Hydrofoil Pioneers...

The Supramar PT Series Hydrofoils

by John R. Meyer, Jr.

(Last Update 15 Jan 99)

The SUPRAMAR series of hydrofoils was an outgrowth of Baron von Schertel's work prior to and during World War II in Germany. It was Russia's good fortune to capture most of von Schertel's hydrofoil team after the War. They became the backbone of hydrofoil development in that country where large numbers of surface-piercing hydrofoils have been built and provide much needed high speed water transportation on the myriad of rivers and lakes of that vast country.

Von Schertel managed to escape the Russian claws. This, combined with the fact that after WWII it was forbidden in Germany to build boats with speeds in excess of 12 knots, led von Schertel and his partner Sachsenberg to move to Switzerland. There, in 1952, at a small shipyard in Stansstad, they completed the PT-10, FRECCIA D'ORO, (Golden Arrow). This 7-ton craft had 32 seats and was capable of speeds up to 35 knots. On 29 May 1952, the Konsortium of Schertel and Sachsenberg joined with the Kredit and Verwaltungs-Bank Zug, to form Supramar, A.G. based in Lucerne. That same year the FRECCIA D'ORO began the world's first regular hydrofoil passenger service on Lake Magiore, between Switzerland and Italy. This is the same lake on which Forlanini made his noteworthy hydrofoil experiments half a century earlier.

FRECCIA D'ORO had an enthusiastic reception, mainly from the Italian public. The PT-10 proved that a hydrofoil could successfully compete with land vehicles as was done when it and an auto began a race from Arona to Ascona. According to von Schertel, "Although the motor car travelled at the highest possible speed on the road, the hydrofoil arrived long before the car even appeared. In most cases the hydrofoil has the advantage of taking a straight course, whereas the land vehicle usually has to follow the coastline."

In 1954 Supramar arranged their first license to build hydrofoil craft of their design with the Leopoldo Rodriquez Shipyard in Messina, Italy. Later, the PT-20 and PT-50 were licensed to be built in Japan, Norway, Holland, and Hong Kong.

Rodriquez started production of the 32-ton PT-20, a 72-passenger hydrofoil with a cruise speed of 35 knots, in 1955. The foils were a standard Schertel-Sachsenberg, surface-piercing type, with 58% of the lift provided by the bow foil and the remaining lift supplied by the aft foil. The angle of incidence of the bow foil could be manually adjusted within narrow limits from the helm position. This was convenient for adjusting for the effects of passenger load variations and sea conditions. Power was provided to a single propeller through a reversible gear by a supercharged, 1,100 hp, 12 cylinder MTU diesel engine with an exhaust turbo-compressor.

The first of the PT-20 series was named FRECIA del SOLE which opened a passenger service across the Straits of Messina. It was built to satisfy maritime regulations and became the first passenger hydrofoil to receive certification authority for carrying passengers at sea.

The FRECCIA del SOLE reduced the port-to-port time from Messina to Reggio di Calabria to one-quarter of that of the conventional ferry boats. This hydrofoil, which completed 22 daily crossings, soon proved its commercial viability. It has been reported that average time between major overhauls of the PT20 engines is approximately 10,000 hours, a notable achievement at the time.

Success of the PT-20 commercial passenger hydrofoil, from both its operation and profit aspects, led to development of the PT-50. Designed for offshore and inter-island operations, the prototype of this 63-ton hydrofoil was completed early in 1958, and production versions have seen extensive use in regular passenger services in various areas including the Baltic, the Mediterranean, and the Japanese Inland Sea.

The foil system of the 91-foot long PT-50 was larger, but very similar to that of the PT-20 in general arrangement. Both craft had about the same maximum speed of 34 knots. The PT-50 of course had two 1,100 hp MTU diesels, instead of the single one for the PT-20, and drove two three-bladed propellers.

Following the PT-50, several other craft in the extensive PT Series of Supramar hydrofoils were developed, including the PT-75 with a displacement of 85 tons. This was an advanced version of the PT-50. Also the PT-100, in turn a variant of the PT-75, was designed for short-haul commuter routes and accommodated 200 passengers.

The next major Supramar hydrofoil design was the PT-150 MkII with a displacement of 165 tons. It carries 250 passengers, and at a length of 124 feet, the PT-150 was the largest sea-going hydrofoil passenger ferry in the free world at the time it was launched.

The PT-150 represented a departure for Supramar with respect to the design of the foil system. Instead of the usual surface-piercing type fore and aft, the PT-150 foil configuration combined a surface-piercing foil forward with a fully-submerged foil in the aft location. The bow foil, which provides the necessary static transverse stability, is of the Schertel-Sachsenberg surface-piercing "V" design and provides 60% of the lift. The rear foil provides the remaining lift and utilizes the Schertel-Supramar air stabilization system. The angle of attack of the rear foil can be also manually controlled hydraulically both during take-off and when foilborne.

The air stabilization system referred to above feeds air from the atmosphere through small ports on the foil upper surface (the low pressure side), thereby decreasing the lift. The amount of lift is varied by the quantity of air admitted to the foil, and it is controlled by valves actuated by signals from a damped pendulum and a rate gyro. Since the system is installed on both port and starboard foils, a stabilizing roll moment is produced by decreasing the available air volume on the more deeply submerged foil and increasing the air available to the foil on the opposite side. This system was a rather ingenious invention of Von Schertel, but has never been widely adopted; the industry prefers to retain the more reliable system of either incidence or flap controls.

The PT-150 was also a major departure from its passenger ferry predecessors in terms of it's powerplant. Two 20 cylinder MTU supercharged diesel engines, each rated at 3,400 hp were installed to provide a cruising speed of 36.5 knots. It has been reported that the maximum permissible wave height in the foilborne mode at full power for passenger acceptability is 10 feet.

More than 150 hydrofoils have been built under license to Supramar of which, by far, the largest number were built by Rodriquez up until 1971.


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International Hydrofoil Society



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