The art of forming fibrous, flexible, and tenacious substances into cordage. The principal aim of the ropemaker is to unite the strength of a great number of fibres. This would be done most effectually, were the fibres long enough, by laying them parallel to each other, and fastening the bundle at each end. They must therefore be combined together in such a manner that the strength of any single fibre shall be insufficient to overcome the resistance of the friction occasioned by the entanglement, but rather break: and this effect is found to be produced most easily by twisting them together, so that they shall mutually compress each other. On the other hand, a skein may be twisted so hard, that any attempt at farther twisting will break it; such a skein can have no strength to support a weight, each fibre being already loaded as much as it can bear, and therefore any weight added would break it. Whatever force is actually exerted by a twisted fibre, in order that it may sufficiently compress the rest to hinder them from being drawn out, must be considered as a weight hanging on that fibre, and must be deducted from its absolute strength of cohesion before the strength of the skein can be estimated.
The strength of the skein is evidently the remainder of the absolute strength of the fibres after the force exerted in twisting them has been deducted. Hence arises that fundamental principle in rope-making, namely, that all twisting beyond what is necessary for preventing the fibres from being drawn out without breaking, diminishes the strength of the cordage, and is, therefore, to be avoided. Thus it is necessary to twist the fibres of hemp together, in order to make a strand; but twisting is not all: something must be done to prevent the skein from again untwisting as soon as it is let loose from the hand; some method must be adopted to make the tendency to untwist in one part, act against and counterbalance the like tendency to untwist in another; in the properly accomplishing this, consists one of the principal difficulties of rope-making. The following observations, for distinctness sake, apply chiefly to the larger cordage, such as forms the standing and r,unning rigging of a ship; but they are easily extended, with proper modifications, to the smaller kinds.
The first part of the rope-making process consists in twisting the hemp; that is, making rope-yarns. These are spun in various ways, according to the nature of the machinery employed, and the cordage to be made. A slip of level ground is enclosed, of about 600 feet long, of a breadth sufficient to contain the number of machines employed, and either covered with a slight roof, or left open at top. A spinning-wheel is set up at the upper end of this walk. The band of this wheel goes over several rollers called whirls, turning on pivots in brass holes. The pivots at one end come through the frame, and terminate in little hooks. The wheel being turned by a winch, gives motion to all these whirls. The spinner has a bundle of dressed hemp round his waist, laid in the same way that women spread the flax on the distaff. He draws out a proper number of fibres, twists them with his fingers, and affixes them to the hook of a whirl. The wheel is now turned, the skein is twisted, becoming what is called a rope-yarn, and the spinner walks backwards down the rope-walk. The spinner supports the yarn in one hand (protected by a wetted piece of coarse cloth or flannel), while with the other he regulates the quantity of fibres drawn from the bundle of hemp by the motion of the twisting yarn.
The greatest fault that can be committed, is to allow a small thread to be twisted off from one side of the hemp, and then to cover this with hemp supplied from the other side; for it is evident that the fibres of the central thread make very long spirals, while the skein of the fibres which covers it must be much more oblique. This covering has but little connexion with what is below it, and will easily be detached. Hut even while it remains, the yarn cannot be strong, for on pulling it, the middle part, which lies the straightest, must bear all the strain. This defect will always happen if the hemp be supplied in a considerable body to a yarn that is then spinning small. Into whatever part of the yarn it is made to enter, it becomes a sort of loosely connected wrapper. A good spinner, therefore, endeavours always to supply the hemp in the form of a thin, flat skein. The degree of twist depends on the rate of the wheel's motion, combined with the retrograde walk of the spinner. We may suppose him arrived at the lower end of the walk, or as far as necessary for the length of the yarn; he calls out, and another spinner immediately detaches the yarn from the book of the whirl, gives it to another, who carries it aside to the reel, and this second spinner attaches his own hemp to the whirl-hook. In the mean time, the first spinner keeps fast hold of the end of his yarn; for the hemp, being dry, is very elastic, and if he were to let it go out of his hand, it would instantly untwist.
He waits, therefore, till the reeler begins to turn the reel, and then walks slowly up the walk, keeping the yarn of an equal tightness all the way.
Rope-yarns, for large rigging, are from a quarter of an inch to somewhat more than the third of an inch in circumference; or of such a size, that 160 fathoms of white yarn weigh from 3 1/2 to 4 pounds. The number of yarns in a strand of cordage varies from sixteen to twenty-five. The yarns are made into cords of any length, by laying them; and that we may have a rope of any degree of strength, many yarns are united into one strand, for the same reason that many fibres are united into one yarn.
The process for laying or closing large cordage, is as follows: - At the upper end of the walk is fixed a tackle-board. This consists of a strong oaken plank, called a breast-board, having several holes in it, fitted with brass or iron plates. Into these are put iron cranks called heavers, which have forelocks and keys, on the ends of their spindles. This breast-board is fixed to the top of strong posts, and well secured by struts or braces. At the lower end of the rope-walk is a similar breast-board fixed to a movable sledge, which may be loaded with weights when necessary. A top, which is a truncated cone, having scores in its sides for the strands, a long staff, and supported on a sledge or carriage, is placed between the strands, and, when necessary, gently forced into the angle formed by their separation. A piece of soft rope, called a strap, is attached to the handle of the top, by the middle, and its two ends are brought back, wrapped several times tight round the rope, and bound down. The yarns are formed into strands, each of which is knotted apart at both ends. The knots at their upper ends are made fast to the hooks of the cranks in the tackle-board; and those at the lower end, to the cranks on the sledge.