Marine propulsion is the mechanism or system used to generate thrust

Thrust

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

 to move a ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

 or boat

Boat

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 across water. While paddle

Paddle

A paddle is a tool used for pushing against liquids, either as a form of propulsion in a boat or as an implement for mixing.-Materials and designs:...

s and sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

s are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting a motor or engine turning a propeller

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...

, or less frequently, in jet drives, an impeller

Impeller

An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.- Impellers in pumps :...

. Marine engineering is the discipline concerned with the design of marine propulsion systems.

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...

s were the first mechanical engines used in marine propulsion, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Nuclear reactors

Nuclear marine propulsion

Nuclear marine propulsion is propulsion of a ship by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships...

 producing steam are used to propel warship

Warship

A warship is a ship that is built and primarily intended for combat. Warships are usually built in a completely different way from merchant ships. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuvrable than merchant ships...

s and icebreaker

Icebreaker

An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels .For a ship to be considered an icebreaker, it requires three traits most...

s, and there have been attempts to utilize them to power commercial vessels. Electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s have been used on submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s and electric boat

Electric boat

While a significant majority of water vessels are powered by diesel engines, with sail power and gasoline engines also remaining popular, boats powered by electricity have been used for over 120 years. Electric boats were very popular from the 1880s until the 1920s, when the internal combustion...

s and have been proposed for energy-efficient propulsion.

Pre-mechanisation

Until the application of the 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...

 to ships in the early 19th century, oars propelled galleys, or the wind propelled sailing ships. Before mechanisation, merchant ships always used sail, but as long as naval warfare

Naval warfare

Naval warfare is combat in and on seas, oceans, or any other major bodies of water such as large lakes and wide rivers.-History:Mankind has fought battles on the sea for more than 3,000 years. Land warfare would seem, initially, to be irrelevant and entirely removed from warfare on the open ocean,...

 depended on ships closing to ram

Battering ram

A battering ram is a siege engine originating in ancient times and designed to break open the masonry walls of fortifications or splinter their wooden gates...

 or to fight hand-to-hand, galleys dominated in marine conflicts because of their maneuverability and speed. The Greek

Ancient Greece

Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 navies that fought in the Peloponnesian War

Peloponnesian War

The Peloponnesian War, 431 to 404 BC, was an ancient Greek war fought by Athens and its empire against the Peloponnesian League led by Sparta. Historians have traditionally divided the war into three phases...

 used trireme

Trireme

A trireme was a type of galley, a Hellenistic-era warship that was used by the ancient maritime civilizations of the Mediterranean, especially the Phoenicians, ancient Greeks and Romans.The trireme derives its name from its three rows of oars on each side, manned with one man per oar...

s, as did the Romans

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 at the Battle of Actium

Battle of Actium

The Battle of Actium was the decisive confrontation of the Final War of the Roman Republic. It was fought between the forces of Octavian and the combined forces of Mark Antony and Cleopatra VII. The battle took place on 2 September 31 BC, on the Ionian Sea near the city of Actium, at the Roman...

. The use of large numbers of cannon

Cannon

A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...

 from the 16th century meant that maneuverability took second place to broadside weight; this led to the dominance of the sail-powered warship.

In modern times, human propulsion is found mainly on small boats or as auxiliary propulsion on sailboats. Human propulsion includes the pole, still widely used in marshy areas, rowing which was used even on large galleys, and the pedals.

Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays and spars and controlled by ropes. Sail systems were the dominant form of propulsion until the nineteenth century. They are now generally used for recreation and racing, although experimental sail systems

Future Boat Developments

Rising oil prices and environmental concerns are driving boat development towards better fuel efficiency and reduced pollution. Global warming impact of shipping also begins to be of concern. According to Professor James J...

, such as the kite

Kite

A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air flows over and under the kite's wing, producing low pressure above the wing and high pressure below it. This deflection also generates horizontal drag along the direction of the wind...

s/royal

Royal (sail)

A royal is a small sail flown immediately above the topgallant on square rigged sailing ships. It was originally called the "topgallant royal" and was used in light and favorable winds....

s, turbosail

Turbosail

-Concept:In 1980, Jacques Cousteau dreamed of creating a ship with a modern engine that would be powered, at least in part, by the wind, a clean, free, renewable energy source...

s, rotorsails, wingsail

Wingsail

A wingsail is a form of marine propulsion similar to conventional sails. However, a wingsail is a built-up structure with airfoil cross-section, like an airplane wing, which shape can provide a much better lift-to-drag ratio than conventional sails....

s, windmills

Windmill ship

A windmill ship, wind energy conversion system ship or wind energy harvester ship propels itself by use of a windmill to drive a propeller.They use wind power through a mechanical or electrical transmission to the propeller...

 and SkySails

SkySails

SkySails GmbH & Co. KG is a Hamburg-based company that sells equipment to propel cargo ships, large yachts and fishing vessels by the use of wind energy. The company was founded in 2001 by engineers Stephan Wrage and Thomas Meyer...

's own kite buoy-system have been used on larger modern vessels for fuel savings.

Reciprocating steam engines

The development of piston-engined

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...

 steamships was a complex process. Early steamships were fueled by wood, later ones by coal or fuel oil. Early ships used stern or side paddle wheel

Paddle wheel

A paddle wheel is a waterwheel in which a number of scoops are set around the periphery of the wheel. It has several usages.* Very low lift water pumping, such as flooding paddy fields at no more than about height above the water source....

s, while later ones used screw propellers.

The first commercial success accrued to Robert Fulton

Robert Fulton

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

's 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...

(often called Clermont) in the US in 1807, followed 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...

 by the 45-foot Comet

PS Comet

The paddle steamer PS Comet was built for Henry Bell, hotel and baths owner in Helensburgh, and began a passenger service in 1812 on the River Clyde between Glasgow and Greenock, the first commercially successful steamboat service in Europe.-History:...

 of 1812. Steam propulsion progressed considerably over the rest of the 19th century. Notable developments included the steam surface condenser, which eliminated the use of sea water in the ship's boilers. This permitted higher steam pressures, and thus the use of higher efficiency multiple expansion (compound) engines. As the means of transmitting the engine's power, paddle wheels gave way to more efficient screw propellers.

Steam turbines

Steam turbines were fueled by coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 or, later, fuel oil

Fuel oil

Fuel oil is a fraction obtained from petroleum distillation, either as a distillate or a residue. Broadly speaking, fuel oil is any liquid petroleum product that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power, except oils having a flash...

 or nuclear power

Nuclear power

Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

. The marine steam turbine

Steam turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

 developed by Sir Charles Algernon Parsons

Charles Algernon Parsons

Sir Charles Algernon Parsons OM KCB FRS was an Anglo-Irish engineer, best known for his invention of the steam turbine. He worked as an engineer on dynamo and turbine design, and power generation, with great influence on the naval and electrical engineering fields...

 raised the power-to-weight ratio. He achieved publicity by demonstrating it unofficially in the 100-foot Turbinia

Turbinia

Turbinia was the first steam turbine-powered steamship. Built as an experimental vessel in 1894, and easily the fastest ship in the world at that time, Turbinia was demonstrated dramatically at the Spithead Navy Review in 1897 and set the standard for the next generation of steamships, the...

at the Spithead

Spithead

Spithead is an area of the Solent and a roadstead off Gilkicker Point in Hampshire, England. It is protected from all winds, except those from the southeast...

 Naval Review in 1897. This facilitated a generation of high-speed liners in the first half of the 20th century, and rendered the reciprocating steam engine obsolete; first in warships, and later in merchant vessels.

In the early 20th century, heavy fuel oil came into more general use and began to replace coal as the fuel of choice in steamships. Its great advantages were convenience, reduced manpower by removal of the need for trimmers

Coal trimmer

A coal trimmer is an occupation involving the positioning of boats to be loaded with coal. It may also involve the spreading of coal evenly using a shovel inside the hold of a ship....

 and stokers, and reduced space needed for fuel bunkers.

In the second half of the 20th century, rising fuel costs almost led to the demise of the steam turbine. Most new ships since around 1960 have been built with 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. The last major passenger ship built with steam turbines was the Fairsky, launched in 1984. Similarly, many steam ships were re-engined to improve fuel efficiency. One high profile example was the 1968 built Queen Elizabeth 2 which had her steam turbines replaced with a diesel-electric

Diesel-electric

Diesel-electric transmission or diesel-electric powertrain is used by a number of vehicle and ship types for providing locomotion.A diesel-electric transmission system includes a diesel engine connected to an electrical generator, creating electricity that powers electric traction motors...

 propulsion plant in 1986.

Most new-build ships with steam turbines are specialist vessels such as nuclear-powered vessels, and certain merchant vessels (notably Liquefied Natural Gas

Liquefied natural gas

Liquefied natural gas or LNG is natural gas that has been converted temporarily to liquid form for ease of storage or transport....

 (LNG) and coal carriers) where the cargo can be used as bunker fuel.

LNG carriers

New LNG carrier

LNG carrier

An LNG carrier is a tank ship designed for transporting liquefied natural gas . As the LNG market grows rapidly, the fleet of LNG carriers continues to experience tremendous growth.-History:...

s (a high growth area of shipping) continue to be built with steam turbines. The natural gas is stored in a liquid state in cryogenic

Cryogenics

In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...

 vessels aboard these ships, and a small amount of 'boil off' gas is needed to maintain the pressure and temperature inside the vessels within operating limits. The 'boil off' gas provides the fuel for the ship's boilers, which provide steam for the turbines, the simplest way to deal with the gas. Technology to operate internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

s (modified marine two-stroke diesel engines) on this gas has improved, however, so such engines are starting to appear in LNG carriers; with their greater thermal efficiency, less gas is burnt. Developments have also been made in the process of re-liquefying 'boil off' gas, letting it be returned to the cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the marine-grade fuel oil burnt in conventional diesel engines, so the re-liquefaction process is starting to be used on diesel engine propelled LNG carriers. Another factor driving the change from turbines to diesel engines for LNG carriers is the shortage of steam turbine qualified seagoing engineers. With the lack of turbine powered ships in other shipping sectors, and the rapid rise in size of the worldwide LNG fleet, not enough have been trained to meet the demand. It may be that the days are numbered for marine steam turbine propulsion systems, even though all but sixteen of the orders for new LNG carriers at the end of 2004 were for steam turbine propelled ships.

Nuclear-powered steam turbines

In these vessels, the nuclear reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 heats water to create steam to drive the turbines. Due to low prices of diesel oil, nuclear propulsion is rare except in some Navy

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 and specialist vessels such as icebreaker

Icebreaker

An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels .For a ship to be considered an icebreaker, it requires three traits most...

s. In large aircraft carrier

Aircraft carrier

An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...

s, the space formerly used for ship's bunkerage could be used instead to bunker aviation fuel. In submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s, the ability to run submerged at high speed and in relative quiet for long periods holds obvious advantages. A few cruisers have also employed nuclear power; as of 2006, the only ones remaining in service are the Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n Kirov class

Kirov class battlecruiser

The Kirov-class battlecruiser is a class of nuclear-powered military ships of the Russian Navy, the largest and heaviest surface combatant warships currently in active operation in the world. The Russian designation is heavy nuclear-powered guided missile cruiser...

. An example of a non-military ship with nuclear marine propulsion

Nuclear marine propulsion

Nuclear marine propulsion is propulsion of a ship by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships...

 is the Arktika class icebreaker

Arktika class icebreaker

The Arktika class is a Russian class of nuclear powered icebreakers. They are owned by the federal government, but were operated by the Murmansk Shipping Company until 2008, when they were transferred to the fully government-owned operator Atomflot. Of the ten civilian nuclear powered vessels...

 with 75000 shp. Commercial experiments such as the NS Savannah

NS Savannah

NS Savannah, named for SS Savannah, was the first nuclear-powered cargo-passenger ship, built in the late 1950s at a cost of $46.9 million, including a $28.3 million nuclear reactor and fuel core, funded by United States government agencies as a demonstration project for the potential...

 have so far proved uneconomical compared with conventional propulsion.

In recent times, there is some renewed interest in commercial nuclear shipping. Nuclear powered cargo ships could lower costs associated with carbon dioxide emissions and travel at higher cruise speeds than conventional diesel powered vessels.

Reciprocating diesel engines

Most modern ships utilise a reciprocating diesel engine as their prime mover, due to their operating simplicity, robustness and fuel economy compared to most other prime mover mechanisms. The rotating crankshaft

Crankshaft

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

 can be directly coupled to the propeller with slow speed engines, via a reduction gearbox for medium and high speed engines, or via an alternator and electric motor in diesel-electric vessels.

The reciprocating marine diesel engine first came into use in 1903 when the diesel electric rivertanker Vandal

Vandal (ship)

* HMS Vandal , a British submarine launched in 1942 and lost in 1943* Vandal, a Russian diesel-powered tanker launched in 1903...

 was put in service by Branobel

Branobel

The Petroleum Production Company Nobel Brothers, Limited,or Branobel , was an oil company set up by Ludvig Nobel and Baron Peter von Bilderling, in Baku, Azerbaijan...

. Diesel engines soon offered greater efficiency than the steam turbine, but for many years had an inferior power-to-space ratio. The advent of turbocharging however hastened their adoption, by permitting greater power densities.

Diesel engines today are broadly classified according to

• Their operating cycle: two-stroke engine or four-stroke engine
• Their construction: crosshead, trunk, or opposed piston
  Opposed piston engine
  An opposed-piston engine is a reciprocating internal combustion engine in which each cylinder has a piston at both ends, and no cylinder head.-Configurations:...
  
  
• Their speed
  • Slow speed: any engine with a maximum operating speed up to 300 revolutions per minute
    Revolutions per minute
    Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
    
     (rpm), although most large two-stroke slow speed diesel engines operate below 120 rpm. Some very long stroke engines have a maximum speed of around 80 rpm. The largest, most powerful engines in the world are slow speed, two stroke, crosshead diesels.
  • Medium speed: any engine with a maximum operating speed in the range 300-900 rpm. Many modern four-stroke medium speed diesel engines have a maximum operating speed of around 500 rpm.
  • High speed: any engine with a maximum operating speed above 900 rpm.

Most modern larger merchant ships use either slow speed, two stroke, crosshead engines, or medium speed, four stroke, trunk engines. Some smaller vessels may use high speed diesel engines.

The size of the different types of engines is an important factor in selecting what will be installed in a new ship. Slow speed two-stroke engines are much taller, but the footprint required, is smaller than that needed for equivalently rated four-stroke medium speed diesel engines. As space above the waterline is at a premium in passenger ships and ferries (especially ones with a car deck), these ships tend to use multiple medium speed engines resulting in a longer, lower engine room than that needed for two-stroke diesel engines. Multiple engine installations also give redundancy in the event of mechanical failure of one or more engines, and the potential for greater efficiency over a wider range of operating conditions.

As modern ships' propellers are at their most efficient at the operating speed of most slow speed diesel engines, ships with these engines do not generally need gearboxes. Usually such propulsion systems consist of either one or two propeller shafts each with its own direct drive engine. Ships propelled by medium or high speed diesel engines may have one or two (sometimes more) propellers, commonly with one or more engines driving each propeller shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine will most likely drive through a clutch, allowing engines not being used to be disconnected from the gearbox while others keep running. This arrangement lets maintenance be carried out while under way, even far from port.

Gas turbines

Many warships built since the 1960s have used gas turbine

Gas turbine

A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

s for propulsion, as have a few passenger ships, like the jetfoil. Gas turbines are commonly used in combination with other types of engine. Most recently, the Queen Mary 2 has had gas turbines installed in addition to diesel engines. Because of their poor thermal efficiency at low power (cruising) output, it is common for ships using them to have diesel engines for cruising, with gas turbines reserved for when higher speeds are needed however, in the case of passenger ships the main reason for installing gas turbines has been to allow a reduction of emissions in sensitive environmental areas or while in port. Some warships, and a few modern cruise ships have also used the steam turbines to improve the efficiency of their gas turbines in a combined cycle

Combined cycle

In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

, where waste heat

Waste heat

Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat...

 from a gas turbine exhaust is utilized to boil water and create steam for driving a steam turbine. In such combined cycles, thermal efficiency can be the same or slightly greater than that of diesel engines alone; however, the grade of fuel needed for these gas turbines is far more costly than that needed for the diesel engines, so the running costs are still higher.

Screws

The technical term for what is often described as a "propeller" on a ship is a screw. The differentiation is necessary as the two systems, although similar in appearance, have very different physical properties. There are many variations of marine screw systems, including twin, contra-rotating, controllable-pitch, and nozzle-style screws. Smaller vessels tend to have a single screw. Some modern aircraft carriers use four propellers, supplemented with bow-

Bow thruster

A bow thruster is a transversal propulsion device built into, or mounted to, the bow of a ship or boat to make it more maneuverable. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard without using the main propulsion mechanism which requires...

 and stern-thrusters. Power is transmitted from the engine to the screw by way of a propeller shaft, which may or may not be connected to a gearbox.

Paddle wheels

The paddle wheel is a large wheel, generally built of a steel frame

Steel frame

Steel frame usually refers to a building technique with a "skeleton frame" of vertical steel columns and horizontal -beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame...

work, upon the outer edge of which are fitted numerous paddle blades (called floats or buckets). The bottom quarter or so of the wheel travels underwater. Rotation of the paddle wheel produces thrust

Thrust

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

, forward or backward as required. More advanced paddle wheel designs have featured feathering methods that keep each paddle blade oriented closer to vertical while it is in the water; this increases efficiency. The upper part of a paddle wheel is normally enclosed in a paddlebox to minimise splashing.

Sailing

The purpose of sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

s is to use wind

Wind

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

 energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 to propel the vessel

Sailboat

A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...

, sled

Ice boat

An ice boat is a boat or purpose-built framework similar in functional design to a sail boat but fitted with skis or runners and designed to run over ice instead of through water. Ice yachting is the sport of sailing and racing iceboats. Sailable ice is known in the sport as "hard water" versus...

, board, vehicle

Land sailing

Land sailing, also known as sand yachting or land yachting, is the act of moving across land in a wheeled vehicle powered by wind through the use of a sail. The term comes from analogy with sailing. Historically, land sailing was used as a mode of transportation or recreation...

 or rotor

Windmill sail

Windmills are powered by their sails. Sails are found in different designs, from primitive common sails to the advanced patent sails.-Jib sails:...

.