Sharma 



-0.10 



-0.05 (Ax/LBP) — .- 



0.05 



Fig. 13 - Contour lines of the ratio of 

 wave resistance with bulb to that with- 

 out bulb for ballast condition (thick 

 lines) and load condition (thin lines) 



was investigated by computing the wave resistance ui corresponding linear com- 

 binations of the empirically derived free wave spectra of the main hull and the 

 bow bulb. The results of this calculation are plotted in Fig. 13 as contour lines 

 of the ratio of wave resistance with a bulb to that without a bulb. The set of 

 thick lines holds for the ballast condition while the thin lines apply to the load 

 condition. 



It will be seen that for each condition there is a definite range of bulb size 

 and location (bounded by the contour line marked 1.0) inside which the bulb pro- 

 duces beneficial action. There also exists in each case a definite optimal 

 choice. The best that can be achieved with this model by merely changing bulb 

 size and longitudinal location (i.e., without altering the basic bulb form) is a re- 

 duction of wave resistance down to about 48 percent in the ballast condition or 

 69 percent in the load condition. Evidently the two optima cannot be realized 

 simultaneously and it is the designer's problem to choose a compromise some- 

 where along a straight line connecting the two optimal points in Fig. 13. The 

 picture also confirms the empirical fact already known to designers that a bulb 

 optimized for the load draft is generally oversized and detrimental at the ballast 



762 



