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TB 55-1900-232-10
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
Surging of synthetic line under tension can cause sufficient frictional heat at the
contact surfaces to result in melting the surface of the line. The melting point of
polypropylene line, for instance, is 320 to 340 , while the softening point is
around 300 F.  Comparable temperatures for nylon and polyester are only
moderately higher. These temperatures are quite quickly produced when a line is
surged on a winch or capstan.
The major special precaution to be taken in the use of synthetic lines that are
heavily loaded is to be constantly alert to the danger of line snap- back if it fails.
Personnel must remain clear of the areas through which the ends of a failed line
may whip or snap. This is vital since the end of the broken line can travel at speeds
up to 500 mph. (Page C-5)
Several factors affect line behavior, such as line condition and specific application.
The tensile loads are tabulated for new line in good condition. Normal working
loads are not applicable when the line is subject to dynamic loading. (Page C-7)
Never pass a stopper on a tension member that is under a strain greater than the
safe working load of the stopper, or on a tension member that might be subjected to
a heavier loading condition while the stopper is in place. (Page E-1)
The craft listed in Table 2-1 are representative of vessels requiring special
consideration. Evaluation of stability characteristics, material condition of the hull,
equipment on board, operational requirements and other applicable considerations
must be made on any craft before towing. Only under extreme emergency
situations should open-ocean towing be attempted when the tow is not considered
seaworthy. (Page 2-1)
River and harbor dredges generally have little or no compartmentation and
machinery occupies most of the below deck space throughout. Additionally, they
tend to have a very low freeboard. Whether towed with or without a riding crew,
dredges should be given extra attention from departure to destination and should be
towed with caution. (Page 2-3)
When towing alongside, keep all lines taut until ready for streaming the tow. This
will prevent the tow from pounding alongside the tug and ensure effective control of
the tow. (Page 2-23)
Chain smaller than about 31/4 will require a pear-shaped link or an anchor shackle
to connect to the standard Smit Bracket. Check dimensions carefully! (Page 2-32)


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