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_ Changes in Collier' S Shape VAL CONSTRUCTOR' S? -F: N ts contributed a paper on : Change of Shape of Recent Colliers', at the December meeting of the Society. of Naval Architects and Marine Engineers, abstracted as follows: This paper contains the results of observations of hogging and sagging on some of the 500-foot colliers re- cently built. for the U. S. navy. It shows that the upper deck, at the mid- dle of the length, may move up or down as much as 6 in. with reference to the ends, depending on the condi- tions of loading; and that a tempera- ture rise of 1 degree Fahr. may cause the deck to rise % in. It contains some observations of the motion of the tank top with reference to the upper deck, and suggests that more extended observations of these points may permit of working backward from the girder deflections and loads to the actual fiber stresses, thus checking the preliminary strength calculations. John G. Tawresey:--It has been my fortune to have had to do some work along the lines considered in this pa- per, and as I found the tendency in some quarters to regard it as a need- less refinement, I am somewhat sur- prised to find the subject treated in this paper and brought before. the so- ciety. | wish that the author had gone on and shown us a way to get around the difficulties which he brings out in the paper. It is true that vessels bend due to lading and due to other causes, and that bending is a great deal more in some classes of vessels than in others. Colliers are mentioned in this paper. The vessels I had to deal with particularly were torpedo boat de- stroyers. Then we have car. floats, floating drydocks and other structures. I have found on the destroyers, which were of much less strength than the 'colliers, quite as much change in shape as is reported in this paper. That change was found to be due to the lading, but the lading would not account entirely for it, and further investigation showed that there was a very considerable change due to differences in temperature. The change due to the difference in temperature was, perhaps, over the range of ob- servation I made, two and sometimes three times as much as that due to the lading, but the lading in a destroyer, you must remember, is the weight of The Effects of Loading and of Tem- perature Upon the Hulls of Vessels her machinery and the weight of fuel oil and different tanks, and the weight of water distributed in certain ways, and the water in the trimming tanks make up the lading to bring the vessel to some desired displacement. The destroyer consists of the machinery, the shell of the vessel, the deck and a few thin bulkheads in between. She ig much in the nature of a girder. The bottom flange of the girder is in the water, and must have practically the same temperature as the water, the upper flange is in the air, exposed to the heat of the sun; and we were not very much surprised, when we took observations on a warm day, with the sun beating down on the deck, to find the destroyer hogged. The ob- servations that I took extended over a number of months, and when we did strike a real cold day, we would: find that the destroyer, with the same load, was sagged, but she still showed hogging, and to about the same ex- tent. I was unable to construct any curve by which I could project the hogging from the difference in tem- perature of the water and the upper deck. That was no doubt, due in part at least, to the effect of the lading, and in part to the method of obser- vation not being sufficiently accurate to take account of very small changes. Passing this part of the subject, it may be-.of interest to state that I made some investigations on a _ bat- tleship, and did not find corresponding conditions. The battleship has a great many more decks, the deck that is heated from the machinery lies nearer the neutral axis of the girder, and as far as my observations went I did not find anything corresponding in a bat- tleship to the changes in shape that take place due to changes in tem- perature on a destroyer. My interest in the matter was not so much in the stresses and the strains as in the dis- placement. Contract trials of our de- stroyers are run at a displacement equal to the weight of the boat plus a certain specified lading. A number of the ship builders have constructed at the same time two or more de- Stroyers from the same plan. Some of these destroyers have run more than one trial, and it was a part of my duty to determine the weight of the vessel, the displacement and draught at which the trial should be run, and it is not to be wondered that the con- -other observation later tractors and ship builders commenced to ask questions when, a few weeks apart, we would give them a very different displacement at which the trial should be run, when the trial -was supposed to be the weight of the vessel plus a definite, specified lading, I might say that every care is taken to examine these displacements as ac- curately as possible. The draughts are all taken by internal draught gages which, you probably know, consist of a glass tube with a proper seat connection and proper needle valve, to choke off the flow of water, and every precaution is taken to flush the gage out, and be certain that the tem- perature of the water in the tube and in the pipes leading to it are as nearly as possible to the temperature of the water outside. After determining the draught inside, by checking the dis- placement off from a small scale curve, we prepare a large diagram that gives the calculated displacement for each inch and this allows us to interpolate and get the displacement very accu- rately for a fraction of an inch dif- ference in draught. These displace- ments are checked with the reported weights, and it had heretofore been customary to take any difference be- tween the displacement of the vessel, observe it as accurately as possible, and the recorded weight, and error in the recorded weight, but in taking observations on the vessel, taking one or two early in the morning, and an- in the same day, when there was any appreciable change of the weight, and when allow- ance could be made for what weight had been carried on board or taken > off, we would find the displacement was five tons less than the required weight, one time, and the next time 10 or 15 tons greater, on a_ vessel of 5,000 or 6,000 tons displacement, at the time the observation was made. Consequently we found it necessary to take up this question and attempt to find some way of treating it. The matter of lading is quite im- portant to the ship builder in run- ning trial trips. Every added ton adds appreciably to the horsepower necessary to be developed to 'secure any given speed. Also, there is an- other matter to which I will refer. On the trial trip, in loading the ves- sel for the run, we found it necessary to take in water for the trimming tank