294, G. J. Wennagel 
David Taylor Model Basin tests of supercavitating propellers revealed that the efficiency of 
such propellers at design advance ratio was essentially independent of cavitation number, 
implying that the efficiency was a little bit less at high cavitation number, that is, under 
fully wetted conditions, than it was in supercavitating operation, and thus indicating that 
very little price was being paid because of the drag incurred by the blunt section operating 
under fully cavitating conditions. With regard to the future, I would not care to speculate on 
what shapes practical supercavitating foils, designed for high performance craft, will take. 
Certainly in the case of fully submerged foils, flaps and perhaps other such devices will be 
included; and I think that we must be patient to see how foil shapes will evolve. 
Glen J. Wennagel 
In regard to Mr. Rader’s comment on the ONR boat, the drag hump during takeoff is due 
in good part to the foil and strut blunt trailing edges. The design gross weight as stated 
was 2550 pounds. With a 2100-in./lb shear pin, which corresponds to 200 hp at 6000 rpm, 
we reach a point where the boat will not take off when the gross weight reaches about 3000 
pounds. This is without forced air. If the pilot turns on the air, the reduction in drag is 
apparent and the boat will take off. 
T. G. Lang (U.S. Naval Ordnance Test Station) 
My comments are directed toward both Mr. Tulin’s paper and Mr. Wennagel’s paper. 
The development of high-speed hydrofoil craft having surface-piercing hydrofoils or 
struts requires a detailed knowledge of the effects of air ventilation on hydrodynamic forces. 
The U.S. Naval Ordnance Test Station has conducted a series of experiments on hydrofoil 
models in which air was forcibly exhausted through ports in the hydrofoil surface. These 
experiments were conducted in the high-speed water tunnel at the California Institute of 
Technology in 1958 and 1959. The objectives of the studies were to investigate the use of 
forced ventilation for the purposes of control and of improving hydrofoil performance 
characteristics. 
Figure D1 shows a model of one hydrofoil used in the tests in which a spanwise series 
of small holes can be seen just behind the leading edge. In this study, the chordwise loca- 
tion of the holes was varied and the spanwise length changed. 
Figure D2 is a top view of this model mounted in the water tunnel showing air being 
exhausted through the series of holes, while Fig. D3 is a side view. The air did not spring 
forward of the exhaust point unless extensive cavitation occurred behind the leading edge 
or unless the hydrofoil was placed at an angle of attack above its fully-wetted stall angle. 
Figure D4 is a top view of this model placed at the stall angle of attack. The air is seen 
to ventilate forward of the holes. 
Figure D5 is a top view of another model having the same contour in which a small 
amount of air is exhausted through a single hole in the upper surface. The angle at which 
the air diverged outward increased as the angle of attack increased. Figure D6 shows this 
same model at the same angle of attack but with an increased air-flow rate. It is noted that 
the sides of the air cavity are more distinct in the latter case and the thin, patchy type of 
ventilation which was seen in the previous figure has disappeared. 
