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 TB 55-1900-232-10
have two sets of Norman pins, one set of which is droppable into the stern caprail. Norman pins always are manually
removable-or, as in the ARS 50 Class, hydraulically retractable. Retractable or movable Norman pins have various
designs, ranging from simple hand-removable round stock or pipe to remotely-controlled, hydrauhcally-operated devices.
See Figures 2-38 and 3-9.
3-5.3.3 Hogging Strap.
CAUTION
A hogging strap may be necessary to prevent the towline from jumping the stern rollers when towing a high-
bowed ship at short stay. A hogging strap may be subject to excessive vertical loads. Care should be taken not
to part the strap. Failure of a hogging strap may result in the loss of tug control or ranging up by the tow.
The hogging strap is used to mitigate the relative movement between the towline and the stern in both vertical and
horizontal planes. See Figure 3-10. Movement in the vertical plane is caused by the stern of the tug dropping faster
than the towline or by the tow ranging up. When a hogging strap IS used, a shackle or a special saddle-like fitting
attaches the hogging strap to the towline. The limitation of the shackle is the high concentration of load it imposes on the
hawser to which it is attached. Saddle-like fittings distribute the load over a wider arc and thus over a large radius, and
are therefore preferred over shackles. Since the hogging strap transfers the tow point aft from the H-bitt, it can cause the
tug to lose maneuverability
3-5.3.4 Lateral Control Wire.
A lateral control wire can be utilized to obtain lateral control of the tug's stern relative to the towline. This rig is similar in
configuration to the hogging strap, but it has the added feature of variable scope. Instead of a fixed length strap holding
the towline to the deck, a snatch block is secured to the deck and the lateral control wire is led through it to a deck winch,
lateral control winch or capstan. In this way, the line can be fully slacked to let the towline sweep free or can be taken in
to give either partial or full snugging like a hogging strap. The lateral control wire is helpful in keeping the towline out of
the propellers. Like the hogging strap, the lateral control wire moves the tow point aft and can limit maneuverability.
3-5.3.5 Two-Leg Slip Method .
The two-leg slip method is an alternative for lateral control when towing a small vessel at very short scope in shallow
restricted waters and prior to final streaming of the tow. See Figure 3-7
3-5.3.6 Active Control of Tow's Rudder.
The tow's rudder can be used to stabilize an unwieldy tow or to maneuver in close quarters. Caution must be exercised,
as improper or excessive use could cause the tow to become directionally unstable. The decision to use active steering
on the tow will depend on the reliability of the tow's steering machinery and the qualifications of the riding crew. The
decision whether to use active steering rests with the tug.
3-5.4 YAWING AND SHEERING OF THE TOW.
Most tows will yaw somewhat i.e., oscillate in heading about the base towing course, usually in response to wave action
on the tow's bow or stern. This is not a serious problem in itself. However, many tows also will sheer off to the side,
where the tow's track is offset from the tug's track. This may be especially prevalent in beam winds for ships with large
deck houses aft. See also Appendix J.
The vessel may remain at a nearly constant sheer angle, or sheer from side to side, with a long period of as much as 10
minutes or more. Excessive sheering will cause poor control of the tow, reduction in tow speed, additional strain on the
towline, possible tow collision or stranding in restricted waters and excessive chafing of the towing rig. In extreme cases,
the tow can range up to a position abeam of, or even ahead of, the tug
3-23
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