As one may note from Table C-1, nylon's water-absorption characteristic changes its comparative rating from
best to intermediate in nearly every category. Consequently, for towing use, the Navy is in the process of
phasing out the use of nylon, probably in favor of polyester. Where springs are required in towline systems,
nylon will probably continue to be used because of its greater elasticity. Polypropylene will also continue to be
used for certain purposes because it is the only one of the three fiber lines that will float.
The elongation or stretch of fiber line under tension loads has both advantages and disadvantages. Elongation
tends to greatly reduce dynamic loads m the towline such as shock loads and wave-induced loads. But
elongation also stores a great deal of energy in ropes under tension and the release of this energy when a rope
fails under tension causes a very dangerous whipping or "snapback" of the line. The stored energy, and
therefore danger, is much greater in the case of synthetic lines than for wire rope under the same load. For this
reason, extreme caution is required when working around fiber lines (especially nylon) which are under load.
Braided fiber lines tend to stretch about one-half to two-thirds as much as plaited or stranded ropes of the same
Under heavy tension loads, nylon line can snap back at speeds up to 700 feet per second (500 mph)
C-5 MAINTENANCE AND CLEANING
Although fiber lines are not subject to corrosion as wire ropes are, they still require careful maintenance and
cleaning. If the line becomes oily or greasy, scrub it with fresh water and a paste-like mixture of granulated
soap. For heavy accumulations of oil and grease, scrub the line with a solvent such as mineral spirits, then
rinse it with a solution of soap and fresh water.
The three different synthetic fibers show different responses to various chemicals In brief
a. Nylon shows weakening upon exposure to acids, particularly mineral acids. Its resistance to alkalis is good at
b. Polyester line will deteriorate with exposure to hot, strong alkali solutions. It is attacked by very strong acid
solutions, therefore, even diluted acid solutions should not be allowed to dry on the rope.
c. Polypropylene is resistant to both acids and alkalis at normal temperatures, but is affected by some organic
solvents such as xylene and metacresol and by coal tar and paint-stripping compounds. These types of
chemicals are most likely to be found in the paint locker in thinners and cleaning compounds.
All synthetics are weakened by exposure to strong sunlight and should, therefore, be stored out of the sun.
Polyester has the best resistance to ultraviolet rays.
C-6 NEW HAWSERS
Synthetic lines are shipped in coils or on wooden
reels. They should be unreeled very carefully to avoid
abrasion and damage to the fibers.
New synthetic hawsers should not be subjected to heavy strain prior to breaking them in. Limit the
towing loads applied to a new hawser until it has been cycled up to its working load.
NSTM 613 (Ref. 15) suggests that a synthetic hawser will be adequately "broken in" after five cycles of
loading/unloading up to its working load or to within 20 percent of breaking strength, whichever is less. This
permits the construction stiffness to be worked out of the line. When new lines are strained, they some