Thruster
Sizing
By definition, any
thruster will to some extent do a job in any boat.
The key is to ensure that the chosen thruster will
do the job you want it to in your boat. This is one
of two main factors deciding the right thruster size
for each boat.
Today most pleasure craft
over 45’ have a bow thruster as standard equipment
which normally will meet the expectations of most
customers when using the boat under normal weather
conditions. The sizes used by the boatbuilders will
vary depending on the boat’s intended usage
and price level.
In today’s production
boats of around 45’-50’, the typical thruster
will push the boat’s bow against a direct sidewind
of 20-22 knots. Some custom built or very high end
boats may have a high power bow thruster that pushes
the bow against a direct sidewind of 24-26 knots.
For boatowners that use their
boats in more demanding conditions or have for example
a strong current in their local marina, or for other
reasons require very high performance, many boatbuilders
offer upgrades to a more powerful thruster system.
However, few pleasure crafts need a thruster that
can push the bow against a direct sidewind of more
than 25-27 knots. The thruster’s performance
on a boat is basically determined by the boat’s
wind area, the wind area distribution and the thruster’s
tunnel position in the hull.
By knowing these factors
we can calculate the wind pressure on the boat and
the centre point of this wind pressure. From these
calculations we can determine what thrust is needed
to counter the wind pressure with the given thruster
position. The boat weight is normally not a major
factor for most pleasure craft.
Conclusion
The two main factors that decide correct thruster
sizing are:
•
boatowner’s performance requirements
•
boat size, type and shape
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