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214 26,600 -- 19,000 160,000 a= 0,283. ft. L-S for 893 ft. in air....=1.62 ft. L-S for 529 ft. in air.... =0.34 ft. --__--__----- --_------_----- L-S for 364 ft, in air.... = 1.28 it. L-S for 662 ft. in water. =0.426 ft. Total L-S for line in air and 'water ..-....% .p a L7T ft Increase of span due to take-up of dip == 3.22 -- 1.71 = 1.51 ft. (d) A continuous uniform, net addi- tional force, such as is assumed would not be likely to occur in practice. The assumption is made to simplify the problem and is sufficient to illustrate the principle involved. (e) The writer made some attempt to obtain data concerning the stretch from several manufacturers and im- porters of wire and manila rope. All hesitated about giving out data on the ground that the stretch is an exceedingly variable quantity depending in part on the lay and condition of the' line. Inasmuch as the calculation neces- sarily involves the stretch of the line the writer obtained samples and made some rough tests to obtain figures with which to work. The wire line was tested for stretch up to a little over half the elastic limit and the extension was at the rate of about 58/100 per cent of the length for a load equal to the elastic limit. This was after the first or second applica- tion of the load when what appeared to be the permanent stretch had been set in the line. The stretch with the first application of the load was more than twice this amount. The stretch of the manila line varied considerably in the different samples, but may be taken at the rate of about 10 times that of the wire line when the former has a tabulated ultimate strength equal to the tabulated elastic limit of the latter. The stretch with the first loading was in one case over four times that resulting from the later equal load- ies. While no claim is made to absolute accuracy in these tests, which had to be made in some haste, the results are not in error to any such extent as would impair their value for the use to which they are put in this paper. (-- t = time in seconds. w = weight of one vessel in net tons. s = distance ft. through which force acts on each vessel = ¥% total motion apart. F = average accelerating force in net tons. THe Marine REVIEW g = acceleration due to gravity = X 0.0058 xX 1,027 322 ft. per second.' -- Substituting values for wire line:-- -- ie x 15,000 X 15 X 32:2 = 1/160 = 12.6891 seconds. Same for manila line. jou SERA 15X20 =V 791 = 28.1297 seconds. (g) The drum dimensions are a con- siderable factor in determining the weight and cost of the machine, and the space occupied. Discussion on Mr. Kemble's Paper. Robert S. Riley.--So little is known of the scientific side of towing prob- lems that Mr. Kemble's paper should be very valuable 'in drawing attention to something beyond what is known among practical towing men. This paper shows very careful preparation and intimate technical knowledge of the subject, and its writer deserves great credit for the care he has taken in reducing to figures some of the hitherto unknown quantities regarding the sag of the line. Of course the great limitation of this paper is that the figures are all relative, and that the time element is missing. Practical towing men are apt to say that such data is of little real service to them. They say it is all very well to figure out how much the line will straighten due to the increased pull, and how much extra it will sag due to a slackening on the pull, but no one knows anything about how much that pull is going to be increased or de- creased, what is the use of knowing what will happen provided the changes were thus and so. It reminds one somewhat of the comment made by the Yankee on hearing the pyramids praised as a wonderful achievement; all he said was, "But there is no de- mand for pyramids where I come from," The average tow-boat or _ barge owner doesn't care much whether his line - sags "1/10: of: a ff, ar 2 3/10 ft: All he cares about is whether or not it will stand the strain under his con- ditions and he looks to his. captain to keep it as taut as possible and to get it in smartly in case he has to slow down, | tae Of course it is true that there are many shoals, both in the lake and coast channels where the sag should not ex- ceed a given amount, and this must be governed by the sense of the captain. practical common In towing over July, 1909 = shoals the water is apt to be smooth and he does not require so much line so the sag is practically dependent on the way he handles his tug. He knows that it will sag if he is obliged to slow down and there is very little chance of referring to catenary curves when such conditions arise. Fortunately the towing machine has abundantly proven its value in pre- venting the breakage of lines. We know that it pays out until the in- creased strain is counterbalanced by the compression of the steam in the cyl- inders, and that it makes an ideal ma- chine for rough weather towing. It would seem, however, that the service that is coming to be most appreciated is in the reeling of the line without manual labor. Of course the towing machine is, and always will be, a big factor in saving the breakage of lines, but the present labor conditions seem to show that its greatest value is in the saving of labor. This applies par- ticularly to smaller tugs working in and out of harbors where the lines have to be handled frequently. The machine does not belong to the union, it never talks back and will work any hour, of .day or night. The average deck hand much prefers to handle a lever and watch the line come in of itself rather than show what he can do in the way of hauling and coiling it himself. It is also a great factor in the manipulation of the tows to be able to handle the line quickly while under way, instead of being obliged to drift idly while the men are hauling in the line by hand. In this connection it will no doubt interest the members of the society to know that manual labor has been still further eliminated by the introduction of an automatic winding device. The towing machines built by the American Ship Windlass Co. are now almost in- variably equipped with a pair of moving guide rolls which automatically guide the lines onto the drum in even layers. They follow along the drum until one layer is complete, then when the line reaches the flange, automatically re- verse their direction so as to lay the next layer evenly on top of the one just laid. They do so _ independently of the action of the towing machine, no matter how quickly it may be re- versed during severe service. The proper laying of the cable on the drum, besides eliminating the manual labor required otherwise, also serves to pre- vent the line climbing up on one side and injuring itself by scraping and jumping into place after it has mounted during the process of reeling in. These automatic guide rolls are con-