Sail-mast unit for surfboard has single sail surface with long side against mast with vertical axis through it so that there are unequal sail surfaces either side of it

摘要

The surfboard (1) has a sail (9) which can consist of a single sail surface with long side against mast with a vertical axis (6) through it so that there are unequal sail surfaces on either side of it. The sail can turn on the line of the vertical axis of the double mast (4) under the application of the wind force to the sail pressure point (SD).