Inside a large diameter mast (a foot or two), have a vertical turbine.
It is fed by a sail attached to a forestay that feeds air into the
vertical turbine. The sail does not provide any lift or forward
force, instead it serves only to collect wind and to redirect it so it
goes up into the mast turning the turbine. The turbine turns a 90
degree coupling that turns a propeller. This sailboat could sail
directly into the wind.
The sail could be reefed by rolling it around a boom at the bottom.