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 TB 55-1900-232-10
towline. This practice has been referred to as keeping the tug and tow m step In tandem tows, this is rarely possible
Keeping m step applies equally to all towing situations whether towing on the dog, hook, brake or on an automatic towing
machine. The benefit of being in step is lower peak tensions.
3-5.3 EQUIPMENT FOR CONTROLLING THE TOWLINE.
As noted m the preceding paragraph, there can be large relative motions between the tug and tow. There also can be
large relative motions, especially m yaw or sway, between the towline and the stern of the tug. The equipment for
controlling these motions has evolved over the history of towing.
3-5.3.1
Stern Rollers.
CAUTION
Use of vertical rollers may put tug in irons, which would seriously limit the tug's maneuverability.
NOTE
Stern rollers should be properly maintained and lubricated to ensure rotation and smooth surface conditions.
Rollers are often frozen and their surface areas grooved and scored from towline wear. Such conditions directly
contribute to the abnormal wear of the towline.
a. Vertical stern rollers act as a fairlead for the towing machine. The long distance between the stern rollers and the
towing machine enables the tow hawser to naturally reel itself onto the drum and the level wind performs only light duty.
The stern rollers are normally used to capture the hawser and to assist when picking up or disconnecting a tow. The
vertical rollers may limit the amount of lateral movement that the tow hawser receives as the tow yaws from port to
starboard
b. The horizontal stern roller is an anti-chafing device. On many tugs the cprail is of small radius and often rough from
constant use. If the stern roller has a large radius horizontal roller, this will present a more suitable surface on which the
tow hawser will ride and also minimize wear. The roller rotates so that the tow hawser is subject to less wear as it heaves
in and pays out. (The ATS and ARS 50 Classes are not equipped with horizontal stern rollers. Instead, they have a large-
radius transom constructed with hardened steel, which serves to minimize wear)
c. Chafing gear is required on the towline when it is scheduled for long periods in the stern roller. Slacking off a few
inches, or "freshening the nip " regularly, is a good practice to reduce wear on the wire.
d. When the towline rides against a vertical stern roller, it is being bent over a small radius. This causes a towline to
fatigue more rapidly and to fail at a lower load
e Vertical stern rollers are designed only as a fairlead device and cannot structurally withstand loads of the magnitude of
which the H-bitt is capable. Strong side loads commonly seen in towing situations could very easily carry the assembly
away. On the ARS 50 Class, the rollers will fold down to their stowed position at a lateral load of 50,000 pounds applied
at mid-roller height.
f. The towline is usually restrained in a stern roller assembly only under light sea conditions. The vertical stern rollers
should always be dropped when maneuvering in restricted waters or in rough seas.
g The presence of the towline in the stern rollers limits the maneuverability of the tug because it moves the tow point
from the H-bitts back to the caprail
3-5 3.2 Norman Pin Use.
The primary tion of Norman pins is to limit the arc of sweep across the stern. The position for Norman pins depends on
the situation. Some tugs
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