Waterjet Propulsion 



0.9 



0.8 



0.7 



0.6 



IL 0.5 



P 0.4 



0.3 



. 0.2 



0.1 







2gH 



Fig. 2 - Hydrodynamic characteristics 

 of waterjet propulsion systems 



In fact, the final or "best" design of a waterjet propulsion system is 

 achieved only after a very sophisticated examination of all the factors which in- 

 fluence achieving maximum payload/unit horsepower as payload/unit cost for a 

 prescribed mission. This inability to compare waterjet systems with conven- 

 tional or supercavitating propellers on the simple basis of v or even P.C. is a 

 serious difficulty that has not yet been universally resolved. It is important that 

 the lack of a simple comparitive "figure of merit" does not exist; however, those 

 who design systems for a specific requirement do recognize that it is indeed 

 "cost effectiveness" that selects the superior system. The problem is discussed 

 in some detail in Refs. (1) and (3), and the general problem is treated further in 

 the following paragraphs. 



Figure 3 illustrates the important factors the designer must treat in estab- 

 lishing an optimum design. These factors are: (1) the influence of the wake ap- 

 proaching the inlet, (2) the effect of the inlet and fairing on the "bare hull" re- 

 sistance of the craft, and (3) the machinery, structure, fuel, and propulsor 

 weight are all dependent on the actual power required for the ship's mission, 

 and this power in turn depends on minimizing these weights. Clearly many en- 

 gineering compromises are required to achieve a final "optimum" design. An 

 example of the results of a study (Ref. (4)), which attempts to compare various 

 propulsion systems over the speed range up to 100 knots, is presented in Fig. 4. 

 The value of P.C. presented as the ordinate does take into account most of the 

 factors previously discussed. Although the results presented in Fig. 4 are gen- 

 erally comprehensive, and the results of such a study are extremely valuable in 

 pointing out possibilities not previously appreciated, much more detailed studies 

 are required for a specific mission to definitely establish the superiority of one 

 propulsion system over another. 



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