Tips on Thruster Selection
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As a rule of thumb, a bow thruster used for docking and undocking
should be capable of producing thrust in pounds of force (lbf)
equal to twice the lateral cross sectional vessel area below
the water in square feet or two to three times the lateral cross
sectional area of the superstructure above the water, whichever
is greater.
Sizing of tunnel thrusters for slow speed maneuvering and
station keeping depends greatly on the vessel operating parameters.
Before making your final selection, consult your naval architect
or one of Thrustmaster’s application engineers.
When using tunnel thrusters in waters with high current or
while the vessel has forward speed, the thruster becomes less
effective. At vessel speeds of 3 knots, the tunnel thruster
may lose as much as 25 percent of its thrust. At speeds
of 7 knots, the thruster may only produce half of its rated thrust.
A Thrustmaster retractable azimuthing thruster may be more appropriate
for these applications.
Tunnel thrusters need to be placed below the waterline to
prevent air ingestion. If the top of the tunnel is too
close to the surface of the water, vortexes may develop, resulting
in air from the surface being sucked into the tunnel. This
causes airlock, substantial reduction in thrust, excessive noise
and vibration, and severe shock leading to the thruster.
Consider the vessel draft in unloaded vessel condition.
If the thruster is to be used out in open seas, consider vessel
heave and roll and consider wave action in determining how far
below the waterline your thruster needs to be placed to prevent
air ingestion. (See also Tips
on Thruster Installation)
If space does not allow proper submergence with a single tunnel
thruster on a shallow draft vessel, two or more smaller tunnel
thrusters, installed side by side, may be used. Multiple
Thrustmaster tunnel thrusters can be powered by a single prime
mover with a common hydraulic system, making the thrusters act
in unison as if they were a single thruster.
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