The action of propelling a boat through water. A boat machinery plant consists principally of a propulsion engine, propulsor (propeller or jet pump), and drive-line components. The engines are almost exclusively of the familiar internal combustion types: gasoline, diesel, or gas turbine. The gasoline engine has traditionally dominated the pleasure-boat field, while the diesel is favored for commercial and military craft. The gas turbine is comparatively rare and is found only in applications where high power from machinery of small weight and volume is essential.