236 H. von Schertel 
attaining economically the present-day speeds of land vehicles, since the average speed of 
fast trains in highly developed countries lies at 43 knots and at 32 for the whole world. But 
in favor of the hydrofoil boat it should be mentioned that regular passenger services and 
experimental trips along coastlines have demonstrated a further advantage, inasmuch as it 
can reach certain destinations in an appreciably shorter time than land vehicles, which — 
travelling with equal speed—must of necessity follow the more or less irregular coastline. 
Such conditions for example prevail in Scandinavia. 
Even better results can be obtained with a projected 300-ton Supramar hydrofoil boat. 
In Fig. 3 is shown the obtainable profit for this type versus speed. Best results are 
achieved at a speed of 50 knots yielding an interest on the invested capital of 57 percent. 
When this project is realized, hydrofoil boats will show a clear superiority over land vehi- 
cles with respect to travelling time whenever they operate between the same points on the 
coast. This diagram also will be discussed in detail later on. 
PS 
S ~ 
S = 2000yearly operat hours 
= = 60% passeng. load 
= 6d Ticket price 7cts./nm. 
110 4 Profi IN 
rofrit 
700 | 50! . N yi 
IN 
904 V, 
go | 4C IA 
INAS 
a KE 
60 | 30}. ZAIN 
IS 
50 | Ss 
40-4 20! ese ole Bee day tL cae meres SAE INES 
ie “a — iS 
301 | | Effective power — XS 
| | | Dit S 
204 104 ce el N real 
= wy 
105 Sern ae i NN 
| 1 Turbine 2Tunbines——3 Turb. IS 
20 30 40 50 60 70 80 90 Vikn) 
Fig. 3. Earning power of the PT 300 type hydrofoil boat (length = 160 feet) 
Another quality distinguishes the hydrofoil boat from conventional craft. At higher 
speeds, displacement and V-bottom boats cause the formation of a wave system of consider- 
able amplitude in their wake which can interfere with the safe operation of other craft and 
damage river banks. For this reason the speed of such boats is generally restricted in nar- 
row waterways. Since hydrofoil boats develop only comparatively small wave-resistance 
the disturbance of the water surface is so slight that the boats can maintain high speeds on 
smaller lakes, rivers, and canals and in congested waters without endangering any other 
craft or shore installations. 
Considering now the airplane as the most serious competitor, we can derive from Fig. | 
that the airplane can attain much higher speeds with lower specific propulsion power than 
the hydrofoil boat. Therefore aircraft represents a very economical means of transportation. 
However its commercial use requires an extensive and very expensive ground organization, 
