Abstract: The invention relates to a boat sail comprising a first (4) and a second (6) sheet, having similar shape and dimensions, coupled each other in correspondence of the outer perimeter and by a plurality of transverse ribs (12), provided between said sheets (4, 6), suitable to divide said sail into multi-sections (11), said sail (2) being characterised in that it provides a valve (14), that can be opened and closed to allow the air to enter within said sail into the space between said first (4) and second (6) sheets, at least a retractor element (15) provided on each rib (12), that can take two positions, respectively for the closure of the rib (12) and for opening the same, in order to make the sail taking a wing contour shape, and means (16) for opening and closing said retractors.