Abstract: This disclosure pertains to a pivotable control mechanism affecting the angular position of a centerboard as a function of the position of the boom of the mainsail. A pivot arm extending radially outwardly from the pivot axis of an extended pivotable centerboard is fastened flexibly and adjustably to the mainsail boom at a point aft of the mainmast. The trailing edge of the centerboard is pivoted outboard in a direction opposite to the trailing edge of the boom, providing thereby automatic compensation for the wind on the sail by allowing a variable pressure to be created on the centerboard therefor.