Oscillating-bladed Propellers 



2. Lerbs, H., and Rader, H,P., "Uber den Auftriebsgradienten von Profilen in 

 Propellerverband," Schiffstechnik, 1962 



DISCUSSION 



L. A. Van Gunsteren 



Lips Propeller Works 



Drunen, The Netherla}ids 



I would like to make two comments. 



1. In my opinion, the value of the paper would be improved if Mr. Bindel 

 would provide a description of the test arrangement. In other words, by which 

 kind of mechanism did he obtain the desired motion of the propeller blades ? 

 This could give an indication about the efforts required for the realization of 

 this device in practice. Also, a sketch of the hub-form would be appreciated, 

 as this is an essential point with regard to blade-root cavitation. ■, ,,. ,, 



2. We considered the oscillating-bladed propeller some years ago with 

 regard to the wake-field of single- screw ships. We dropped the idea because 

 of the continuous energy losses due to mechanical friction in the actuating 

 mechanism. This, despite the fact that field-wake irregularity of single-screw 

 ships is practically unavoidable. The nonuniformity of flow due to shaft incli- 

 nation, however, can be avoided by simply placing the shaft in the direction of 

 flow. In order to achieve this, the propeller shaft could be connected to the in- 

 clined shaft by some special kind of coupling, or by a gearing of two wheels with 

 conical teeth. Such a device seems to be more attractive than any hub mecha- 

 nism required for the oscillation of blades. 



DISCUSSION 



Prof. L. Mazarredo 

 Asociacion de Investigacion de la Construccion Naval 

 Madrid, Spain ,,. , .,^. 



Although these results don't appear to be very promising, I don't think this 

 idea should be rejected at once. The cavitation which appears with oscillating 

 blades may be due to the curvature of the relative flow, since it is stronger in the 

 leading and trailing halves of chords at ±90° from the "longitude" where the root 

 cavitation has been eliminated. If the movement was sinusoidal the rotation speed 

 of the blades and the corresponding flow curvature would be maximum at that 

 position. 



1519 



