Marine steam engine in the context of "Reciprocating engine"

Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.

Human-powered paddles and oars, and later, sails were the first forms of marine propulsion. Rowed galleys, some equipped with sail, played an important early role in early human seafaring and warfare. The first advanced mechanical means of marine propulsion was the marine steam engine, introduced in the early 19th century. During the 20th century it was replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Marine nuclear reactors, which appeared in the 1950s, produce steam to propel warships and icebreakers; commercial application, attempted late that decade, failed to catch on. Electric motors using battery packs have been used for propulsion on submarines and electric boats and have been proposed for energy-efficient propulsion.

Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars (and other motor vehicles), agricultural engines used for ploughing or threshing, marine engines, and the steam turbines used as the mechanism of power generation for most nuclear power plants.

The development of the steam engine was gradual. They were introduced during the 18th century and widely made for the whole of the 19th century and most of the first half of the 20th century, only declining as electricity supply and the internal combustion engine became more widespread. Over time, they would improve in pressure, expansion and speed.

A steamboat is a boat that is propelled primarily by steam power, typically driving propellers or paddlewheels. The term steamboat is used to refer to small steam-powered vessels working on lakes, rivers, and in short-sea shipping. The development of the steamboat led to the larger steamship, which is a seaworthy and often ocean-going ship.

Steamboats sometimes use the prefix designation SS, S.S. or S/S (for 'Screw Steamer') or PS (for 'Paddle Steamer'); however, these designations are most often used for steamships.

Boulton & Watt was an early British engineering and manufacturing firm in the business of designing and making marine and stationary steam engines. Founded in the English West Midlands around Birmingham in 1775 as a partnership between the English manufacturer Matthew Boulton and the Scottish engineer James Watt, the firm had a major role in the Industrial Revolution and grew to be a major producer of steam engines in the 19th century.

On a ship, the engine room (ER) is the compartment where the machinery for marine propulsion is located. The engine room is generally the largest physical compartment of the machinery space. It houses the vessel's prime mover, usually some variations of a heat engine (steam engine, diesel engine, gas or steam turbine). On some ships, there may be more than one engine room, such as forward and aft, or port or starboard engine rooms, or may be simply numbered. To increase a vessel's safety and chances of surviving damage, the machinery necessary for the ship's operation may be segregated into various spaces.

The engine room is usually located near the bottom, at the rear or aft end of the vessel, and comprises few compartments. This design maximizes the cargo carrying capacity of the vessel and situates the prime mover close to the propeller, minimizing equipment cost and problems posed from long shaft lines. On some ships, the engine room may be situated mid-ship, such as on vessels built from 1900 to the 1960s, or forward and even high, such as on diesel-electric vessels.