Water-Jet Propulsion for High-Speed Surface Ships 



from the own apparent weight Wa p of the propulsion unit 

 (circuit, pump, etc.), the power-transmission gear and 

 emersed part of circuit-water. 



from the lift L p of the propulsion unit due to external 

 flow around the drowned parts of this unit, and/or the eventual 

 inclination of the jet. 



We propose to consider the "relative weight balance" of the 

 propulsion unit : 



W AP ' L P 

 RWB = —** H. 



T g 



This parameter should be normally related to cruise conditions, 

 but it may be interesting also to refer to RWB under take-off 

 conditions. 



3.3. We have mentionned earlier that the cruising speed condition 

 is not the only one to be considered when dealing with high speed 

 surface ships. The thrust requirement may be rather severe at 

 intermediate speeds, in relation with some kind of "take-off" proced- 

 ure. It is not possible to express these "medium speed" requirements 

 in general terms since they depend largely upon the type, the size 

 and more generally the "project programme" of the ship. 



On the other side it seems rather easy to summarize approxim- 

 ately the "medium-speed thrust performance" of a given propulsion 

 unit into two simple parameters which we propose to designate 

 respectively by : 



"peak thrust ratio" : tp = 



"peak thrust relative speed : vp = 



T c 

 v c 



where : T is the maximum, thrust as defined below, 

 T is the rated thrust at cruising speed, 

 V is the "peak thrust velocity" as defined below, 



