Fiber Rope Construction
613-2.3.1 TWISTED FIBER ROPES. Twisted fiber ropes are constructed of natural or synthetic fibers that are twisted into yarns. In the case of synthetics, three yarns are plied together to prevent the fibers from untwisting.
These yarns are then grouped together to form strands, with the size and number of yarns in each strand varying according to the strand size required to make the particular rope size.
613-2.3.2 LARGE LAID ROPES. All Navy used fiber ropes 1-3/4 inch in circumference or larger are required to be right-laid ropes. This requirement averts hazards which would be encountered should a left-laid rope be attached to a right-laid rope. Under strain, ropes in a left-right combination would unlay each other, resulting in sudden rupture with a load far lighter than the normal maximum limit. Large fiber rope specifications are given in Table 613-2-1.
|
TYPE OF ROPE |
CIRCUMFERENCE (in) |
SPECIFICATION |
|
Aramid 4-Strand |
3-3/8 to 8-3/16 |
CID A-A-50435 |
|
Polyester Double-Braided |
3/4 to 16 |
MIL-R-24677 |
|
Polyester 12-Strand |
1-1/8 to 15 |
MIL-R-24750 |
|
Polyester 8-Strand Plaited |
3/4 to 16 |
MIL-R-24730 |
|
Polyester 3-Strand |
5/8 to 12 |
MIL-R-30500 |
|
Polyester Double-Braided (Staple Wrap) |
3/4 to 5 |
MIL-R-24536 |
|
Polyester Plaited (Staple Wrap) |
3/4 to 4 -1/2 |
MIL-R-24537 |
|
Nylon Double-Braided |
3/4 to 16 |
MIL-R-24050 |
|
Nylon 8-Strand Plaited |
3/4 to 16 |
MIL-R-24337 |
|
Nylon 3-Strand |
5/18 to 12 |
MIL-R-17343 |
|
Polypropylene 3-Strand |
5/18 to 12 |
MIL-R-24049 |
|
Manila and Sisal |
5/18 to 12 |
Fed Spec T-R-605 |
613-2.3.3 PLAIN-LAID ROPES. Plain-laid ropes are normally constructed of three strands twisted in an alternate pattern. Natural fiber ropes have a ZSZ twist pattern; the yarn has a right (Z) twist, the strand has a left (S) twist, and the rope has a right (Z) turn. Synthetic fiber ropes have a plied yarn construction with an SZSZ pattern; the single yarns have a left (S) twist, the ply a right (Z) twist, the strand a left (S) twist, and the rope a right (Z) lay. (See Figure 613-2-1). Four strand aramid fiber rope is constructed of parallel yarns in each strand, left laid helically around a strand core. The four parallel laid strands are twisted together in the opposite direction around a center core.
613-2.3.4 CABLE-LAID ROPES. Cable-laid ropes consist of three right plain-laid ropes twisted together in the opposite direction (Figure 613-2-2). The final turn in the cable-laid rope is always to the left.
613-2.3.5 PLAITED ROPES. Plaited ropes are available with synthetic fibers. The construction of the strands is similar to three strand synthetic plain-laid rope, except there are four right (Z) and four left (S) twist strands. These strands are plaited together in pairs, two parallel strands of left turn going to the right and two parallel strands of right turn going to the left (see Figure 613-2-3). These ropes are available in sizes from 3/4 inch to 16 inches in circumference and are spliceable by cross-braiding of the strands.
Figure 613-2-1. Synthetic Fiber Plain-Laid Rope
SINGLE VAAN
Figure 613-2-1. Synthetic Fiber Plain-Laid Rope
SINGLE YARN
Figure 613-2-2. Synthetic Fiber Cable-Laid Rope
SINGLE YARN
Figure 613-2-2. Synthetic Fiber Cable-Laid Rope
- Figure 613-2-3. Plaited Rope
613-2.3.6 BRAIDED ROPES. Braided ropes have been reclassified from special to general purpose use. There are several different types of braided ropes: namely, hollow braid, stuffer braid, solid braid, and double braid. With the exception of double braid, braided ropes range in sizes up to 1-inch circumference. Double braided ropes are available up to 16 inches in circumference. The chief advantage of double braided rope is that it can be made in long continuous lengths (up to 20,000 ft) without noticeable splice bulge, and it will not kink or twist in a single part operation while under load.
613-2.3.7 DOUBLE BRAIDED ROPES. Double braided ropes are constructed of two hollow braid ropes with one rope located inside the other (Figure 613-2-4). The inner core rope is made of large single yarns having a slack, limp braid. The cover rope is made of larger single yarns having a tight braid to compress and hold the core. These ropes have a variety of uses, ranging from halyards to mooring lines. They range in size from 3/4 inch to 12 inches in circumference. Double braid is spliceable as described in paragraphs 613-2.5.5 and 613-2.5.12 with the use of special hollow fids shown in Figure 613-2-5.
- Figure 613-2-4. Synthetic Fiber Double Braided Rope
Figure 613-2-5. Fids Used for Splicing Double-Braided Line
Figure 613-2-5. Fids Used for Splicing Double-Braided Line
613-2.3.8 SMALL CORDAGE ROPES. Small cordage ropes, or small stuff, are lines with a circumference less than 1-3/4 inches. Natural fiber lines, with the exception of cotton, are usually sized by the number of threads they contain and by circumferences, the largest being 21-thread. Other designations denote the specific use. For small cordage rope specifications, refer to Table 613-2-2.
|
Type of Cordage |
Specification |
|
Cord, Cotton, General and Special Purpose, Sash and Venetian Blind |
FED SPEC T-C-571 |
|
Twine, Hemp, Polished |
FED SPEC T-R-650 |
|
Rope, Hemp, Tarred (Ratline, Seizing) |
FED SPEC T-R-650 |
|
Yarn, Plied, Hemp, Tarred (Marline, Spun Yarn, Houseline, Roundline) |
FED SPEC T-R-650 |
|
Cord, Fibrous (Lines, Lead) |
MIL-L-1145 |
|
Halyard Signal Braided Treated |
MIL-H-226 |
613-2.3.9 MARLINE. Marline is a two-ply, left-laid (ZS) line used for sennit, braided cord, or fabric-made flat-plaited yarns. When tarred, it is used for seizing, serving, and worming.
613-2.3.10 POLYETHYLENE ROPE. Polyethylene rope has a three strand twisted structure primarily designed for ring buoy lifelines where its lightweight and floating characteristics are distinct advantages. Polyethylene rope is obtained commercially.
613-2.3.11 SIGNAL HAYYARDS. Signal halyards are used for flying signal flags. Braided cotton halyards are no longer suitable for shipboard operations because of higher ship speeds, higher stack temperatures, and stack gases. However, where these conditions do not prevail, such as at land bases, cotton halyards are still usable. Plaited polyester rope (1-1/2 inch circumference) has been designated to replace nylon ropes for halyards according to NAVSEA dwg 804-5184208, Signal Halyards and Dressing Lines Arrangements. In the same drawing, plaited polyester is specified instead of nylon rope (plain laid and double braid) for dressing lines.
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