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Page Title: Synthetic Fiber Lines
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below before the ship gets outside in heavy weather. If line must be stowed wet, it should be laid up on gratings in long fakes so that it may dry as quickly as possible. It should never be covered over. SYNTHETIC FIBER LINES LEARNING   OBJECTIVES:   Describe   the general usage and care of synthetic line. List safety precautions for handling synthetic line. Aramid,  nylon,  polyester,  polypropylene,  and polyethylene, in the descending order of strength are the synthetic fibers used to make line. Synthetic  fiber  line  has  several  advantages  over manila. Size for size, it is 1.7 to nearly 6 times as strong and lasts 5 times as long. On a strength for strength basis, a synthetic fiber line of less than half the size of a manila line is required for the same task. For these reasons, synthetic fiber is cheaper in the long run, even if its initial price is more. Because synthetic fiber does not rot or age as does natural fiber line, its strength is more stable throughout its life. It is less bulky, more flexible and, therefore, easier to handle and requires less stowage   space.   Other   advantages,   and   a   few disadvantages,  are  pointed  out  later  in  this  discussion. NAVSEA has also approved a new synthetic fiber, aramid fiber line (Kevlar), for use aboard ship as mooring and tending lines. aramid rope is lighter, easier to handle, and smaller than nylon or polyester of equivalent strength. It also requires less hawser reel storage  space.  However,  since  it  stretches  only  6 percent at minimum breaking strength, tattle-tale cords cannot be used to determine the strain on their line, and the line will respond differently compared to other synthetic lines, which stretch 30 to 65 percent at minimum  breaking  strength.  Also,  this  aramid  line  does not fuse and smoke when surged around the bitts. The line surges smoothly around bitts compared to other synthetic  mooring  lines.  Aramid  line  safety  precautions that should be observed will be discussed later. A coil of synthetic fiber line, unlike natural fiber line, is not opened by pulling the end up through the eye of the coil. It should be unreeled in the same manner as wire  rope.  (See  the  section  on  Wire  Rope  in  this chapter.) Normally, plain-laid nylon line is right-handed and  should  be  coiled  on  capstans  and  reels  in  a clockwise direction. Cable-laid nylon or synthetic line is left-laid and should be coiled on capstans or reels in a  counterclockwise  direction. Because  of  the  characteristics  of  synthetic  line, safety precautions more explicit than those for manila line must be observed. A complete list of precautions is located in chapter 613 of the Naval Ships’ Technical Manual (NSTM), but some of the more important safety  precautions  to  be  observed  are  listed  below: 1. Because of the lower coefficient of friction of synthetic fiber line, exercise extreme care when a line is being payed out or eased from securing devices (bitts, cleats). For control in easing out, take two round turns and no more than two figure-eight bends. Any more than this will present danger to personnel and difficulty in handling the line. All lines on capstans and gypsy heads shall be payed out using power and never by surging. Figure 3-1 shows the method of securing a mooring line to the bitts. 2.   Since a snap-back action inevitably occurs when a line parts under tension, never allow personnel to stand in the direct line of pull of the line when it is being pulled or  when  it  is  under  tension.  A  synthetic  line  parting  under tension will snap back at near the speed of sound, and reaction time to clear the area will not be available. Where possible, position line handlers 90° from the direction of the tension force (fig. 3-2). 3.   Synthetic line has higher breaking strengths than equal sizes of manila line. Failures of blocks, pad eyes, shackles, and line couplings can be caused by improper substitutions.  For  this  reason,  personnel  should determine the identification and capacity of all gear and fittings used with synthetic fiber line to ensure that their strength  exceeds  the  minimum  breaking  strength  of  the line. 4. Synthetic line has poor knot-holding character- istics. Some knots that offer good characteristics for securing manila line, such as the square knot, are not adequate for belaying or securing synthetic line. The bowline  is  one  knot  known  to  offer  reasonable  security when  bending  together  or  securing  synthetic  line. Figure 3-1.–Securing lines to bitts. 3-4

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