Performance of Partially Submerged Propellers 



0.2 0.3 0.4 0.6 O.e 1.0 



2 3.0 4.0 6.0 so 10.0 



Ct' 



Fig. 21 - cj. - r;^ - J diagram of propeller 3767 partially submerged 



At the low advance coefficients, after transition, the flow pattern remained 

 similar to that at transition, except that the amount of spray increased in quantity 

 and amplitude as the advance coefficient was reduced. Forward of the propeller 

 it was noted that the water surface increased in elevation, the amount varying 

 inversely with the advance coefficient. At one point the increase just before 

 entry into the propeller was more than 1 in., thus indicating a blockage of flow 

 and a positive pressure field forward of the propeller. It was also noted that 

 there was an extensive amount of spray extending forward of the propeller. 



In conjunction with these observations a special test was made at 1-knot 

 intervals from 1 to 9 knots, when the propeller rpm at transition was recorded. 

 During the measurements it was noted that just as transition occurred there was 

 a sudden increase in the rpm, which made it difficult to obtain a consistant 

 value for the transition advance coefficient. 



ANALYSIS OF PERFORMANCE 



Before undertaking an interpretation of the test results for the guidance they 

 can offer in predicting the performance of a partially submerged propeller, it is 

 helpful to examine the flow regime around a super cavitating- type section under 

 ventilated flow conditions. To assist there is a small but growing body of informa- 

 tion on hydrofoils with ventilated flows of which Refs. [9j and [lOj are most 



1471 



