CABLE

( Cable , Fr.; Ankertau , Germ.) A strong rope or chain, connecting the ship with the anchor for the purpose of mooring it to the ground. The sheet anchor cable is the strongest, and is used at sea; the stream cable is more slender, being used chiefly in rivers. A cable’s length is 120 fathoms. The greatest improvement in mooring ve els has been the introduction of the chain cable, which, when duly let out, affords in the weight of its long catenary curve, an elastic tension and play to the ship under the pre ure of wind. The dead strain upon the anchor is thus greatly reduced, and the sudden pull by which the flukes or arms are readily snapped is in a great measure obviated. The best iron cables are chains made of links, bound and braced by rods acro their middle. Experience has taught that the ends of these links wear out much sooner than the sides. To remedy this evil, Mr. Hawkes, iron manufacturer, obtained a patent in July, 1828, for constructing these anchor chains with links considerably stouter at the ends than in the middle. With this view, he forms the short rods of iron, of which the links are to be made, with swells or protuberances about one third of their length from each of their ends, so that when these are welded together, the slenderer parts are at the sides, and the thicker at the ends of the elliptic links. Such rods as the above are formed at once by rolling, swagging, or any other means. When the link is welded, it may be strengthened, by a brace or stretcher fixed acro the middle. The first avowed proposal to substitute iron cables for cordage in the sea service, was made by Mr. Slater, surgeon of the navy, who obtained a patent for the plan in 1808, though he does not seem to have had the means of carrying it into effect; a very general misfortune with ingenious projectors. It was Captain Brown of the West India merchant service who, in 1811, first employed chain cables in the ve el Penelope, of 400 tons burden, of which he was captain. He made a voyage in this ship from England to Martin i que and Guadaloupe and home again, in the course of four months, having anchored many times in every variety of ground without any accident. He multiplied his trials, and acquired certain proofs that iron might be substituted for hemp in making cables, not only for mooring ve els, but for the standing rigging. Since this period chain cables have been universally introduced into all the ships of the royal navy, but the twisted links employed at first by Brown, have been replaced by straight ones, stayed in the middle with a cro rod, the contrivance of Mr. Brunton, which was secured by patent in this country and in France; but the latter patent was suffered to fall from not being acted upon within the two years specified by law. The first thing to be considered in the manufacture of iron cables is, to procure a material of the best quality, and, in using it, always to keep in view the direction of the strain, in order to oppose the maximum strength of the iron to it. The best form of the links may be deduced from the following investigation. IMG:4147767755307473660_illo0203a.png:Chain link Let A B fig. 215. be a circular link or ring, of one inch rod iron, the outer circumference of the ring being 15 inches, and the inner 9. If equal opposite forces be applied to the two points of the link C D , pulling C towards E , and D towards F , the result will be, when the forces are sufficiently intense, that the circular form of the link will be changed into another form with two round ends and two parallel sides, as seen in fig. 216. The ratio of the exterior to the interior periphery which was originally as 15 to 9, or 5 to 3, is no longer the same in fig. 216. Hence there will be a derangement in the relative position of the component particles, and consequently their cohesion will be progre ively impaired, and eventually destroyed. In fig. 215. the segment M N of the outside periphery being equal to 3 inches, the corresponding inside segment will be 3 ⁄ 5 of it, or 1 4 ⁄ 5 inches. If this portion of the link, in consequence of the stretching force, comes to be extended into a straight line, as shown in fig. 216. , the corresponding segments, interior and exterior, must both be reduced to an equal length. The matter contained in the 3 inches of the outside periphery must therefore be either compre ed, that is, condensed into 1 4 ⁄ 5 inch, or the inside periphery, which is only 1 4 ⁄ 5 inch already, must be extended to 3 inches; that is to say, the exterior condensation and the interior expansion must take place in a reciprocal proportion. But, in every case, it is impo ible to effect this contraction of one side of the rod, and extension of the other, without dis rupture of the link. Let us imagine the outside periphery divided into an infinity of points, upon each of which equal opposite forces act to straighten the curvature: they must undoubtedly occasion the rupture of the corresponding part of the internal periphery. This is not the sole injury which must result; others will occur, as we shall perceive in considering what pa es in the portion of the link which surrounds C D , fig. 216. , whose length is 4 1 ⁄ 2 inches outside, and 2 1 ⁄ 10 inside. The segments M P and N O , fig. 215. , are actually reduced to semi-circumferences, which are inside no more than half an inch, and outside as before. There is thus contraction in the interior, with a quicker curvature or one of shorter radius in the exterior. The derangement of the particles takes place here, in an order inverse to that of the preceding case, but it no le tends to diminish the strength of that portion of the link; whence we may certainly conclude that the circular form of cable links is an extremely faulty one. IMG:4147767755307473660_illo0203b.png:Chain link Leaving matters as we have supposed in fig. 215. , but suppose that G is a rod introduced into the mail, hindering its two opposite points A B from approximating. This circumstance makes a remarkable change in the results. The link pulled as above described, must a ume the quadrilateral form shown in fig. 217. It offers more resistance to deformation than before; but as it may still suffer change of shape, it will lose strength in so doing, and cannot therefore be recommended for the construction of cables which are to be exposed to very severe strains. Supposing still the link to be circular, if the ends of the stay comprehended a larger portion of the internal periphery, so as to leave merely the space nece ary for the plan of the next link, there can be no doubt of its opposing more effectively the change of form, and thus rendering the chain stronger. But, notwithstanding, the circular portions which remain between the points of application of the strain and the stay, would tend always to be straightened, and of consequence to be destroyed. Besides, though we could construct circular links of sufficient strength to bear all strains, we ought still to reject them, because they would consume more materials than links of a more suitable form, as we shall presently see. The effect of two opposite forces applied to the links of a chain, is, as we have seen, to reduce to a straight line or a straight plane every curved part which is not stayed; whence it is obvious that twisted links, such as Brown first employed, even with a stay in their middle, must of nece ity be straightened out, because there is no resistance in the direction opposed to the twist. A cable formed of twisted links, for a ve el of 400 tons stretches 30 feet, when put to the trial strain, and draws back only 10 feet. This elongation of 20 feet proceeds evidently from the straightening of the twist in each link, which can take place only by impairing the strength of the cable. From the preceding remarks, it appears that the strongest links are such as present, in their original form, straight portions between the points of tension; whence it is clear that links with parallel sides and round ends, would be preferable to all others, did not a good cable require to be able to resist a lateral force, as well as one in the direction of its length. IMG:4147767755307473660_illo0204a.png:Chain link Let us suppose that by some accident the link fig. 216. should have its two extremities pulled towards Y and Z , whilst an obstacle X , placed right opposite to its middle, resisted the effort. The side of the link which touches X , would be bent inwards; but if as in fig. 218. , there is a stay A G B , the two sides would be bent at the same time; the link would notwithstanding a ume a faulty shape. IMG:4147767755307473660_illo0204b.png:Chain link In thus rejecting all the vicious forms, we are naturally directed to that which deserves the preference. It is shown in fig. 219. This link has a cast-iron stay with large ends, it presents in all directions a great resistance to every change of form; for let it be pulled in the direction a b , against an obstacle c , it is evident that the portions d e and d f , which are supported by the parts g e and g f , cannot get deformed or be broken without the whole link giving way. As the matter composing g e and g f cannot be shortened, or that which composes d e and d f be lengthened, these four sides will remain nece arily in their relative positions, by virtue of the large-ended stay h , whose profile is shown in fig. 220. IMG:4147767755307473660_illo0204c.png:Chain link We have examined the strength of a link in every direction, except that perpendicular to its plane. Fig. 221. represents the a emblage of three links in the above predicament; but we ought to observe, that the obstacle C , placed between the links A B , must be nece arily very small, and could not therefore resist the pre ure or impact of the two lateral links.