PURPOSE: To reduce a resistance area when a sail is folded under a strong wind and to save energy, by a method wherein a hinge, serving as a fulcrum when the sail is folded and unfolded, is located closer to the central part of a moving hard sail which is symmetrically divided at its center into two sections.

CONSTITUTION: When sails are unfolded, they are brought to a condition shown by reference numerals without a mark of ('), and when folded, they are brought to a condition shown by the numerals with the mark of ('). A pivoting mast 12, extending through the medium of a pivoting device 13, from a stationary mast 14 installed on an upper deck 15, stands upright. A top 6 of the piston rod of a hydraulic cylinder 5 secured to the pivoting mast is vertically moved by hydraulic pressure. Since a pin 11 is secured to the pivoting mast, when the top end 6 of the piston rod is moved vertically, levers 18 and 19 are actuated through a pin 16 or 17, and actuating hinges 8 and 10 are moved close to and away from the fixed pin 11 through pins 7, 9 and levers 20, 21 to perform operations to furl and unfurl the sails.