148 S. Schuster and H. Schwanecke 
Fig. 1. Hydrofoil models simplified for pressure distribution measurement 
49 borings of 1.5-mm diameter. The holes were arranged in sections parallel to the longitu- 
dinal axis and connected to each other parallel to the lateral axis. For measurement all the 
sets of holes but one have been covered with thin plastic strips. Thus, successively, the 
pressure distribution around the profile for 6 cross sections for the flat foiland 7 cross sec- 
tions for the dihedral foil has been measured and photographically recorded during each run 
in the deepwater channel. For the flat foil the angle of attack has been varied from —1 degree 
to +6 degrees, and the depth of submergence from 30 mm to 240 mm at a speed of ug = 3.7 
m/sec; for a special series the speed was also varied, from 0.4 to 3.7 m/sec. For the di- 
hedral foil the angle of attack has been kept corstant at +] degree while the rolling angle 
has been varied from 0 to 33 degrees, one arm of the hydrofoil being parallel to the water 
surface when the rolling angle was 33 degrees. The measured pressure in relation to’ the 
ram pressure has been plotted versus the profile length for every section. Integration of the 
pressure curves results in the local lift coefficients, which in turn by integration over the 
span supply the total coefficient. For checking these values and for finding the drag three 
component tests have been made. 
Flat Foil 
The variation with speed for the flat foil first of all confirmed the shallow water effect 
as found by Laitone [1], Parkin, Perry, and Wu [2] and Plesset and Parkin [3], which occurs 
especially at the critical speed u, = gh (Fig. 2), where h denotes the distance between 
the trailing edge and the undisturbed water surface.* At a speed sufficiently above this 
value the ratio between depth of submergence and length of profile only is authoritative for 
the course of the pressure curve. Samples are shown in Figs. 3 and 4. Herein the charac- 
teristics of the diagrams versus h/c and © are different. The local lift coefficients indeed 
change in the same sense as depth of submergence and angle of attack, but in the first case 
the pressure distribution is unchanged, while it is varying much in the second case. There- 
fore, approaching the surface cannot be substituted by a reduction of the angle of attack. 
*A nomenclature list is given at the end of the paper. 
