Quantcast Establishing the Relative Drift.

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TB 55-1900-232-10
and direct communication with personnel on the tow and all parties involved in the towing vessel is crucial.
3-8.2.1. Establishing the Relative Drift. For collision avoidance and positioning, the first step in approaching a tow to
be picked up at sea is to establish the drift differential between the vessels involved. Despite obvious differences m size
and configuration, vessels' rates of drift are also affected by a host of other variables. Drift characteristics are affected
by displacement draft, stability, trim, damage, seas, wind, sail area and location of the superstructure and currents, as
well as a variety of other factors The above-water hull configuration will determine the tow's relative heading into the
wind. Depending on trim, ships having a greater portion of their superstructure aft will have a tendency to head into the
wind; ships having a greater portion of superstructure forward will have a tendency to he with the wind from aft of the
beam to astern. A midship superstructure will normally cause the ship to lie with the wind abeam. With the relative drift
between tug and tow determined, and the state of the seas and wind taken into consideration, the tug can make its
3-8.2.2 Similar Drift Rate. Figure 3-12 describes a tug's approach across the wind and seas where similar drift rates
exist. The tug begins an approach leading to pass close aboard on the weather bow; the messenger and towline can
then be passed. The tug keeps station while passing messengers and making the connection.
3-8.2.3 Downwind Approach. Where dissimilar drift rates exist, a downwind approach may be executed as seen in
Figure 3-13. In such an approach to a ship lying broadside to the wind, the speed of the tug should be slow, but still fast
enough to offer good steerageway. Passing of the messenger must be timely, as the on-station time is short. Passing
the towline can be accomplished in the lee of the ship's bow. Great care is required to keep all lines clear of the
propellers. Once the tow is connected, acceleration should be slow and maneuvering sequences gradual.
Approaching at too small an angle in the lee of the larger vessel is not recommended.
When working in the lee of a larger ship, establish an attitude that permits the tug to maintain a safe distance from the
more rapidly-drifting tow
3-8.3 PASSING THE TOWLINE. The towline is passed by messenger to the tow. It is generally desirable to have the tug
pass the messenger and towline. The messenger may be passed by a hand-thrown heaving line, rocket, or line-throwing
gun, boat, buoyant float, helicopter or any other expedient way. The hand-thrown heaving line, backed up with a line-
throwing gun, is a common and practical way of passing a messenger.  An experienced seaman, under favorable
circumstances, can throw a heaving line over 100 feet with accuracy. However, time considerations and attendant
dangers make it prudent to give as much time as possible to pass the messenger. Thus, the use of the line-throwing gun
is the preferable procedure.
a. It may be imprudent to navigate the tug close aboard the distressed ship. In the event that such navigation is ill-
advised, a boat can be used to pass the messenger. Line, free for running, should be faked down in the boat and on
board the tug, with the maximum amount possible in the boat
b. A buoy, lifejackets, salvage floats, foam fenders or drums can be attached to the messenger's bitter end and floated to
the distressed ship. This can be expedited by the tug crossing the disabled ship's bow with the messenger streamed.
c. Line-throwing guns can carry the bitter end of the messenger and an experienced seaman can fire the gun with
accuracy and safety a distance of over 300 feet. A


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