256 H. von Schertel 
fuel consumption the interest on the invested capital earned with a turbine-driven boat is 
only 85 percent of that of a Diesel-powered vessel. However, the fact that the modest 
space requirements for turbines permit the accomodation of additional passengers has not 
been taken into consideration. The conditions will be changed if prices and consumption 
figures for turbines can be further reduced in the future. 
We shall now consider the field of application for the commercial hydrofoil boat within 
the framework of modern transportation and with regard to any competing craft. We will also 
investigate its limitations as far as technical practicability, speed, and economy is 
concerned. 
Table 1 presents the principal data as they affect the economy of the hydrofoil boat 
and its three competitors: the conventional displacement boat, the airplane, and the heli- 
copter. The data are based on an assumed distance of 100 nautical miles. For an estimate 
Table l 
Comparison of Prices and Operating Costs 
Block- Operat. costs 
speed V | No. of 
passeng. mi 
(¢) 
Passenger Boat | 26.5 tons : 700 
Hydrofoil PT 20 2,800 
Airplane Convair 18,000 
Helicopter Sikorsky ~40,000 
S-55 
*V,= WV anes. boat « 
of economy the two last columns are the most interesting. They indicate price per seat 
divided by block-speed (port-to-port speed) and the direct operating costs per passenger 
mile (expenditures less cost of ground organization). It appears that the foilborne craft is 
very economical compared with the other means of transportation and under the assumed 
conditions. In spite of the slightly lower “initial capital expenditure per passenger mile” 
and operation costs of the displacement boat, the attainable revenues within a certain 
operation period are higher for the hydrofoil boat because it travels three times as fast. It 
must also be taken into consideration that the public is generally willing to pay higher 
fares for faster transportation. The comparison with the commercial airplane reveals that 
its initial costs are higher and its total operation costs very much higher if the expenditures 
for the ground organization are taken into regard. With total operating expenses estimated 
to be at least 7 times those of the hydrofoil craft, the helicopter cannot be considered to 
represent an economical instrument of transportation at present. 
In order to find the speed ranges within which the hydrofoil boat and its competitors 
can be successfully employed we have already shown in Fig. | the power coefficient for 
the craft in question over speed. First of all the eaming power for a hydrofoil boat with 
