Pien 



for a cylinder; 



n = 0.6 D/L + ... 



for a body of revolution; 



n = 19(CgB/L)2 



Granville's formula for shiplike bodies. 



The primitive character of these relations indicates that quite a bit of re- 

 search work should be done before the author's optimistic statement can be ac- 

 cepted, e.g., with regard to dependency of the drag of full forms upon propor- 

 tions. Contrary to his optimism, Dr. Guilloton has recently expressed the 

 opinion (Bull. Ass. Technique Maritime, 1964) that our knowledge of viscous 

 drag as function of the hull form is almost nil. 



The difference in the total resistance R^ of Model 4946 and Model 4953 can 

 be explained by viscous as well as by wave effects. The former are estimated 

 by Rjotai at low F (as pointed out by the author), the latter by the intersection 

 of resistance curves at F = 0.30. The difference in the prismatic coefficients 

 is helpful for such a phenomenological discussion. 



The author emphasizes as a new result that the wave drag of a fat ship can 

 be smaller than for a thin ship. In the light of Taylor's findings (and those de- 

 duced from theory) this may be trivial in a range where R^ depends strongly 

 upon the prismatic coefficient. Examples based on theoretical calculations 

 have been frequently given; some caution, however, in the quantitative applica- 

 tion is advisable. 



The shift of the measured wave drag curve to higher F as compared with 

 theory has been firmly established by Wigley and Havelock. 



The author asserts that in the field of comparison between theory and facts 

 almost only the work done by Prof. Inui counts. Although I am an admirer of 

 the valuable contributions made by our distinguished chairman the author's state- 

 ment is in my opinion erroneous; the most valuable experiments are those by 

 Mr. Wigley (TINA 1924) and the TMB Report where the so-called friction plate 

 furnished by mistake the ideal thin ship model. 



It is erroneous to assume that wave resistance results by computation are 

 always larger than those derived by experiment; this certainly does not apply to 

 hull forms which by theory are extremely advantageous (due to strong interfer- 

 ence effects which may be destroyed by viscosity). 



The hull form proposed by the author appears to be promising for medium 

 Froude numbers (Cp= 0= 0.58, moderate bulb, gentle turns of bilge). The raised 

 bulb, however, may be unfavorable in a seaway, especially under ballast condi- 

 tions. 



The attempt of applying theoretical reasoning to actual design problems is 

 highly appreciated. 



1138 



