To create a rigid, three-dimensional structure for active sailing positions and for converting to a non-rigid, two-dimensional structure during sailing manoeuvres and when not in use, a sail consists of two cloth layers which are connected to one another on the leech side. Pressure chambers (14-19) are formed between the cloth layers by means of spacer webs (22-27) adhesively bonded in place. The pressure chambers (14-19) are orientated in the longitudinal direction of the sail (10) and pressure gas can be admitted to them and they can be pressure-relieved via a controllable valve arrangement. <IMAGE>
