NOTES ON FUEL ECONOMY. 235 



DISCUSSION. 



The President: — The paper by Mr. Rigg on "Notes on Fuel Economy as 

 Influenced by Ship Design," is now before you for discussion. 



Mr. Mason S. ChacE, Life Member: — I am very much interested in what Mr. 

 Rigg has said, but I feel that the work done by the shipbuilder, the naval architect, 

 and the engineer, is so closely associated and so overlaps that it is very hard for one 

 of the trio to make any progress without either pushing or pulling the others along. 

 I am sure we all agree that the data which has been obtained from experimental 

 model tanks has been of the greatest benefit to all engaged in building ships. 

 To-day few designs are made without using such data in one form or another, and 

 we can thank the Froudes for giving us the law of comparison in such practical 

 form that we can use it. In using the law of comparison to make deductions from 

 model basin experiments we must not stretch the law too far. The members of 

 this Society as a society of engineers— using the term "engineers" in its broadest 

 sense, as opposed to a society of lawyers — believe that it is as bad to stretch a law 

 too far as it is to break it. When we use large operative models, 30 to 40 feet long, 

 as a step intermediate between the small model, 10 to 15 feet long, and the ship, we 

 have more accurate data on which to base the performance of the ship than is 

 obtained from the small model. The Cunard Company was undoubtedly well 

 repaid for the expense of building the large operative model of the Mauretania and 

 Lusitania by the accuracy of the results which were obtained. When we use small 

 models and split hairs over the results based on their performance, we are likely 

 to fall into error. So, also, when we take the results of ship trials, unless the trials 

 have been carefully conducted and are really comparable, and draw too general 

 conclusions from them, we are likely to fall seriously into error. 



I agree with what Mr. Rigg has said as to how much naval architects have 

 benefited by the knowledge obtained from model tank tests. We in this country 

 are particularly indebted to Naval Constructor Taylor and the authorities of the 

 Washington Experimental Model Basin. All of us who have experimented there 

 have, I am quite sure, met with uniform courtesy on the part of those gentlemen. 

 Naval Constructor Taylor has presented in the form of papers before this Society 

 many of the results which he has obtained in his tank tests, and he has also written 

 a book on "The Propulsion of Ships," in which he has made an analysis of the 

 results obtained from a number of tank tests on a large series of models, which 

 series of tests would be far too expensive for any individual experimenter to conduct. 

 By means of contours of residuary resistance based on the results obtained from 

 this series it is possible for those working within the limits of ratios of beam to 

 depth, longitudinal coefficients and displacement-length coefficients, covered by 

 the series, to very closely approximate the residuary resistance of the proposed 



