rope 14 the other end 15 of which extends through an opening in the mast preferably via a first pulley wheel 16 and a second pulley wheel 17 arranged at an opening 18 in the mast the outer end 15 of the ropes 17 is secured to the tack 19 of a sail as is shown sketchily on the figures a force applied in the direction of arrow 20 will thus cause an amplified force acting in the direction of the arrow 21 on the sail fig2 4 show a preferred embodiment of the invention according to which a mast extender 1 or a mast end is provided with a rope drum 2 with a cylindrical part 4 on which a rope 5 which is secured to the drum can be winded up by turning the rope drum 2 the rope drum may be provided with end flanges 3 3 39 but these are not absolutely necessary and the drum may consist of a straight preferably cylindrical shaft the rope drum can be turned with the aid of a crank 6 or a fulcrum which is arranged on the outside of the mast extender or mast and is connected to the rope drum according to the figure this connection is provided by a shaft 7 on which the rope drum is arranged said shaft 7 being mounted in bearings in opening 8 in the mast extender or mast said openings may optionally.