should be that at which the (C) value begins 

 to rise steeply, i.e., where the resistance is 

 beginning to increase at a rate higher than 

 the square of the speed. It is realized that 

 today many considerations other than economic 

 performance, so defined, come into the choice 

 of ship speed, either for defense reasons or 

 because of a demand for high speed for certain 

 specialized cargoes. However, all the models 

 were run to considerably higher speeds in the 

 course of the tests and these results are given 

 here in the form of tables and charts, so that 

 similar comparisons can be made at higher 

 speeds if desired. 



The minimum resistance values for 

 ships with the lines and proportions of the 

 Series 60 parents are shown in Figure 31. An 

 analysis of the resistance of single-screw 

 ships has been published by Lap of the NSMB, 

 Holland, ^^ and it is of some interest to compare 

 these two sets of data. He carried out a survey 

 of the results obtained from single-screw ship 

 models run in that establishment over the last 

 20 years, determined the most important 

 parameters, and produced curves of optimum 



Cjf values. He found these parameters to be 



L B 



- — , — , C p, LCB location. % tt r-, and C y . 



the same, incidentally, as those chosen as the basis of the Series 60 variations. Fe gave 

 diagrams of sectional area curve ordinates for different values of the prismatic coefficients 

 of fore and aft bodies which agree very closely with those for Series 60. 



Professor Troost has compared the NSMB results with those of the Series 60 parents. "* 

 For the Dutch results, he found that the optimum LCB position could be approximated by the 

 equation 



a= 17.5 Cp - 12.5 [3] 



where a equals the distance of LCB from j^J as a percentage of Lgp,* and is positive if 

 LCB is forward of and negative if aft. For Series 60, the optimum positions from this 



* LCe FROM 3i AS % Lbp f 



Figure 34 — Recommended Locations of LCB 



*For Series 60 parents, as originally tested, the LCB positions correspond to the equation a = 20 Ca ~ 13.5. 



VI-17 



