Water-Jet Propulsion for High-Speed Surface Ships 



mechanism. 



Z flow propeller - 45 knots 



V a - 0, 50 approximately 



t = 1,12 to 1,2 approximately 



P 



The limitation seems to be due to the constant power condition more 

 than to cavitation limitation. 



RWB = 0, 10 to 0, 15 



Super -cavitating propeller - 55 knots 



V g = 0, 63 



Vn = 0, 57 



RWB = 0, 15 to 0,20 



tp = slighthy higher than one ; the limitation 

 is the "constant power", not the cavitat- 

 ion limit. 



IV. EFFECT OF CAVITATION LIMITS UPON CERTAIN JET 

 PROPULSION UNIT CHARACTERISTICS 



Certain conditions must be respected to avoid the inception of 

 cavitation within the internal circuit of a jet propulsion unit. These 

 conditions directly affect the efficiency which is to be expected of 

 such units with the limit of efficiency depending, among other things, 

 upon the forward speed of the vessel for which the propulsion unit is 

 designed. 



4. 1. Z Flow jet propeller (ZFJP) 



As already stated, these propulsion units are fitted with a 

 scoop and a forward intake followed by an elbow. Vaned elbows are 

 generally used to reduce external dimensions and head losses to a 

 minimum while avoiding cavitation. 



The critical cavitation condition of an elbow is expressed by 

 the Thoma parameter : 



11 



