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