Sec. 67.7 



UNDERWATER-HULL DESIGN 



511 



).5 Stations .qj 



Fig. 67.E Bow Peofilb, Bulb Bow, and Cutwater for ABC Ship 



series B, for which Cp is 0.65, the displacement- 

 length quotient is 150, and the B/H ratio is 3.20. 



The next step is to determine the residuary 

 resistances of two vessels without bulbs, having 

 parent forms identical with those of the Taylor 

 Standard Series, and proportions as given in 

 the preceding paragraph. In Table 67.a this 

 derivation is set down in tabular form. The four 

 points corresponding to the Rr/A. values calcu- 

 lated for the series A and series B ships without 

 bulbs, at T, values of 0.8 and 0.9, are indicated 

 as such on the plot of Fig. 67. F. The Rg/A values 

 to be saved by fitting bulb bows to the two ships 

 are indicated by the vertical intercepts between 

 the four points just mentioned and the curves 

 for the corresponding ships with bulbs. 



Reducing these intercepts to percentages of 

 Rr/A. of the parent-form ships without bulbs, 

 as in Table 67. b, the savings to be expected are 

 of the order of 11 to 18 per cent at a T, of 0.8 

 and 14 to 18 per cent at a T, of 0.9. This is certainly 



enough to justify fitting a bulb bow to the ABC 

 design, even for the sustained speed of 18.7 kt, 

 where T, = 0.828. 



J. M. Ferguson has very recently (August 1955) 

 prepared an analysis of D. W. Taylor's test data 

 by which it is possible to determine by inspection 

 the saving in total (not residuary) resistance by 

 using the best values of the terminal value t 

 and the FP area ratio /, or other combinations 

 of t and /, without making the special calculations 

 just described. Ferguson's data are unpublished 

 but they are on file in the TMB Ubrary. 



The ABC bulb bow is to extend forward of the 

 FP, hence the area corresponding to /e is meas- 

 ured at that station. If the bulb were rounded into 

 the FP, the area would be that at the plane of 

 the forward perpendicular lying within the bulb 

 surfaces when extended to that station, disregard- 

 ing the rounding. 



Since the bulb volume should be as far below 

 the designed waterline as possible the bottoms of 



