blade section shape represented the blade cavity shape. Following characterization 

 and observation, Propeller 4717B was finish cut to the final design version, Pro- 

 peller 4717C. 



Propeller 4738A is a six bladed propeller with the same expanded area as the 

 previous four bladed propeller, and is designed for the same conditions as the other 

 propellers. 



EXPERIMENTAL PROCEDURE 



Cavitation performance characteristics and cavitation observations were ob- 

 tained in the 36-in. variable pressure water tunnel. Tunnel water velocities were 

 measured by the tunnel venturi system. The scope of the experiments is given in 

 Table 5. 



Tunnel pressure and water velocity were set to establish each cavitation number 

 and then propeller revolution rate was varied to cover a range of advance coeffi- 

 cients. Propeller thrust and torque were measured at each condition and sketches 



were made of the cavitation present. The Reynolds number, R , during the experiments 



S 6 



ranged from 7.5 x 10 to 5.6 x 10 . 



PRESENTATION OF DATA AND DISCUSSION 



The thrust and torque data were reduced to nondimensional coefficients of K and 

 K . Propeller efficiencies were calculated from faired values of K and K . The 

 cavitation performance characteristics of the three propellers are presented in 

 Tables 6 through 8. 



Curves representing the faired data, from Tables 6 through 8, are shown as an 



2 

 example in Figure 35. Curves of maximum-speed thrust loading (K /J ) have been 



2 

 added to the performance curves for Propeller 4738A. The intersection of the K J 



curve and the K curves at the design sigma (o) determines the predicted operational 

 point for each propeller. A comparison between the design operational points and 

 the points predicted by the experimental data is given in Table 9. 



Sketches of the back cavitation present on the propellers at two cavitation 

 numbers are given in Figures 36 through 38. These sketches cover a range of advance 

 coefficients from partially cavitating to fully cavitating conditions. If advance 

 coefficients had lower values than those shown, the propellers, at the same cavi- 

 tation number, would also be fully cavitating. With only one exception, propellers 



34 



