97 



For double models and bodies of revolution a formula has been given 

 by Welnig . ^^ 



It is obviously erroneous to calculate the ratio of viscous pressure 

 resistance of ship forms to corresponding total viscous drag results valid 

 for cylinders of the same B/L ratios as can be found even in serious books. 



The concept "fairness of lines" which Includes some postulates as to 

 the continuity of their derivatives has been developed only empirically. 



The present theories of wave resistance do not yield any answer as 

 to the order of "smoothness of lines" required since they deal really with 

 image distributions, not with the actual ship form. 



There exist, however, some results on the influence of discontinuity 

 in curvature on the pressure distribution in the two-dimensional case. At 

 such points the pressure curve is characterized by a vertical tangent, i.e., 

 a sudden change in pressure must be expected. When these critical points lie 

 in a region of rising pressure, an increasing tendency to separation may be 

 expected. 



Even a discontinuity in the third derivative of a ship line leads 

 to an indentation in the pressure curve; it is, however, less probable that 

 the boundary layer may be adversely affected by it. ■'■■'•*' 



Our actual knowledge as to how the ship resistance depends on such 

 peculiarity of lines is practically nil. 



REFERENCES 



LIST OF ABBBEVIATIONS 



TIKA Transactions of the Institution of Naval Architects (London) 



TSNAME Transactions of the Society of Naval Architects and Marine Engineers 



(Hew York) 



J.S.T.G. Jahrhuch der Schiffbautechnischen Gesellschaft (Berlin) 



TNBCIMES Transactions of the North-East Coast Institution of Marine Engineers 

 and Shipbuilders (Newcastle) 



Proc. Eoyal Soc. Proceedings of the Eoyal Society, A, (London) 



ZAMM Zeitschrift fUr Angewandte Mathematik und Mechanlk (Berlin) 



