National Geographic : 1957 Apr
Foils Fly in Water; the Hull Rides in Air Hydrofoil boats can race over rough seas that immobilize ordi nary craft. Their water-borne foils act so much like aircraft wings that designers say of a successful model, "It flew." These boats, like airplanes, lose flying speed and stall when slowed down. Normally they descend gently, but occasionally hit the water with a bump. Because of the steep V form, part of the Arrow's hydrofoils always remains submerged to give lift. Unlike Dr. Alexander Graham Bell's HD-4 (page 496), the vessel is driven by an under water propeller. This view ex poses the shaft, which slopes down from midships, keeping the propeller at proper depth. Here the Arrow returns to the mainland. + Using a boat hook, a crewman fends the unshielded bow foils from a Messina pier. These Sfoils may be tilted up or down to change fore-and-aft trim. Q National Geographic Society Gilbert Grosvenor (left. above) and Luis Marden 495 + Steel Fender Protects Vulnerable Stern Foils A hydrofoil boat's jutting underwater planes require delicate handling at dock side. Some experimental naval landing craft employ retractable hydrofoils. Inclined struts connect foils to hull. Designed by a German, the 27-ton ferry was built of aluminum alloy in Messina. In trials she made the Naples Palermo run in 42 hours, as against the 12 hours required by the overnight ship. + Figures on bow foil indicate the keel's height above water (in centimeters). When cruising, the hull rides about two feet clear.