Yim 



It has shown a 17.5 percent gain in total resistance at maximum speed of 

 v^ = 1.75 m/sec and up to higher speeds (from V//L = 1.10 upwards). Compar- 

 ative wave formations at certain speed ranges are shown in Fig. 5. 



It may be concluded that, the ordinary ship bulb as fitted near the keel does 

 not perform as well as a bulb fitted at the designed waterline. The wave forma- 

 tion being a surface phenomena, the surface bulb becomes more effective, in 

 taking the core of the bow wave, transforming thus the original solid bow wave 

 into a sheet wave. 



The water at the trailing edge is accelerated at its lower edge, trailing aft. 

 Submerged bulbs of greater sizes may similarly influence the downwash, but the 

 penalty paid for their extra resistances, due to their bulkiness thwarts off the 

 advantage brought by their adoption. A badly designed bulb, is therefore, worse 

 than having no bulb at all. 



The bulb is destined to kill the bow wave which is the father wave and once 

 it is killed, next of kin will not be as predominant. However, the effect of shoul- 

 der wave does still retain its place of importance and however the use of shoul- 

 der bulbs were also resorted to, it still needs careful considerations, calcula- 

 tions and a good programme of experimenting, to find its proper shape and place. 

 It might be a denting instead of bulbing. 



The devices shown in Fig. 2 as wave suppressors, scrapers or spears are 

 impressive and effective in quenching or suppressing the waves, which is dem- 

 onstrated by smoothed surface around the hull, yet their resistances are so 

 high that their use for calm water alone may not be justifiable. Therefore, the 

 term (waveless form) should not essentially implicate a form of least resist- 

 ance, in every case. 



The type, form, size and placement of the bow devices have to be decided 

 according to the designed speed/length ratio, angle of entrance and other form 

 characteristics of the ship. Some of the tests carried out with the model of a 

 motor launch and the placement of the bulb or spear and the resulting wave 

 formations are shown in Figs. 6, 7 and 8. The spear, solely an experimental 

 device, piercing the water with a finer angle of entrance is also seen at speed. 



The waterline bulb may invite suspicion of many of us as conservative naval 

 architects, also due to its higher resistances up to the cruising speed range. 

 Yet, apart from the fact that the part of the resistance curve we are most in- 

 terested in, is in the high speed ranges, we may well go to introduce inflated rubber 

 bulbs or appendages to suit the different speed ranges of the ship. Nearly every 

 modern vehicle, from cars to ground effect machines are benefitting from its 

 advantages. We may thus inflate it only at the speed ranges we want. 



Naval architects of today trying to design sea kindly ships with solid walls 

 of steel are preoccupied with problems of seakeeping and slamming. A bulb 

 properly designed and fitted at design waterline may be a better antipitching 

 device than its submerged contemporary, also insuring less loss of power in a 

 seaway. 



1104 



