Munk and Prohaska 



PHP 



30000 



K)000 



INTERL. PROPS. INW. DIST. 0^8. D,P No. 5915 



DIST. q? .D,PNo.6l37 



. OUTW. DIST. a77«Cl R No. 5915 



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FULLY LOADED 



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V A 



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71— 



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SERVICE 

 SPEED 



BALLASTED 



Fig. 8 - Comparison between best results 

 from tests with inward- and outward- 

 turning interlocking propellers 



has a great influence on the total efficiency, the optimum distance between the 

 propeller axes must be a function of the propeller load. A general optimum 

 distance, therefore, cannot be given at present. For cases considered most 

 important, shaft distance is clearly the best. 



The differences corresponding to inward- and outward -rotating interlocking 

 propellers are due to the wake components in the propeller disk plane. It is 

 possible to get an impression of this component if the normal force on a blade in 

 a certain position is compared to the normal force on the blade in the same posi- 

 tion, but with the propeller turning in the opposite direction. The difference 

 between the normal forces is due to the differences between the tangential 

 velocities as shown in the velocity diagram, Fig. 13. The tangential wake ve- 

 locity, w^, is seen to change the resulting inflow velocity from v^ to Vj j when 

 the direction of rotation is altered, and this largely influences the normal force. 



1532 



