Outboard motors are used to propel boats through the water at speeds faster than any set of oars. The motors come in a variety of power levels used for everything from small rowboats to large fishing boats, though they all share the similar trait of being self-contained propulsion systems attached to a boat.
Outboard motors come in both electric and gasoline powered versions. The electric versions are generally smaller and provide less horsepower in exchange for a quieter ride. They are beneficial for smaller watercraft, or for fishing to limit noise that may scare away fish. Gasoline powered outboard motors, on the other hand, are louder but are able to provide much more power. They start as low as two or three horsepower for small craft and can reach well into the hundreds to power large fishing boats. Another possibility for increased power is for a boat to have multiple outboards. It's not uncommon to see a large fishing boat powered by two or even four outboard motors all connected to the same steering wheel.
For the gasoline powered outboard motors there are both two and four stroke engines. Four stroke engines provide a cleaner and smoother ride, while two stroke engines are generally more powerful but noisier and contribute more pollution. Some bodies of water only allow the cleaner and quieter four stroke engines, and the trend is towards the four stroke models in the future. High performance speed boats, on the other hand, benefit greatly from the extra power, so two strokes are always the preferred choice.
Outboard motors provide steering by literally turning themselves. Some have a built in rudder to direct water flow even when the propeller is not turning. On larger craft, the motors are sometimes attached to a steering wheel to provide the necessary power to turn such large motors. Smaller outboard motors often have a lever that the boat operator turns by hand to direct the engine and the boat.
Outboard motors are generally very durable and can be expected to last a long time, but proper care is still required. The two biggest threats are heat and carbon. Owners should always ensure that the engine's cooling system is working to combat heat. Most outboards flush the very water they're sitting in to cool the engine, and a visible spray of water can be seen exiting the motor. To reduce the carbon build-ups in the engine there are a number of additives that can be added to the gasoline tank or it can be brought to a mechanic for servicing. With this care, outboard motors can provide many years of service for their owners.