42 Boating New Zealand
being the way to go, with a big T-foil on the bottom of a long
vertical keel shaft. The problem with that is that the Moth
works only because the crew weight provides such high
righting moment.
The rest of the craft is so light at sub-30kg compared
to the 60-90kg crew sitting out on 2.25m wide wings. To
scale that to 75ft would make the K-boat look mediocre
and require quite high crew numbers, and/or very wide
wings (making sprinters rather than cyclers the next
cross-discipline athletes?).
One inescapable difference is that a catamaran is stable
at rest, while a foil-stabilised mono-hull without a keel has
no foil-derived stability if there is no flow over the foil. So,
in a down-speed pre-start manoeuvre for example, there
could be issues!
The AC75 has addressed this with ballasted foils:
between 1.0t to 1.5t each has been reported from ETNZ’s
Technical Director Dan Bernasconi. When lowered these
offer the same effect as a ballasted keel by lowering the
vertical centre of gravity sufficiently to prevent the yacht
from falling over.
This would apply to a docking-in or docking-out, long
tow-out to or back from the race area rather than a sailing
mode, but could possibly allow the yacht to hold up head to
wind in a dial up. It also gives the yacht the required degree
of self-righting in the event it all goes pear-shaped
The two sailing modes are interesting, given the
requirement for racing in a wider range of windspeeds
and sea states than in Bermuda, with a high-speed sailing
mode and a stable sailing mode described.
The high-speed mode involves the leeward foil being
deployed to generate lift and side-force, and also oppose
the heeling moment, while the windward foil is raised to
reduce drag. Righting moment is generated by the lever