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The
choice of bowthruster is unusual due to it being of the 'Archimedes Screw'
type rather than the conventional single or twin propeller propulsion.
These screw types are made by
ARS in Norfolk who realised that space (packaging) is important in all
boat layouts and secondly, so is the trapping of rubbish. Props,
particularly thrusters have a habit of sucking in debris and sometimes
clogging to a halt as the rubbish wraps around the blades.
The ARS Archimedes
Screw thrusters are hydraulically driven from the engine and generate
excellent thrust in either direction. They also act as a mincing-machine,
grinding semi-floating plastic bags, etc. into pulp. An additional benefit
is the positioning of the angled thrust tube; as you will see from the
illustration on the left, the tube the Archimedes screw lays in is curved,
the reason for this is rather cleaver. If you use a straight tube
transversely mounted across the hull, each outlet port inevitably becomes
oval due to the curvature of the bow or stern shape at these points. Blame
the need for good hydrodynamics!
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| The curve
of the ARS
thruster enables the ports to be angled and in consequence, round ported,
generating a greater thrust for the given effort, where oval ports lose
thrust. Imagine placing a funnel in the end of your garden hose, you will instantly see a drop in
flow pressure where reducing the hoses diameter by squeezing the end,
increases it. We will be using them in both the stern and bow of JENAL
with the piston motors facing towards the barge centre to keep the ports
square to the sides. This will simplify manoeuvring... compensating for
our limited navigational experience and, being hydraulically driven, they
will keep working 24/7 without complaint. |
