They are now made of copper (which is the best of conductors) nailed on in double strips, about 1 inches wide and 4 feet long each, on the after side of masts and lower side of jib boom and bowsprits. The connection is formed at the caps by a hinged flap, which may be turned back whilst handling the spar, but should always be replaced. Each upper mast-head is adapted to receive a spindle which terminates the conductor at top, and the lower ends of the conductors are connected with bolts passing through the ship's bottom. Besides this there are similar strips of copper leading under the decks, from the fore and main masts to the stem and stern; and others which traverse the beams, and terminate also in bolts through the bottom, which are clenched on the sheathing. When the top-gallant-masts are down, the spindle should be placed on the top-mast head. CHAP. X. EQUIPMENT. RIGGING. EXCEPTING the wheel ropes, which are usually of hide, all Rope used in the navy is hempen. The size of rope is denoted by its circumference, and its nature by the manner of its fabrication. It is either white or tarred; contains three or more strands; and up to the size of five inch, is made up in Coils. The hemp is first spun into Yarns or Threads, each of which is supposed to be equal in strength to bear a weight of 100 pounds. Several yarns spun up together form Strands. Three or four strands laid up together form Hawser-laid rope. (Figs. 72, 73.) Three such three-stranded ropes laid up together form Cable: the smaller kinds of which are called Cablets and Hawsers. (Fig. 74.) Yarns are spun up right handed. Strands intended for right-handed rope are spun up left-handed; and those for left handed rope right-handed. Fig. 73. Fig. 72. Fig. 74. The large four-stranded hawser-laid rope which is made up round a small rope in the heart, being chiefly used for standing rigging, is commonly called Shroud-laid rope. The rope represented in the sketch Figs. 72, 73., is right-handed. Threads usually of an inferior quality twisted up moderately taut, and seldom exceeding 9, are called Spun yarn. Spun yarn plaited into a soft flat rope is called Sennit. Threads, usually two, unlaid, rubbed down, twisted up the reverse way, and then spun up together right-handed, are called Nettle stuff. Threads twisted together by hand in short lengths, are called Foxes. Foxes plaited together after forming an eye, make Reef Points or Gaskets. "In hawser-laid rope the strength of each yarn is greatest in the smaller sizes: thus, in a 12-inch rope the average strength is 76 pounds; in 6-inch, 78 pounds; in 1-inch, 93 pounds; in 1inch, 95 pounds; and in 4-inch, 104 pounds per thread. "All rope made with 4 strands is weaker than that which is made with 3 in proportion of about }. "A strain of half the full strength of any rope or chain, constantly or even frequently applied, will eventually (before its evident decay from wear) break it: this maxim applying with greater force to crane chain than to chain cable, and with still greater force to rope, particularly cable laid." * Italian hemp is considered superior to all others. Three-and-a-half-inch ropes were tested in 1856; and whilst the one made of Riga hemp broke at 3 tons 15 cwt., that of Neapolitan did not carry away until a strain of 5 tons was applied. Cat-falls, gunners' gear, bolt rope, lanyards of lower rigging, topsail ties, halyards, lifts and braces are all made of Italian hemp. Coir Rope is made from the fibres of the cocoa-nut tree. It is equal in strength to hempen rope of the same size, and is but two thirds of the weight. As it floats it is most useful for warps, but decays rapidly when stowed away wet. The rough rule for measuring the strength of ropes, is to multiply it by its circumference and divide by five; but this applies only to the very best cordage. To ascertain its weight, the square of the circumference divided by 4 equals the weight of a fathom in pounds; or multiply the square of the circumference by the length in fathoms, and divide by 480 for weight in cwts. When ropes are broken, they are joined by Splices. If they reeve through blocks, a Long splice is used; otherwise a Short splice. In short splices when there is no service the ends should be put through twice each way; when the ends are served down, once and a half is sufficient. All splices are weaker than the rope itself by one eighth. When a strand of a rope is chafed, it is cut out and another interwoven in lieu. When rope is exposed to much chafe, it is preserved by filling up the openings with spun yarn or strands, a process which is called Worming. This is covered with strips of tarred canvass ; which is called Parcelling; and this is again with turns of spun yarn, called Serving. Tar before worming; worm and parcel with the lay, and serve against the lay, as a general rule; but as it is an object to exclude wet, the eyes of standing rigging are parcelled towards the centre: thus the upper edges are covered after the manner of slate roofing. Tinmouth. Backing is smaller stuff laid in after worming, so as to make the rope more round. Throat Seizings are put on when ropes cross; the turns are passed round and round six over seven, without any crossing turns. Round Seizings have two cross turns. Flat Seizings have no riding or upper turns. All Seizing Stuff should be well stretched before use. Of the three different modes of turning in dead eyes, the splice is the weakest; the cutter stay fashion next; and the old way of securing with throat and end seizings, is so strong as to break the rope.* In forming cables, the splicing tails are stronger than the artificial eye, but the tails must be well covered. Straps made of small rope are said to be Warped; when of yarns, salvagee. The warped are stronger than rope of the same size. Two men can worm and serve seven fathoms of 31-inch rope in an hour; or worm, parcel, and serve 3 fathoms of 7-inch in an hour. Three men can worm, parcel, and serve 2 fathoms of 12-inch in an hour. One man can make 9 feet of 9 yarn sennit in an hour. Six men can make an Elliott's eye in 1 day in a 24-inch cable. Four men can do the same with a 15-inch cable but will require an occasional help for a pull. TABLE, showing the sized chain or wire rope which is used as a substitute for hempen rope. |