Titoff, Russetsky, and Georgiyevskaya 



For vessels whose speed is not very high (35-40 knots), use is often made 

 of the propeller design method that is based on drawing an analogy between the 

 elements of cavitating and subcavitating propellers. According to this method, 

 developed by O.V. Rozhdestvensky (3), the elements of the optimal subcavitating 

 propeller designed for the prescribed K^ and Kp (Fig. 7) are close to the ele- 

 ments of the cavitating propeller designed for K^* and kp . 





0,1 



0,2 



0,^ 



£(6 0,7 ^8 0,S /,0 V ^>2 /.3 /,<- /,S ^p 



Fig. 7 - Analogy between the de- 

 sign elements of a subcavitating 

 (K^) and cavitating (k1) propeller 



With the value k^* being given, the first stage of calculation consists in the 

 determination of the value Kj . This is effected by means of diagrams based on 

 systematic model tests. Subsequent calculation is the same as for the ordinary 

 cavitating propeller. The comparison made between the elements of propellers 

 designed for cavitation and those based on the above analogy shows that the 

 method mentioned above gives somewhat lower values of curvature, the differ- 

 ence being the greater, the smaller the assumed cavitation number. 



The efficiency of the above design methods has been proven in the develop- 

 ment of propellers for the hydrofoil vessels "Raketa" and "Meteor." The origi- 

 nal variants of propellers for these vessels were subject to intensive erosion, 

 as a result of which 10-to-12mm-deep cavities developed on the pressure side 

 of the blade by the end of the navigation season. 



Figure 8 illustrates a propeller after 500 hours of operation. The analysis 

 of operating conditions and assumed propeller elements has shown that the cavi- 

 tation erosion was caused by excessive curvature of the pressure face. The 

 distribution of curvature over the radius of the propeller blades of "Raketa," as 

 adopted in the original variant of the propeller, is correlated in Fig. 9 with that 

 calculated with allowance for the inclination of the flow (4). 



On the basis of the above calculations, new variants of propellers were de- 

 signed for these vessels. Their blades are fully free from cavitation erosion 

 after 6000 hours of operation, i.e., after three navigation seasons. 



926 



