Movement of the tailvane is transferred
to the main wing by the belt and pulley system.
Since the tailvane pulley is of a smaller diameter than the mainwing
pulley, the wing moves about 15 degrees less on each tack, giving it a
suitable angle of attack to drive the boat. As the wind comes ahead,
this angle of attack diminishes until when the wind is directly in front
it is zero.
Before testing, I imagined that this setup would give reduced performance
on windward courses, but I found in practice that the reduced angle of
attack at say, 45 degrees was no handicap, and was probably exactly what
was needed to improve the L/D ratio to penetrate the wind.