Abstract: A sail with a tubular portion is pulled over a mast and/or a stay of a sailing vessel. The tubular portion is inflatable through a sail mouth opening at the fore leech thus forming an air envelope of the sail due to the relative wind effects. A plurality of telescoping contour sleeves formed of a lightweight, floating, elastic material are arranged in the tubular portion and sheath the mast and/or stay as well as selected portions of the rigging. The formation of an air envelope from a part of the sail and the use of rotatable streamlined contour sleeves inhibit complete heeling over of the sailing vessel and simplify the erecting of surfboards and sailboats. The telescoping arrangement of the contour sleeves permits an alteration of the sail surface and the sheathing of the rigging further decreases the wind resistance leading to an increased speed capability without need for greater inclination of the vessel. Thus the sails are better able to utilize the wind energy.