The Outboard Motor

The outboard combines an engine, a drive shaft, a gearbox and a propeller in one unit that clamps or bolts to a boat's transom and steers by turning.

Early history

Inventors experimented with portable boat motors in the late nineteenth and early twentieth centuries. Ole Evinrude, a Norwegian-born machinist in Milwaukee, built an outboard and began selling them commercially around 1909. Companies such as Johnson and Mercury followed.

The two-stroke era

For much of the twentieth century, outboards were two-stroke engines, lubricated by oil mixed with fuel. They were light, powerful and simple, but released unburned fuel and oil into the water and air. Rules adopted from the late 1990s pushed manufacturers toward four-stroke and direct-injection engines, which are cleaner and more fuel-efficient.

How it works

The powerhead holds the engine. A vertical drive shaft runs down through the midsection to the lower unit, where gears turn the propeller shaft. A rubber impeller pump draws raw water to cool the engine. Anodes protect aluminum parts from galvanic corrosion. Tilt and trim raise the engine for shallow water and set the running angle.

Service

Common tasks include lower-unit oil changes, impeller replacement, fuel system cleaning, spark plugs, anode replacement, rigging controls and electronic diagnostics.

Programs and credentials

Marine Engine / Outboard; Small Engine & Power Equipment. Credentials: ABYC Marine Engine; manufacturer certifications.