When boats are out of service or being drawn through shallow waters, outboard motors can be tilted up (tilt forward over the transom mounts) to elevate the propeller and lower unit out of the water to avoid accumulation of seaweed, underwater hazards such as rocks, and to clear road hazards while trailering.

Portable

• to power small craft such as jon boats, dinghies, canoes, etc.
• to provide auxilliary power for sailboats,
• for trolling aboard larger craft, as small outboards are typically more efficient at trolling speeds. In this application, the motor is frequently installed on the transom alongside, and connected to, the primary outboard, to enable helm steering.

Large Outboards

Large outboards are usually bolted to the transom (or to a bracket bolted to the transom), and are linked to controls at the helm. These range from 2- 3- and 4-cylinder models generating 15 to 115 horsepower suitable for hulls up to in length, to powerful V-6 and V-8 cylinder blocks rated up to . , with sufficient power to be used on boats of or longer.

Electric-Powered

Commonly referred to as "trolling motors", electric outboards are used

• on very small craft or on small lakes where gasoline motors are prohibited,
• as a secondary means of propulsion on larger craft, and
• as repositioning thrusters while fishing for bass and other freshwater species in the US,

and any other application where their quietness, and ease of operation and zero emissions outweigh the speed and range deficiencies.

Diesel

Diesel outboards are also available, but their weight and cost make them impractical for most purposes. An additional issue with diesel outboards is toxic exhaust emissions.

Pump-jet

Pump-jet propulsion (replacing the conventional propeller) is available as an option on most outboard motors. Although less efficient than an open propeller, they are particularly useful in applications where the ability to operate in very shallow water is important.

History and developments

The outboard motor, as a portable propulsion system for boats that would otherwise be powered manually by oars, was made possible by the advent of the two cycle motorbike gasoline engine. The Waterford outboard engine appears to be the first real gasoline-powered outboard offered for sale. Starting with two dozen built in 1907, the company went on to make thousands of the units in the next 5 years. The inboard boat motor firm of Caille Motor Company of Detroit were instrumental in making the cylinder and engines.
The creation of the first practical and marketable outboard motor is often credited to Norwegian-American inventor Ole Evinrude in 1909. Between 1909 and 1912 Evinrude made thousands of his outboards and the three horse units were sold around the world. His Evinrude Outboard Co. was spun off to other owners, and he went onto success with ELTO. The 1920s were the first highwater mark for the outboard with Evinrude, Johnson, ELTO, Atwater Lockwood and dozens of other makers in the field.