SYNTHETIC FIBER LINE TOWLINE COMPONENTS
The material presented here does not supersede any Fleet or NAVSEA directives on the operational use or
care of synthetic towlines, particularly concerning nylon line. The user of this manual must keep abreast of such
directives which discourage the use of nylon hawsers except for emergency use, training exercises, tow-and-
be-towed operations, tow of yard and service craft, ocean tows of ships up to the size of minesweepers, and
specially-designed tows where the use of wire is not practical. These proscriptions resulted from increasing
numbers of failures of nylon hawsers as their use proliferated. Special circumstances should be discussed with
NAVSEA and the Fleet commenced pilot programs to evaluate the use of large (14-inch circumference)
polyester towing hawsers in early 1988. A key element of this effort is careful control and laboratory analysis of
samples periodically taken from active hawsers The purpose of this effort is to develop reliable, practical
methods for predicting the useful life of polyester towing hawsers. This has not been practical for nylon
Fiber lines, either natural or synthetic, can be found serving two functions in towline systems. In some systems
the main towing hawser is made of fiber lie In other systems the hawser is wire rope and fiber lines are used as
springs to provide relief from dynamic tension loads. In both uses, the fiber line should be kept in excellent
condition, protected against wear and inspected regularly
When fiber line is used as the main towing hawser or as a spring, a written record of its history is required by
the Naval Sea Systems Command in the form of the Towing Hawser Log listed in Appendix F.
Traceability, the ability to trace a line and what has happened to it back to its source, is an important element m
accident investigation as well as in general product-improvement efforts. Some of the needed information is
maintained in the Towing Hawser Log. See Appendix F American-made fiber line and some brands of foreign-
made rope can be identified by special marker tapes inserted into the fiber lines, special-colored monofilaments
and metal tags and other data on the reel upon which the line is delivered Identification of manufacturing
source through the marker coding may be particularly useful in cases where the reel markings have been lost.
Additional information on a specific domestic rope producer's identification marking practices is available on
request from the Cordage Institute, Suite 568, 314 Lincoln Street, Hingham, MA 02043. Telephone (617) 749-
C-3 STRENGTH AND LIFETIME
The failure of synthetic fiber lines under high tensile loads can be extremely dangerous. Stay out of
bights and areas through which the end of a failed line may whip.
C-3.1 GENERAL. Most synthetic fiber lines are stronger than manila (natural fiber) lines, and they usually have
C-3.2 SPECIFIC. The primary types of fiber lines in current use by the Navy are nylon, polyester and
polypropylene. Of these three, nylon is the strongest for equal size when dry. However, nylon loses strength
because of water absorption when wet and becomes weaker than polyester even though it is still stronger than
polypropylene. Table C-1 presents a qualitative summary of pertinent characteristics of three fiber lines.