Ducted and Contrarotating Propellers on Merchant Ships 



Contrarot. propellers 

 Single propeller 



Conv. twin screw arr 



Prop, i 



(Section through txjssj 



Fig. 26 - Pressure amplitudes. Comparison 

 between different propeller arrangements. 



(5) The conventional way of splitting up the propulsive coefficients ap- 

 pears to be less suitable for unconventional propulsive devices. 



(6) The cavitation properties of contrarotating and ducted propellers 

 seem to be similar to or better than those of the corresponding conventional 

 propellers. In the contrarotating case, however, there is a risk that the cavi- 

 tating tip vortex from the forward propeller might cause erosion on the aft pro- 

 peller. 



(7) The investigations with ducted propellers have to be completed 

 with further cavitation-tunnel experiments. 



1299 



