In the summer of 1919 Alexander Graham Bell’s HD-4 tore across Bras d’Or Lake in Nova Scotia at 71 miles per hour, its 10,000 pound hull held clear of the water by underwater wings and pushed by two 350 horsepower Renault aircraft engines. A hydrofoil works because water is nearly a thousand times denser than air, so a small foil can deflect water down and use Bernoulli pressure differences to lift a whole hull. The idea goes back to Emmanuel Denis Farcot’s 1869 British patent, Enrico Forlanini’s ladder foils in Italy, and the Comte de Lambert’s twin hull boat on the Seine in 1904. Bell read about these experiments in Scientific American in 1906 and in 1910 rode Forlanini’s craft on Lake Maggiore with engineer Casey Baldwin.

Speed ran into a hard limit called cavitation: near 60 knots the pressure over a foil drops so low that water boils into vapor bubbles that kill lift and implode hard enough to pit metal. After World War II the technology split. Hans von Schertel’s Supramar built V foil boats for Mediterranean tourists, while Rostislav Alexeyev gave the Soviet Union river commuter fleets including more than 400 Meteors. Navies struggled with fragile foils, and ferries lost out to catamarans that could carry cars. Today carbon fiber and fly by wire controls have revived foils for racing yachts and for electric boats that cut drag by up to 80 percent.

• V shaped surface piercing foils right themselves naturally, while fully submerged inverted T foils ride smoothly but need computer control.
• The jet powered White Hawk of the early 1950s could barely beat Bell’s 30 year old record.
• Germany’s World War II VS-6 minelayer hit 47 knots but its foils proved too fragile for production.
• Canada’s HMCS Bras d’Or reached 63 knots, yet lifting the hull also lifted its sonar out of the water.
• Candela builds electric hydrofoil ferries now running in Mumbai, Saudi Arabia, and Lake Tahoe.