The wind passing over a sail generates differential
pressures, acting at 90 degrees to the surface. The "Centre of Effort" (C of E)
of the "Total Aerodynamic Force" generated acts through a point 25% back from
the leading edge of the sail.
The FreeWing rig couples the jib, the mast
and the mainsail into a single, slotted aerofoil.
The aerodynamic forces
from the jib, the mast and the mainsail balance each other.
Their
combined "Centre of Effort" is at a point just behind the rigs rotational axis.
This ensures that the load on the mainsail is light and keeps the "C of E" close to the centre line of the
yacht, whatever the apparent wind direction
The FreeWing rig's rotating wing
mast eliminates the mast-induced turbulence that degrades the performance of a
conventially rigged mainsail.
The diagram shows the attached airflow over the FreeWing rig when beating.
It also shows the "C of E" and how the total aerodynamic force is converted into a driving force and a heeling force.
When the yacht turns down wind,
easing the mainsheet allows the FreeWing rig to rotate.
On a standard rig the the sails stall, but with
the FreeWing rig the attached airflow is maintained.
The "C of E"
and therefore the driving force from the rig remains close to the centre
line.
The resultant neutral helm makes
helming easy.
The driving force from the
stalled sails of a standard rig act through a point a long way from the yacht's
centre line.
The resultant weather helm makes the yacht directionally unstable.
Broaching is a danger in heavy weather.
Off the wind in gusty
conditions, a standard rig has to be sailed conservatively.