THE EXPANSION OR CONTRACTION OF DIMENSIONS AND THE 



EFFECT UPON RESISTANCE. 



By Professor Herbert C. Sadler, Member of Council. 



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



New York, December 10 and 11, 1914.] 



In the preparation of the plans for a new vessel it frequently happens that the 

 designer has at hand the trial data as to speed and power for a vessel, similar, so 

 far as the coefficients of form are concerned, but whose ratios of dimensions are 

 not the same as those of the proposed vessel. 



From former experience and results of model tests already published, it may 

 be possible to estimate the effect of change in ratios of dimensions with a fair 

 degree of accuracy, but in order to obtain additional data upon this subject and 

 to bring the results into a more concrete form the following investigations were 

 undertaken : 



Three different types of ordinary mercantile forms were designed ranging in 

 longitudinal coefficients at the deepest draught from .551 to .674. Each model 

 was tested at three different draughts, but the same actual draughts were used in 

 each case. 



A number of models of each type were made of varying breadths, by simply 

 expanding or contracting the parent form in this direction only, the length and 

 draught in each case remaining constant. 



In a similar manner the length and breadth were held constant and the 

 under-water form changed by varying the distance between the original waterlines 

 only, i. e., expanding or contracting the draught. Also, the breadth and draught 

 were kept constant and a series of models made by expanding or contracting the 

 distance betwen the transverse stations, i. e., expanding or contracting the length. 



Finally, the three forms were tried of the same displacement, breadth and 

 draught, but of different lengths and hence different coefficients of form. 



The coefficient of midship section was kept constant throughout the series. 



In all of the foregoing, therefore, the displacement for each type was allowed 

 to vary in the same ratio as the variation of the particular dimension. 



