Precautions And Techniques For The Uses Of Ropes
613-2.4.1 GENERAL. Precautions and techniques for the safe use of natural and synthetic ropes are discussed in paragraphs 613-2.4.2 through 613-2.4.5.2.
613-2.4.2 UNCOILING AND UNREELING. Proper procedures for uncoiling and unreeling natural and synthetic rope are covered in paragraphs 613-2.4.2.1 through 613-2.4.2.3.
613-2.4.2.1 Uncoiling Natural Fiber-Laid Ropes. If natural fiber ropes are furnished in coils, uncoil them by drawing the rope up from the eye in a counterclockwise direction to avoid rope kinking. Should kinks develop as a result of improper uncoiling, DO NOT pull them out as they develop into permanent strand cockles and reduce the rope strength by 1/3. When kinks develop, lay the rope out straight and remove the unbalanced turn before use. Fake down ropes that are to be used in blocks and falls and allow them to relax for at least 24 hours before reeving. After reeving, tension the completed tackle under a load equal to 1/10 of the total strength of the number of parts making up the falls.
613-2.4.2.2 Uncoiling Synthetic Fiber-Laid Ropes. If synthetic fiber ropes are furnished in coils, uncoil them by rolling or by drawing from a turntable. DO NOT attempt to draw up through the eye or from the outer flakes of the coil. Should a coil of synthetic fiber rope collapse, causing kinking and tangling, DO NOT try to pull the rope free as it will form permanent cockles. The recommended practice is to secure one end of the rope and drop the remainder of the coil into the sea (with no way on) where it will gradually uncoil as it relaxes without forming permanent kinks and cockles. This treatment will also remove bulges in and harden the structure of new soft-lay ropes.
613-2.4.2.3 Unreeling Synthetic Fiber Ropes. When synthetic fiber ropes are unreeled, it is recommended that a pipe mandrel be inserted through the center holes of the reel heads to hold the reel clear of the deck. The rope may then be drawn from the lower reel surface with no danger and without rope damage. DO NOT throw twisted synthetic fiber ropes off reel heads, as tangles and kinks will develop. It is also recommended that new, twisted synthetic fiber ropes be faked down on the deck and allowed to relax for 24 hours. Lengths of new twisted synthetic fiber ropes less than 50 feet long will relax within 1 hour when laid out straight. Fake down double braided rope in a figure-eight pattern. If double braided rope is faked down in the same fashion as described for twisted rope, it will develop twists.
613-2.4.2.4 Unwinding Aramid Lines. Care should be taken to properly unwind the rope from delivery reels onto the ship's hawser reels. Since new aramid line has similar construction to wire rope, it is installed on reels in the same manner as wire rope. Paragraph 613-1.9.1 identifies the proper procedure.
613-2.4.3 RECOILING AND REREELING. Recoil or Flemish all twisted ropes in the clockwise direction. Rereeling may be done in either direction, but take care that the turns are laid closely together to prevent binding in the underturns.
613-2.4.4 ELONGATION AND PERMANENT STRETCH. All ropes stretch under loads.
613-2.4.4.1 Natural Fiber Ropes. Load stretching is permanent and irreversible in natural fiber ropes such as manila and sisal. With each successive load increase, an additional amount of permanent stretch occurs until the stretch limit is reached and the rope fails. The stretch limit for a natural fiber rope is approximately 20 percent of its original length; for example, a 10-foot length of rope will break when its stretch limit is reached at 12 feet.
613-2.4.4.2 Synthetic Fiber Ropes. A portion of the load-stretch in synthetic fiber ropes is permanent and irreversible. However, this permanent stretch is small and is not progressive with successive loadings, provided that safe working limits are not exceeded. Under safe load conditions, the permanent stretch of nylon and polyester ropes is usually no greater than 7 percent of the original length; aramid is much less. After a synthetic fiber rope has reached its maximum stretch point (usually at the fifth loading), it will stretch and recover repeatedly without serious damage. The approximate stretch limits (at breaking strength) for synthetic fiber ropes vary widely: only 6 percent for aramid 4-strand; 30 percent for polyester double braid and polyester 12-strand; 35 percent for polyester 3-strand; 40 percent for nylon double braid; 45 percent for polyester 8-strand plaited and polypropylene 3-strand; 55 percent for nylon 3-strand; and 65 percent for nylon 8-strand plaited.
613-2.4.5 SHRINKAGE AND SWELLING Most natural and synthetic fiber ropes, when wetted, will shrink in length and swell in diameter to some extent. The shrinking and swelling do not seriously affect rope strength, but stiffness which occurs after drying out will cause some difficulty in splicing.
613-2.4.5.1 Natural Fiber Ropes. Wetting causes natural fiber ropes to shrink and swell. Shrinkage varies with rope size, ranging from 5 to 8 percent, with a corresponding amount of swelling and stiffening. After drying, natural fiber ropes remain in the shrunken state. Rope in this condition is not weakened, but does kink easily; therefore, the rope shall be roused out from lockers or coils with care.
613-2.4.5.2 Synthetic Fiber Ropes. Synthetic ropes shrink slightly when wetted, and minimal swelling may occur. The only noticeable effect of wetting is a slight increase in weight, with the exception of nylon which has approximately 15 percent strength loss from water being absorbed by the nylon molecules. (Nylon regains most of this strength loss if dried out.) Absorbed water will be squeezed out when the ropes are tensioned. Under working loads, the expelled water will appear as a steamlike water vapor. This vapor is beneficial because it cools the fibers when friction develops under repeated stretching conditions, as in towing.
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