CHANGE OF SHAPE OF RECENT COLLIERS. 

 By Naval Constructor Stuart Farrar Smith, U. S. N., Member. 



[Read at the twenty-first general meeting of the Society of Naval Architects and Marine Engineers, held in 



New York, December 11 and 12, 1913.] 



That ships bend in the middle has, of course, been well known for genera- 

 tions ; and the tendency of wooden ships to hog was so well known that their keels 

 were laid to a curve, which it was judged from experience would be approximately 

 straightened out after they were afloat. The old records of the Bureau of Con- 

 struction and Repair contain much interesting information as to the allowance for 

 hogging in the case of our old wooden sailing and steam vessels, as well as informa- 

 tion as to the changes in shape due to launching and loading. 



But with the introduction of iron and steel vessels, at first of short length and 

 heavy scantlings, the changes in shape were so slight that they were practically 

 neglected. At the same time, the importance of calculating the strength of these 

 comparatively new structures was brought to the notice of designers, and the 

 present strength diagram was developed. As the ships grew longer, it was appar- 

 ent that weight could be saved if the superstructures were not built to resist the 

 stresses arising in the upper part of the girder ; hence arose the expansion joint in 

 long deck houses on passenger steamers which has brought itself loudly to the atten- 

 tion of the unfortunate land-lubbers whose staterooms were near it. 



It has, therefore, been known for many years that steel ships worked, but the 

 subject of observing the amount of flexion and from that deducing the stresses to 

 see how they compared with the results provided for as a result of the strength dia- 

 gram, does not seem to have been investigated in proportion to its importance, or to 

 the opportunities which exist for obtaining data. 



The observations which are here presented to the Society are not as complete 

 as they should be, and consequently only rough deductions can be made. This is 

 partly because as the observations were made it appeared that additional data of dif- 

 ferent sorts should have been taken. In other words, hindsight was clearer than 

 foresight, and if the observations were to be repeated a good deal more could be 

 learned with very little additional trouble. 



Crude as they are, it is hoped that the results may interest some of us enough 

 to make similar observations in such form that strength calculations can be checked, 

 and possibly our designs improved. 



The loss of the Cobra and Viper in England led to an elaborate series of tests 

 on one of the British destroyers. Observations more or less extensive have been 

 made on several of our destroyers, and it is common practice to erect battens or take 

 sights before launching so that any great change in shape when afloat can be ascer- 



