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Designer's
Checklist No.1
Azimuth Stern Drive Tugs
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GENERAL
LAYOUT
Forecastle
Stern drive tugs for harbour use should be designed
without a forecastle. The normal direction of work
is "over the bow" and thus the main towing point
and winch are installed on the foredeck. A forecastle
will bring the towing point considerably higher
deteriorating the stability. Also on coastal tugs
the forecastle should be kept as low as possible,
preferably only as half height forecastle. Fig.
18 Stern drive tugs for harbour and coastal duty
should have the foredeck as low as possible, as
most of the normal operation is "over the bow".
A high forecastle causes a high heeling moment due
to the towing point position
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A good stern deck has large-radius rounded corners
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Aft
Deck
The stern "corners" should be rounded with a large
radius, enabling turning against a ships hull during
ship handling operations. The fendering should be
smoothly continuing without sharp corners between
the bow and side fendering and the stern and side
fendering, as the ASD tug is able to push with either
bow, stern or sides against the assisted vessel.
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Towing
Hook / Aft Towing Winch
If the tug is equipped with an aft towing point
/ hook it should be positioned as far forward as
possible on the main deck and have to be in front
of the propulsion units, in order to improve / enable
manoeuvring while working over the stern.
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A narrow and central superstructure and wheelhouse
is required, especially for the handling of vessels
with high flare
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Superstructure
The superstructure should be designed as narrow as possible,
with a small wheelhouse far from the sides to enable
the operation under the flair , bow or stern of large
vessels e.g. container vessels, without the risk for
damage on the tug or the assisted vessel. Also smoke
stacks and fire monitors should be as close to the centreline
as practically possible. |
Wheelhouse
The wheelhouse should be designed as small and compact
as practicable, in order to ensure the efficient
use of a single control position layout. The tug
master should have as good view as possible from
the steering position - minimum requirement is that
the bow fender as well as the aft corners are visible
as well as the bow winch and aft towing hook or
winch.
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The important lines of sight from the wheelhouse
are to the bow fender and stern corners; ideally
to the winch and as much of aft deck as possible.
Visibility upwards is also important for tugs assisting
high freeboard / high sheer vessels
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A single steering position wheelhouse layout, with
a "walk-through" control stand. The helmsman's chair
is installed on tracks to enable it to be moved out
of the way. |
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A
typical single steering position layout. The distance
between the control levers should be 55-65 cm.
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Control Layout The azimuth propulsor controls should
be positioned in a way to enable the helmsman to easily
concentrate on the tug operations, not on how to handle
his tug. The optimum solution is to place the control
cabinets on each side of the steering position. The
distance between the cabinets should allow the (possible)
helmsman's chair to fit between them, but the distance
between the propulsor controls should be kept between
55 cm and 65 cm. |
