Performance of Partially Submerged Propellers 



is concerned with the number of blades in partially submerged propellers. Al- 

 though this aspect is directly linked to the question of vibratory output in par- 

 tially submerged propellers, I think there is a strong need for testing partially 

 submerged propellers with larger numbers of blades than commonly in use in 

 fully submerged propellers. In fact, I am quite certain that in more sophisti- '■ 

 cated installations the partially submerged propellers will only stand a chance, 

 from the vibration point of view, if the number of blades is sufficiently high, 



I would like to ask the authors whether they share this point of view. 



Finally, I would like to mention that at Berlin Technical University an ex- 

 perimental investigation into the performance of partially submerged propellers 

 will be carried out in the near future. The tests will be conducted in the free- 

 surface cavitation tunnel of the cavitation laboratory. All together, 8 propellers 

 will be tested in the first phase of the program, among them propellers of the 

 Newton-Rader series that have successfully been used for fully submerged pro- 

 pellers in the fully cavitating mode, but do not make use of blunt trailing edges. 

 It is planned to extend the program eventually to measuring the fluctuating 

 forces on individual blades and to investigate possible advantages of skew-back. 

 The paper presented by the authors provides extremely valuable guidance for 

 this work. 



DISCUSSION 



K. Suhrbier 



Vosper Ltd. 



Portsmouth, England 



The authors presented an interesting and stimulating paper, which contains 

 very useful information on this subject. 



We have recently carried out some limited experiments with three super- 

 cavitating propellers on a race boat (described in the panel discussion on Planing 

 Craft by Cdr. E>u Cane). All propellers were designed for the same boat and had 

 about the same characteristics in the fully submerged condition; they were: 



1. a wedge-type SC propeller (P. Rolla, Switzerland), designed for semi- 

 submerged condition; 



2. a wedge type SC propeller, designed for fully submerged condition; 



3. a Newton-Rader SC propeller (modified airfoil section), designed for 

 fully immersed condition. 



In the semisubmerged mode, good performance could be achieved with the 

 first two propellers; the hump was no problem ~ in particular with Propeller 1, 



1495 



