Dupovt, Visoonti , and Mevle 



We propose to designate by Rp this "propeller own resistance" 

 (which includes the resistance of associated struts). 



_ the flow around the hull (or foils in case of hydrofoils) can 

 be modified due to the presence of the propulsion unit (shape 

 modification) or the suction effect of the intake mouth. If it is 

 so, the ship resistance may be modified, compared to the ob- 

 served figure in the absence of the propulsion unit. This may 

 occur for instance if a nacelle type SFJP or the scoop of a 

 ZFJP is combined with the wing systems of a hydrofoil ship : 

 the drag of the wing system can then be altered. We shall 

 designate by Ri the supplementary resistance induced by the 

 propeller (this introduces a correction factor which to some 

 extent is analogous to the "suction coefficient" of conventional 

 propellers, but does not at all respond to the same approach). 



The net thrust is : 



T = T - R - R. 

 n g p l 



It must be noticed that separate determination of Rp and Ri 

 is not always possible, since it may happen that they cannot be simp- 

 ly added. 



Anyhow the value of R p + R^ can be reached through the 

 thrust and resistance balance of the ship with and without propeller. 

 This value depends not only upon the propeller design but also the 

 ship design. For that reason it is interesting to consider gross 

 efficiency as well as net efficiency. 



gross efficiency r)„ is the one determined from the gross 

 thrust : 



3. 2. Weight balance of the ship is also an important parameter when 

 rapid surface ships are concerned, since they normally operate with 

 either partially or fully emersed hulls. The contribution of the pro- 

 pul si on unit on this balance results : 



