Waterjet Propulsion 



PUMPS 



The principal requirements of pumps for waterjet propulsion systems are 

 that they be cavitation-free and light-weight. As usual, these requirements are 

 not compatible. 



The most severe conditions for cavitation-free operation exist at the low- 

 speed "hump" situation. At this condition large thrusts are demanded at low 

 suction heads. K the pump is designed to operate nearly cavitation-free at the 

 hump condition, the additional suction head obtained from ram recovery is more 

 than adequate to prevent pump cavitation at cruise. 



A detailed discussion of the pump selection problem is given in Ref. (2). 

 Figure 5 (taken from Ref. (2)) illustrates the type of pump required for a typical 

 hydrofoil craft as a function of speed and size of craft (as indicated by the static 

 lift parameter h ). This figure assumes that the pump is single-stage and is 

 noncavitating at the hump speed (taken as one -half the cruise speed). The ordi- 

 nate of Fig. 5 is the specific speed n^ =: rpm(gpm)^ ^ (ft)3/4 This parameter is 

 indicative of the type of pump required. For example. Fig. 5 illustrates that, at 

 high speeds, the pumps should be centrifugal. 



Fig. 5 - Single-stage non- 

 cavitating pump types for 

 waterjet propulsion systems 



It is also explained in Ref. (2) that pump sizes can be reduced for a given 

 requirement by dividing the total discharge required into a number of parallel 

 units. Double -suction centrifugal pumps are examples of a simple division of 

 the total flow into two equal parts. Figure 6 (taken from Ref. (2)) illustrates the 

 use of multiple, parallel, double -suction, centrifugal pumps. The Boeing Com- 

 pany has utilized this scheme in the design of the pumps for the U.S. Navy Pa- 

 trol Craft "Tucumcari" (Fig. 7), shown in Fig. 8 prior to installation in the craft. 



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