A mast (1) is in the form of an egg-shaped closed loop that extends abeam of a hull (7). A main spar (2) is supported on the mast (1) and extends upwardly from a lower, fore position on the bowsprit (4) to a higher, aft position above the stern (12). A lateen sail (3) of triangular form has its longer side attached to the main spar (2) with its shorter sides depending from the main spar (2). The free corner of the sail (3) is tethered by ropes or sheets (14) to points on the sides of the hull (7) or deck such that it is positioned substantially above the centre line of the hull (7). The sail (3) can be fully deployed within the closed loop shape of the mast (1) without fouling the mast (1). This allows the sail (3) full and unrestricted deployment, results in exceptionally good sailing and provides swift and easy tacking.