Model Tests on Contrarotating Propellers 



130 



120 



110 



90 



18 



18.5 



19 ia5 20 205 21 



Speed in knots 



21.5 



20000 



15000- 



IQOOO 



ia5 



19 195 20 



Speed In knots 



2Q5 



215 



Fig. 10 - Power and rpm curves for the 

 cargo liner 



In the upper and lower part of the aperture, the tip-vortex of the forward 

 propeller of the contrarotating propellers interfered with the blades of the aft 

 propeller, especially for the cargo liner propellers, which led periodically to 

 unfavorable cavitation phenomena. The chance for the appearance of these phe- 

 nomena depends on the angular conjunction of the blades of the forward and the 

 aft propeller. To avoid these phenomena it may be useful to reduce the diame- 

 ter of the aft propeller slightly more. 



149 



