CHANGE OF SHAPE OF RECENT COLLIERS. 149 



the weight of fuel oil in the different tanks, and the weight of water distributed in certain 

 ways, also the water in the trimming tanks to make up the loading to bring the vessel to 

 some desired displacement. A destroyer consists of the machinery, loaded on the shell of 

 the vessel, the deck over and a few thin bulkheads in between. She is 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. 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 observations extended 

 over a number of months, and when we did strike a really cold day we expected to find that 

 the destroyer, with the same load, was sagged; but she still showed hogging, and to about 

 the same extent. We then noted, that to protect the machinery and pipes from freezing, 

 steam was on the vessel, the living quarters were heated throughout, the fire rooms and en- 

 gine rooms were warm; we observed the temperatures of the deck plates, and found that 

 the deck was much warmer than the water, and consequently the destroyer was still hogged. 

 I was unable to construct any curve by which one could predict the hogging from the dif- 

 ference in temperature of the water and the upper deck. That was, no doubt, due in part to 

 the effect of the loading, and in part to the method of observation not being sufficiently accu- 

 rate to take account of very small changes. 



In passing this part of the subject, it may be of interest to state that I made some in- 

 vestigations on a battleship, 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 battleship to the changes in shape that take place due to changes in temperature on a 

 destroyer. 



My interest in the matter was not so much in the stresses and strains as in the eflfect on 

 displacement. The contract trials of our destroyers are run at a displacement equal to the 

 weight of the boat plus a certain specified loading. A number of the shipbuilders have con- 

 structed at one time two or more destroyers 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 trials should be run. It is no wonder that 

 the builders commenced to ask questions when, only a few weeks apart, we would give them 

 a very different displacement at which the trial should be run. 



I may say that every care is taken to determine these displacements as accurately as pos- 

 sible. The draughts are all taken by internal draught gauges which, you probably know, con- 

 sist of a glass tube with a proper sea connection and a needle valve to choke off the flow of 

 water; precaution is taken to flush the gauge, to be certain that the temperatures of the water 

 in the tube and in the pipes leading to it are as near as possible the temperature of the water 

 outside. Instead of taking off the displacement 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 accurately for a fraction of an inch difference in draught. 

 This displacement is checked with the reported weight, and it had been customary to take 

 any difference between the displacement of the vessel, observed as accurately as possible, and 

 the recorded weight, as an error in the recorded weight. In taking observations on a vessel, 

 taking one or two early in the morning, and another observation later on the same day, when 

 there was no appreciable change of the weight, and when allowance could be made for what 

 weight had been carried on board or taken off, we would find the displacement say five tons 



