Unusual Two-Propeller Arrangements 



.PROPELLER TURNING OUTWARD 



NG INWARD 



NG INW. OR OUTW. AXIAL WAKE ONLY. 



PROP TURNING OUTWARD. ADDITIONAL NORMAL FORCE 

 FROM TANGENTIAL WAKE COMPONENT. 



8r RIGHT PROP 



OUTWARD TURN. 

 RIGHT PROP 

 INWARD TURN. 



Fig. 16 - Normal force curves for only one 

 interlocking propeller, inward- and outward- 

 rotating 



Fig. 17 - Velocity diagram for a propeller 

 blade in the interlocking zone, inward- and 

 outward - rotating 



CONCLUSION 



The results of the test series show that from a propulsion point of view 

 both of the new arrangements may be used with advantage. 



In the case of interlocking propellers, a higher total efficiency is obtained 

 than for the normal single- screw and twin-screw systems. However, the direc- 

 tion of rotation of the propellers has a great influence on the results, and it is 

 obvious that the wake components in the plane of the propeller disk must be 

 taken into account, as they are a part of the mean wake. 



The auxiliary propeller arrangement has in this case shown a decrease 

 and not an increase in the total efficiency in comparison with the normal single- 

 screw arrangement. However, the tests with the system were primarily carried 



1539 



