266 H. Von Schertel 
© . («) against «). This would convert Mr. Wennagel’s diagram from B to C. From the 
latter we see most clearly that the conditions imply two regimes of broadly constant but 
different ©) . (2) values. ‘What is the significance of these two regimes? Incidentally the 
© . «® product reduces to (P/AV)/ «). ‘The term in parentheses, i.e., power per ton- 
knot, is the transport coefficient and is a direct commercial measure of the design efficiency. 
Our discussions include many references to Froude number, i.e., Froude speed-length 
number. I doubt, however, so far as hydrofoil craft are concerned, whether we have a truly 
representative length to use in the Froude number. [| suggest therefore, since for these craft 
displacement or weight is constant, that the Froude displacement-speed factor, i.e., 
K = 0.5834 V/A”®, should always be used for their performance nondimensional presentation. 
H. Von Schertel 
The Froude number is based on the distance between the fore and aft hulls. 
Douglas Hill (Grumman Aircraft Engineering Corporation) 
We continue to be indebted to Baron Von Schertel for his reporting of the operating 
experience of the craft of his design, as well as for his pioneering work in the development 
of hydrofoils and their introduction into commercial service. Those of us interested in the 
development of hydrofoils look to the experience with these craft as a milestone on the road 
leading to the large-scale introduction of hydrofoils for commercial and naval use. 
There can be little quarrel with Baron Von Schertel’s evaluation of the potential of 
commercial hydrofoils on the basis of the evidence he presents and the scope of his presen- 
tation. In the publicity which has attended the growing awareness of the potentialities of 
hydrofoil craft, it is perhaps true that the feasibility of future vessels —a transatlantic pas- 
senger liner, for example —has been overemphasized by the standards of today’s commercial 
realities. Assuming that hydrofoil craft are better suited to coach than to stateroom accom- 
modations, we can draw on the experience of other modes of coach transport to substantiate 
Baron Von Schertel’s observations on the practical operating range of passenger-carrying 
hydrofoils. A comparison of the length of journeys of travelers by air, railroad coach, and 
intercity bus in the United States reveals that, while the average distance travelled varies 
substantially between the modes of transport, the average duration of the journey is remark- 
ably consistent: 
Average Length of Average Average 
BOT ETER ES Journey (statute miles) Speed (mph) Time (hr) 
Airplane 577 220 2.6 
Railroad Coach 110 40 Pa | 
Intercity Bus 79 30 (est.) 2.6 
It would seem reasonable to expect that the widespread use of hydrofoils for coach 
transportation would likewise result in an average trip duration of about 2.6 hours. 
Most journeys would be shorter than the average, some perhaps much longer. The peak 
trip length can therefore be expected to be shorter than the length of the average trip. On 
domestic United States airlines, for example, the most common trip length is of the order of 
