Inboard Outboard
Boat Motors
Inboard motors may be of
several types, suitable for the size of craft they are fitted to. An
inboard motor is a marine propulsion system for boats. As opposed to
an outboard motor where an engine is mounted outside of the hull of
the craft, an inboard motor is an engine enclosed within the hull of
the boat, usually connected to a propulsion screw by a driveshaft.
Outboard motors for a boat are developed as a self-contained unit with
engine, subsidiary systems, and propeller, designed to be mounted at
the stern (rear) of the craft. They are the most common motorized method
of propelling small watercraft.
When boats are out of service
or being drawn through shallow waters, outboard motors can also be tipped
forward over their mounts to elevate the propeller and transmission
shaft out of the water to avoid accumulation of seaweed or hitting underwater
hazards such as rocks.
Small outboard motors are truly self-contained, with integral fuel tanks
and controls mounted on the body of the motor and steered by a "tiller"
directly connected to the motor. Such small motors can weigh as little
as 12 kilograms (approximately 26 pounds) and provide sufficient power
to move a small dinghy at around 15 km/h (9 mph), far faster than possible
with oars. They are highly portable, able to be removed by simply loosening
their mounting clamps. Small outboards usually use a manual pull start
ignition system while larger models often have electric start similar
to a car.
Manufacturers have produced
large outboard designs, with sufficient power to be used on boats as
long as 9 metres (30 feet) or more. Manufacturers have also produced
electric outboards. These are used for specialised applications, notably
trolling for bass in the US, where their quietness and zero emissions
outweigh the range deficiencies shared with electric cars. Diesel outboards
are also available, but their weight and cost make them impractical
for most purposes.
A few outboard motors have
been produced with pump-jet propulsion replacing the conventional propeller.
Like other types of pump-jet propulsion systems, they offer virtually
no cavitation, giving the boat more maneuverability and the ability
to operate in very shallow water. However, the low efficiency compared
to propellers has seen them restricted to specialized applications.
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