GC32 and Flying Phantom: the two foiling cats according to Mario Caponnetto

Foiling Week, the week dedicated to “flying boats,” came to an end on Lake Garda. The success of the event confirms the growing interest around foil technology, which, although born in the 1950s, has been the subject of great development only in recent times, after the exploits of the Hydroptère and after Emirates Team New Zealand, taking advantage of a “gap” in the regulations of the 34th America’s Cup, was able to equip its trimaran with foils and thus make it fly.

In just a few years, foiling (i.e., sailing with hulls lifted from the water) has transformed from a “luxury” for sailing stuntmen to a thrill that anyone can experience. first with the advent of the Moth then with small flying catamarans. We asked one of the “brains” behind Foiling Week, Mario Caponnetto (a Genoese naval architect born in 1961, who gave a lecture on the garda entitled “CFD: tools for foils design”) to “explain” two boats that are making a good impression. The GC32 and the Flying Phantom, the first one-design foiling cat.

We couldn’t have chosen a better lecturer: Caponnetto was on Oracle’s design team in the winning campaigns of 2010 and 2013, and he was involved in CFD, which is all about fluid dynamics. Having finished his adventure in the stars and stripes, he is now serving Luna Rossa. Here’s what he told us:

THE GC32 EXPLAINED BY CAPONNETTO
“The GC32 is a catamaran born from the pencil of Martin Fischer, a brilliant German designer who has been living in New Caledonia for years now. In the first version launched about two years ago, the boat had “S” foils and was not capable of full foiling, that is, with the hulls completely out of the water. In the wake of the America’s Cup AC72 catamarans, the boat has been revised and in particular has been fitted with “L” foils capable of giving truly enviable sustenance and flight stability.

HOW IT WORKS.
As a relatively small manned boat for its size (4 people for about 9 meters of boat), the need for as “automatic” a flight control as possible is obvious. This was brilliantly achieved with generously sized foils, but more importantly, equipped with tips that were very angled with respect to the horizontal plane. Practically the control of the foil rake angle, which is expected anyway, is minimized. In fact, controlling the foil rake on the GC 32 is still quite complicated to do while sailing although there are plans to improve the control system which should reduce friction in the mechanism. In practice this is now done before the race depending on the expected wind strength or while sailing by acting on the upwind foil before tack change. There is also currently no provision for in-navigation control of the angle of incidence of the elevators, the horizontal wings mounted at the bottom of the rudders, but again upgrades are expected in the near future.

THE TRICKS TO MAKE IT GO STRONG
The full GC 32 weight is only 800 kg with a maximum racing crew weight of 340 kg. With these proportions, it is obvious the importance of having the crew as far upwind as possible to maximize the righting moment, which in practice happens as early as a few knots of wind. Normally a crew member will also move longitudinally when the boat is in the air to try to optimize trim.

ANOTHER GOOD EXAMPLE: THE FLYING PHANTOM
The Flying Phantom is another brilliant design by Martin Fischer, born in the period between the making of the non-foiling GC32 and the foiling version. Initially born as a traditional F18, it soon became the world’s first production foiler catamaran.

FLIGHT TIPS
Very similar to the GC32 (foil with very angled tip) however, it allows more active rake control by the crew, 2 people on the trapeze. In this case the weight of the crew is even percent more important, and much of the trim adjustment is done by longitudinal displacement of the sailors, requiring virtually no elevator control. According to those who have tried it, the boat has exhilarating performance.” (Mario Caponnetto)

In the next issue of the Journal of Sailing Mario Caponnetto will reveal the secrets of foiling: how do boats fly?