466 



ROPEMAKING. 



Rope- ropes should be as moderate as possible. A slight de- 

 making. g ree o f tv/ist, however, which would give most strength 

 ^V^ 1 ^ 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 pre- 

 vent it from rotting. 



The degree of twist commonly employed was such 

 that the rope was two-thirds the length of theyarns which 

 composed it. M. 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 518?lbs. where- 

 as the other bore only 432 libs. He next caused these 

 ropes to be made with different twists, and obtained 

 the following results. 



Weight borne by each. 



Degree of twist. One expt. Another expt. 



4098 4250 

 4850 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 three-fourths 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 TV eve 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 common ones, 

 they run easier through the blocks, and did not run 

 into what are technically called kinks ; that the new 

 cordage required fewer hands to work it, in the pro- 

 portion 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 ut- 

 most limit, and to try what could be effected by aban- 

 doning 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 covered the skeins with a coating woven 

 as is done with ropes used for house furniture ; but 

 this required to be put on at great expence, in order 

 to be put on with proper tightness. He also wove 

 some small ropes solid, which turned out very strong, 

 but all these combinations were unfit for service, and 

 became soft and pervious to water. 



Wherever ropes, however, are not exposed to short 

 bendings, as in the case of standing rigging, where 

 they can be defended from water by tarring, &c. the 

 least twisted cordage may be advantageously employed, 

 and should, according to M. Duhamel's experiments, 

 be made from strands ; for it is demonstrable that in 

 fine stranded cordage, when the twist of the strands is 

 exactly equal to the twist in the laying, the strands 

 lie less obliquely to the axis than in other ropes, and 

 therefore bear a greater load. M. Duhamel made two 



small hawsers, one of which had three strands and Rope- 

 the other six with a heart. The first bore 865, and making. 

 the other 1325 pounds ; and in comparing hawsers 

 with three with those with four strands, he always 

 found the four stranded cordage greatly superior, 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. 



In examining the strength of cordage, Sh inches of 

 circumference and under, M. Duhamel found that the 

 strength increased a little faster than the number of 

 equal threads, thus : 



Ropes of 9 threads bore 1014 instead of 946 Ibs. 

 12 1564 1262 



18 2148 1893 



According to the experiments of Mr. Huddart, no 

 strength is lost in the common way when there are 

 only three yarns in the strand. When there are three 

 yarns, the loss is one-sixth, and with a hundred yarns 

 it is about one-half. His registered cordage, according 

 to theory, loses nothing, but by actual experiment it 

 loses one-eighth. 



The following rule is given by Dr. Robison for ob- 

 taining the strength of ropes. 



Multiply the circumference of the rope in inches by 

 itself, and thejijth part, of' the product will lie the number 

 of tons which the rope will carry. 



For example, if the rope is 6 inches in circumfe- 

 rence, we have 6 times 6 = 36, the fifth of which is 

 7i tons. 



There is no branch of the rope manufacture more 

 important than that which relates to the tarring of the 

 cordage. The following experiments were therefore 

 made by M. Duhamel on the relative -strength of tar- 

 red and white or untarred cordage. 



August 8th, 1741. 



Untarred Rope. Tarred Rope. Differences 

 Broke with 4500 pounds. 3400 pounds. 1100 



4900 3300 1600 



4300 3250 1550 



April 25th, 1743. 



Broke with 4600 pounds. 3500 pounds. 1100 



5000 3400 1600 



5000 3100 1900 



Sept. Sd, 1746. 



Broke with 3300 pounds. 3000 pounds. 800 



4000 2 TOO 1300 



42uO 2800 1400 



The ropes with which the preceding experiments 

 were made, were three French inches in circumfe- 

 rence, and were made of the best Riga hemp. 



M. Duhamel next examined the relative strength of 

 a parcel of tarred and untarred cordage, which had 

 been manufactured on the 12th of July, 174-6. It had 

 been laid up in the storehouse, and the following re- 

 sults were obtained at the dates mentioned. 



Mr. Hud. 



dart's expe- 

 riments. 



Dr. Robi- 

 son's lule 

 for the 

 strength of 

 ropes. 



Duhamel's 

 experiments 

 on tarred 

 and untar- 

 red ropes. 



