Designof "Z" Drives for Propulsion of Hydrofoil 



DISCUSSION 



William B. Morgan 



Naval Ship Research and Development Center 

 Bethesda 3 Maryland 3 U.S.A. 



1. Reference to Figure 3 what is the definition of a p ? Is ae 

 on Figure 3 the cavitation number or does it have some other defini- 

 tion ? Were the experimental data presented in this figure obtained in 

 the cavitation towing tank. 



2. In 1963 at the 10 ITTC, results were presented from the 

 Kryloff Shipbuilding Research Institute on a propeller which was vent- 

 ed with air and operating behind a ship's hull. The results were much 

 the same as shown in Figure 3. However in 1969 at the 12" 1 ITTC, 

 results presented from the Kryloff Shipbuilding Research Institute on 

 a cavitating propeller operating behind a hull in the cavitation towing 

 tank. These results indicated that the thrust deduction might go up 

 with increasing cavitation. Would the author please comment on the 

 discrepancy between these results ? 



DISCUSSION 



Horst Nowacki 



University of Michigan 

 Ann Arbor 3 'Michigan, U.S.A. 



I would appreciate clarification as to whether the definition 

 of the wake fraction W p used in connection with Figure 2 of the pape 

 is actually the same as in equation (2) of the paper. In the context of 

 equation (Z) one would expect the wake fraction on the propeller axis 

 in the propeller plane to be used whereas in Figure 2 the volume 

 average of the nominal wake fraction in the propeller plane might 

 have been presented. Is this understanding correct ? 



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