THE INFLUENCE OF SHAPE OF TRANSVERSE SECTIONS UPON 



RESISTANCE. 



By Professor Herbert C. Sadler, Member of Council, and 

 Professor E. M. Bragg, Member. 



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



in New York, November 17 and 18, 1921.] 



From time to time results of experiments on the influence of shape of bow and stern sec- 

 tions upon the resistance of ships' forms have been recorded, but usually these have re- 

 ferred to special cases, sometimes accompanied by other changes of form and generally for 

 vessels of somewhat high speed. 



Froude's original dictum of U-shaped sections forward and V-shaped aft still lingers 

 in the minds of most designers as applicable to all forms at all speeds. Some years ago 

 some experiments on models of full form were conducted in the experimental tank at the 

 University of Michigan (see Vol. 17, Society of Naval Architects and Marine Engineers), 

 in which it appeared that the V-shaped sections, both forward and aft, gave the better 

 results. 



The following investigation was therefore undertaken with the object of covering the 

 field more fully, especially for the slower and moderate speed types. 



The parent body plans and curve of sectional areas are shown in Fig. 1, Plate S3, and 

 indicate the changes in type of sections used. They are based upon a vessel 425 feet B. P. 

 by 56 feet, with a normal load draught of 24 feet 9 inches and a deep load of 27 feet 9 inches. 

 The vessel has a cruiser stem and a length on the deep load line of 435 feet, this length 

 forming the basis for the spacing of sections. 



The shape of the cruiser stem had to be modified slightly with different lengths of run 

 for fairing purposes, but at the 24-foot 9 inch draught the change in length was negligible. 



The various percentages of ends and middle bodies are given in terms of the length 

 between perpendiculars. All the results have been reduced to a temperature of 65° F. 



In general, two parent forms were taken as follows : 



1. A model with a fixed length of run and with "medium" type of stem sections. 



2. A model with a fixed length of entrance and "medium" type of bow sections. 

 Each model was further modified in the following manner : 



Fixed run 40.5 per cent Five lengths of entrance Each type with U, Me- 



L. B. P. from 23.7 per cent to dium, and V-shaped 



48.5 per cent L. B. P. sections forward. 



Fixed entrance 27 per Four lengths of run from Each type with U, Me- 



cent L. B. P. 24.3 per cent to 48.6 dium, and V-shaped 



per cent L. B. P. sections aft. 



The parent forms, with the above lengths of entrance and run, were selected from a 

 former series of experiments covering some hundred types and appeared to be those that 



