240 H. von Schertel 
in Fig. 6 corresponding to an extremely long wave of ten times the foil distance shows the 
typical increase of acceleration with increasing Froude number. Accelerations in medium 
waves, however, equaling the foil distance, are less dependent on the Froude number as 
may be seen from the thin curve. The calculations represented in Fig. 7 are based on a foil 
distance of 66 feet and a speed of 46 knots. The wave height for each respective wave- 
length is shown by the dashed curve. Figure 7 shows that under the assumed conditions the 
vertical accelerations increase only up to wavelengths approximately equal to the foil dis- 
tance and decrease beyond that size, which is due to the decrease of the slope of the wave 
with its increasing length. 
Figure 8 shows the influence on vertical accelerations of the direction of travel with 
regard to the wave direction for two different relations of wavelength to foil distance. Under 
WAVE L/H= 15,7 | 
WAVE SLOPE ¢ =/7,3 
FROUDE-NUM BER F = 1,7 
o° 30° 60° 90° 120° 150° 180° 
WA meer Esra oi 7/ON— <a 
Fig. 8. Influence of the wave direction on vertical accelerations 
the given conditions (L/H = 15.7, F = 1.7) the maximum values are attained against the sea 
and with a following sea, while at a course of about 80 degrees the boat remains at the same 
place in the wave, which results in the disappearance of accelerations. 
TECHNICAL CHARACTERISTICS OF THE TWO BASIC FOIL SYSTEMS 
Having examined the suitability of hydrofoil craft for commercial transportation in gen- 
eral, we shall now consider the main design problem in hydrofoil engineering, i.e., the foil 
system itself, as it naturally has a decisive influence on the all-round performance of the 
craft. Since it is not the purpose of this paper to present a survey of all the various designs 
