234 H. von Schertel 
most modern and fastest ships on European lakes surpass their 100 years older predecessors 
only by twice their speed. The reason for this lagging behind of waterborne craft compared 
with other means of transportation lies in the well-known large increase of drag with 
augmented speed. 
It is, therefore, not surprising that inventors, engineers, and scientists of several 
nations have been endeavoring for many decades to find solutions which will result in com- 
parable speeds on the water. Conviction that the shape of modern displacement bodies can 
hardly be further improved, and that the solution can only be found in a reduction of the 
immersed volume and of the wetted surface, led to the development of gliding or planing 
vessels (V-bottom boats), in which dynamic lifting forces take the place of the static dis- 
placement lift, and later on to the construction of hydrofoil boats in which the hull is finally 
lifted completely out of the water. 
The planing boats did not solve the problem of attaining the travelling times of land 
vehicles under economically acceptable conditions and with good behavior in a seaway. The 
reason for this must be attributed to the relatively high drag/weight ratio at the required 
speed and to the extremely hard buffeting to which planing boats are exposed and which the 
passengers cannot be expected to endure. 
SPECIFIC CHARACTERISTICS OF HYDROFOIL BOATS IN COMPARISON WITH OTHER 
FAST WATER CRAFT 
Drag, Speed, and Economy 
In Fig. 1 in which the specific power requirements of various water- and aircraft are 
plotted against speed, displacement boats, planing vessels, and hydrofoil boats are compared 
Displacement Commercial 
boat Hydrotoil boat 
Fig. 1. Power coefficient of various craft 
