18
ENG
2.1 TUNNEL LO CATION
To obtain the best result, locate the tunnel of the bow
thruster as close as possible to the bow of the boat
(Fig. 1). Because of the leverage effect, the thrust of the unit is
detriment from the distance from the tunnel relative to the
rotation point of the boat.(Fig. 2).
Example:
A: 55Kg of thrust x 10m of leverage = 550Kgm Torque.
B: 55Kg of thrust x 9m of leverage = 495Kgm Torque.
In position A is noted a 10% of torque more.
In a plaining hull boat, locating the tunnel in such a way will
result with the tunnel over the water line level, so to avoid
any obstacle. (Fig. 3).
In case of large dimension boats, one can install two bow
thrusters one after the other. In this case, according to
meteorological conditions, the units can be used separately or
simultaneously (Fig. 4).
The position of the tunnel has to be as low as possible for the
following reasons (Fig. 5):
•
To prevent from any air which can be pulled resulting in
weakening the thrust available.
•
To have the highest pressure of water possible to utilise
the maximum efficiency of the propeller.
Generally the highest part of the tunnel must be 1/2 x Diameter
of the tunnel bellow the water line level. This is just the
minimum poss ible but we recommend that at least 3/4 x
Diameter under the water line. The optimal distance is
approximate 1/1 x Diameter.
The optimal length of the tunnel should be 2 or 4 times the
diameter of the tunnel; mus t be avoided tunnels longer than
6/7 times the diameter, to avoid losses of thrust. Should the
tunnel be so long, the internal distance will reduce the velocity
of water and so the thrust. Should the tunnel be very short
(normally in the lower part of the tunnel) could result in
cavitations and so reduction of the performance and create
noise (Fig. 6 e 7).
PointofBoat
Rotation
A=10mt
B=9mt
Tunnel
Fig. 1
Fig. 2
Fig. 5
Tunnel
PLAINING HULL BOAT
Water Level
Fig. 3
IMBARCAZIONE DI GROSSE DIMENSIONI
Bow-thruster
Water Level
Fig. 4
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