DATA ON HOG AND SAG OF MERCHANT VESSELS. 147 



ore carriers on the Great Lakes on account of the fact that alterations of draught occurred 

 between Duluth or West Superior and the Sault Ste. Marie canal of as much as six or seven 

 inches, so that it was necessary to allow for this change after loading in order to be able to 

 pass through the canal, and invited suggestions from the Society for some remedy. Differ- 

 ent methods of loading the various hatches had been tried without success. It occurred to 

 me at that time that probably the extraordinary changes in draught could be accounted for by 

 the changes in temperature, and the abnormal temperature differences between the keel and 

 upper deck that exists in the season of open navigation on Lake Superior. It is generally 

 known that the waters of Lake Superior are extremely cold even in summer. A long ore 

 vessel passing down the lake from April to October would be in effect a box girder of some 

 600 feet in length, about 32 feet in depth, with the lower member in a temperature of per- 

 haps 40° F., and the upper member, especially when exposed to the rays of the sun, a great 

 many degrees warmer. Applying the coefficient of expansion of steel to this girder, it was 

 seen at once that a draught change due to hogging of half a foot or more could be easily 

 accounted for. I suggested to Mr. Smith that a remedy ought to be found by playing the 

 cold water of the lake over its deck and top sides of these ore vessels by using their deck 

 hose a sufficient time before arriving at the canal. Mr. Smith now informs me that this 

 simple remedy was applied and proved a cure for their trouble, and that they are able to 

 load the ore carriers half a foot deeper in consequence. 



When the fact is considered that more than forty million tons of ore are now passed 

 through this canal each season, an increase of even two to three per cent is a considerable 

 item. 



It seems an opportune time to call attention to the considerable effects which may be 

 produced in a ship's structure by temperature differences in the hull, not only for commercial 

 and navigational purposes, but possibly for its effect in gunnery. The salvos of a battleship 

 are "bunched"' only after the most accurate and delicate bore sighting and adjustment. Any 

 warping in the hull thereafter would necessarily increase dispersion to some extent. Range 

 finding would be affected from the same cause. 



Mr. Cornbrooks: — The data which Professor Everett has given with reference to the 

 Atlantic and Pacific are of considerable interest in connection with this paper, and I am sorry 

 that we have omitted to give the temperature of the water and of the deck at the time 

 these observations were taken. I will endeavor to secure these and add them. You will 

 note, however, that on each curve the date on which it was taken is given. 



In the original paper by Constructor Smith we took some observations early in the 

 morning (8.30 a.m.), and during the heat of the day (2.30 p.m.) on the Neptune, which 

 showed, I think, about % inch difference, for somewhere near 7 degrees difference in the 

 temperature. I am not sure of that difference in the temperature — that sounds like a rather 

 big difference in temperature — but at that time we did not take any observation early in 

 the morning or during the middle of the day. Those experiments were simply carried out 

 in order that we might secure the benefit of any sag when it came to loading the vessel for 

 a trial trip, and accomplished these results. 



I am sorry there are no data available for these long, shallow vessels which are used 

 on the Lakes. If you will note in the last paragraph in the paper there is reference to a 

 discussion before the Institution of Naval Architects in London this year, in which Mr. 

 French said that some of the Lake vessels were sagged as much as ten inches, which would 



