outboards

Outboards are propulsion units mounted on the exterior of a boat's stern. They combine an internal combustion engine, gear reduction, a propeller, and steering controls in a single unit that is bolted to the transom. Because the unit can be detached, outboards are widely used on small and mid-sized craft such as fishing boats, runabouts, tenders, and many sailboats' auxiliary power.

Most modern outboards are gasoline engines and can be two-stroke or four-stroke. Two-stroke designs are lighter and can deliver high power for their size, but burn more fuel and produce more exhaust; four-stroke engines are heavier but tend to be cleaner and more fuel-efficient. Contemporary models often use electronic fuel injection and electric start, with features such as power trim and tilt, steering via a handle or remote control, and integrated mounting for various transom heights.

Key components include the engine, the lower unit with the gearcase and propeller, the water-cooling system, and the control cluster. Cooling is usually achieved by drawing water from the surrounding environment. Performance modifications may include the propeller type, anti-ventilation plate, and, in higher-end models, digital engine-management systems.

Outboard power spans a wide range—from compact trolling motors under a few horsepower to high-output units exceeding 300 hp for larger boats. Common maintenance tasks include flushing saltwater units, checking and replacing gear-case oil and impellers, inspecting the propeller, and winterizing.

The first practical outboard motor appeared in the early 20th century, with Ole Evinrude contributing to the development and commercialization of the technology, leading to the broad adoption of outboard propulsion.