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Boat motors

Outboard motors for a boat are developedoutweigh the range deficiencies shared
as a self-contained unit with engine,with electric cars. Diesel outboards are
subsidiary systems, and propeller,also available, but their weight and
designed to be mounted at the sterncost makes them impractical for most
(rear) of the craft. They are the mostpurposes.
common method of propelling smallA few outboard motors have been produced
watercraft.with pump-jet propulsion replacing the
As well as providing propulsion,conventional propeller. Like other types
outboards provide steering control, asof pump-jet propulsion systems, they
they are designed to pivot over theiroffer virtually no cavitation, making
mountings and thus control thethe boat more manoeverable, and can
orientation of the propeller. Theoperate in very shallow water. However,
transmission leg in the water also actsthe low efficiency compared to
as a rudder even when the propeller ispropellers has seen them restricted to
not providing power.specialised applications.
When boats are out of service or beingHistory and developments
drawn through shallow waters, outboardThe first practical outboard motor was
motors can also be tipped forward overcreated by Norwegian-American inventor
their mounts to elevate the propellerOle Evinrude in 1909.
and transmission shaft out of the waterHistorically, most outboards have used
to avoid accumulation of seaweed ortwo-stroke cycle engines due to their
hitting underwater hazards such assimplicity (and consequent reliability),
rocks.low cost, and high power-to-weight
Types of motorsratios - weight issues being
Small outboard motors are trulyparticularly important as too much
self-contained, with integral fuel tanksweight over the stern of boats tends to
and controls mounted on the body of theimpede their handling. However, the high
motor and steered by a "tiller" directlyemissions, and thus both environmental
connected to the motor. Such smallconcerns and the cost of technology to
motors can weigh as little as 12meet emissions standards, has led to the
kilograms (approximately 26 pounds) andgradual gain in popularity of
provide sufficient power to move a smallfour-stroke cycle outboards,
dinghy at around 15 km/h (9 mph), farparticularly for lower-end machines.
faster than possible with oars. They areHigh-end outboards have tended to remain
highly portable, able to be removed bytwo-stroke designs, as the fuel
simply loosening their mounting clamps.injection technology required to meet
Small outboards usually use a manualthe emissions standards and fuel economy
pull start ignition system while largertargets costs proportionally less for
models often have electric start similarthese motors and weight issues are more
to a car.important.
Manufacturers have produced largeMarine engines also benefit from their
outboard designs, with sufficient powerproximity to an endless supply of cold
to be used on boats as long as 9 metreswater by using it once for cooling and
(30 feet) or more. Manufacturers havethen ejecting the now-heated water. This
also produced electric outboards. Theseallows marine engines to avoid the cost
are used for specialised applications,and weight of radiators and cooling fans
notably trolling for bass in the US,normally associated with land-based
where their quietness and zero emissionsengines.



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