146 DATA ON HOG AND SAG OF MERCHANT VESSELS. 



Professor W. Selkirk Owen, Member: — In connection with temperature deflection, I 

 had occasion to notice the deflection in the colHer Cyclops at Cramp's. That, as we know, is 

 a large single-deck vessel, and the upper deck, being unsheathed, is exposed to the temper- 

 ature of the elements, etc. The way attention was first directed to it was when the vessel 

 was fitting out and lying at the builder's dock. It used to be the practice of the staff in 

 the draughting office to go down and take readings of the draught to check up the weight 

 going on board the vessel. We noticed there was an erratic variation from day to day in 

 the mean draughts obtained from reading the draught marks on the ends of the vessel. 

 The draughts were measured by a man in a boat alongside the ship. The water in the Dela- 

 ware is never quiet; there are changes of density in the water, too, and tide and currents, 

 etc., but even at that the indications were so erratic that it was thought the temperature 

 might have something to do with it. Following several cool days in the summer we took 

 draught readings on the ends of the vessel, and then in the middle of the afternoon, which 

 seemed to be the hottest time of the day, we took similar readings again, and the mean 

 draughts were decidedly different. Something was going on. The ship was being completed 

 and without interfering with the work on deck we undertook to see if we could trace this 

 variation, so we took about six stations along the length of the ship, and got the carpen- 

 ters to measure down on the outside of the vessel from the deck line with battens while she 

 was floating in the water and put draught works on the ship's side. This was done on both 

 sides of the ship. Draught readings on all these stations were measured at four o'clock one 

 morning, following several cool days, and about two hours later on, but there was prac- 

 tically no change. They were measured again at three o'clock of the same day, when it 

 was quite hot, and we saw this tendency to hog the vessel, due to temperature, which indi- 

 cated itself by an otherwise straight water line on the ship becoming a fair curve, with 

 relation to the water surface. Of course our method was crude for actually measuring the 

 points. It was clearly defined. It went to show that the tendency existed, and we laid down 

 the curve, and there was a matter of 5 inches springing in the straight line of the ship. 

 It was submitted to the naval constructor at the time, and he allowed 2 inches to be 

 deducted from the mean draught of the ship obtained by readings from the ends of the 

 vessel; thus the contractors were allowed that consideration for change of form due to 

 temperature in making the weight of the vessel for their contract displacement. 



Mr. Elmer A. Sperry, Member: — There is evidence of lateral deflection, too, in cases 

 of the sun on one side of the vessel and the other side in the shade. We recently had an 

 opportunity to determine that in a long base range finder, where our stations were 444 

 feet apart and the vessel immersed and floating, and exposed all day on the south side. 

 These stations were equipped with apparatus by which we could read to less than the half of 

 1/1000 of a degree. We found the maximum deflection to be about .015 degree. This 

 makes no difference with the range finder as it is provided against this contingency. But 

 we see that there is a lateral deflection also due to temperature. 



Commander F. L. Sawyer, U. S. N. (Retired), Member: — It will be recalled that Naval 

 Constructor Smith read a paper before the meeting of this Society in 1913 on the subject of 

 the alterations in the deck lines of a collier after launching. In the discussion at that time 

 one of our members, Mr. F. B. Smith, the chief engineer of the Pittsburgh Steamship Com- 

 pany, related the difficulties which his company experienced in loading their large fleet of 



