CHAPTER IX 



DESIGN CHARTS 



The resistance and propulsion results for ships exactly similar to each of the 45 

 models of the geometrical series have been given in Chapter VIII. This form of presentation 

 is not very useful to the designer, however, since he will almost always have to do some 

 interpolation to fit his particular problem of the moment. A great deal of thought was given 

 to the most desirable method of plotting these data so as to make them of the greatest value 

 and yet simple to use. It was finally decided to present the resistance information in the 

 form of contour charts sim.ilar to those made so familiar by Taylor. 



To reduce the data to this form presented a formidable proposition in fairing since 

 there were 45 models in all and contours had to be drawn for a number of values of 



and (ji) . To expedite this phase of the work, the fairing was done on the UNIVAC 

 computer in the Applied Mathematics Laboratory at Taylor Model Basin. The process is 

 described in detail in Appendix C. The contours are given in Appendix B. 



The first set shows contours of residuary resistance in pounds per ton of displacement 



m 



B V 



each individual chart showing, for given values of — and . , the variation of 



H y^wL 



^R . . . L- 



~ — with block coefficient and — ratio. 

 A B 



The second ^et is of iJie same kind but shows contours of (c) for a ship with LBP of 

 L ^^ B 



400 ft against Cg and — for chosen values of \]{) and — . 

 B H 



The third set gives contours of wake and thrust deduction fractions plotted against 



L V B 



C g and — for chosen values of , and — . 



Both the and the (?) values have been derived on the basis of the Froude assump- 

 tion that the total resistance can be divided into two parts, the skin friction of an "equivalent 

 plank" and the residuary resistance, the latter obeying Froude's Law of Comparison. In the 

 present work, the skin friction resistance for both model and ship has been calculated in 

 accordance with the ATTC 1947 line, the appropriate values of C p and Reynolds number 

 being taken from previous Model Basin reports. ^^'^^ 



In using the first set of contours, the value of — is first determined fa- the 

 desired speed-length ratio. To it must be added the frictional resistance, which can be 



expressed in the form , where S is the wetted surface. The total resistance is then 



IX-1 



