SOME EXPERIMENTS WITH MODELS HAVING RADICAL 

 VARIATIONS OF AFTER SECTIONS. 



By Naval Constructor D. W. Taylor, U. S. N., Vice-President. 



[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.] 



When we determine the form of a ship there are two things which must be 

 done in connection with ever}^ station or section. We must, by some means, fix 

 the area and then determine the form or shape to be given the section having the 

 given area. Taking ships as they are, for given dimensions and displacement there 

 is not room for very large optional variations of sectional area except near the ex- 

 tremities. The designer has a fairly free hand, however, when it comes to the 

 shapes of the sections, particularly toward the extremities. 



There are, of course, matters to be considered in connection with these shapes 

 other than the question of resistance, such as seaworthiness, carrying capacity, 

 etc., but it should be understood that in this paper questions of resistance only are 

 taken up. Broadly speaking, as regards the shape of sections, the accepted prac- 

 tice is to approach the U-type forward and the V-type aft. From our experience 

 at the U. S. Model Basin this practice, as regards resistance, would appear fully 

 justified as to the bow, the U-type of section being nearly always desirable for- 

 ward. Moreover, the resistance seems to be more affected by changes forward 

 than by the changes aft, or, to put it in another way, to depend more upon the for- 

 ward form than upon the after form. 



Systematic variations of form of entrance generally result in systematically 

 varying resistance and allow definite conclusions to be drawn. When it comes to 

 the run, however, we find it much harder to draw definite conclusions. Changes 

 in the form of the after sections appear to affect the resistance less than do 

 changes forward, and changes of resistance for systematic changes of after form 

 are not always systematic. So, while we feel that the standard practice is prob- 

 ably right and that V-sections aft are desirable from the point of view of resist- 

 ance, we do not feel that here we are upon such firm ground as with regard to 

 the U-sections forward. 



In view of the difficulty of obtaining definite characteristic results from com- 

 paratively small changes of shape aft, we have recently made some experiments 

 with after forms of radically differing shapes, and it is the object of this paper to 

 put before the Society the results obtained. Six after bodies were tested for re- 

 sistance, all with the same fore body and all having the same curve of sectional 

 areas. All models were 20 feet long in accordance with the standard practice at 

 the U. S. Model Basin. The beam was 1.828 feet; draught, 1.179 feet; displace- 



