Performance of Partially Submerged Propellers 



Propeller 3767 



FUIIY SUBMERGED 



a 0.601 



1 . 25 ■ 



1.679- 



a 3.9m 



Fig. 23 - Cj - Tj ^ - ] diagram of propeller 3767 fully submerged 



Fully Vented Region. In this regime a cavity greater than one chord length 

 exists on the suction side starting from the leading edge, thus the suction side 

 and the base of the foil are fully vented to atmospheric pressure. At this condi- 

 tion there is a drop in lift coefficient when compared to base-vented regions and 

 a corresponding drop in lift-to-drag ratio. 



The results of these flow regimes may be readily summarized on the follow- 

 ing force diagrams as a function of angle of attack, Fig. 24. The forces are shown 

 in the usual convention — lift and drag coefficients parallel and normal to the flow. 

 The break in the lift curve is the transition point from the partially cavitating to 

 the fully vented region. This transition is accompanied by violent oscillation in 

 the forces identified as buffeting. The angle of attack where the transition takes 

 place, as well as its magnitude, is a function of a number of variables, most of 

 which are dependent upon the section geometry. Increasing the base thickness- 

 to-chord ratio tends to increase the transition angle of attack and results in a 

 larger shift in the lift coefficient. The details of the suction surface, particularly 



1473 



