Rope
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have high tensile strength and can be used for dragging and lifting. Rope is thicker and stronger than similarly constructed cord, string, and twine.
Construction
Rope may be constructed of any long, fibrous material, but generally is constructed of certain natural or synthetic fibres. Synthetic fibre ropes are significantly stronger than their natural fibre counterparts, they have a higher tensile strength, they are more resistant to rotting than ropes created from natural fibres, and they can be made to float on water. But synthetic ropes also possess certain disadvantages, including slipperiness, and some can be damaged more easily by UV light.Common natural fibres for rope are Manila hemp, hemp, linen, cotton, coir, jute, straw, and sisal. Synthetic fibres in use for rope-making include polypropylene, nylon, polyesters, polyethylene, Aramids and acrylics. Some ropes are constructed of mixtures of several fibres or use co-polymer fibres. Wire rope is made of steel or other metal alloys. Ropes have been constructed of other fibrous materials such as silk, wool, and hair, but such ropes are not generally available. Rayon is a regenerated fibre used to make decorative rope.
The twist of the strands in a twisted or braided rope serves not only to keep a rope together, but also enables the rope to more evenly distribute tension among the individual strands. Without any twist in the rope, the shortest strand would always be supporting a much higher proportion of the total load.
Size measurement
Because rope has a long history, many systems have been used to specify the size of a rope. In systems that use the inch, large ropes over diameter – such as those used on ships – are measured by their circumference in inches; smaller ropes have a nominal diameter based on the circumference divided by three. In the metric system of measurement, the nominal diameter is given in millimetres. The current preferred international standard for rope sizes is to provide the mass per unit length, in kilograms per metre. However, even sources that otherwise use metric units may still give a "rope number" for large ropes, which is the circumference in inches.Use
Rope has been used since prehistoric times. It is of paramount importance in fields as diverse as construction, seafaring, exploration, sports, theatre, and communications. Many types of knots have been developed to fasten with rope, join ropes, and utilize rope to generate mechanical advantage. Pulleys can redirect the pulling force of a rope in another direction, multiply its lifting or pulling power, and distribute a load over multiple parts of the same rope to increase safety and decrease wear.Winches and capstans are machines designed to pull ropes.
Knotted ropes have historically been used for measuring and performing mathematical calculations. For example, Ancient Egyptian rope stretchers used knotted ropes to measure distances, medieval European shipbuilders and architects performed calculations using arithmetic ropes, and some pre-colonial South American cultures used quipu for numerical record-keeping.
History
The use of ropes for hunting, pulling, fastening, attaching, carrying, lifting, and climbing dates back to prehistoric times. It is likely that the earliest "ropes" were naturally occurring lengths of plant fibre, such as vines, followed soon by the first attempts at twisting and braiding these strands together to form the first proper ropes in the modern sense of the word. The earliest evidence of a suspected rope is a very small fragment of three-ply cord from a Neanderthal site, dated to approximately 50,000 years ago. This item was so small, it was only discovered and described with the help of a high-power microscope. It is slightly thicker than the average thumbnail and would not stretch from edge to edge across a little fingernail. There are other ways fibres can twist in nature, without deliberate construction.A tool dated between 35,000 and 40,000 years old found in the Hohle Fels cave in south-western Germany has been identified as a means for making rope. It is a strip of mammoth ivory with four holes drilled through it. Each hole is lined with precisely cut spiral incisions. The grooves on three of the holes spiral in a clockwise direction from each side of the strip. The grooves on one hole spiral clockwise on one side, but counterclockwise on the other side. Plant fibres have been found on it that could have come from when they fed through the holes and the tool twisted, creating a single ply yarn. Fiber-making experiments with a replica found that the perforations served as effective guides for raw fibers, making it easier to create a strong, elastic rope than simply twisting fibers by hand; spiral incisions would have tended to keep the fibres in place. But the incisions cannot impart any twist to the fibres pulled through the holes. Other 15,000-year-old objects with holes with spiral incisions, made from reindeer antler, found across Europe are thought to have been used to manipulate ropes, or perhaps some other purpose. They were originally named "batons", and thought possibly to have been carried as badges of rank.
Impressions of cordage found on fired clay provide evidence of string and ropemaking technology in Pavlov I, Moravia, dating back between 24,000 and 26,000 years. Fossilized fragments of "probably two-ply laid rope of about diameter" were found in one of the caves at Lascaux, dating to approximately 15,000 BC.
The ancient Egyptians were probably the first civilization to develop special tools to make rope. Egyptian rope dates back to 4000 to 3500 BC and was generally made of water reed fibres. Other rope in antiquity was made from the fibres of date palms, flax, grass, papyrus, leather, or animal hair. The use of such ropes, pulled by thousands of workers, enabled the Egyptians to move the heavy stones necessary for building their monuments. Starting from approximately 2800 BC, rope made of hemp fibres was in use in China. Rope and the craft of rope making spread throughout Asia, India, and Europe over the next several thousand years.
From the Middle Ages until the 18th century, in Europe ropes were constructed in ropewalks, very long buildings where strands the full length of the rope were spread out and then laid up or twisted together to form the rope. The cable length was thus set by the length of the available rope walk. This is related to the unit of length termed cable length. This allowed for long ropes of up to long or longer to be made. These long ropes were necessary in shipping as short ropes would require splicing to make them long enough to use for sheets and halyards. The strongest form of splicing is the short splice, which doubles the cross-sectional area of the rope at the area of the splice, which would cause problems in running the line through pulleys. Any splices narrow enough to maintain smooth running would be less able to support the required weight. Rope intended for naval use would have a coloured yarn, known as the "rogue's yarn", included in the layup. This enabled the source to be identified and to detect pilfering.
Leonardo da Vinci drew sketches of a concept for a ropemaking machine, but it was never built. Remarkable feats of construction were accomplished using rope but without advanced technology: In 1586, Domenico Fontana erected the 327-ton obelisk on Rome's Saint Peter's Square with a concerted effort of 900 men, 75 horses, and countless pulleys and meters of rope. By the late 18th century, several working machines had been built and patented.
Some rope is still made from natural fibres, such as coir and sisal, despite the dominance of synthetic fibres such as nylon and polypropylene, which have become increasingly popular since the 1950s.
Nylon was discovered in the late 1930s and was first introduced into fiber ropes during World War II. Indeed, the first synthetic fiber ropes were small braided parachute cords and three-strand tow ropes for gliders, made of nylon during World War II.
Styles
Laid or twisted
Laid rope, also called twisted rope, is historically the prevalent form of rope, at least in modern Western history. Standard twisted rope generally consists of three strands and is usually right-laid, or given a final right-handed twist. The ISO 2 standard uses the uppercase letters and to indicate the two possible directions of twist, as suggested by the direction of slant of the central portions of these two letters. The handedness of the twist is the direction of the twists as they progress away from an observer. Thus, the Z-twist rope is said to be right-handed, and the S-twist to be left-handed.Twisted ropes are built up in three steps. First, fibres are gathered and spun into yarns. A number of these yarns are then formed into strands by twisting. The strands are then twisted together to lay the rope. The twist of the yarn is opposite to that of the strand, and that in turn is opposite to that of the rope. It is this counter-twist, introduced with each successive operation, which holds the final rope together as a stable, unified object.
Traditionally, a three strand laid rope is called a plain- or hawser-laid, a four strand rope is called shroud-laid, and a larger rope formed by counter-twisting three or more multi-strand ropes together is called cable-laid. Cable-laid rope is sometimes clamped to maintain a tight counter-twist rendering the resulting cable virtually waterproof. Without this feature, deep water sailing was essentially impossible, as any appreciable length of rope for anchoring or ship-to-ship transfers would become too waterlogged – and therefore too heavy – to lift, even with the aid of a capstan or windlass.
One property of laid rope is that it partially untwists when used. This can cause spinning of suspended loads, or stretching, kinking, or hockling of the rope itself. An additional drawback of twisted construction is that every fibre is exposed to abrasion numerous times along the length of the rope. This means that the rope can degrade to numerous inch-long fibre fragments, which are not easily detected visually.
Twisted ropes have a preferred direction for coiling. Regular right-laid rope should be coiled clockwise to prevent kinking. Coiling this way imparts a twist to the rope. Rope of this type must be bound at its ends by some means to prevent untwisting.