Marine steam engine

This article deals mainly with marine steam engines of the reciprocating type, which were in use from the inception of the steamboat in the early 19th century to their last years of large-scale manufacture during World War II.[1] Rivaling inventors James Rumsey and John Fitch were the first to build steamboats in the United States.Paddle propulsion gradually gave way to the screw propeller, and the introduction of iron and later steel hulls to replace the traditional wooden hull allowed ships to grow ever larger, necessitating steam power plants that were increasingly complex and powerful.Most early marine engines had the same cylinder technology (simple expansion, see below) but a number of different methods of supplying power to the crankshaft (i.e. connection mechanism) were in use.It remained the dominant engine type for oceangoing service through much of the first half of the 19th century however, due to its relatively low centre of gravity, which gave ships more stability in heavy seas.[7] It was also a common early engine type for warships,[8] since its relatively low height made it less susceptible to battle damage.Because the cylinder was above the crankshaft in this type of engine, it had a high center of gravity, and was therefore deemed unsuitable for oceangoing service.The type proved to have remarkable longevity, with walking beam engines still being occasionally manufactured as late as the 1940s.Their popularity in the United States was due primarily to the fact that the walking beam engine was well suited for the shallow-draft boats that operated in America's shallow coastal and inland waterways.[17] Walking beam engines remained popular with American shipping lines and excursion operations right into the early 20th century.There were also technical reasons for retaining the walking beam engine in America, as it was easier to build, requiring less precision in its construction.Fuel was also much cheaper in America than in Europe, so the lower efficiency of the walking beam engine was less of a consideration.[20] In early examples of the type, the crosshead assembly was rectangular in shape, but over time it was refined into an elongated triangle.[21] Steeple engines began to appear in steamships in the 1830s and the type was perfected in the early 1840s by the Scottish shipbuilder David Napier.This let the timing be varied to enable expansive working (as in the engine in the paddle ship PD Krippen).The first patented oscillating engine was built by Joseph Maudslay in 1827, but the type is considered to have been perfected by John Penn.The interior of the trunk is open to outside air, and is wide enough to accommodate the side-to-side motion of the connecting rod, which links a gudgeon pin at the piston head to an outside crankshaft.In this configuration, it was very useful to navies, as it had a profile low enough to fit entirely below a ship's waterline, as safe as possible from enemy fire.[28] Trunk engines were normally large, but a small, mass-produced, high-revolution, high-pressure version was produced for the Crimean War.[29] An original trunk engine of the gunboat type exists in the Western Australian Museum in Fremantle.[30] The engine's mode of operation, illustrating its compact nature, could be viewed on the Xantho project's website.There is only one known surviving back-acting engine—that of the TV Emery Rice (formerly USS Ranger), now the centerpiece of a display at the American Merchant Marine Museum.In this type of engine, the cylinders are located directly above the crankshaft, with the piston rod/connecting rod assemblies forming a more or less straight line between the two.A compound engine first recycles the steam into one or more larger, lower-pressure secondary cylinders, to use more of its heat energy.[40][41] To fully realise their benefits, marine compound engines required boiler pressures higher than the limit imposed by the United Kingdom's Board of Trade, who would only allow 25 pounds per square inch (170 kPa).The combination of higher boiler pressures and a compound engine gave a significant increase in fuel efficiency, so allowing steamships to out-compete sail on the route from the UK to China, even before the opening of the Suez Canal in 1869.Aberdeen was fitted with two double ended Scotch type steel boilers, running at 125 psi (860 kPa).This provided the technical solution that ensured that virtually all newly built ocean-going steamships were fitted with triple expansion engines within a few years of Aberdeen coming into service.All 2,700 Liberty ships built by the United States during World War II were powered by triple-expansion engines, because the capacity of the US to manufacture marine steam turbines was entirely directed to the building of warships.Inclined and horizontal cylinders could be very useful in naval vessels as their orientation kept the engine profile as low as possible and thus less susceptible to damage.