THE HYDRODYNAMICS OF HIGH-SPEED HYDROFOIL CRAFT 
Marshall P. Tulin 
Hydronautics, Incorporated 
Rockville, Maryland 
A general discussion of some important hydrodynamic problems associ- 
ated with the operation of high-speed hydrofoil craft is presented. The 
difficulties that arise from the necessity to either avoid cavitation or 
design for supercavitating operation, and at the same time to deal with 
those high-gust loadings that accompany flight in a seaway are empha- 
sized. Theoretical results pertaining to the effect of a seaway on foil 
loadings and cavitation inception are given, as well as results describ- 
ing the influence of the free surface on inception speed. The importance 
of flaps is stressed and new theoretical results concerning flap effec 
tiveness in both sub- and supercavitating flows are presented. Finally, 
the effect of near-surface operation on the lift-drag ratio of supercavitat- 
ing foils is discussed and some new theoretical results are given. 
INTRODUCTION 
I should like at the very beginning to state two warnings. The first concerns the title 
of this paper which was poorly and immodestly selected. Rather than “The Uydrodynamics 
of High-Speed Hydrofoil Craft” it should read “Some Hydrodynamics of High-Speed Hydrofoil 
Craft.” In excluding from discussion many important problems, I have sought to emphasize 
others which are, in my opinion, most needy of discussion at this time. The second warning 
is addressed to the very small number of you who not only expect from me but even look for- 
ward to highly mathematical content. I am sorry to announce that not a single integral sign 
is to be displayed here. For this reason, I have already been accused of a kind of scientific 
degeneracy. Such a charge must, of course, be vigorously denied and | hasten to point out 
that between the lines and behind the figures lies, I think, enough mathematics to satisfy all 
but the most jaded theoretician. 
The hydrofoil boat together with the airplane has been evolving now for over 50 years. 
It has appeared in many and varied configurations and performed with mixed success; until 
recently its future as a marine vehicle remained uncertain. The inevitably growing need for 
high-speed transport over water would seem to be well enough recognized at this time, how- 
ever, so that the serious and continued development and use of the hydrofoil boat may be 
considered safely assured. 
The advantages of the hydrofoil craft over displacement or planing craft for high Froude 
number operation is well-known. Only the edge jet vehicle (or hydroskimmer or ground effect 
machine as it is sometimes called) offers competitive performance and then, we believe, 
only in large sizes, say several thousand tons displacement. In Fig. 1 are outlined on a 
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