In the Royal Navy cordage is described by reference to the circumference of the rope measured in inches and to the the material from which it is made - for example, 4.5 inch manila. In some countries, and commercially in Great Britain, cordage is sometimes measured by its diameter. The size of a strand is that of the rope from which it was taken; thus a 2 inch strand is one taken from a 2 inch rope. The length of a rope is measured in fathoms.
The strands tend to unlay unless the end of the rope is whipped (i.e. firmly bound) with twine.
The rope will stretch under load, but may be expected to regain its normal length when slack, provided that the load applied is well within the breaking strength of the rope; a greater load, however, even if it does not part the rope, will cause a permanent extension in its length and thereby render it unfit for service. The older and more worn the rope, the less elasticity it will possess and the weaker it will become. Rope under load will tend to twist in the opposite direction to that of its lay and thereby tend to unlay itself, but it should regain its normal form when slack.
When wet, rope will usually shrink in length in proportion to the amount by which it swells in diameter, but it will recover its original length when dry and after use. Rope which is continually subjected to heat and damp - when in the tropics, for example - will lose its elasticity and strength sooner than rope used under normal conditions of temperature and humidity.
The ropes supplied to the Royal Navy are made from various kinds of vegetable fibre which may differ in strength, weight, flexibility, hardness or resistance to wear, elasticity, resistance to weather, or behaviour when wet. The fibre selected, therefore, depends on the use for which the rope is intended.
When made of manila or sisal, the fibres of the rope are treated with a rot-proofing solution during the first stage of rope making, when the fibres are being combed into ribbons. Rot-proofing neither weakens the rope nor increases its weight, but makes it watertight to the extent that, when wet, it absorbs hardly any water and is nearly as light and as easily handled as when it is dry.*
To assist in distinguishing the different types of cordage a coloured jute yarn known as a rogue's yarn is woven into the strands of each type of rope manufactured at the Admiralty Ropery. A rogue's yarn is also used in commercially manufactured rope to indicate the type of fibre, its quality, and perhaps the particular manufacturer.
* Rot-proofing was discontinued in 1963, because rot-proofed cordage has deteriorated in hot and humid conditions.
This rope is made from the fibre of the abaca plant, which is grown extensively in the Philippine Islands and shipped from the port of Manila (whence its name), and also in Central America, Sumatra and Borneo. When mature the abaca plant, which grows to a height of from 10 to 30 ft, is felled and the fibre from the leaf sheaths is stripped off. The quality of the finished rope depends upon the thorough cleaning of the fibre during this stripping process. When new and untreated it is deep golden-brown in colour. The rope is flexible, durable, strong, and stands up well to wear and weather. It is impervious to salt water, and so it is very suitable for slings, falls, berthing hawsers and tow-ropes. Manila hawser-laid rope is supplied to the Royal Navy in coils of 120 fathoms, and it is marked with one red rogue's yarn in each of two strands. Manila cable-laid rope is supplied in coils of l00 fathoms.
Commercially manufactured manila ropes over 2 inches in circumference and complying with the specification of the British Standards Institution are identified as follows:
This rope is made from the leaves of the Agave sisalana plant, which is a member of the cactus family. It is grown in Kenya, Tanganyika, Haiti and Java and, when new and untreated, is hairy and of a pale straw colour. New sisal rope is as strong as second-grade manila, but it is less flexible, durable and resistant to wear and weather. It should therefore be examined frequently for signs of deterioration. Because it is not so reliable as manila it is not used for boats' falls, slings or for any purpose where the parting of the rope may endanger life. Sisal hawser-laid rope is supplied to the Royal Navy in coils of 120 fathoms; it is marked with one yellow rogue's yarn in each of two strands.
Commercially manufactured sisal rope over 2 inches in circumference and complying with the specification of the British Standards Institution is identified with one red rogue's yarn in one strand.
This rope is made from the fibres of the stems of the hemp plant which is grown in many parts of the world, but notably in Italy, Russia, China, U.S.A., New Zealand, St. Helena and India. New Zealand and St. Helena hemps are not true hemps like Italian, but produce hard fibres similar to those of sisal. Italian hemp is the strongest vegetable fibre used in rope-making. Indian hemp is not reliable for cordage. American hemp is about equal to European hemp, but is not used by the Admiralty.
Hemp is very much softer than the other fibres described above. The quality varies greatly with the soil in which it is grown, and for purposes of Admiralty specification it is graded for quality in the order Italian, European, New Zealand and St. Helena, and Indian. New and untreated hemp rope is hard, smooth, pale grey in colour and of a lighter shade than manila but darker than sisal. It is marked with a red rogue's yarn in each strand.
Hemp is heavier than manila and the best quality is stronger than the manila supplied to the Royal Navy. Its wearing qualities are about the same as those of manila, but it is far more flexible. It is used in the Royal Navy only for small lines and small stuff.
This rope is made from the fibres in the husks of coconuts grown in Ceylon. It is very hairy, and brown in colour. A Coir rope is the weakest of all cordage, but it has the advantage of being so light that it floats on water. It is flexible and very springy, but soon rots if stowed away wet, and does not stand up well to chafe or weather. Coir rope is half the weight and one-fifth the strength of manila or sisal of equal size. It is supplied to the Royal Navy in coils of 120 fathoms. and is marked with one yellow rogue's yarn in one strand.