The advent of the Foiler, the first flying yacht that for a year now has been the the heart of every boat show in which it participates, has
The advent of the Foiler, the first flying yacht that for a year now has been the the heart of every boat show in which it participates, has brought back the attention of the nautical enthusiasts on a typology of very particular boats: the hydrofoils. In fact, it is the first time that they meet with the luxury boating and the result leaves speechless. The history of the hydrofoils is however much older and has been characterized by Made In Italy more than one might believe.
Before we start, I remind you that at the following link you can find a thematic index of all the Tecnoseal Answers released until today.
History: Development of an idea
It all start with Enrico Forlanini, well-known inventor of Italian origins, who in 1898 began working on the studies of the Parisian Emmanuel Denis Farcot (dated 1869) to develop the first project of Hydrofoil. This is so promising that Forlanini obtains certificates for testing in both Britain and the United States. In parallel with Forlanini, English John Thornycroft began working between 1899 and 1901 on a series of "single-foil" models, eventually developing, in 1909, the Miranda III (considered the progenitor of boats of this type).
In 1906 an American scientific article on the operating principles of hydrofoils inspired the Scottish inventor Alexander Graham Bell to work on a concrete project. The experiments of Bell and of Casey Baldwin, his chief engineer, begin in 1908 and start from the results obtained previously by Forlanini. The three scientists also have the opportunity to meet, in 2011, for a test trip on the hydrofoil developed by the Italian. An illuminating experience that spurs Bell to create the famous HD-4 (thanks also to the funding of the US Navy).
On 9 September 1919 the HD-4 imposed a world speed record on water of 114 km/h. This remained unbeaten for two decades. It should be noted that in the 50s an English couple built the White Hawk, a hydrofoil that had the specific purpose of beating this record. But the boat could barely match the speed of the HD-4. Unbeknownst to them, the two engineers had discovered a phenomenon that still limits the speed of the hydrofoils: the cavitation.
History: from project to trade
Shortly before the Second World War the German engineer Hanns von Schertel started working on hydrofoils and continued during the conflict (despite the capture by the Russians). After the war, the Germans were no longer allowed to develop fast boats and Schertel then moved to Switzerland where he founded the Supramar which, in 1952, launched the first commercial hydrofoil: the PT10 Freccia d'oro. This was used as a high-speed passenger boat right on Lake Maggiore!
In 1968 Hussain Najadi bought the Supremar and made it active also in Japan, Hong Kong, Singapore, United Kingdom, Norway and United States of America. In the latter nation he began to work with General Dynamics and the American Navy while in Japan he works with the Hitachi shipyards in Osaka. Most of the numerous models developed in these years were designed by Cantieri Navali Rodriguez of Messina, in Italy.
In the same period, the Soviet Union also began to experiment in the creation of hydrofoils with many projects carried out during the Cold War period. In 1957 the Raketa, the first commercial hydrofoil in the Soviet Union, was produced. One of the most successful inventors was Rostislav Alexeyev that many consider to be the father of modern hydrofoils due to the valuable contribution made by his studies to their development. It was always Alexeyev who created the famous Ekranoplan in the 70s. Since then the hydrofoils have continued to be used occasionally in the civil and military sectors. Currently the most capacious hydrofoil in the world (350 passengers) is the Italian Gianni M..
Operating Principle
The hydrofoil can be defined as a boat that at standing or low speed is kept afloat, according to the Archimedes principle, from the hydrostatic thrust (ie from the displacement). However, when this reaches a certain speed, either by motor or sailing propulsion, it emerges totally giving the impression of flying over water. This is allowed by the lift, that is the component of the global aerodynamic force calculated in a direction perpendicular to the relative wind direction, generated by the immersed foils connected to the hull (basically is the same principle that allows aircraft to fly).
At low speeds, the hydrofoil behaves like a conventional ship. As the speed increases, the water pressure under the foils, combined with the depression forming above them, generates a lift force opposite to the weight of the vehicle. Beyond a certain speed this force causes the complete escape of the hull from the water. The only parts that remain submerged, in addition to the foils naturally, are the propeller (connected to the end of a long shaft) and any steering rudder. When the hull is completely raised, the only hydrodynamic resistance encountered by the boat is that produced by the foils that hold it up. For this reason an hydrofoil can reach remarkable speeds in the face of a moderate energy expenditure.
Existing Types
Currently there are two different types of hydrofoils that are differentiated by the foils arrangement. The first model, as well as the oldest one, is the one with the partially submerged foils or also the hydrofoil SP (surface-piercing). This name is due to the fact that part of the foils (which have a V-shape) is visible above the surface of the water when the hydrofoil has reached its maximum emergence. The main advantage of these hydrofoils is to automatically adapt themselves to the height of the waves encountered during navigation.
The second type of hydrofoils is the one with completely submerged foils or also hydrofoils FS (fully submerged). These are modern designs that have foils with an inverted T shape that, in fact, remains completely submerged even after reaching the maximum emergence. The hydrofoils of this type are less subject to wave action and therefore are more stable and comfortable for crew and passengers. The big cons however is that does not automatically adapt themselves to wave height and the lift of the foils must therefore be constantly changed (the process is usually managed by sensors, computers and other technological systems).
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