Editing Compound steam engine (section)

===Marine applications===
{{Main|Marine steam engine}}
[[Image:TripleExpansion.jpg|thumb|upright|Model of a triple-expansion engine]]
[[File:Christopher Columbus whaleback ccengine crop.jpg|thumb|upright|1890s triple-expansion (three cylinders of 26, 42 and 70&nbsp;inch diameters in a common frame with a 42-inch stroke) marine engine that powered the [[Christopher Columbus (whaleback)|SS ''Christopher Columbus'']].]]
[[File:SS Ukkopekka steam engine.jpg|thumb|upright|[[S/S Ukkopekka|SS ''Ukkopekka'']] triple-expansion marine engine]]
[[File:Liberty ship 140-ton VTE engine.jpg|thumb|right|140-ton &ndash; also described as 135-ton &ndash; vertical triple expansion steam engine of the type used to power [[World War II]] [[Liberty ship]]s, assembled for testing prior to delivery. The engine is 21 feet (6.4 meters) long and 19 feet (5.8 meters) tall and was designed to operate at 76 [[Revolutions per minute|rpm]] and propel a Liberty ship at about 11 knots (12.7 mph; 20.4&nbsp;km/h).]]
In the marine environment, the general requirement was for autonomy and increased operating range, as ships had to carry their coal<!--and water?--> supplies. The old salt-water boiler was thus no longer adequate and had to be replaced by a closed fresh-water circuit with condenser. The result from 1880 onwards was the '''multiple-expansion engine''' using three or four expansion stages (''triple-'' and ''quadruple-expansion engines''). These engines used a series of double-acting cylinders of progressively increasing diameter and/or stroke (and hence volume) designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. Where space is at a premium, two smaller cylinders of a large sum volume might be used for the low-pressure stage. Multiple-expansion engines typically had the cylinders arranged in-line, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple-expansion engines. Y-S-T engines divided the low-pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the [[Olympic class ocean liner|Olympic class]]), but was ultimately replaced by the virtually vibration-free [[steam turbine]].

The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water could be reclaimed to feed the boiler, which was unable to use [[seawater]]. Land-based steam engines could simply exhaust much of their steam, as feed water was usually readily available. Prior to and during [[World War II]], the expansion engine dominated marine applications where high vessel speed was not essential. It was superseded by the steam turbine when speed was required, such as for warships and [[ocean liner]]s. [[HMS Dreadnought (1906)|HMS ''Dreadnought'']] of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.