Duportj VisoontisOnd Merle 



6. 2. The following figures can be directly derived from the measure- 

 ments made with a propeller of diameter D on the test rig described 

 above : 



. the head H applied between the external limits of the pro- 

 pulsion unit model ; this head simulates the effect of kinetic 

 energy due to the forward speed V of the ship. 



the rate of mass-flow M passing through the propeller. 



the component of the jet momentum "') in the axial direc- 

 tion. 



the shaft power P 



r s 



the rotational speed N 



the net positive suction head NPSH. 



From these figures, it is possible to determine : 



The equivalent ship speed : V = \ 2gH 



The gross thrust : T = Tf\ - MV 



(i. e. the gross thrust obtainable at speed V from a propulsion unit 

 operating under the same internal hydraulic conditions as the model) 



V. T 

 The gross efficiency V = G_ 



g P 



T 2 



g . , „ n d 



The thrust coefficient C_ = — ^ — with S = 



2 S R 



ND 

 The rpm coefficient u = 



The cavitation coefficient h 



V 



NPSH 



NA V 2 /2g 



The dimensionless parameters defined above can be plotted in 

 a diagram as the one represented in fig. 7 and then applied through 

 similarity considerations to the determination of a prototype propul- 

 sion unit of given dimension and speed. 



20 



