Abstract: There is discussed a sail apparatus having a sail with one or more battens. A furling system varies the area of deployed sail between a furled state and an unfurled state by rotating the sail about the leading edge. At least one batten comprises a single extendible sheet member operable to switch between a rigid three-dimensional longitudinal state and a coiled planar state, such that a deployed portion of said at least one batten is in said rigid, three-dimensional longitudinal state and a furled portion of said at least one batten is in a coiled planar state. The batten is resiliently baised towards the leading edge of the sail, while allowing movement of the batten towards the trailing edge of the sail during furling.