| Outboard motors for a boat are developed as a | | | | outweigh the range deficiencies shared with electric |
| self-contained unit with engine, subsidiary systems, | | | | cars. Diesel outboards are also available, but their |
| and propeller, designed to be mounted at the stern | | | | weight and cost makes them impractical for most |
| (rear) of the craft. They are the most common | | | | purposes. |
| method of propelling small watercraft. | | | | A few outboard motors have been produced with |
| As well as providing propulsion, outboards provide | | | | pump-jet propulsion replacing the conventional |
| steering control, as they are designed to pivot over | | | | propeller. Like other types of pump-jet propulsion |
| their mountings and thus control the orientation of | | | | systems, they offer virtually no cavitation, making |
| the propeller. The transmission leg in the water also | | | | the boat more manoeverable, and can operate in |
| acts as a rudder even when the propeller is not | | | | very shallow water. However, the low efficiency |
| providing power. | | | | compared to propellers has seen them restricted to |
| When boats are out of service or being drawn | | | | specialised applications. |
| through shallow waters, outboard motors can also be | | | | History and developments |
| tipped forward over their mounts to elevate the | | | | The first practical outboard motor was created by |
| propeller and transmission shaft out of the water to | | | | Norwegian-American inventor Ole Evinrude in 1909. |
| avoid accumulation of seaweed or hitting underwater | | | | Historically, most outboards have used two-stroke |
| hazards such as rocks. | | | | cycle engines due to their simplicity (and consequent |
| Types of motors | | | | reliability), low cost, and high power-to-weight ratios - |
| Small outboard motors are truly self-contained, with | | | | weight issues being particularly important as too much |
| integral fuel tanks and controls mounted on the body | | | | weight over the stern of boats tends to impede their |
| of the motor and steered by a "tiller" directly | | | | handling. However, the high emissions, and thus both |
| connected to the motor. Such small motors can | | | | environmental concerns and the cost of technology |
| weigh as little as 12 kilograms (approximately 26 | | | | to meet emissions standards, has led to the gradual |
| pounds) and provide sufficient power to move a | | | | gain in popularity of four-stroke cycle outboards, |
| small dinghy at around 15 km/h (9 mph), far faster | | | | particularly for lower-end machines. High-end |
| than possible with oars. They are highly portable, able | | | | outboards have tended to remain two-stroke |
| to be removed by simply loosening their mounting | | | | designs, as the fuel injection technology required to |
| clamps. Small outboards usually use a manual pull start | | | | meet the emissions standards and fuel economy |
| ignition system while larger models often have | | | | targets costs proportionally less for these motors |
| electric start similar to a car. | | | | and weight issues are more important. |
| Manufacturers have produced large outboard designs, | | | | Marine engines also benefit from their proximity to an |
| with sufficient power to be used on boats as long as | | | | endless supply of cold water by using it once for |
| 9 metres (30 feet) or more. Manufacturers have also | | | | cooling and then ejecting the now-heated water. This |
| produced electric outboards. These are used for | | | | allows marine engines to avoid the cost and weight |
| specialised applications, notably trolling for bass in the | | | | of radiators and cooling fans normally associated with |
| US, where their quietness and zero emissions | | | | land-based engines. |