NYC Tug Boat Compound Marine Steam Engine model
This is a rare one-of-a-kind, scratch-built at the turn-of-the-century, compound marine engine model. It is extremely fine crafted and uses traditional wedge fasteners in the bearing blocks. The detail and craftsmanship is remarkable. The model maker is unknown, but is believed that is could have been built by an engineer who worked on the full-size engine used on a New York City tug boat from which this model is patterned after. This engine features a powered, steam cylinder activated Stephenson reversal movement.
A similar but more modern, full-size compound steam engine is the De Klop engine built in Holland circa 1930. The De Klop is 2050 mm in height, rated at 120 HP and has an oiler arrangement much like the NYC Tug Boat engine model.
A history of NYC tug boats can be found at WNYC.org.
A very detailed historical reference for British tug boats can be found at TyneTugs.
The Marine Steam Engine
A marine steam engine is a steam engine that is used to power a ship or boat. A compound engine is a steam engine that operates cylinders through more than one stage, at different pressure levels. Compound engines were a method of improving efficiency. Until the development of compound engines, steam engines used the steam only once before they recycled it back to the boiler. A compound engine recycles the steam into one or more larger, lower-pressure second cylinders first, to use more of its heat energy. Compound engines could be configured to either increase a ship's economy or its speed. Broadly speaking, a compound engine can refer to a steam engine with any number of different-pressure cylinders—however, the term usually refers to engines that expand steam through only two stages, i.e., those that operate cylinders at only two different pressures (or "double-expansion" engines)
Note that a compound engine (including multiple-expansion engines) can have more than one set of variable-pressure cylinders. For example, an engine might have two cylinders operating at pressure x and two operating at pressure y, or one cylinder operating at pressure x and three operating at pressure y. What makes it compound (or double-expansion) as opposed to multiple-expansion is that there are only two pressures, x and y.
The first compound engine believed to have been installed in a ship was that fitted to Henry Eckford by the American engineer James P. Allaire in 1824. However, many sources attribute the "invention" of the marine compound engine to Glasgow's John Elder in the 1850s. Elder made improvements to the compound engine that made it safe and economical for ocean-crossing voyages for the first time. (Source: Wikipedia)