Hence we have absolute strength of yarns 6480 Real strength - 4552 Loss of strength by twisting 1928 lbs.
As the diminution of strength in the yarns, demon strated by the preceding example, obviously arises from their position when twisted, in consequence of which they do not all bear the load at the same time; and not from any permanent weakness produced by the twisting, it became reasonable to believe, that the twist given to ropes should be as moderate as possible. A slight degree of twist, however, which would give most strength to the rope, would expose it to various accidents which would injure its texture; so that a certain degree of hardness and compactness, which can only be derived from twisting, is absolutely necessary to the perfection of a rope, which ought to be to keep out water to prevent it from rotting.
The degree of twist commonly employed was such that the rope was Iwo-thirds the length of the yarns which composed it. Duhamel, who made many valuable experiments on this subject, in the royal dock yards of France, caused some rope to be worked with only three-fourths of the length of the yarn. This last rope, with the inferior degree of twist, bore 51871bs. whereas the other bore only 432 llbs. He next caused these ropes to be made with different twists, and ob tained the following results: Weight borne by each.
Degree of twist. One cxpt. Another cxpt.
2 4098 42504850 6753 6205 7397 So far these experiments were highly satisfactory; but it still remained to be seen, whether or not the ropes which had an inferior degree of twist, had not also an inferior degree of useful solidity, notwithstand ing their superiority of strength in carrying weights.
In order to determine this point, M. Duhamel had a considerable quantity of rigging made with yarns, wrought up into only of their length, and got them put into actual use on ship-board, during a whole campaign. The report given by the officers of the ship was highly satisfactory. They proved that the ropes thus manufactured were one-fourth lighter than the common kind;—that they were nearly one eighth more slender, so as to give less hold to the wind; that from their being more pliant than the com mon ones, they run easier through the blocks, and did not run into what are technically called the new cordage required fewer hands to work it, in the proportion of two to three; and that it was at least one-fourth stronger.
Having obtained such important results, M. Duha mel was led to push his experiments to the very utmost limit, and to try what could be effected by abandoning altogether the process of twisting. He began by laying the yarn in skeins, covering it with a worming or coating of small line. These ropes had great strength but no duration, because the coating opened at every short bending and was soon rubbed off. He next cov ered the skeins with a coating woven as is done with ropes used for house furniture; but this required to be put on at great expense, in order to be put on with proper tightness. He also wove some small ropes solid, which turned out very strong, but all these com• binations were unfit for service; and became sow- and pervious to water.
Wherever ropes, however, are not expeoed to short bendings, as in the case of standing .igging, where they can be defended from water br tarring, Sze. the least twisted cordage may be antas-cously employ ed, and should, according to M. Duhamers expell ments, be made from strands:Kir it is demonstrable that in fine stranded cordage, when the twist of the strands is exactly to the twist in the laying, the strands lie less oPaluely to the axis than in other ropes, and therefo-c• bear a greater load. M. Duhamel made two srrt hawsers, one of which had three strands the other six with a heart. The first bore 865, anti the other 1325 pounds; and in comparing riawsers with three with those with four strands, he always found the four stranded cordage greatly supe rior, and he found also that a heart judiciously put in not only rendered the work easier and more perfect to the eye, but also stronger and more durable.