An outboard motor is a propulsion system for boats, consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the transom. They 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 also acts as a rudder when the engine is not running. Unlike inboard motors, outboard motors can be easily removed for storage or repairs.
In order to eliminate the chances of hitting bottom with an outboard motor, the motor can be tilted up to an elevated position either electronically or manually. This helps when traveling through shallow waters where there may be debris that could potentially damage the motor as well as the propeller. If the electronic motor required to move the pistons which raise or lower the engine is malfunctioning, every outboard motor is equipped with a manual piston release which will allow the operator to drop the motor down to its lowest setting.
The first known outboard motor was a small 5 kilogram electric unit designed around 1870 by Gustave Trouvé, and patented in May 1880. Later about 25 petrol powered outboards may have been produced in 1896 by American Motors Co—but neither of these two pioneering efforts appear to have had much impact.
The Waterman outboard engine appears to be the first real gasoline-powered outboard offered for sale. Developed by Cameron Waterman, a young Yale Engineering student, it was developed from 1903, with a patent application filed in 1905 Starting in 1906, the company went on to make thousands of his "Porto-Motor" units, claiming 25,000 sales by 1914. The inboard boat motor firm of Caille Motor Company of Detroit were instrumental in making the cylinder and engines.
The most successful early outboard motor, was created by Norwegian-American inventor Ole Evinrude 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 high-water 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 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 1964 Honda Motor Co. introduced arguably the world's first four-stroke powerhead. In 1984, Yamaha introduced their first four-stroke powerhead. These motors were only available in the smaller hp range. In 1990 Honda released 35 hp and 45 hp four-stroke models. They continued to lead in the developement of four-stroke engines throughout the 1990s as US and European exhaust emissions regulations such as CARB (California Air Resources Board) led to the proliferation of four-stroke outboards. At first, North American manufacturers such as Mercury and OMC used engine technology from Japanese manufacturers such as Yamaha and Suzuki until they were able to develope their own four-stroke engine. The inherent advantages of four-stroke motors included: noise reduction, increase fuel economy, low end torque, and smoother operation.
Honda Marine Group, Mercury Marine, Mercury Racing, Nissan Marine, Suzuki Marine, Tohatsu Outboards, Yamaha Marine, and China Oshen-Hyfong marine have all developed new four-stroke engines. Some are carbureted, usually the smaller engines. The balance are electronically fuel-injected. Depending on the manufacturer, newer engines benefit from advanced technology such as multiple valves per cylinder, variable camshaft timing (Honda's VTEC), boosted low end torque (Honda's BLAST), 3-way cooling systems, and closed loop fuel injection. 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.
Outboard motors benefit from the use of a submerged pump to draw water for cooling, obviating the need for radiators and cooling fans, thereby simplifying the design and lowering component weight, however constant usage in seawater is liable to cause corrosion.
Sweden, 2002, S.G.?, Scott; 2442d.
Source: Wikipedia