An 'Olympic' Class Propulsion System

How the White Star Line's greatest ships were propelled.

Titanica!

The decision to incorporate a Parsons low-pressure turbine in the new vessels of the ‘Olympic’ class, was a departure for the White Star Line from the conventional system of two piston-based reciprocating engines driving twin propellers. This was taken primarily, it is believed, following the results of improved efficiency and performance following the installation of a low-pressure turbine taking the exhaust steam from the reciprocating engines, in the White Star liner Laurentic of 1909. (1)

The conventional system had been employed in the ships of the ‘Celtic’ (‘Big Four’) class of 1901 – 1907, producing a steady moderate service speed of 16 knots combined with great economy; each ship burned a mere 280 tons of coal per day. However, owing to the enlarging of Baltic during construction in order to make her the largest vessel in the world, she had difficulty maintaining her schedule with the same originally designed engine power and the engines were subsequently modified for a greater power output. (2) Although the choice of engines had produced perfectly satisfactory results in these vessels, the horsepower needed to propel the larger ‘Olympic’ class at a service speed of 21 knots in any weather, it was claimed, would be far greater, stretching the system to its limits, and the Laurentic’s improved performance with the addition of the low-pressure turbine convinced the White Star Line to adopt the combination method of propulsion in the new vessels.

Two inverted direct-acting triple-expansion reciprocating steam engines, developing a designed 15,000 horsepower at seventy-five revolutions, would drive the wing propeller shafts and the 23 feet 6-inch three-bladed propellers, while the low-pressure turbine, driven by the waste steam from the main engines, would produce 16,000 horsepower at 165 revolutions per minute while moving the central 16-foot 6-inch four-bladed propeller. On trials, however, Olympic’s engines performed superbly, and although the usual 46,000 horsepower figure appeared in contemporary publicity, the engines were registered to develop 50,000 horsepower, producing a maximum of some 59,000 shaft horsepower with the main engines running at 83 revolutions per minute and the turbine at full power, according to Olympic’s Chief Engineer Fleming. Standard ‘normal full revolutions’ in service were 78 revolutions.

(This contradicts Bruce Ismay’s American enquiry testimony that these engines had a normal specified full speed of 78 revolutions but could work up to 80 revolutions; but as the Managing Director, he may not be so familiar with their working and it is surely better to accept the Chief Engineer’s estimate. It is interesting to note that following the ship’s maiden voyage Ismay noted that the engines had reached 81 revolutions at one point, but he told the White Star Line officials that at no point were the engines working at full speed; this would seem to back-up the Chief Engineer’s figures.)

Time would prove the combination machinery’s economy; on Olympic’s maiden crossing she burned a mere 620 tons of coal per day with no more than ninety percent of the furnaces ever operating, compared to the predicted 720 tons, which drove the ship at an average speed of 21.7 knots over the ground for four days, even though the liner had encountered bad weather and also a strong breeze on June 17th 1911, not to mention the fact that she was running against the current. When she docked in New York, the passengers were unanimous in their praise for her, declaring her as a big luxurious hotel in which it was hard to imagine being afloat, and mentioning that there was ‘very little vibration.’ In fact, as the reciprocating engines turned in opposite directions, this assisted to prevent vibration; although it must be mentioned that the propellers can be the prime cause of vibration, rather than the engines themselves.

Yet, although the turbine’s addition had made such performance possible, giving a huge power increase for the same fuel consumption, time would prove that the turbine, still really in its infancy, was prone to excessive wear. This never became apparent on Titanic as she unfortunately was not afloat long enough for any problems to develop. In fact, although the new technology was being fitted into more and more ships, with great results, it was developing with the ships, unlike the tried and tested reciprocating engines.

Matters came to a head following the Olympic’s refitting of late 1912/early 1913. Following her return to service, on April 9th 1913 the British Board of Trade were concerned that a close watch be kept on the turbine, and placed the turbine (although not the actual Olympic) on their ‘Confidential List’ so that the turbine rotor’s blades and binding could be checked.

Olympic’s performance was, however, still satisfactory. Before the war she maintained a speed well in excess of 24 knots over the ground for more than a day, running Eastbound.

It was following the war that the turbine underwent repairs owing to deterioration. Following Olympic’s post war refitting, at Belfast on June 11th 1920 the Surveyor noted that the turbine had been ‘opened up, inspected and repaired to my satisfaction.’

To be precise, the first and second binding strips on all blades of the rotor were replaced with a new brass material, the composition of which was seventy percent Copper and thirty percent Zinc, a replacement and improvement of the composition of the original ‘ordinary soft brass.’ It is a possibility that the original had been affected by a phenomenon called ‘creep,’ deforming the material over the length of time. The original material’s ‘melting temperature, which has a direct relation to the creep activation temperature, may have been low enough in the alloy for creep to occur.’ While it is hard to establish whether this occurred, it is certainly a plausible theory. Brass alloys have a copper-zinc concentration ranging from ninety percent copper and ten percent zinc to fifty-five percent copper and forty-five percent zinc; while creep activation temperatures range from about 262° Centigrade to 200° Centigrade. At a nine pound per square inch pressure at the inlet of the turbine, the temperature could certainly have been high enough to activate creep, ‘especially if the original alloy had a higher concentration of zinc.’

The new material had somewhat better properties with its different composition. Copper, with its high melting point and resistance to corrosion, and Zinc in a presumably smaller quantity than the old composition, with its oxide coating giving a resistance to corrosion, but having a lower melting point, were commonly used together as an alloy, but it was the new material’s improved composition that gained over the old.

All of the turbine’s blading was examined, tested and then defective parts were cut away and new ones fitted. Internal casing and rotor parts were scaled, scraped and then coated with ‘Apexior’ non-corrosive paint. Following trials in Belfast Lough, the turbine ‘worked under all conditions,’ and was perfectly satisfactory despite the ‘teething troubles.’

With the other improvement to the ship’s propulsion plant, the conversion from coal-burning to oil-burning, Olympic’s performance was just as high, if not higher, than that of her pre-war self. On several occasions during the 1920s she clocked-up crossings of 23 knots, and even after twenty years in service matched her pre-war record of over 24 knots,. She regularly averaged 22.5 knots.

Her reciprocating engines underwent major overhaul and repairs during her refitting of 1932/1933, but for that necessity to only occur after twenty-one years over one-and-a-quarter million miles (about 255,000,000 revolutions assuming an average speed of twenty-two knots) was surely a mark of their quality. Following 1933, Olympic performed well, and despite nit-picking, lengthy and careful inspections of her engines and bedplates, over the next two years there were no troubles whatsoever. In mid 1933, on her third round trip following the overhaul of her engines, the engines were run at an easy seventy-six revolutions, allowing the liner to achieve an average speed of 21.5 knots in spite of the fact that the weather on the Atlantic was going through a bad patch at the time; this would translate into a rough crossing time in the region of five days fifteen hours. The Board of Trade were impressed with the improvement, and even on her last trip in October 1935, sadly to the scrap yard, her Chief Engineer mentioned that the engines were sounder than when originally fitted in 1911.

The skill of Harland & Wolff’s designers and high-quality of manufacture and design ensured a sound propulsion system which achieved almost the same economy of fuel usage per one horsepower/per hour of the quadruple-screw turbine liners of the ‘Lusitania’ class; yet as the engines developed a maximum of 59,000 shaft horsepower compared to the more than 75,000 shaft horsepower of the Lusitania, the operating costs were somewhat lower. While Mauretania had burned about 850 tons of coal per day during her Westbound maiden trip, Olympic had used far less, 620 tons, especially impressive considering her larger displacement and hull surface. In spite of all the criticisms sometimes heard, citing that the combination plant soon died-out to be favoured by all turbine plants, it cannot be denied that it was a superb piece of engineering, entirely in keeping with the ‘Olympic’ class vessels, especially Olympic which was one of the most successful ocean liners this century.

 


Sources
Author’s conversation with Dean Manning, who was very helpful and not only shared some of his research, but provided a most interesting discussion and literally made a big part of this article possible.
Michael Moran and Howard Shapiro (2000) Fundamental of Engineering Thermodynamics, 4th edition. John Wiley and Sons, Inc.
White Star Liner Titanic, Engineering, May 26th 1911. (Online document: www.geocities.com/Pentagon/2519/titanic/engr1911.html)
History of steam turbine technology Encyclopedia Britannica online (www.britannica.com/eb/article?eu=108534&hook=66513#66513.hook)
Sir Charles A. Parsons The Steam Turbine (Online document: www.history.rochester.edu/steam/parsons/index.html)
William Callister Jnr. (2000) Materials Science and Engineering, An Introduction, 5th edition, John Wiley and Sons, Inc.
(1) Duncan Haws (1990) Merchant Fleets: Volume 19: White Star Line TCL publications
(2) John H. Shaum and William Flayhart (1981) Majesty at Sea: The Four Stackers. Patrick Stephens Ltd


Text Copyright © 2000 Mark Chirnside

Contributor
Mark Chirnside

Cite this page
(2001) An 'Olympic' Class Propulsion System Titanica! (ref: #1477, accessed 23rd June 2017 06:49:38 PM) URL : https://www.encyclopedia-titanica.org/an-olympic-class-propulsion-system.html

  • Leave a comment

  • Add a new story to Encyclopedia Titanica

  • Link to this article

    Link
    Please link to this page using the following URL
    https://www.encyclopedia-titanica.org/an-olympic-class-propulsion-system.html

    Or copy the link text below

    Added to Encyclopedia Titanica Thursday 28th August 2003, last updated .