How did a Dutch windmill use an auxiliary vane to face the wind?

To face the wind efficiently, windmills—including those in the Netherlands—utilized a mechanism known as the fantail, invented by Edmund Lee in 1745.

The fantail consists of a set of five to eight smaller vanes mounted at a right angle to the main sails, typically on the tailpole of a post mill or the cap of a tower mill. These vanes are connected via gearing to wheels that run on a track around the mill's body or cap. When the wind changes direction, it strikes the sides of the fantail vanes, causing them to rotate. This rotation drives the geared wheels, which automatically turn the mill's body or cap until the main sails are once again positioned squarely into the wind.12

Before this invention, millers had to turn the mill manually using a long tailpole or winches, a labor-intensive process that the automatic fantail effectively replaced.12