20 



For comparison with experiments the coefficients c referred to the wetted 

 surface S is advantageous. 

 We write 



c = R_ = r iizic 2 b' 



W p/2 U 2 S ° SP 



(If w- 



or introducing a surface coefficient S (Reference 17) 



C s = S/ttDL 



r 



C 



(!)' H; »'.£(*) '. i«] 



iv Cn \ a. i v -pi; u i/n 



with y Q = 1/2P 2 . For elongated spheroids C g = O.79. 



The importance of the resistance coefficient c referred to the 

 wetted surface S justifies a short digression on the calculation of S for 

 bodies of revolution. Solutions of the exact expression (Equation [29]) can 

 be obtained in a closed form in exceptional cases only, as for the spheroid. 

 Of course it presents no difficulties to evaluate the integral numerically, 

 but a simple approximate formula can be derived at least for the surface area 

 of a restricted class of very elongated bodies of revolutions complying with 

 the condition that the end tangents of their meridianal contour do not become 

 vertical; it is similar to the well-known expression for the length of a 

 slightly curved arc, see Appendix I. 



4.2 RESISTANCE CURVES OP SIMPLE SYMMETRICAL BODIES 



Since the presentation and the discussion of resistance curves is 

 the main subject of the present report, various sets of such curves have been 

 computed. Essentially, the resistance properties of the following three 

 groups of body forms (distributions) have been investigated: 



(a) A set embracing a wide range of prismatic coefficients, which fur- 

 nishes a general review of the resistance as function of the form (IV,2). 



(b) A set dealing with four TMB models. This raises the problem of 

 the influence of asymmetry with respect to the midship section (IV, 3). 



(c) A group consisting of systematically chosen forms belonging to the 

 two-parameter family (2, 4, 6; <f> ; t) (VI); for the same family some calcula- 

 tions of shapes of least resistance are presented (V). 



The procedure adopted leads to repetitions which, having in view 

 the importance of the subject, have been thought to be advisable. Because 

 of the complicated dependencies involved the interested reader can more 



