ECONOMICAL CARGO SHIPS—SOME MODEL EXPERIMENTS. 
By Atrrep J. C. Ropertson, Esg., MEMBER. 
[Read at the twenty-eighth general meeting of the Society of Naval Architects and Marine Engineers, held in New 
York, November 11 and 12, 1920.] 
This paper is in a sense a continuation of the paper of last year in which the 
writer analysed the effect of size and speed upon the economy of freight ships. 
The purpose of this second paper is to present the results and particulars of 
some model experiments carried out with the object of arriving at the best form 
for propulsion of full cargo ships such as were referred to in the previous paper, 
and these results are placed before you in a form which it is hoped will readily 
admit of their application to the design of cargo ships. 
The type of lines suitable for vessels of slow and moderate speeds and of full 
form has received much attention of late years at the various experimental model 
basins; and special mention is due to the very thorough series of tests made at 
the Froude National Tank, London, and reported through the Institution of 
Naval Architects by Messrs. G. S. Baker and J. L. Kent in several recent years, 
and to Mr. McEntee’s recent papers presented to this Society, as well as to the 
earlier contributions to our knowledge of the subject made by Admiral Taylor, 
Dr. Sadler and other investigators. 
In results of full form Admiral Taylor has shown that a certain amount of 
parallel middle body is necessary to produce minimum resistance, and Messrs. 
Baker and Kent have supplied the results of tank tests of vessels with 10 per cent, 
30 per cent and 50 per cent parallel body located amidships. 
Mr. McEntee’s recent papers, confirmed by Mr. Semple (T. I. N. A., 1919), 
have shown that the location of the parallel body forward of amidships has dimin- 
ished the resistance of the model and also increased the efficiency of propulsion. 
This paper covers somewhat similar ground for vessels of several prismatic 
coefficients exceeding .70, covering the field somewhat more fully and also supplying 
some further information regarding the form of areas curve associated with mini- 
mum resistance. 
The experiments about to be described were conducted in two series inde- 
pendent of one another. The first set, designated Model 1107, consisted in the 
modification of the curve of areas of the after body (both in its area and in its 
curvature) of a successful cargo ship of high prismatic coefficient. The second 
set, based on Model 1130, was more extensive and consisted in the development 
of several entrances and runs each of identical form as to cross-section and curve 
of areas but of varying length, and combined with various lengths of parallel 
middle body, and these various fore and after bodies so united as to secure two or 
