However, this law of theory is only valid for the
lateral thrust in one direction. The opposite direction
will produce a lower performance by the same percentage
and, ultimately, nothing is gained. Furthermore, to manufacture
a bow thruster with two propellers faces quite a few obstacles,
both technically and price wise:
- Two
propellers, rotating in the same direction,
will have slightly enhanced performance if the "downstream"
propeller turns much faster than the "upstream" one,
or if it has a larger pitch. But, given the fact that
a bow thruster should operate in two directions,
this requirement is completely unattainable, as it
would involve the installation of three electric motors
and three drive systems. Even if this were the case,
the improvement in performance would be negligible.
- In
the situation where two propellers are rotating
in opposite directions, again, the "downstream"
propeller should have a larger pitch. But, if the
sense of rotation is reversed, then the "downstream"
propeller becomes the "upstream" one, producing the
negative effects, described above.
- Logically,
the mass inertia of two propellers is much higher
than that of one propeller. This is even more so,
if the propellers are not made of light-weight plastics.
In other words: the required thrust power comes with
a considerable delay.
- The
more components that are installed, the costlier the
product will be and the more sensitive to failure.
Furthermore, two propellers in one tunnel are far
less accessible than a single one.
VETUS has come to the conclusion that they will not
introduce bow thrusters with two propellers into their
range. The performance of VETUS bow thrusters with a
single propeller has been calculated and tested with
utmost care. Due to the carefully calculated power transmission,
the specially constructed electric motors and the exactly
dimensioned tunnels of minimum diameter, VETUS bow thrusters
provide optimum thrust power per horsepower.
And
that is the only thing which really matters with bow
thrusters!
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