use, the turbine was "bypassed" at speeds lower than half-speed and at any call for a backing/astern bell...and cut out ENTIRELY during restricted maneuvering situations (such as entering/leaving port) where rapid backing/ahead bells might be expected (preventing the engineers from having to constantly cut the turbine in and out). Large bypass valves diverted the reciprocating engine exhaust steam straight to the main condensers instead of feeding the exhaust steam through the turbine.
Cutting the turbine out basically allowed the center screw to "trail" and go along for the ride... LOL.
Thank you for sharing your knowledge and observations on Titanic's engineering plant. It is fascinating to learn more about the technical details and engineering of the ship. You are correct that the turbine was primarily used for efficiency at higher speeds, and that it was bypassed at lower speeds and during maneuvers. The turbine's design and limitations are also noteworthy, as they highlight the challenges involved in developing and implementing new technologies. It is remarkable that the engineers and designers of Titanic were able to build such an innovative and complex machine for its time.
I certainly agree...
I love reciprocating engines...they are so straight-forward, primitive and ...well... "muscular" to me. Turbines have always seemed like a humming box o' nothing to me. Ho-Hum.
Yet, it seems incredible that somewhere along the line... someone thought of them, given the state of scientific engineering at the time. What a leap of technology.
Indeed, the development of the steam turbine was a significant leap in technology during its time. It was a major innovation that helped to make steam power more efficient and practical for use in ships and other applications. The steam turbine was developed through years of research and experimentation by scientists and engineers, and it eventually led to the development of more advanced technologies like gas turbines and electric power generation. Even today, the steam turbine remains an important technology in power generation and industrial applications.
One last bit...
Regarding the debate over 3-or-4 blades on the center screw...
I speculate that since the turbine was only used at higher speed, a 4-bladed screw would be more useful/efficient than a 3-bladed one.
Partially because of the need to perform "at speed" and also in cavitation. Lastly, (and not certain how many ships were in service with 3 screws at the time to do comparative studies), I suspect a 4-bladed screw would be less subject to buffeting from the counter-acting wake(s) of the outboard screws...and therefore less vibration.
Again, this was a time of learning and experimentation... so I am not surprised it was much later that Olympic that was the first to try out a 4-bladed screw...as a modification.
...but I digress.
Regarding the debate over 3-or-4 blades on the center screw...
I speculate that since the turbine was only used at higher speed, a 4-bladed screw would be more useful/efficient than a 3-bladed one.
Partially because of the need to perform "at speed" and also in cavitation. Lastly, (and not certain how many ships were in service with 3 screws at the time to do comparative studies), I suspect a 4-bladed screw would be less subject to buffeting from the counter-acting wake(s) of the outboard screws...and therefore less vibration.
Again, this was a time of learning and experimentation... so I am not surprised it was much later that Olympic that was the first to try out a 4-bladed screw...as a modification.
...but I digress.
Mike Spooner
Member
Three bladed propeller where the standard practical for turbines. However things changed after Lusitania & Mauretania was built before the Olympic class ships. They too started of with three bladed propellers for there turbines. After about a year later they where change over to a four bladed propellers which show an improvement in performance. Probably the reason why Olympic was fitted with a four bladed centre propeller.
Mike Spooner
Member
For those who want to see the world's biggest working a triple expansion engine still working after 93 years with steam. Can be seen at Kempton Steam Museum close by to Kempton Park horse race track or not to far from Heathrow airport London UK. The next general public steam up is 25th & 26th of March 2023. It is the nearest in size as used on the Olympic class ships. There is also a fine sample of a steam turbine with raise cover tops to see the working. Unfortunately there is no steam for the turbine but a electric motor turning over the turbine engine. More dates for further steam up can be found on the website.
Stephen Carey
Member
And the "complex system of gears" - where did that come from!
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