ECONOMICAL CARGO SHIPS. 

 By Alfred J. C. Robertson, Esq., Member. 



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



in New York, November 13 and 14, 1919.] 



The circumstances of the late war and the necessity of largely rebuilding the 

 shipping trade of the world have called the attention of naval architects to the need 

 of a careful mathematical and scientific analysis of the cost of operation of ships, 

 and, as a result, several investigators have recently given us the benefit of valu- 

 able papers on the subject. Particular reference might be made to the paper by 

 Mr. John Anderson to the Institution of Naval Architects, London, March 20, 

 1918; by Alexander Urwin to the Northeast Coast Institution of Engineers and 

 Shipbuilders, January 14, 1919; and by Messrs. G. S. Baker and J. L. Kent to 

 the Institution of Engineers and Shipbuilders in Scotland, February 18, 1919. 



Mr. Anderson, in his paper, devotes special attention to working out a theory 

 of operating efficiency based on the number of cargo derricks and winches that can 

 be used and the derrick speed which can be employed in loading or unloading ves- 

 sels. Mr. Urwin tabulates in a very methodical manner the various elements that 

 go to produce an efficiency figure, and has given us one or two examples worked 

 out. Messrs. Baker and Kent have also treated the matter in this way, but, in ad- 

 dition, give considerable attention to the actual ship form for economical move- 

 ment of freight. 



In the opinion of the writer greater progress could probably be made if naval 

 architects were able to place before ship operators the actual operating costs under 

 certain assumed conditions and with various combinations of size, speed and form 

 of ship. Figures compiled in this way showing the cost of operation for certain 

 German ships on four stated routes were published in Shipbuilding and Shipping 

 Record of January 2, 19 18, and figures have also been compiled by the United 

 States Shipping Board covering the operation of certain ships over various routes. 

 In each case, however, these figures were for vessels varying in their general char- 

 acteristics, and it appears to the writer that any true comparison can only be made 

 if the variation in the characteristics of the vessels is directly limited to that fea- 

 ture which it is desired to investigate. He has therefore prepared some calcula- 

 tions in this direction and takes the liberty of placing before the Society of Naval 

 Architects and Marine Engineers such figures and results as he thinks may prove 

 of value. 



The method adopted has been to take vessels of four different sizes, of stand- 

 ard proportions, and to work out on the same basis the first cost and the cost of 

 operation for each vessel at each of four different speeds. In addition, the writer 



