The most common motorized method of propelling small watercraft is the outboard motor. They are a self-contained unit with an engine, propeller, subsidiary systems and are designed to be fixed at the rear (stern) of the craft.
Outboard motors provide propulsion and steering control as they are designed to be able to be pivoted on their mountings therefore controlling the direction in which the propeller thrusts. Even when the engine is not providing propulsion the transmission leg acts as a rudder and can be used to direct the watercraft.
The mounting of the outboard also allows the engine to be tipped forward to elevate the transmission and propeller shaft out of the water to avoid collecting seaweed or striking various underwater hazards such as rocks.
Types of motors
Smaller outboards are completely self-contained, have integral fuel tanks and controls and are steered using a "tiller" that is directly connected to the unit. The power provided by a smaller motor is sufficientto move a small boat at around 9mph, much faster than what is possible with oars, they can weigh as little as 12kg. The lightweight portable nature of small outboards allow them to be removed simply by loosening their mounting clamps. Starting of smaller engines usually involves a manual pull start ignition system whereas larger engines often have electris starts, like that in a car.
Large outboard engines have been designed, that have sufficient power to be used on watercraft 9 metres long or greater. Electric outboards have been produced inmore recent times and are used for specialised applications such as fishing, where quietness and zero emissions are of benefit. Diesel outboards are available, however their weight and cost makes them unpractical for many purposes.
Pump-jet propulsion outboard engines have been produced replacing the conventional propeller design. Like other pump-ket propulsion systems available, they boast virtually no cavitation, allowing the boat to be maneuvered and operated in very shallow water without fear of damaging the engine. the low efficiency of these engines compared to propellers has seem them to be restricted to only speciailized applications.
Written for Bob spalding. Online retailers of marine, leisure and extreme sport gear.