Thomas Rouxel in
the ‘galley’ of the
trimaran’s cuddy –
a JetBoil and some
flask holders for
rehydrated meals
Gitana
›
‘gitana 17 will start to fly in as little
as 15 knots of true wind’
Gitana 15, on which they and designer Guillaume Verdier
experimented by trialling C- and L-shaped foils. That gave
them the knowledge and data to start work on designing
this 100ft class trimaran.
“We already knew how to sail the boat and the sensation
was not new,” Josse says. “When the boat starts to fly there
is a different way to drive and a different way to trim the
sails. We already knew that, but it [had taken] two years to
fly properly, and understand how to be stable.”
When I ask what he means, he says: “When the boat
starts to fly because the acceleration is faster, the apparent
wind moves a lot so you have to trim for a different
trajectory. To keep on foils you have to keep the boat and
all this power on this 4m^2 – you just think about the water
touching four points [leeward foil and T-foil rudder,
central daggerboard and T-foil rudder] and the balance
between those four points, not the 32m of hull you have in
the water in normal sailing.”
Gitana 17 starts to fly at 26-28 knots of boatspeed, which
it can reach in around 15 knots of true wind.
Foil profile angles and loads are shown in the cockpit so
Josse and Rouxel can monitor side force and compression
loads on the foils. A graphic interface beside the wheels
shows the load on the foils and Josse explains “then we
know if we can push harder or not.”
Ride height is adjusted by feel. As with the America’sCup boats, if the boat flies too high it starts
to go sideways. But flying high on the foils is,
says Josse, “just for the future. To fly 50cm
above the water is enough. We call that
skimming.”
Josse’s “big surprise” was finding that
Gitana 17 can easily fly in seas of up to 2.5m – “if the seas
are long enough,” he adds. It can reach speeds of 40 knots
in moderate reaching conditions and, remarkably, “we
know we can fly 50-60 per cent of the time in tradewinds
with two people,” says Josse. The top speed of around 46
knots was achieved with one reef in the main and the
smaller J2 headsail – under full sail, the greater windage
means peak speeds can actually be lower.
Class rules for these new 100ft multihulls prohibits
direct electronic control of the angle of foils so they have
to be designed to be inherently stable. Designer
Guillaume Verdier, who was also behind the winning
Emirates Team New Zealand America’s Cup design,
explains: “They behave a bit like a helicoil. When the boat
raises up in the water it makes more leeway, and when it
makes more leeway there is a component of the force that
pushes you down. But the difference [compared with the
America’s Cup boats] is that these are huge foils compared
to any other boat in the past.
“It makes a boat that is a little heavier because there are
more systems to control the foil, more hydraulics and the
platform is stiffer in torsion,” he adds.
But while the America’s Cup knowledge Verdier
brought to the project was critical to its success, the
Gitana design had to cope with many more variables. Photos; Yann Riou/GitanaS.A