Abstract: A sail (1) for sailing-boats which is provided with a shielding device (3) arranged substantially horizontally on the sail (1). The shielding device at least partly bridges the concavity formed on the upwind surface of the sail when the wind fills the sail (1). The shielding device preferably includes a cloth (3) sewn along one of its own side edges to the sail along a horizontal line so that, in use, the cloth stand out substantially horizontally from the concave upwind surface of the sail (1) between the two edges (4, 5) of the sail. A similar shielding device is provided at a corresponding location on the opposite surface of the sail, and structure provided for collapsing the respective shielding device on the downwind surface of the sail and erecting the respective shielding device on the upwind surface of the sail.