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March, 1914 to get the vessel down to the required displacement, and we took in five or ten tons of water in. the trimming tank, to get the required draughts and the displacement, and we found that the displacement increased 10 er: 20. tons. The means which. were adopted for the vessels to which I am referring, to observe its changed shape, was to fit an additional internal draught gage, as close between the other two as practicable, which means that. the gage was fitted amidships. We then read accurately the draught shown by the three needles, and took the difference between the readings. of the middle' gage, and the mean of the other two, and that would give us the amount that the ship was hogged or sagged between these two gages. We had a curve, the correction for dis- placement, the calculated amount to be added or subtracted, in proportion to the difference in reading. Of course, the ship might show the same difference in reading of the gages at different times, the difference in dis- placement not being the same, that is to say, might not always be bent into the same shape, but any correction of that kind, if you stop to think of the long flat curve, whether a parabola, a circle or a triangle, will give you a nearer result than to correct the curve altogether. That is what we found in a large number of these deck comparisons. Theré was never a time when the application of that correction did not bring together the results of different observations so that they were much more consistent with one another, and much nearer to the recorded weights. : Amount of Deflection Ernest H. Rigg:--Mr. Tawresey has given us a very interesting description of the methods adopted on the de- stroyer to find the amount of deflec- tion and to allow for it in the specifi- cations. It has been my fortune, or misfortune, to have to get that dis- placement right on some destroyers, to Mr. Tawresey's satisfaction, and we had plenty of fun in doing so. The midship draught gage he refers to in the destroyer, as you all know, comes pretty near the fire room, but in one case it came right in the fire room, and we started to read it under air pressure, and we had some trou- ble then. After we found that point out, we did not read it under air pressure, and we got along very nicely. In the discussion on Mr. Rodgers' paper, some reference was made to the shape of the lake vessels. These col- liers are similar in type, but single deckers, and anyone who has had THE MARINE REVIEW anything to do with keeping track of the weights, or anything of. that sort, in connection with these vessels, will know at once the difficulties of the situation. As an instance of hog- ging that takes place, due to differ- ence in temperature, I will cite a case which came to our attention of a car float, 330 ft. long, and lying in the sun with nothing on her at all. We tried to get a check of the weight. We found they were not anywhere near what they should be. We dis- covered that the' sun was strong and the water was cool. We took a transit and shot a line along, and found a hog of 8 in. in what should be a straight line. These deflections had taken place, and I think it is valuable and important that we should devise means of getting on to that. The midship gage is of practically little value in the trial trips, where weight is particularly important. As Mr. Taw- resey said, a slight increase of weight on a destroyer means a whole lot of horsepower at 30 knots. Draughts and Hogging Joseph H. Linnard:--I think Mr. Smith's paper will call more generally to the attention of ship builders the great importance of this temperature question with reference to draughts and hogging, and other phenomena, that are exhibited under the influence of temperature. I have had some ex- perience in the past in that matter, and the one that particularly drew my attention to it was the case of the tests of a floating drydock that was built for the government some years ago and tested in Chesapeake bay. The contract required that two very heavy ships, one of the short type of a battleship, and the other of the long cruiser type, should be docked and the deflection of the dock ascer- tained under the conditions in which certain maxima deflections were not to be exceeded. We found that our time was very limited, owing to the circumstance of the service of the ships, and the members 'of the board of civil engineers who had established very exact lines for the ascertainment of these deflections were, of course, limited as to the times when they could take their observations, although they had established transits and sight stations in the most careful manner. And on taking these observations in- explicable deflections were observed, such as were utterly contrary to what would have been expected judged by the results of the loading of the deck or the ship. We devoted considerable thought to the matter, and we came to the conclusion, after some calculations, that it was probable that the tempera- 121 ture distortion, that is, the distortions due to temperature in the upper mem- ber of the floating dry dock, subject to the hot sun, were -greater than the 'deflections in the known strength of the dock, due to the loading of the dock or the ship. Francis B. Smith:--We are very much' interested in this subject of the hogging and sagging of ships in load- ing and carrying their load. Our com- pany is. going to a good deal of ex- pense at the present time in making tests in connection with this matter, and I am interested in getting all the information I -can. "Our ships are long and flat, single deckers. They are pretty high for the dock we have to load from, loading iron ore, so, as a consequence, we have to begin from the back end of the ship to load, and work forward as she goes down, as the ship is too high forward for the height of the spouts. We begin at the back end and take every other hatch , as we work forward. The hatches are 12 ft. centers, and when we do this we do not have any bad effects, that is, we can load our ship pretty nearly in shape, but sometimes they put a little too much freight in mid- ships, before they get clear forward, on account of the bow being so high for the spout. The boat gets sagged this way in the middle, and after she once gets a sag in there we cannot get it out. We have to be very care- ful to see that they do not get this sag at all in being loaded. That is a point I would like to get all the information on that I can. Herbert C. Sadler:--I ask the last speaker if he has actually measured the amount of sag in his vessels, and what he considers to be the max- imum permissible sag? I think it is, perhaps, generally noted that the lake freighters have draught marks amid- ships as well as at each end. I think any information of that kind would be valuable, as to the maximum amount which is observed in any case, and its effect on the ship. Destructive Effect on Hull Francis B. Smith:--We had a very serious case during the last season, where the ship, when loaded, had the same draught at midships, and drew a foot less forward, and it had quite a destructive effect on the hull of the ship and loosened up a great many rivets. Usually, we do not calculate to get more than 2 or 3 in. sag in the middle. Francis T. Bowles:--I would sug- gest that the practical value of this paper would be much enhanced if either the author or Mr. Tawresey would add to their remarks an exact