Thomas Wilson founded the Hull based Wilson Line in 1841. The company specialised in trading to Scandinavian and Baltic ports, to India and the carriage of immigrants to North American ports, carrying grain and general cargo on the return journey. At the start of WW1, the company owned 84 seagoing ships. Shipping losses for the Wilson line during WW1 were considerable, the company losing 36 ships and 300 crew members through torpedo, gunfire and mines. Replacements consisted of new building, and of war reparations in the form of ten ships including a 3,500 ton passenger and cargo ship built in 1898, which became the Calypso, the first full time cruise ship for the company, on which my parents celebrated their honeymoon with a cruise to the Baltic in 1933. At the end of WW1, the company was sold to Sir John Ellerman, thereafter operating as Ellerman’s Wilson Line.
War again in 1939-1945 took a heavy toll, with 170 seagoing personnel losing their lives. At the outbreak of war in 1939, Wilson’s fleet comprised of 35 steamships; by May 1945 only 10 ships remained. New ships were built and ordered during the war, notably Ariosto and Angelo, built by Swan Hunter in 1940 and fitted with low pressure exhaust turbine added to the traditional triple expansion steam reciprocating engine, and Tasso launched in June 1945 with the same machinery arrangement. Tasso was the prototype for the new Malmo class of eight ships constructed between 1946 and 1947. All were 1,797 ton general cargo ships of pre-war design and specification. Wilson’s were experienced steam ship operators and to them it made sense to build new, using tried and tested, easily managed and operated machinery, but to modern thought and design.
Thermal efficiency of the marine boiler and the reciprocating engine remained a constant consideration for ship owners and builders alike. The problems with steam powered machinery was that right from the moment of heat generation turning water into an expanding gas, everything connected with the generated power contrives to rob the steam of its energy. Heat escapes up the funnel and is conducted away through metal contact. There are losses through radiation, incomplete combustion, exhaust steam, thermal losses within the engine, losses in condensation, mechanical friction, propeller losses, wasted energy at the condenser. Owners were lucky if 6% of the original power arrived at the propeller. Some of these losses plague ship owners today, but some can be countermanded by a lick of non-stick silicone based paint to the ships underwater parts, a product that was unknown 50 years ago.
In simple engines, the steam was used once, arriving at the condenser with most of the generated energy unused. Compounding (steam going from a high pressure cylinder to a low pressure and then to the condenser) was more efficient but still with a lot of waste energy. Taking the steam through three expansions was, for most of the life of the triple expansion system, the best that could be hoped for, but still with big energy losses. Developments in boiler efficiency with high pressures and temperatures made great strides in economy and efficiency. The development of the superheat where generated steam was routed through tubes either surrounding the furnace or in the smoke box at the base of the funnel was a great factor in improving thermal efficiency.
The prime exponent in the development of superheat was North Eastern Marine (NEM), whose system used a superheated Scotch boiler at 220 psi, with a superheat temperature of 620 degrees F, achieving a reduction in steam consumption of about 30%.
For a 10,000 ton cargo vessel this would see a reduction from 50 tons of coal per 24 hours to 39 tons, a saving of 1,000 tons of coal for a 102 day voyage. (Coal as boiler fuel was still being used by elderly ships well into the late 20th century; the excursion paddle steamer Kingswear Castle on the river Dart in Devon has a hand-fired coal fuel boiler generating steam for its 100 year old machinery).
But there was still a lot of wasted energy, and with the development of the steam turbine, a lot of engineers saw the advantages in routing the low pressure steam from the engine into a low pressure turbine on its way to the condenser. Amazing gains were shown where a ship fitted with Swiss Brown Boverei exhaust turbine gained an additional 1,200 horsepower on top of its existing 4,200. NEM also pioneered the steam re-heat system where the steam was routed again to the funnel uptake after use in the high pressure and intermediate pressure cylinders before going to the exhaust turbine, thence to the condenser. In effect the steam was being taken to seven stages of expansion thus giving an efficiency in operation almost equalling that of an internal combustion motor ship. What could not be overcome was the take up of space by the boilers, using up valuable cargo area that motor ships used to their great advantage.
All the ships in the Wilson fleet constructed between 1945 and 1955 had the common factor of being powered by triple expansion, three crank reciprocating engines coupled to a low pressure exhaust turbine with double reduction gearing and Fottinger hydraulic coupling to the screw shaft. All turbines were to the Bauer-Wach system, developed in Germany in the 1920’s. Steam was generated in two traditional Scotch boilers using the Clyde oil firing system.