Outboard motor is a gasoline engine or electric motor attached to the rear of a boat. The motor operates a vertical drive shaft to which a propeller is geared. The propeller spins underwater to propel the boat. On inboard-outboard motors, the engine is inside the vessel and the driveshaft and propeller are in the water.
Gasoline engines are the most common type of outboard motor. Such engines may have either horizontal or V-shaped cylinder blocks. Electric outboard motors are powered by rechargeable batteries. They are less common because they are less powerful than gasoline motors and must be recharged often.
Most gasoline outboard engines operate at high speed and deliver their full power at 4,500 to 6,000 revolutions per minute. They are seldom used on boats larger than 30 feet (9 meters) in length. Some smaller types of outboard engines are used to fish by trolling—that is, by trailing a fishing line behind a slowly moving boat.
