It is definitely advantageous to use fore and afterbody coefficients 

 like 



The differences (C^p - Cg.), (C p - C . ) can be connected to a good approxi- 

 mation with the ratio ^, where x denotes the distance of the L. C.B. from the 

 midships section. (It is an offense against the spirit of approximate calcu- 

 lus to refer the longitudinal position of the CB to the fore or aft perpen- 

 dicular.) The normal ship form consists of a main part sjmmietrical with re- 

 spect to the midship section roughly characterized by Cg, Cp and an asym- 

 metrical part described by 



^BF " ^BA _ '^F - ^A 1^ ^0 [2] 



where k is a factor depending on the fineness and the form of the sectional- 

 area curve. Values of coefficients depending on the longitudinal distribution 

 of volume, etc., are useless if the reference lengths (Lpm-. Lpp ) are not 

 clearly stated. Where Lp^r ^ Lpp. both values like Cg^(dy) and Cgp((Jp) should 

 be given. 



The basic form coefficients have been developed with respect to prob- 

 lems of buoyancy and stability; it is a furtunate coincidence that they are 

 characteristic for resistance problems too. Parameters introduced from hydro- 

 dynamic considerations are: 



a. t =-g- tany= -g; ll^l ^ (Taylor's tangent value) [3] 



X = 2 



b. Length of parallel body. 



c. Position of the point of inflection. 



d. Curvature at the midship section. 



e. Position of the centrold of the forward and aft parts of a 

 waterline (sectional-area curve). 



f . Bulb-area ratio f defined by Taylor as the ratio of intercept of 

 the sectional- area curve at the bow to the maximum ordinate. 



Items c to e have not been much used. The list may be Increased by using: 



g. Moments of Inertia, or 



h. Higher moments with respect to suitable axes. 



However, graphical procedures become cumbersome when all these coefficients 

 have to be considered, so that It Is preferable to introduce mathematically 

 defined ship lines. 



