34 Boating New Zealand
ballast is required. Unlike the catamarans, which have high
initial form stability at rest, the monohulls need a low centre of
gravity to keep the rig pointing skywards.
he mass of the ballast – around 2.3-tonnes shared
equally in the two foils – is added mass that needs to be both
accelerated and lifted, increasing the loads on the foils and
making them more sensitive.
Certainly, scale efects and inertia will esnure things
happen slower than on a foiling moth, and Dan Bernasconi has
explained how, in the simulator at least, a partial loss of foil
area to ventilation is not catastrophic, leading only to loss of
ride height, slowing a pitch down by the bow.
In addition, the top of the mainsail has a ‘gaf ’ with a yoke
that allows twist control without high leech tension. In this way
heeling moment can be controlled quite precisely to mitigate
against capsize.
Again, as explained by ETNZ, the added mass (approx three
times that of an AC50) actually makes the yacht more powerful
at higher speeds, even though the lighter AC50 is quicker on
the foils in lighter winds initially.
So it could be argued that adopting the monohull is solving a
problem that didn’t need solving: a catamaran is already known
to be a good option for a foiling race boat. Being light, stif and
carrying no parasitic ballast weight, with wetted area and drag
that reduces by half with a small increase in heel angle, the
multihull option is hard to beat.
Why not just stick the new, double-skin mainsails on the
AC50s and solve the one big negative aspect of operating
those cats?
he counter-argument goes along the Kennedy-esque lines
of ‘we do this – and the other things – not because they are
easy, but because they are hard’. Why dismiss what the future of
monohull sailing might become?
At some point in the future displacement sailing will be seen
in the same light as square-riggers and old gafers – a quaint,
sepia-toned nostalgic indulgence. he real business of sailing
eiciently (because burning fossil fuel will be outdated too) will
be foiling, no matter what the coniguration of vessel.
Now, I’m not saying the cruising yacht of the future will look
like an AC75, but just as the Wright Brothers’ Kittyhawk bears
little resemblance to a Gulfstream corporate jet, or the Model
T Ford to a Formula 1 car, both can trace their lineage back to
those points in time. We can identify the steps on the way that
were necessary to reach the current state of design.
We’re only at the beginning of this particular evolutionary
journey.LOA (hull)(m) 21.95 20.70
Beam (m) 5.68 5.0
Weight (T) 16.7 6.2
Ballast (T) 10 2.3
Crew** 22 11
SAILS
Mainsail (sq.m) 187 135
Headsail (sq.m) 126 92
A-SAIL/CZ (sq.m) 490 195
Upwind Area (sq.m) 313 227
Downwind (sq.m) 677 330
BOATSPEEDS 16kn TWS
Upwind (kn) 10.5 30^^
Downwind (kn) 15.0 40^^
Heel (o) 25 c.5
RM at Heel 37.5T.m c.45T.m^^^ Info courtesy of Mills Design
^^based on Belle Mente/Quantum Racing AC Challenge announcement
at NYYC Feb 7th 2018
*Sail areas are indicative only and have been scaled of AC75 rule sail plan.
**Rule 27.1 There shall be eleven crew members, unless reduced by
accident, who shall all be human beings.IRC MAXI 72 – AC 75 COMPARISONIRC MAXI 72 AC75RIGHT Articulated
foils ensure the
AC75 will be self-
righting in the
event of a capsize.