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hull and therefore require rigging with
spreaders,
• fitted to existing hulls with conventional
staying arrangements,
• depowered by rigging adjustment,
and
• reefed and stowed.
Of the several available soft-wing
sail designs, not one can meet all the
criteria listed above. A common shortfall
is that the mast must be freestanding
so it can rotate and accommodate
a pocket luff sail or a split luff sail.
The structural requirements of such
designs must be taken into account
during a yacht’s design and build.
That’s not to say these rigs don’t have
advantages, it’s just that they are by
definition often a radical departure
from a conventional setup.
The wing-section mast on a highperformance
catamaran will constantly
sail the boat on its moorings,
and in extreme weather conditions
cannot be depowered, due to the
mast’s aerofoil section and area. Highperformance
catamarans have been
lost at sea in high winds simply
because the bare wing mast was
unable to be depowered, leading to
capsize.
Principles of
VGWS Operation
Stiffened with battens, the two
sails of the VGWS connect to either
side of a rotating mast at the leading
edge of the section and to each
other at the trailing edge. Thickness
and asymmetry are induced by mast
rotation. This places the battens in
compression on one side of the foil
and the battens on the other side, in
tension. The compressed side of the
foil curves, with the amount of convex
curvature, or camber, determined
by the angle of mast rotation.
The di rect ion of asymmet ry is
determined by the direction of mast
rotation. Figure 1 is a view from
underneath the sail on a port tack
with about 40° mast rotation and full
outhaul.
Additional camber can be introduced
to the foil by reducing outhaul.
This allows the windward batten to
bow more under the wind load, thus
increasing the camber of both windward
and leeward battens. Controlling
the mast rotation and the outhaul
tension produces a variety of section
shapes (Figure 2).
Figure 1.
Figure 2.
Figure 1—View from underneath the sail on a port tack. The two plies are attached
at the mast and leech. Figure 2—Once rotated, the VGWS effectively becomes a
semi-rigid structure.
December/January 2013 61
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