A marine steam engine is a reciprocating

Reciprocating engine

A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 steam engine

Steam engine

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

 that is used to power a ship or boat. Steam turbines and diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

s largely replaced reciprocating steam engines in marine applications during the 20th century, so this article describes the more common types of marine steam engine in use from their inception in the early 19th century to their last years of large-scale manufacture during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

History

The first commercially successful steam engine was developed by Thomas Newcomen

Thomas Newcomen

Thomas Newcomen was an ironmonger by trade and a Baptist lay preacher by calling. He was born in Dartmouth, Devon, England, near a part of the country noted for its tin mines. Flooding was a major problem, limiting the depth at which the mineral could be mined...

 in 1712. The steam engine improvements brought forth by James Watt in the later half of the 18th century greatly improved steam engine efficiency and allowed more compact engine arrangements. Successful adaptation of the steam engine to marine applications in England would have to wait until almost a century later after Newcomen, when Scottish

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 engineer William Symington

William Symington

William Symington was a Scottish engineer and inventor, and the builder of the first practical steamboat, the Charlotte Dundas.-Early life:...

 built the world's "first practical steamboat

Steamboat

A steamboat or steamship, sometimes called a steamer, is a ship in which the primary method of propulsion is steam power, typically driving propellers or paddlewheels...

", the Charlotte Dundas

Charlotte Dundas

The Charlotte Dundas is regarded as the world's "first practical steamboat", the first towing steamboat and the boat that demonstrated the practicality of steam power for ships....

, in 1802. In 1807, the American Robert Fulton

Robert Fulton

Robert Fulton was an American engineer and inventor who is widely credited with developing the first commercially successful steamboat...

 built the world's first commercially successful steamboat, simply known as the North River Steamboat

North River Steamboat

The North River Steam Boat or Clermont was the first commercially successful steamship of the paddle steamer design. It operated on the Hudson River between New York and Albany...

, and powered by a Watt engine.

Following Fulton's success, steamboat technology developed rapidly on both sides of the Atlantic. Steamboats initially had a short range and were not particularly seaworthy due to their weight, lack of horsepower, and tendency to break down, but they were employed successfully along rivers and canals, and for short journeys along the coast. The first successful transatlantic crossing by a steamship occurred in 1819 when sailed from Savannah, Georgia

Savannah, Georgia

Savannah is the largest city and the county seat of Chatham County, in the U.S. state of Georgia. Established in 1733, the city of Savannah was the colonial capital of the Province of Georgia and later the first state capital of Georgia. Today Savannah is an industrial center and an important...

 to Liverpool, England. The first steamship to make regular transatlantic crossings was the sidewheel steamer  in 1838.

As the 19th century progressed, marine steam engine and steamship technology developed alongside it. Paddle propulsion

Paddle steamer

A paddle steamer is a steamship or riverboat, powered by a steam engine, using paddle wheels to propel it through the water. In antiquity, Paddle wheelers followed the development of poles, oars and sails, where the first uses were wheelers driven by animals or humans...

 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.

Types of marine steam engine

A wide variety of reciprocating marine steam engines were developed over the course of the 19th century. The two main methods of classifying such engines are by connection mechanism and cylinder technology.

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

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 (i.e. connection mechanism) were in use. Thus, early marine engines are classified mostly according to their connection mechanism. Some common connection mechanisms were side-lever, steeple, walking beam and direct-acting (see following sections).

However, steam engines can also be classified according to their cylinder technology (simple expansion, compound, annular etc.). One can therefore sometimes find examples of engines which were classified under both methods, such as the compound walking beam (compound being the cylinder technology and walking beam being the connection method). Over time, as most engines became direct-acting but cylinder technologies were growing more complex, engines began to be classified solely according to their cylinder technology instead.

Some of the more commonly encountered types of marine steam engine are listed in the following sections. Note that not all of these terms may have been used exclusively in relation to marine applications.

Side-lever

The side-lever engine was the first type of steam engine to be widely adopted for marine use in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. In the early years of steam navigation, the side-lever was the most common type of marine engine for inland waterway and coastal service in Europe, and it remained for many years the preferred engine for oceangoing service on both sides of the Atlantic.

The side-lever was an adaptation of the earliest form of steam engine, the beam engine

Beam engine

A beam engine is a type of steam engine where a pivoted overhead beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used by Thomas Newcomen around 1705 to remove water from mines in Cornwall...

. The typical side-lever engine had a pair of heavy horizontal iron beams, known as side-levers, each secured in the centre by a pin near the base of the engine, allowing the levers to pivot through a limited arc. The engine cylinder stood vertically between this pair of levers at one end, with the piston rod attached to a horizontal crosshead, from each end of which a vertical rod, known as a side-rod, extended down each side of the cylinder to connect to the end of the side-lever on the same side. The far ends of the two side-levers were connected to one another by a horizontal crosstail, from which extended a single, common connecting rod

Connecting rod

In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

 which operated the crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 as the levers rocked up and down around the central pin.

The main disadvantages of the side-lever engine were that it was large and heavy, and for inland waterway and coastal service, it was soon replaced by lighter and more efficient designs. 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. It was also a common early engine type for warships, since its relatively low height made it less susceptible to battle damage.

The side-lever engine was a paddlewheel engine and was not suitable for driving screw propellers

Propeller

A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...

. The last ship built for transatlantic service to be fitted with a side-lever engine was the Cunard Line

Cunard Line

Cunard Line is a British-American owned shipping company based at Carnival House in Southampton, England and operated by Carnival UK. It has been a leading operator of passenger ships on the North Atlantic for over a century...

's paddle steamer , considered an anachronism when it entered service in 1862.

Grasshopper

The grasshopper engine was a variant of the side-lever engine. The grasshopper engine differs from the conventional side-lever in that the location of the lever pivot and connecting rod are more or less reversed, with the pivot located at one end of the lever instead of the centre, while the connecting rod is attached to the lever between the cylinder at one end and the pivot at the other.

Chief advantages of the grasshopper engine were cheapness of construction and robustness, with the type said to require less maintenance than any other type of marine steam engine. Another advantage is that the engine could be easily started from any crank position. Like the conventional side-lever engine however, grasshopper engines were disadvantaged by their weight and size. They were mainly used in small watercraft such as riverboat

Riverboat

A riverboat is a ship built boat designed for inland navigation on lakes, rivers, and artificial waterways. They are generally equipped and outfitted as work boats in one of the carrying trades, for freight or people transport, including luxury units constructed for entertainment enterprises, such...

s and tugs

Tugboat

A tugboat is a boat that maneuvers vessels by pushing or towing them. Tugs move vessels that either should not move themselves, such as ships in a crowded harbor or a narrow canal,or those that cannot move by themselves, such as barges, disabled ships, or oil platforms. Tugboats are powerful for...

.

Crosshead (square)

The crosshead engine, also known as a square, sawmill or A-frame engine, was a type of paddlewheel engine used in the United States. It was the most common type of engine in the early years of American steam navigation.

The crosshead engine is described as having a vertical cylinder above the crankshaft, with the piston rod secured to a horizontal crosshead, from each end of which, on opposite sides of the cylinder, extended a connecting rod which rotated its own separate crankshaft. The crosshead operated within vertical guides that enabled the assembly to maintain the correct path as it moved. The engine's alternative name "A-frame" presumably derived from the shape of the frames supporting these guides. Some crosshead engines had more than one cylinder, in which case the piston rods were usually all connected to the same crosshead. An unusual feature of early examples of this type of engine was the installation of flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

s—geared to the crankshafts—which were thought necessary to ensure smooth operation. These gears could apparently be very noisy in operation.

Because the cylinder was placed above the crankshaft in this type of engine, it had a high center of gravity and was therefore deemed unsuitable for oceangoing service, so that its use was largely confined to vessels plying inland waterways. As marine engines grew steadily larger and heavier through the course of the century, the high center of gravity of square crosshead engines became increasingly impractical, leading to their abandonment by the 1840s in favor of the walking beam engine.

The name of this engine can sometimes lead to confusion as "crosshead" is also an alternative name for the steeple engine (see below). Many sources thus prefer to refer to it by its informal name of "square" engine to avoid confusion. Additionally, the marine crosshead or square engine described in this section should not be confused with the term "square engine

Stroke ratio

In a reciprocating piston engine, the stroke ratio, defined by either bore/stroke ratio or stroke/bore ratio, is a term which is used to describe the ratio between the diameter of the cylinder bore and the length of the piston stroke within its cylinders...

" as applied to combustion engine

Combustion engine

Combustion engine may refer to:* Internal combustion engine* External combustion engine...

s, which in the latter case refers to an engine whose bore is equal to its stroke.

Walking beam

The walking beam, also known as a "vertical beam", "overhead beam", or simply "beam", was another early adaptation of the beam engine, but its use was confined almost entirely to the United States. After its introduction, the walking beam quickly became the most popular engine type in America for inland waterway and coastal service, and the type proved to have remarkable longevity, with walking beam engines still being occasionally manufactured as late as the 1940s. In marine applications, the beam itself was generally reinforced with iron struts that gave it a characteristic diamond shape, although the supports on which the beam rested were often built of wood. The adjective "walking" was applied because the beam, which rose high above the ship's deck, could be seen operating, and its rocking motion was (somewhat fancifully) likened to a walking motion.

Walking beam engines were a type of paddlewheel engine and were rarely used for powering propellers. They were used primarily for ships and boats working in rivers, lakes and along the coastline, but were a less popular choice for seagoing vessels because the great height of the engine made the vessel less stable in heavy seas. They were also of limited use militarily, because the engine was exposed to enemy fire and could thus be easily disabled. Their popularity in the United States was due primarily to the fact that the walking beam engine was well suited for the shallow-draft

Draft (hull)

The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...

 boats which operated in America's shallow coastal and inland waterways.

Walking beam engines remained popular with American shipping lines and excursion operations right into the early 20th century. Although the walking beam engine was technically obsolete in the later 19th century, it remained popular with excursion steamer passengers who expected to see the "walking beam" in motion. 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. Wood could be used for the main frame of the engine, at a much lower cost than typical practice of using iron castings for more modern engine designs. Fuel was also much cheaper in America than in Europe, so the lower efficiency of the walking beam engine was less of a consideration. The Philadelphian

Philadelphian

Philadelphian is most commonly used to describe someone who is from the city of Philadelphia, Pennsylvania.* List of people from Philadelphia, Pennsylvania"Philadelphian" may also refer to:...

 shipbuilder Charles H. Cramp blamed America's general lack of competitiveness with the British shipbuilding industry in the mid-to-late 19th century upon the conservatism of American domestic shipbuilders and shipping line owners, who doggedly clung to outdated technologies like the walking beam and its associated paddlewheel long after they had been abandoned in other parts of the world.

Steeple

The steeple engine, sometimes referred to as a "crosshead" engine, was an early attempt to break away from the beam concept common to both the walking beam and side-lever types, and come up with a smaller, lighter, more efficient design. In a steeple engine, the vertical oscillation of the piston is not converted to a horizontal rocking motion as in a beam engine, but is instead used to move an assembly, composed of a crosshead and two rods, through a vertical guide at the top of the engine which in turn rotates the crankshaft connecting rod below. In early examples of the type, the crosshead assembly was rectangular in shape, but over time it was refined into an elongated triangle. The triangular assembly above the engine cylinder gives the engine its characteristic "steeple" shape, hence the name.

Steeple engines were tall, though not as tall as walking beams, but much narrower laterally, saving both space and weight. Because of their height and high centre of gravity, they were, like walking beams, considered to be less appropriate for oceangoing service, but they remained highly popular for several decades, especially in Europe, for inland waterway and coastal vessels.

Steeple engines began to appear in steamships in the 1830s and the type was perfected in the early 1840s by the British shipbuilder David Napier

David Napier (marine engineer)

This article is about the marine engineer. For other people of the same name see David Napier David Napier was a Scottish marine engineer....

. The steeple engine was gradually superseded by the various types of direct-acting engine.

Siamese

The Siamese engine, also referred to as the "double cylinder" or "twin cylinder" engine, was another early alternative to the beam or side-lever engine. This type of engine had two identical, vertical engine cylinders arranged side-by-side, whose piston rods were attached to a common, T-shaped crosshead. The vertical arm of the crosshead extended down between the two cylinders and was attached at the bottom to both the crankshaft connecting rod and to a guide block that slid between the vertical sides of the cylinders, enabling the assembly to maintain the correct path as it moved.

The Siamese engine was invented by British engineer Joseph Maudslay (son of Henry

Henry Maudslay

Henry Maudslay was a British machine tool innovator, tool and die maker, and inventor. He is considered a founding father of machine tool technology.-Early life:...

), but although he invented it after his oscillating engine (see below), it failed to achieve the same widespread acceptance, as it was only marginally smaller and lighter than the side-lever engines it was designed to replace. It was however used on a number of mid-century warships, including the first warship fitted with a screw propeller, .

Direct acting

There are two definitions of a direct-acting engine encountered in 19th-century literature. The earlier definition applies the term "direct-acting" to any type of engine other than a beam (i.e. walking beam, side-lever or grasshopper) engine. The later definition only uses the term for engines which apply their power directly to the crankshaft via the piston rod and/or connecting rod. Unless otherwise noted, this article uses the later definition.

Unlike the side-lever or beam engine, a direct-acting engine could be readily adapted to power either paddlewheels or a propeller. As well as offering a lower profile, direct-acting engines had the advantage of being smaller and weighing considerably less than beam or side-lever engines. The Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 found that on average a direct-acting engine (early definition) weighed 40% less and required an engine room only two thirds the size of that for a side-lever of equivalent power. One disadvantage of such engines is that they were more prone to wear and tear and thus required more maintenance.

Oscillating

An oscillating engine was a type of direct-acting engine that was designed to achieve further reductions in engine size and weight. Oscillating engines had the piston rods connected directly to the crankshaft, dispensing with the need for connecting rods. In order to achieve this aim, the engine cylinders were not immobile as in most engines, but secured in the middle by trunnions which allowed the cylinders themselves to pivot back and forth as the crankshaft rotated, hence the term oscillating. Steam was supplied and exhausted through the trunnions. The oscilating motion of the cylinder was used to line up ports in the trunnions to direct the steam feed and exhaust to the cylinder at the correct times.

The first patented oscillating engine was built by Joseph Maudslay in 1827, but the type is considered to have been perfected by John Penn

John Penn (engineer)

John Penn FRS, was a marine engineer, whose firm was pre-eminent in the middle of the nineteenth century due to his innovations in engine and propeller systems, which led his firm to be the major supplier to the Royal Navy as it made the transition from sail to steam power...

. Oscillating engines remained a popular type of marine engine for much of the 19th century.

Trunk

The trunk engine, another type of direct-acting engine, was originally developed as a means of reducing an engine's height while retaining a long stroke (a long stroke was considered important at this time because it reduced the strain on components). Early examples of trunk engines had vertical cylinders; however, it was quickly realized that the type was compact enough to be laid horizontally across the keel

Keel

In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

. In this configuration, it was very useful to navies, as it had a profile low enough to fit entirely below a ship's waterline

Waterline

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...

, where it would be as safe as possible from enemy fire. The type was generally produced for military service by John Penn.

This type of engine had a horizontal cylinder, through the centre of which passed a cylindrical "trunk" or passage containing the connecting rod. The walls of the trunk were either bolted to the piston or cast as one piece with it, and moved back and forth with it. The working portion of the cylinder was annular or ring-shaped, with the trunk passing through the centre of the cylinder itself.

Trunk engines were quite common on mid-19th century warships, and were also to be found in commercial vessels, where though valued for their compact size and low centre of gravity, they proved expensive to operate. Trunk engines however proved poorly adapted to the higher boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

 pressures that became prevalent in the latter half of the 19th century, and were abandoned in favour of other solutions.

Normally large engines, a small mass-produced, high-revolution, high-pressure version was produced for the Crimean War. In being quite effective, the type persisted in later gunboats. An original trunk engine of the gunboat type exists in the Western Australian Museum

Western Australian Museum

The Western Australian Museum is the state museum for Western Australia.The Western Australian Museum has seven main sites: two in Perth within the Perth Cultural Centre, two in Fremantle , and one each in Albany, Geraldton, and Kalgoorlie-Boulder...

 in Fremantle

Fremantle

Freemantle is a suburb of Southampton in England.Fremantle or Freemantle may also refer to:- Places :* Fremantle, the port city to the capital Perth, Western Australia...

. After sinking in 1872, it was raised in 1985 from the and can now be turned over by hand. The Trunk Engine's mode of operation, illustrating its compact nature can be viewed on the Xantho project's website.

Vibrating lever

thumb
The vibrating lever, or half-trunk engine, was a development of the conventional trunk engine conceived by Swedish

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

-American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 engineer John Ericsson

John Ericsson

John Ericsson was a Swedish-American inventor and mechanical engineer, as was his brother Nils Ericson. He was born at Långbanshyttan in Värmland, Sweden, but primarily came to be active in England and the United States...

. Ericsson needed a small, low-profile engine like the trunk engine to power the U.S. Federal government's monitors

Monitor (warship)

A monitor was a class of relatively small warship which was neither fast nor strongly armoured but carried disproportionately large guns. They were used by some navies from the 1860s until the end of World War II, and saw their final use by the United States Navy during the Vietnam War.The monitors...

, a type of warship developed during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

 that had very little space for a conventional powerplant. The trunk engine itself was however unsuitable for this purpose because the preponderance of weight was on the side of the engine containing the cylinder and trunk, a problem which could not be compensated for on the small monitor warships.

Ericsson resolved this problem by placing two horizontal cylinders back-to-back in the middle of the engine, working two "vibrating levers", one on each side, which by means of shafts and additional levers rotated a centrally located crankshaft. Vibrating lever engines were later used in some other warships and merchant vessels, but their use was confined to ships built in the United States and in Ericsson's native country of Sweden, and as they had few advantages over more conventional engines, were soon supplanted by other types.

Back acting

The back-acting engine, also known as the return connecting rod engine, was another engine designed to have a very low profile. The back-acting engine was in effect a modified steeple engine, laid horizontally across the keel of a ship rather than standing vertically above it. Instead of the triangular crosshead assembly found in a typical steeple engine however, the back-acting engine generally utilized a set of two or more elongated, parallel piston rods terminating in a crosshead to perform the same function. The term "back-acting" or "return connecting rod" derives from the fact that the connecting rod "returns" or comes back from the side of the engine opposite the engine cylinder to rotate a centrally located crankshaft.

Back-acting engines were another type of engine popular in both warships and commercial vessels in the mid-19th century, but like many other engine types in this era of rapidly changing technology, they were eventually abandoned for other solutions. There is only one back-acting engine known to be still in existence—that of the TV Emery Rice (formerly ), now the centerpiece of a display at the American Merchant Marine Museum.

Vertical

As steamships grew steadily in size and tonnage through the course of the 19th century, the need for low profile, low centre-of-gravity engines correspondingly declined. Freed increasingly from these design constraints, engineers were able to revert to simpler, more efficient and more easily maintained designs. The result was the growing dominance of the so-called "vertical" engine (more correctly known as the vertical inverted direct acting engine).

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. The configuration is similar to that of a modern internal combustion engine (one notable difference being that the steam engine is double acting, see below, whereas an internal combustion engine generates power only in the downward stroke). Vertical engines are sometimes referred to as "hammer", "forge hammer" or "steam hammer" engines, due to their roughly similar appearance to another common 19th-century steam technology, the steam hammer

Steam hammer

A steam hammer is a power-driven hammer used to shape forgings. It consists of a hammer-like piston located within a cylinder. The hammer is raised by the pressure of steam injected into the lower part of a cylinder and falls down with a force by removing the steam. Usually, the hammer is made to...

.

Vertical engines came to supersede almost every other type of marine steam engine toward the close of the 19th century. Because they became so common, vertical engines are not usually referred to as such, but are instead referred to based upon their cylinder technology, i.e. as compound, triple expansion, quadruple expansion etc. It should be noted that the term "vertical" for this type of engine is imprecise, since technically any type of steam engine is "vertical" if the cylinder is vertically oriented. An engine described as "vertical" should therefore not be assumed to be of the vertical inverted direct-acting type unless the term "vertical" is unqualified.

Simple expansion

A simple expansion engine is a steam engine that expands the steam through only one stage, which is to say, all its cylinders are operated at the same pressure. Since this was by far the most common type of engine in the early period of marine engine development, the term "simple expansion" is rarely encountered; rather, an engine is assumed to be simple expansion unless otherwise stated.

Compound

A compound engine is a steam engine which operates cylinders through more than one stage, i.e., at different pressure levels. Compound engines were a method of improving efficiency. Up until the development of compound engines, steam engines used the steam only once before being recycled back to the boiler, but a compound engine recycles the steam into one or more larger, lower pressure second cylinders first, in order to utilize more of its heat energy. Compound engines could be configured to either increase a ship's economy or its speed. Although broadly speaking a compound engine can refer to a steam engine with any number of different-pressure cylinders, the term usually refers to engines which expand steam through only two stages, i.e. those which operate cylinders at only two different pressures (or "double expansion" engines).

Note that a compound engine (including multiple expansion engines, see below) 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

Glasgow

Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...

'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.

Triple or multiple expansion

A triple expansion engine is a compound engine that expands the steam in three stages, i.e. an engine which has cylinders operating at three different pressures. A quadruple expansion engine expands the steam in four stages, and so on.

Multiple expansion engine manufacture continued well into the 20th century. All 2,700 Liberty ship

Liberty ship

Liberty ships were cargo ships built in the United States during World War II. Though British in conception, they were adapted by the U.S. as they were cheap and quick to build, and came to symbolize U.S. wartime industrial output. Based on vessels ordered by Britain to replace ships torpedoed by...

s built by the United States during World War II were powered by triple-expansion engines, because the capacity of the US to manufacture steam turbines and diesels

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

 was still limited. The biggest manufacturer of triple expansion engines during the war was the Joshua Hendy Iron Works

Joshua Hendy Iron Works

The Joshua Hendy Iron Works was an American engineering company that existed from the 1850s to the late 1940s. It was at one time a world leader in mining technology and its equipment was used to build the Panama Canal, amongst other major projects...

. Toward the end of the war, turbine-powered Victory ship

Victory ship

The Victory ship was a type of cargo ship produced in large numbers by North American shipyards during World War II to replace shipping losses caused by German submarines...

s were manufactured in increasing numbers.

Annular

An annular engine is an unusual type of engine that has an annular (ring-shaped) cylinder. Some of American pioneering engineer James P. Allaire's early compound engines were of the annular type, with a smaller, high pressure cylinder placed in the centre of a larger, ring-shaped low-pressure cylinder. Trunk engines were another type of annular engine. A third type of annular marine engine which was sometimes produced utilized the Siamese engine connecting mechanism, but instead of two separate cylinders, had a single annular-shaped cylinder wrapped around the vertical arm of the crosshead (see diagram).

Other terms

Some other terms are encountered in marine engine literature of the period. These terms, listed below, are usually used in conjunction with one or more of the basic engine classification terms listed above.

Simple

A simple engine is an engine with only one cylinder. Up until about the mid-19th century, most ships had engines with only one cylinder (although some vessels had more than one engine). Simple engines are always also simple expansion engines by necessity.

Double acting

A double acting engine is an engine where steam is applied to both the up and down stroke of the piston. Earlier steam engines applied steam in only one direction, allowing momentum or gravity to return the piston to its starting place, but a double acting engine uses steam to force the piston in both directions, thus increasing RPM and power. Like the term "simple expansion", the term "double acting" is infrequently encountered in the literature since almost all marine engines were of the double acting type.

Vertical, horizontal, inclined, inverted

These terms refer to the orientation of the engine cylinder. A vertical cylinder stands vertically with its piston rod operating above it. An inverted cylinder (or "vertical inverted" cylinder) can be thought of as a vertical cylinder positioned upside down. With an inclined or horizontal type, the cylinder and piston are positioned at an incline or horizontally. An inclined inverted cylinder is an inverted cylinder operating at an incline. These terms are all generally used in conjunction with the engine types above. Thus, one may have a horizontal direct-acting engine, or an inverted walking beam, and so on.

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. They could also be used in a low profile ship or to keep a ship's centre of gravity lower. In addition, inclined or horizontal cylinders had the advantage of reducing the amount of vibration by comparison with a vertical cylinder.

Geared

A geared engine or "geared screw" turns the propeller at a different rate to the engine's RPM. Early marine propeller engines were geared upward, which is to say the propeller was geared to run at a higher RPM than the engine itself. As engines became faster and more powerful through the latter part of the 19th century, gearing was often dispensed with and the propeller ran at the same RPM as the engine.

See also

• Steam engine
  Steam engine
  A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
  
  
• Steam boat
• Evaporator (marine)
  Evaporator (marine)
  An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation...
  
  – apparatus for obtaining boiler feedwater from sea water

External links

• Video of model vibrating-lever engine of USS Monitor, www.youtube.com.
• Inclined inverted oscillating engine video, www.youtube.com.