An outboard motor is a propulsion In marine propulsion, propulsion systems for ships and boats vary from the simple paddle to the largest diesel engines in the world - or even nuclear propulsion. These systems fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes the pole, still widely used in marshy areas, rowing which was system for boats A boat is a watercraft of modest 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 something small enough to be carried aboard another, consisting of a self-contained unit that includes engine, gearbox A transmission or gearbox provides speed and torque conversions from a rotating power source to another device using gear ratios. In British English the term transmission refers to the whole drive train, including gearbox, clutch, prop shaft , differential and final drive shafts. The most common use is in motor vehicles, where the transmission and propeller A propeller is a type of fan which 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 air or water is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's principle and Newton's third law or jet drive A jetboat is a boat propelled by a jet of water ejected from the back of the craft. Unlike a powerboat or motorboat that uses a propeller in the water below or behind the boat, a jetboat draws the water from under the boat into a pump inside the boat, then expels it through a nozzle at the stern, designed to be affixed to the outside of the transom In naval architecture, a transom is the surface that forms the stern of a vessel. Transoms may be flat or curved and they may be vertical, raked forward , or raked aft. The bottom tip of the transom can be approximately on the waterline, in which case the stern of the vessel is referred to as a "transom stern", or the hull can continue and are the most common motorized method of propelling small watercraft. As well as providing propulsion, outboards provide steering control, as they are designed to pivot over their mountings and thus control the direction of thrust. The skeg A skeg is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line. The term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard. In more recent years, the name has been used for a fin on a surfboard which improves directional stability and to a moveable fin on a also acts as a rudder A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft, or other conveyance that moves through a fluid . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus when the engine is not running. Compared to inboard motors An inboard motor is a marine propulsion system for boats. As opposed to an outboard motor where an engine is mounted outside of the hull of the craft, an inboard motor is an engine enclosed within the hull of the boat, usually connected to a propulsion screw by a driveshaft, outboard motors can be easily removed for storage or repairs.

When boats are out of service or being drawn through shallow waters, outboard motors can be tilted up (tilt forward over the transom mounts) to elevate the propeller and lower unit out of the water to avoid accumulation of seaweed Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae. Seaweeds can also be classified by use, underwater hazards such as rocks, and to clear road hazards while trailering.

General uses

Portable

Small outboard motors, up to 15 horsepower or so are easily portable. They are affixed to the boat via clamps, and thus easily moved from boat to boat. These motors typically use a manual pull start system, with throttle A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated. What and gearshift controls mounted on the body of the motor, and a tiller A tiller or till is a lever attached to a rudder post or rudder stock (English terminology) of a boat that provides leverage for the helmsman to turn the rudder. The tiller is normally used by the helmsman directly pulling or pushing it, but it may also be moved remotely using tiller lines for steering. The smallest of these weigh as little as 12 kilograms (26 lb), have integral fuel tanks, and provide sufficient power to move a small dinghy at around 8 knots (15 km/h; 9.2 mph) This type of motor is typically used:

• to power small craft such as jon boats, dinghies A dinghy is a type of small boat, often carried or towed by a larger vessel. The term can also refer to small racing yachts or recreational open sailing boats. Utility dinghies are usually rowboats or have an outboard motor, but some are rigged for sailing. Because the smaller sailing dinghy responds more quickly to maneuvers, it is more suitable, canoes A canoe or Canadian canoe (British English) is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes usually are pointed at both bow and stern and are normally open on top, but can be decked over (i.e. covered, similar to a kayak), etc.
• to provide auxiliary power for sailboats 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 size are not strictly defined and what constitutes a sailing ship, sailboat, or a smaller vessel varies by region and culture,
• for trolling Trolling is a method of fishing where one or more fishing lines, baited with lures or bait fish, are drawn through the water. This may be behind a moving boat, or by slowly winding the line in when fishing from a static position, or even sweeping the line from side-to-side, eg when fishing from a jetty. Trolling is used to catch pelagic fish such aboard larger craft, as small outboards are typically more efficient at trolling speeds. In this application, the motor is frequently installed on the transom alongside, and connected to, the primary outboard, to enable helm steering.

Large Outboards

Large outboards are usually bolted to the transom (or to a bracket bolted to the transom), and are linked to controls at the helm. These range from 2- 3- and 4-cylinder models generating 15 to 135 horsepower suitable for hulls up to 17 feet (5.2 m) in length, to powerful V-6 and V-8 cylinder blocks rated up to 350 hp (260 kW).^[1], with sufficient power to be used on boats of 18 feet (5.5 m) or longer.

Electric-Powered

Commonly referred to as "trolling motors", electric outboards are used

• on very small craft or on small lakes where gasoline motors are prohibited,
• as a secondary means of propulsion on larger craft, and
• as repositioning thrusters while fishing for bass Bass is a name shared by many different species of popular gamefish. The term encompasses both freshwater and marine species. All belong to the large order Perciformes, or perch-like fishes, and in fact the word bass comes from Middle English bars, meaning "perch." and other freshwater species,

and any other application where their quietness, and ease of operation and zero emissions outweigh the speed and range deficiencies.

Diesel

Diesel 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 during the final stage of compression. This is in contrast to spark ignition engines such as a petrol engine (known as a gasoline engine in North America) or gas engine (using a outboards are also available, but their weight and cost make them impractical for most purposes other than extended trolling. An additional issue with diesel outboards is toxic exhaust emissions.

Pump-jet

Pump-jet A pump-jet, hydrojet, or water jet, is a marine system that creates a jet of water for propulsion. The mechanical arrangement may be a ducted propeller with nozzle, or a Centrifugal pump and nozzle. The first functioning man-made pump-jet engine was created by New Zealand inventor Sir William Hamilton in 1954 propulsion is available as an option on most outboard motors. Although less efficient than an open propeller, they are particularly useful in applications where the ability to operate in very shallow water is important. They also eliminate the laceration dangers of an open propeller.

History and developments

The outboard motor, as a portable propulsion system for boats that would otherwise be powered manually by oars, was made possible by the experimentations of Cameron Waterman, a young Yale Engineering student. The Waterman outboard engine appears to be the first real gasoline-powered outboard offered for sale. It was four stroke. Between 1903 and his patent in 1905 he successfully created the outboard. Starting with two dozen built in 1907, the company went on to make thousands of the units in the next 5 years. The inboard boat motor firm of Caille Motor Company of Detroit were instrumental in making the cylinder and engines. Kiekhaefer eventually bought out Cameron Waterman and used magazine ads with references to the Waterman.

The creation of the first practical and marketable outboard motor is often miscredited to Norwegian-American Predominantly Evangelical Lutheran Church in America and Lutheran Church–Missouri Synod inventor Ole Evinrude Ole Evinrude, born Ole Evenrudstuen was a Norwegian-American inventor, known for the invention of the first outboard motor with practical commercial application in 1909. Between 1909 and 1912 Evinrude made thousands of his outboards and the three horse units were sold around the world. His Evinrude Outboard Co. was spun off to other owners, and he went onto success with ELTO. The 1920s were the first highwater mark for the outboard with Evinrude, Johnson, ELTO, Atwater Lockwood and dozens of other makers in the field.

Historically, a majority of outboards have been two-stroke A two-stroke engine is an internal combustion engine that completes the thermodynamic cycle in two movements of the piston . This increased efficiency is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way two- powerheads fitted with a carburetor due to the design's inherent simplicity, reliability, low cost and light weight. Drawbacks include increased pollution, due to the high volume of unburned gasoline in their exhaust, and louder noise.

In the 1990s US and European exhaust emissions regulations led to the proliferation of four-stroke outboards. Though fewer in number, four-stroke outboards have always been available. For example Honda Marine has been marketing small four-stroke outboards since the early 70s. Other brands have been produced for over a 100 years, but again in fewer numbers.

Mercury Marine Mercury Marine, founded in 1939, is a division of Brunswick Corporation of Lake Forest, Illinois, in the United States. Mercury provides engines for private, commercial and government sales. Mercury even has its own line of racing engines with less fuel efficiency and more focus at power and speed. The company's primary business is outboard motors, Mercury Racing, Tohatsu Outboards, Nissan Marine, Honda Marine, Suzuki Marine, and Yamaha Marine, China Oshen-Hyfong marine have all developed new four-stroke Today, internal combustion engines in cars, trucks, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion , and exhaust strokes that occur during two crankshaft rotations per working cycle of the gasoline engine and diesel engine engines. Some are carbureted, usually the smaller engines. The balance are electronically fuel-injected. Some models benefit from variable camshaft timing, and multiple valves per cylinder. Mercury Verado four-strokes are unique in that they are supercharged.

Mercury Marine, Mercury Racing, Tohatsu, Yamaha Marine, Nissan and Evinrude each developed computer-controlled Direct-Injected two-stroke engines. Each brand boasts a different method of DI.

Fuel economy on both direct injected and four-stroke outboards measures from a 10 percent to 80 percent improvement, compared with conventional two-strokes. Depending on rpm and load at cruising speeds figure on about a 30 percent mileage improvement.^[2]

Outboard motors benefit from the use of a submerged pump to draw water for cooling, obviating the need for radiators Radiators are used for cooling internal combustion engines, chiefly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine and cooling fans, thereby simplifying the design and lowering component weight, however constant usage in seawater is liable to cause corrosion.

For boats which are moored rather than trailered, bronze propellers are unsuitable owing to galvanic effects. It is a surprising fact that quite often sacrificial anodes are found which have been painted over. One can only assume that owners notice that these parts were corroding and thought that the factory forgot to paint them. Severe damage is usually the result.

Outboard motor selection

It is important to select a motor that is a good match for the hull in terms of power and shaft length.

Power requirements

Overpowering is a dangerous condition^[3] and underpowering often results in a boat that is incapable of performing in the role for which it was acquired. Boats built in the U.S. have a Coast Guard Rating Plate which specifies the maximum recommended horsepower for the hull. A motor with less than 75% of the maximum will most likely result in unsatisfactory performance.

Shaft length

Outboard motor shaft lengths are standardized to fit 15-inch, 20-inch and 25-inch transoms In naval architecture, a transom is the surface that forms the stern of a vessel. Transoms may be flat or curved and they may be vertical, raked forward , or raked aft. The bottom tip of the transom can be approximately on the waterline, in which case the stern of the vessel is referred to as a "transom stern", or the hull can continue. If the shaft is too long it will extend farther into the water than necessary creating drag In fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity, which will impair performance and fuel economy. If the shaft is too short, the motor will be prone to ventilation. Even worse, if the water intake ports on the lower unit are not sufficiently submerged, engine overheating is likely, which can result in damage beyond economic repair.

Operational issues

Motor mounting height

Motor height on the transom In naval architecture, a transom is the surface that forms the stern of a vessel. Transoms may be flat or curved and they may be vertical, raked forward , or raked aft. The bottom tip of the transom can be approximately on the waterline, in which case the stern of the vessel is referred to as a "transom stern", or the hull can continue is an important factor in achieving optimal performance. The motor should be as high as possible without ventilating or loss of water pressure. This minimizes the effect of hydrodynamic drag In fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity while underway, allowing for greater speed. Generally, the antiventilation plate should be about the same height as, or up to two inches higher than, the 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. Only the ship's launching is considered more, with the motor in neutral trim.

Trim

Trim is the angle of the motor in relation to the hull, as illustrated below. The ideal trim angle is the one in which the boat rides level, with most of the hull on the surface instead of plowing through the water. If the motor is trimmed out too far, the bow The bow is a nautical term that refers to the forward part of the hull of a ship or boat, the point that is most forward when the vessel is underway. Both of the adjectives fore and forward mean towards the bow. The other end of the boat is called the stern will ride too high in the water. With too little trim, the bow rides too low. The optimal trim setting will vary depending on many factors including speed, hull design, weight and balance, and conditions on the water (wind and waves). Many large outboards are equipped with power trim, an electric motor on the mounting bracket, with a switch at the helm that enables the operator to adjust the trim angle on the fly. In this case, the motor should be trimmed fully in to start, and trimmed out (with an eye on the tachometer A tachometer is an instrument that measures the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common. The term comes from Greek Ταχος, tachos, "speed", and metron, "to measure&) as the boat gains momentum, until it reaches the point where further trim adjustment results in an RPM Revolutions per minute is a unit of frequency of rotation: the number of full rotations completed in one minute around a fixed axis. It is used as a measure of rotational speed of a mechanical component reduction. Motors not equipped with power trim are manually adjustable.

Ventilation

Ventilation is a phenomenon that occurs when surface air or exhaust gas (in the case of motors equipped with through-hub exhaust) is drawn into the spinning propeller blades. With the propeller pushing mostly air instead of water, the load on the engine is greatly reduced, causing the engine to race and the prop to spin fast enough to result in cavitation Cavitation is the formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Cavitation is usually divided into two classes of behavior: inertial cavitation, and noninertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing, at which point no thrust is generated at all. The condition continues until the prop slows enough for the air bubbles to rise to the surface.^[4] The primary causes of ventilation are: motor mounted too high, motor trimmed out excessively, damage to the antiventilation plate, damage to propeller, foreign object lodged in the diffuser ring.

Cavitation

Cavitation Cavitation is the formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Cavitation is usually divided into two classes of behavior: inertial cavitation, and noninertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing as it relates to outboard motors is often the result of a foreign object such as marine vegetation caught on the lower unit interrupting the flow of water into the propeller blades.

Preventive Maintenance^[5]

• Lower unit gear lubricant—change annually.
  • Inspect the old oil for metal fragments and if found, disassemble gearbox for inspection and repair.
  • Inspect old oil for evidence of water intrusion and if found, replace seals at propshaft, drive shaft and shift rod.
• Water pump impeller An impeller is a rotating component of a centrifugal pump, usually made of iron, steel, bronze, brass, aluminum or plastic, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the -- replace every two years (annually in a salt water environment).
  • Inspect pump housing, and replace if scored or damaged.
  • Inspect old impeller for missing pieces and if found, remove thermostat housing and water jacket cover if necessary, to recover the liberated material.
• Powerhead—annual inspection
  • Inspect engine wiring for corrosion, burned/chafed/missing insulation. Check all connections for tightness.
  • Inspect fuel lines for signs of aging.
  • Inspect spark plugs A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark and replace when necessary.
  • Check all fasteners Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container, etc. There are also special-purpose closing devices, e.g. a bread clip. Fasteners used in these manners are often temporary, in that they may be for tightness, torque to manufacturer specification if necessary.
  • Clean and inspect throttle A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated. What, shift, spark advance Ignition timing, in a spark ignition internal combustion engine, is the process of setting the time that a spark will occur in the combustion chamber relative to piston position and crankshaft angular velocity linkages, lubricate according to manufacturer recommendations.
  • Starter motor A starter motor is an electric motor that rotates an internal combustion engine to cause the engine to begin powering itself (if equipped) -- apply two drops of light oil to the bendix gear threads.
  • Test overtemp warning horn or light (if equipped).

Manufacturers

• British Anzani The Anzani was an engine manufacturer founded by the Italian Alessandro Anzani , which produced proprietary engines for aircraft, cars, boats, and motorcycles in factories in Britain, France and Italy
• British Seagull British Seagull was a British manufacturer of Two stroke outboard engines from the early 1930s until the mid 1990s. The company went out of business due to the motor design not being able to keep up with more modern boat engines and increasingly tight emissions regulations. British Seagull no longer produces new engines but still operates for
• Briggs & Stratton Briggs & Stratton is one of the world's largest manufacturers of air-cooled gasoline engines for primarily outdoor power equipment. Current production averages 11 million engines per year
• Evinrude/Johnson Johnson Outboards was a US based manufacturer of outboard motors. The original company to make Johnson inboard motors and outboard motors was the Johnson Bros. Motor Company of Terre Haute, Indiana, United States. A few years after the Johnson brothers' factory in Terre Haute was destroyed by a tornado in March 1913, the brothers relocated to, a division of Bombardier Recreational Products Bombardier Recreational Products or BRP is a Canadian company that traces its roots back to the year 1942 when Joseph-Armand Bombardier founded L'Auto-Neige Bombardier Limitée in Valcourt in the Eastern Townships, Quebec
• China Parsun Marine
• Honda Marine
• Mercury Mercury Marine, founded in 1939, is a division of Brunswick Corporation of Lake Forest, Illinois, in the United States. Mercury provides engines for private, commercial and government sales. Mercury even has its own line of racing engines with less fuel efficiency and more focus at power and speed. The company's primary business is outboard motors/Mariner Mercury Marine, founded in 1939, is a division of Brunswick Corporation of Lake Forest, Illinois, in the United States. Mercury provides engines for private, commercial and government sales. Mercury even has its own line of racing engines with less fuel efficiency and more focus at power and speed. The company's primary business is outboard motors
• Nissan Marine
• Honda Honda Motor Company, Ltd. listen (help·info) (TYO: 7267) is a Japanese multinational corporation primarily known as a manufacturer of automobiles and motorcycles
• Selva Marine
• Suzuki Suzuki Motor Corporation is a Japanese multinational corporation headquartered in Hamamatsu, Japan that specializes in manufacturing compact automobiles, a full range of motorcycles, all-terrain vehicles (ATVs), outboard marine engines, wheelchairs and a variety of other small internal combustion engines. Suzuki is the 9th largest automobile
• Tohatsu
• Yamaha Motor Corporation
• Yanmar Diesel Power
• Ul'yanovsk Motor Plant
• Oshen-Hyfong Marine

See also

• Air engine
• Sterndrive
• Luxury yacht tenders

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