Problems of Commercial Hydrofoils 267 
200 miles, corresponding to a flight of about 55 minutes. It is not surprising to find, 
therefore, that the hydrofoil routes described as the most prosperous are also the shortest, 
requiring runs of less than an hour. A journey of 300 to 400 miles, requiring 6 to 8 hours 
of travel at 50 knots, would seem to be approaching the limit of coach-passenger endurance, 
and we must agree with Baron Von Schertel that longer trips do not promise commercial 
success. 
If indeed the time required for a trip is the factor limiting the number of passengers 
which may be attracted, it follows that faster boats will draw more passengers for a given 
route. In the example of Fig. 3, it is indicated that the most profitable speed of the boat 
under consideration is 50 knots, assuming a constant load factor. If the load factor itself 
increases with velocity, however, the most profitable speed will be greater than 50 knots. 
This only serves to point out that the best speed of a hydrofoil craft from a commercial 
standpoint is influenced by market considerations as well as by hydrodynamic performance 
and operating costs. To arrive at general conclusions as to the characteristics of a com- 
mercial craft which will be most profitable, a more comprehensive analysis than the one 
presented is required. We shall have to examine the entire range of feasible speeds, sizes, 
route lengths, power plants, types of foil, and possible payloads. We shall have to examine 
not only how variations in these basic parameters affect hydrodynamic performance but how 
they may affect the operating costs and the value of the craft as transportation equipment. - 
And all of these must be examined in the context of the environment — physical and 
economic —in which the hydrofoil is expected to operate. 
Such an analysis is not made in this paper, and we must read it with this caution. It 
may appear to be more than it claims to be; it may seem to present conclusions where it 
provides illustrations. -We have no reason to doubt, for example, that under the conditions 
assumed the most profitable speed for the PT 300 is 50 knots, or that a Diesel-powered 
PT 20 is more profitable than one which is powered by a gas turbine. We should not neces- 
sarily infer, however, that 50 knots is thus the optimum speed for hydrofoil craft nor that 
Diesel engines are generally more profitable than gas turbines. 
The promise of hydrofoils would seem to justify a more searching evaluation: first, of 
their economic characteristics and, second, of where these characteristics may pay off. 
The Von Schertel boats have demonstrated that the hydrofoil may successfully perform the 
role of a waterborne bus. - Why isn’t consideration being given to the analogous — and poten- 
tially larger—role of ocean-going truck? 
At present, the vast majority of waterborne commerce moves at speeds of 15 knots or 
less. As Baron Von Schertel points out, no other waterborne vehicle has been developed to 
provide higher speed service, as the motor vehicle and railroad do on land. - The need for 
express cargo transport by water has been clearly demonstrated. Twenty-knot Mariner class 
ships have been able to draw traffic away from slower ships. Shippers pay premium rates 
to ship by fast passenger liner, at speeds of less than 30 knots. And at the far end of the 
speed spectrum, transoceanic air cargo has been growing at the rate of 10 to 15 percent 
per year. 
In a great many respects, the hydrofoil craft seems to qualify as an “answer” to the 
cargo aircraft for steamship lines: 
1. Its speed range is more than double that of displacement ships of comparable size. 
