Outboard motors are the product of intelligent design, and are the most common type of propulsion used on boats today. They are some of the most sophisticated engineering that man has ever created and are most commonly used for boats and are developed as a self-contained unit. They are typically 2 stroke motors that require a fuel/oil mixture, and are generally considered to be very durable.
Outboard motors are generally interchangeable and not committed by design for any particular boat. They come in both electric and gasoline powered versions and are more cost effective because they generally use less fuel than the inboards. In addition to providing propulsion, outboards also deliver steering control, as they are designed to pivot over their mountings and so control the direction of the propeller.
