Ducted and Contrarotating Propellers on Merchant Ships 

 0.7 ^ 



7o 



0.6 



0.5 



O.A 



0.3 



0.2 



Of 



I 



- 10 



L L J 



Results at design pitch ratio 

 ^ A Results with prop- set No- 1 ^ 



D ■ Z 



■ 3 



4. 



See Table I 



0.6 1.0 



Advance ratio J 



Fig. 8 - Contrarotating propeller family. Effi- 

 ciency and torque balance at different pitch ratios. 



the law of Bernoulli. Allowance is made for the drag of the propeller blades and 

 the duct. 



The shape of the duct can be determined either by applying the continuity 

 law on the flow inside the duct or by satisfying the boundary condition at the duct. 



Since the singularities representing duct and propeller are placed upon cyl- 

 inders with constant diameters and not on the real streamsurfaces, the two 

 methods give different results. The decisive factor on the boundary -condition 

 method is the radial velocity induced by the propeller. When calculating this 



1277 



