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