Sail for the propulsion of means of transport

A sail comprising a sheet body comprised of flexible material which is connected at a first edge to a supporting mast, said sheet body comprising at least one pocket containing at least one stiffening rib which at least one stiffening rib extends between said supporting mast and a second edge of said sheet body that is opposite to the first edge of said sheet body that is connected to said supporting mast, wherein said at least one stiffening rib comprises a concave, substantially arc shape adapted to generate lift, at least one traction element connecting said ribs at one end for varying an orientation of said at least one stiffening rib with respect to said supporting mast wherein said at least one stiffening ribs comprises at least one flexible body having an elongated extension, said at least one stiffening rib having a bending moment applied thereto, in order to produce an arc-shaped bending of said at least one flexible body.