CHANGE OF SHAPE OF RECENT COLLIERS. 151 



inches in what should have been a straight Hne. These deflections undoubtedly take place, 

 and it is important that we should devise means to check them up. The midship gauge is 

 of practical value in destroyer trial trips, where weight is particularly important; as Mr. 

 Tawresey said, a slight increase of weight on a destroyer means a big increase of horse- 

 power at 30 knots. 



Naval Constructor J. H. Linnard, Member: — ^I think Mr. Smith's paper will call 

 more generally to the attention of shipbuilders the great importance of this temperature ques- 

 tion with reference to draughts and hogging and other phenomena that are exhibited un- 

 der the influence of temperature. I have had some experiences in the past in that matter, and 

 the one that particularly drew my attention to it occurred during the tests of a floating dry- 

 dock 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 in succession, and the deflection of the dock 

 ascertained with the condition that certain maxima deflections were not to be exceeded. We 

 found that our time was very limited, owing to 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 obser- 

 vations, although they had established transits and sight stations in the most careful manner. 

 On taking these observations, inexplicable deflections were observed, such as were quite dif- 

 ferent from what might have been expected from the loading of the dock by the ship. We 

 devoted considerable thought to the matter, and we came to the conclusion, after some cal- 

 culations, that it was probable that the temperature distortions, that is, the distortions due to 

 temperature in the upper member of the floating dry-dock, subject to the hot sun, were 

 greater than the deflections calculated from the known strength of the dock, due to the load- 

 ing of the dock by the ship. 



Mr. Francis B. Smith, Member: — We are very much interested in this subject of the 

 hogging and sagging of ships in loading and carrying their load. Our company is going to a 

 good deal of expense 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 and, 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 feet 

 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 we put a little too much freight in midships, before 

 we 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 

 by loading in the two ends forward and aft; she gets a permanent set there which cannot be 

 taken out until she is unloaded, and we have to be very careful of that matter, to see we do 

 not get this sag at all in being loaded. That is a point I would like to get all the informa- 

 tion on that I can. 



Professor Herbert C. Sadler, Member of Council: — I should like to ask the last 

 speaker if he has actually measured the amount of sag in his vessels, and what he considers to 



