158 S. Schuster and H. Schwanecke 
Fig. 12. Comparison of lift coefficients versus relative depth 
1. The test results of fully submerged flat foils can be transferred to emerging foils by 
means of the strip method. The lift decrease toward the outer regions becomes also measur- 
able for h/c < 2 and essential for h/c <1. Enlarging the profile length in the outer regions 
therefore seems to be less practical since the h/c value will be smaller and the influence of 
the water surface will be extended to larger regions of the span. According to item 2 in the 
summing up for the preceding subsection, it would be better to increase the angle of attack, 
i.e., to distort the foil. 
2. Since the strip method can be used for the rolling dihedral hydrofoil too, there is no 
special need for investigating the influence of the roll angle. Even for hydrofoils in a side- 
slip motion the measurement of the pressure distribution can be retained, for in this case 
only the local angles of attack are changed, the influence of which has been determined for 
the flat parallel submerged foil. 
STATE OF FLOW EXAMINATION 
If the existence of a shallow water effect could be concluded from the pressure measure- 
ment, then the transition from the subcritical to the supercritical range of the Froude depth 
number must be perceptible by a change of the surface deformation. Tests with a flat paral- 
lel submerged hydrofoil, extending sideways to the walls of a circulating water channel, 
proved that there is indeed a transition from a steady flow to a rapid flow with a hydraulic 
jump between. With regard to the speed increment above the foil and to the slope of the 
water surface connected herewith, a local Froude depth number 
u 3/2 
Bin, = U (3 + alll «) 
h lsh! 2 
where h’ denotes the minimum depth above the foil, can be defined as a barrier. The defor- 
mation corresponds to pictures shown in the publication of Parkin, Perry, and Wu [2]. 
