An outboard is a portable, self-contained package of an engine, gear case, and propeller that is attached to the transom of a boat.
A growing number of outboard engines are of four-stroke design, but many are still conventional two-stroke engines that burn oil as a lubricant along with the fuel. New-technology two-stroke outboards are direct-injection engines and burn over 75% cleaner than conventional two-stroke outboards.
Outboards have more power per kilogram of weight than do inboard engines.
Steering of outboard boats is controlled by a tiller or steering wheel that swivels the entire engine to direct propeller thrust.