The outboard motor is probably the most common means of propulsion for boats. This machine is nearly always a two-stroke spark-ignition (gasoline) engine, mounted vertically at the stern of a boat in order to drive a shaft that in turn drives a conventional screw propeller through right-angle gears. It has the great virtue of being mounted external to the hull, thus being easily adaptable to almost any boat. Outboard motors operate on a mixture of gasoline and marine oil.
The development of the outboard motor was rather slow in the early years of the 20th century. After World War I (1914-1918), the popularity of the outboard motor grew steadily, and as a result its power gradually was increased, and it was made more reliable. The popularity of the outboard motor increased tremendously after World War II (1939-1945), and small cruisers, runabouts, utility boats, and various classes of racers became available. By the late 1970s, powerful outboard motors, ranging up to 200 horsepower rating, were available, as was special equipment for handling such engines at the water's edge. The use of two outboard motors on cruisers and runabouts was common.
Because of the great power available and because the low transom required by this type of motor creates the danger of the boat being swamped, the safety of the outboard motorboat has become a matter of public and governmental concern. The popularity of this type of boat also has produced crowded waters at lake and seaside resorts. In many areas measures have been adopted to prevent accidents caused by excessive speed, careless or reckless operation, and poor boat design
Outboard motors, like the ones mounted on these skiffs, are the most common means of propulsion for boats. Because it is mounted external to the hull, the motor is adaptable to almost any boat.