Tugboat and Towboat
Notch tugs are a relatively recent development, and despite their
sometimes odd appearance they provide a very practical solution
to many of the problems of marine towing. The notch tug operates
with a matching tow that is fitted with a notch in the contour of
the tug's bow. In cable retained towing rigs, the tug is fitted
with additional fenders amidships that ride in extended portions
of the tow's notch and retaining cables are run out to the tow.
The tug is a tight fit into the notch and is allowed only limited
degree of movement. It can take in its towing cables and back free
if needed, but normally this would not be done except in the case
of a towing emergency that requires the tug to pull clear of the
tow, or in the most extreme weather conditions. Disengagement in
rough weather carries the risk of damage to the tug and tow, so
most tug captains prefer to stay in the notch if possible. The tug
is however fully equipped with a towing winch and is capable of
astern towing if the situation requires it. Operating in the notch
shields the tug from sea conditions and is the most advantageous
position for maneuvering the tow.
Above: The IOT (Interstate and Ocean Transport)
tug Enterprise is shown underway with a large fuel barge.
IOT became Maritrans and later was a part of Sonat Marine. Another
IOT tug, Freedom, is shown in the image at the beginning
of this section.
Tug Barge (ATB)
Articulated Tug Barge is a relatively new technology
that takes the concept of the notch tug one step further, fitting
the tug and tow with an interconnecting coupling arrangement. The
tug enters the notch and deploys a hydraulically operated pin assembly
that engages a rack in each side of the notch. The rack is necessary
to accomodate the changes in the load trim of the tow. Locked into
the notch, the tug has only one degree of movement, its fore and
aft pitch around the pin connection. Any side to side roll is done
in unison with the tow. Operating in the lee afforded by the notch
shields the tug from battering by sea conditions, while its ability
to pitch fore and aft helps keep the propellers in water rather
than having them draw air and cavitate in rough seas. The coupling
of the tug and tow can be done in a wide range of sea conditions,
and there are no cables or hawsers involved. Maneuverability and
propulsive efficiency are improved by not having the tow trailing
in the wash of the tug's propellers, and there is no risk of the
tow tripping the tug as can occur with astern towing. Due to the
great change in freeboard of the tow between loaded and unloaded
condition, the notch tugs are usually fitted with an upper pilothouse.
Above: The Gulf Coast Towing tug Betty Wood
is shown underway with the notch barge Marie Flood.
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