Model Tests on Contrarotating Propellers 



Conventional screw 

 Kj-0.174 0-0=12.38 



Contra -rotating propellers ; 



KT=0t69 c-o-1241 

 forwa^ propeller aft propeller 



Fig. 12 - Cavitation patterns of conventional 

 and contrarotating propellers behind tanker 



Measurements of Propeller-Induced Vibratory Forces -' • 



Comparative tests on propeller induced vibratory forces have been carried 

 out on the cargo liner model equipped with successively the conventional screw 

 propeller and the contrarotating screw propellers. To measure these forces, a 

 special arrangement had to be made in the case of the contrarotating propellers 

 to use the existing measuring equipment (15). The forward propeller was driven 

 by the normal dynamometer, installed in the ship model. The aft propeller was 

 driven by a dummy dynamometer. This dummy dynamometer was installed in 

 an open-water test boat, mounted behind the ship model. A stiff coupling shaft 



151 



