HiAll .1 Twisted vs. Braided Ropes
There are two broad categories of rope: twisted and braided. A twisted rope is formed by coiling three strands together in the same direction. Twisted ropes have a tendency to unravel at the ends. All ends of such ropes must be fused, taped or spliced to prevent unravelling. The lay of rope is a term used to describe the nature of the twist that produces the completed rope. The purpose of alternate twisting of fibre, yarns and strands is to prevent the rope from becoming unlayed during use. Twisted ropes may be of a right-hand lay or left-hand lay, but the most common is the right-handed. It is essential to realize that each of the components is turned (twisted) in the opposite direction to that of its predecessor, e.g., in right-hand lay, strands are laid up right-handed (clockwise), yarns laid up left-handed, and fibres laid up right-handed. There are three general categories of braided rope construction: diamond braid with a core, hollow braid (diamond braid without a core) and solid braid. Diamond braid is done by weaving ends of yarn over and under, just like the maypole dance is done. When a core is present, the rope cannot be spliced. When no core is present (hollow braid), the rope can be spliced relatively easily. Solid braided ropes are very firm, and because they are tightly woven, they do not tend to unravel easily when cut or torn. Solid braided ropes also have good chafing resistance, but they cannot be spliced. When both the rope and its core are braided, the rope is referred to as "braid-on-braid" or "double braid." This construction usually makes very strong (end expensive) ropes. Fibre ropes are made from either natural or synthetic fibres. Natural fibres include manila, sisal hemp and cotton, and synthetic fibres traditionally include nylon, polyethylene, polypropylene and the polyesters. Twisted, braided rope atural Fibre Rope Natural fibre ropes are usually manufactured from manila, sisal, cotton or hemp fibres. Most natural fibre ropes are twisted. Natural fibres are rarely braided (the exception being cotton). Natural fibre ropes should be maintained in a clean and dry state, as rot and mildew are their main causes of deterioration. They are, however, more resistant to heat than traditional synthetic fibre ropes: they do not burn quickly and their breakdown is slower. Manila ropes deteriorate by prolonged exposure to sunlight; they should be covered or shaded if possible. Although they have been extensively used in the past, natural fibres are slowly but surely becoming a rarer sight in the maritime industry. Sisal Obtained from the leaves of the plant Agave Sisalana, a large plant of the cactus family, sisal comes largely from Russia, America, East Africa, Italy, Java, and countries in Central America. The plant prefers a temperate or tropical climate. The sisal rope is hairy, coarse, and white. It is neither as pliable as manila nor as strong. When wet, it swells more than manila, as the water is absorbed more quickly, and the rope becomes slippery to handle. Sisal rope was once extensively used in the shipping industry, either in its own state or mixed with manila fibres, a good sisal being similar in strength to a low-grade manila. The cost of production is better suited to the ship owner, and the supply is more accessible than manila. Today, sisal is also used as core in wire ropes. For handling purposes, the fibres have a brittle texture, and continued handling without gloves could cause the hands to become sore and uncomfortable. It is generally used for mooring ropes in ships and most other general duties aboard, where risk of life is not an issue. When the rope is expected to be continually immersed in water, it may be coated with a water repellent. This chemical coating, usually tar-based, will prevent rotting and mildew. Hemp Hemp is obtained from the stem of the plant Cannabis Sativa, which yields flax for the production of canvas. (The word canvas is derived from the Latin "cannabis," which means hemp). This was accepted as the best rope in the marine industry from the early developing days of sail. Cannabis Sativa is cultivated in many parts of the world - New Zealand, Russia, China, India, and the USA - but has been replaced mainly by man-made fibre ropes and manila. The hemp fibres are light cream in colour when supplied to the rope manufacturer. They have a silky texture and are of a very fine nature: hence the extra flexibility of hemp rope compared to sisal or manila. Most hemp ropes are treated during production, and the result is a tarred, brown rope that is hard and hairy to the touch. Its strength will depend on the place of production. Italian hemp ropes are now considered to be the best quality, having about 20% greater strength than a high-grade manila. However, quality varies considerably, and hemp ropes are rarely seen at sea today except in small uses like lead line, cable laid hemp, sea anchor hawsers, bolt rope, etc. The advantage of hemp rope is that it is impervious to water and does not shrink or swell when wet. For this reason, it was extensively used for the rigging of sailing vessels and roping sails. When used for running rigging, it was preferred to manila or sisal because it did not swell and foul the blocks. However, for vessels navigating in cold climates, hemp ropes do have the tendency to freeze up. Not all hemp ropes are supplied tarred, so the weight and the strength will vary. Manila Manila is obtained from the abaca (wild banana) plant, which grows to about 9 m (30 ft) in height, largely in the Philippine Islands, and is exported via the port of Manila, from which it acquires its name. Manila rope is not as durable as hemp, but is certainly more pliable and softer. It is goldbrown in colour, and never tarred. Unfortunately, it swells when it is wet, but it is still considered by far the strongest natural rope made. It is very expensive and its availability will depend on the political climate.3 Synthetic Fibre Ropes Synthetic ropes are stronger than natural fibre ropes as they have individual fibres running along their entire length, rather than short, overlapped fibres. They are generally impervious to rot, mildew and fungus, and have good resistance to chemicals. They do not stiffen when wet, do not freeze and have good dielectric properties when clean and dry. Polypropylene in particular absorbs no moisture at all. Synthetic ropes are also lighter, easier to handle, and have good abrasion resistance. They far outwear manila ropes. Although natural fibre ropes are still used throughout the marine industry, they have been superseded by synthetic fibres for a great many purposes. Not only do the majority of synthetic ropes have greater strength than their natural fibre counterparts, but they are more easily obtainable and now considerably cheaper. List of synthetic fibres used in making ropes table Caption: List of synthetic fibres used in making ropes Summary: List of synthetic fibres used in making ropes Fibre Characteristics Nylon High elasticity Polyesters, Dacron®, Terylene® Low elasticity. Note: Dacron and Terylene were the very first polyester fibres produced. Kevlar® High heat resistance, low elasticity and high strength Vectran® High strength and low elasticity HMWPE, UHMWPE, Dyneema®, Spectra® High strength, low elasticity and floating capability. Notes: HMWPE refers to High Molecular Weight Polyethylene UHMWPE refers to Ultra High Molecular Weight Polyethylene Technora® Low elasticity, high strength, high heat resistance Polyolefin® Light weight, floating capability. Nylon Nylon is the best known and most used of the synthetic fibre used in ropes. It has high breaking strength, whether wet or dry, and good sunlight and weather resistance. It is highly elastic, and its elongation under a load is 10% to 40%. When the load is released, the increase in length is approximately 7%. Nylon ropes are used for such functions as shock absorbing when coupled with a mooring wire, and are attached to fenders to permit movement as the vessel moves up and down against the dock. Nylon ropes are light to handle, twice as strong as an equivalent-sized manila, and give the appearance of a smooth slippery surface. They have a high melting point, 250°C, and are pliable in normal temperature, which is desirable for most forms of rigging. The disadvantages of nylon ropes are that they do not float, and in cold climates, they tend to stiffen and become difficult to handle. They also have a tendency to become slippery when wet. They will lose approximately 10% of their strength when wet, but they regain it when they dry out. They should not be exposed to strong sunlight or stowed on hot deck surfaces, as their useful life will be impaired. They should thus be stored away from heat and sunlight. Nylon ropes are attacked by most acids and paints, and contact with chemicals should be avoided. The significant point with these ropes is that they are used when great stress occurs. Should they give way under such stress, there is a tendency for them to act like an elastic band. Serious injury could occur if someone happened to be in the path of the rope at that time. The nylon rope will give no audible warning when about to give way; however, during excessive stress, the size of the rope will reduce significantly. These ropes are difficult to render on a set of bitts, and should never be allowed to surge. Any splices in nylon ropes tend to draw more easily than in natural fibre when under stress. Polyesters Polyesters (initially known as Dacron® and Terylene®) are not as strong as nylon and have inferior stretch properties. They have a similar abrasion and temperature resistance to those of nylon. Polyesters are considered to be more resistant to acids, oils and organic solvents than their nylon counterparts, while their strength remains the same in wet or dry conditions. These characteristics make them ideal for most running rigging of sailboats. The disadvantage of polyester is very similar to that of nylon. It will not float. It should be kept to a minimum when working about bitts or warping drums. The melting point is between 230 and 250°C. Polypropylene Polypropylene is light and floats on water, but it has lower strength than nylon and polyester. It is unsuitable for use in hot conditions, as it softens progressively with increases in temperature and has a relatively low melting point (165°C). Friction-generated heat should also be avoided. Should the fibres fuse together, the rope is permanently damaged and weakened. Polypropylene ropes degrade in sunlight, but do not lose strength when wet and are not attacked by rot and mildew. They are highly resistant to acids and alkalis, but solvents and bleaching agents may cause deterioration. They are used extensively for mooring ropes, running rigging and towlines. Polypropylene neither absorbs nor retains water, and for this reason has recently been used for the inner core of wire ropes, eliminating inner corrosion in the wire. However, the wire still needs to be lubricated externally. 3 Knots, Bends, Hitches and Related Items General Knots have many uses in the maritime world. However, not all knots are equal. Some knots are better than others. This section lists various knots that meet the three important conditions for all good knots: * easy to do; * easy to undo; * safe (if used as recommended). Before going any further into this topic, the reader must understand that any fastening (knot, bend or hitch) reduces the strength of a rope. Knots and bends reduce the rope strength by up to 50%, while hitches reduce it by 25%. Well-executed splices can be used to join ropes while retaining 80% or more of rope strength. Most knots in polyethylene or polypropylene monofilament ropes tend to slip. These knots must be "doubled-up" in order to hold, due to the waxy monofilament surfaces. Knots . Bowline The bowline is one of the most valuable knots for day-to-day use on a boat. It is really a variation of the sheet bend, made with a single rather than two lengths of line. It is a non-slip knot and easy to untie after it has been under load. Two bowlines can safely join two towlines of equal or unequal size. 5. Square Knot Also called a reef knot, the square knot is used to fasten two lines of equal size when no great load is anticipated. If used to connect lines of different sizes, it will slip. If used to join two towlines, the knot will jam under heavy stress and be extremely difficult to untie. The square knot needs tension on both lines, for a sharp pull on one of the ends may cause the knot to fall into two half hitches. Warning: Never use this knot to join two lines when significant loads are anticipated. Never rely on this knot when life, limb or valuable property is involved. Severe injury or damage could result from misuse of this knot. 5. Figure-eight Knot The figure-eight knot is very strong, especially when doubled. It can be used to make a loop (as an alternative to the bowline) to fasten two lines of equivalent diameter together. Sailors also use it to ensure that halyards remain in their pulleys. Bends Bends are used when it is necessary to lengthen one line by joining it to another. They are not intended to be permanent, but rather are used as a temporary means of adding length to a line. 5. Sheet Bend A single sheet bend, also known as a becket bend, is used to join lines of unequal thickness. The double sheet bend gives a more secure connection when unequal-sized lines are used, particularly when one line is considerably thicker than the other. With the ends on opposite sides, it is especially useful with slippery synthetic lines. 5. Fisherman's Bend Used to secure a rope to a buoy, or a hawser to the ring or harp of an anchor. Hitches Hitches are used to secure lines to objects such as rings or eyes. They are generally used to make temporary fastenings; one of their distinct advantages is that they can be untied quickly. 5. Half Hitch These can be useful to bend the end of a rope to a spar, stanchion, bollard or ring. To reinforce or strengthen the single half hitch, two half hitches may be used. The resulting knot is known as a double half hitch. 5. Timber Hitch Like the double half hitch, this hitch can also be used to bend the end of a rope to a spar, stanchion, bollard or ring. 5. Clove Hitch The clove hitch is a good choice to use when temporarily securing a line to another rope, a railing, spar or similar object. It can work loose and should not be left unattended. Under heavy load, it can jam tightly. Various knots 5.5.5 Whipping Whenever a fibre rope is cut, the rope ends must be bound or whipped to prevent the rope from untwisting or fraying, and the strands from slipping in relation to each other, causing one of them to assume more or less than its share of the load. Each of these conditions results in shortened rope life. Ordinary whippings are made with fine twine as follows. Make a loop in the end of the twine and place the loop at the end of the rope, as shown in the illustration. Wind the standing part around the rope, covering the loop of the whipping, but leave a small loop uncovered, as shown. Thread the remainder of the standing end up through the small loop and pull the dead end of the twine, thus pulling the standing end and the small loop (through which it is threaded) back towards the end of the rope underneath the whipping. Pull the dead end of the twine until the small loop with the standing end through it reaches a point midway underneath the whipping. Trim both ends of the yarn close up against the loops of the .1 Short Splice Never knot a rope at a break. Cut away the broken ends and splice it together. A short splice is used when the rope does not have to be put through a small pulley or when only a small amount of rope can be used to make a splice. Long Splice This splice is used for pulley work, as the spliced ropes run through sheave blocks without jamming. Eye Splice This splice is used for forming an eye or loop in the end of a rope. ********************************************************************** This message and its attachments may contain legally privileged or confidential information. If you are not the intended recipient, you must not disclose or use the information contained in it. If you have received this e-mail in error, please notify the sender immediately by return e-mail and delete the e-mail. Any content of this message and its attachments which does not relate to the official business of Eraring Energy must be taken not to have been sent or endorsed by Eraring Energy. 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