46
SVN Solovelanet Global
First, these boats won't have a fixed keel; on the
contrary, they will be equipped with two canting,
moving appendixes called foils. Second, the bo-
ats will get back to the traditional mainsail, in-
stead of the rigid one, both for a more practical
use (remember the crane needed to haul it to the
mast?) and for sake of cost reduction. Let's see
together the first of these two
topics.
The hidrofoils
The term "foil" normally refers to an aerodyna-
mic surface which, thanks to its shape, produ-
ces a consistent amount of lift at the cost of a
minor drag when moving into water. The wings
of aircrafts and helicopters work in a similar way
(see the Deepening Box "The Lift"). But not only
aeronautics: think about the use of DRS (Drag
Reduction System) in Formula 1, which is -not
surprisingly- also called "adjustable rear wing".
Or think about a kitesurfer's kite or a windsur-
fer's sail. They are all examples of aerodynamic
surfaces which are based on the same physical
principle: the lift. The suffix –hydro stands for
the use of foils into this element.
Every AC75 has two foils and a rudder, which ser-
ve to multiple scopes. Of the two foils, only one at
a time is in the water (see afterwards). This foil is
able to produce the amount of lift required to ful-
ly lift the boat and to keep it steadily out of the
water (compared to the Imoca 60 class, which
basically glides for many meters over the wa-
ter before re-touching it). Moreover, like tra-
ditional keels, foils apply a transversal force,
perpendicular to boat's direction and poin-
ting upwind, to mitigate leeward. Third,
the windward foil, which is lifted while the
boat is foiling, contributes to the righting
moment thanks to its intrinsic weight of
circa 1,2-1,5 tons (see Deepening Box
"The Righting Moment").
The main difference with the foils of
the AC catamarans is the shape. In
the AC75, both the foils and the rud-
der have a "T" shape, while in the
AC50 and AC72 the foils had an L-
like configuration and only the rud-
der had a "T" shape.
