WIRE ROPE TOWLINE COMPONENTS
A towing hawser is the key element in the tug-tow connection. For Navy towing ships, the hawser is usually wire rope. It
is especially important to keep a wire rope hawser in excellent condition, protect it against excessive wear and inspect
and lubricate it regularly.
To provide a written reference of a wire rope towline's history, the Naval Sea Systems Command requires that a Towing
Hawser Log be kept by all U.S. Naval vessels regularly engaged in towing operations. An example of this log is shown in
Traceability, or being able to trace a rope and what has happened to it back to its source, is an important element in
accident investigation as well as m efforts for general product-improvement. Some of the needed information is
maintained in the Towing Hawser Log American-made wire rope and some brands of foreign-made rope can be identified
by special core marker materials used as a part of, or layered around, the core of the wire rope as well as by the metal
tags and other data on the reel upon which the rope is wound when delivered Identification of manufacturing source
through core markers may be particularly useful in cases where the color coding has not been applied to a strand.
Additional information on a specific domestic wire rope producer's core color marking practices is available on request
from that manufacturer
At present, steel wire rope provides the strongest towing hawser for a given diameter and is usually specified by the Navy
as the preferred hawser for towing Target sleds are virtually the only tows for which a synthetic fiber line hawser is
currently specified Wire rope strength varies with the type of construction and material as well as with size.
Consequently, it is important to be certain that all wire ropes used in towing are of the proper construction, core and
B4 ELONGATION (STRETCH)
Wire rope stretches under load far less than most natural and synthetic fiber lines and
thus has a smaller zone of danger to bystanders from loose ends "snapping back" in the
event that it fails under high loads. The elongation under load is sufficient, nonetheless,
to be dangerous. The recoil can be extremely violent and all personnel should stay well
away from any potential recoil path.
In addition to the above-noted danger, the sudden release of tension can sometimes cause a popped core or a "bird cage"
in the rope when a failure in the towline or its connections allows the rope to rebound from an overload. These conditions
also can result from operating a wire rope through an undersized sheave groove See Figures B-1 and B-2 for illustrations
of these phenomena.
B-5 MAINTENANCE, CLEANING AND LUBRICATION
Wire rope, like a machine, is made up of many moving parts The individual steel wires slide independently and must be
kept clean and protected by adequate lubrication against the effects of movement and pressure.
Corrosion damage is also a danger. There is no way of estimating the exact loss of strength resulting from corrosion of
wire rope. Fresh water washdown and lubrication of the tow hawser as it is being retrieved after each use can help retard
corrosion This, however, is not a cure-all, since the core remains saturated with salt water.