A wingsail for a powered watercraft comprising: a first aerofoil element; a second aerofoil element; and a third aerofoil element; wherein: each of the aerofoil elements is rotatable about an axis (10x, 11x, 12x) and has an aerofoil section with a centre of area which is closer to its leading edge than its trailing edge; the aerofoil elements are movable to a configuration in which flow from the trailing edge of one of the first or third element is directed toward the leading edge of the second element, and flow from the trailing edge of the second element is directed toward the leading edge of the other of the first or third element; the aerofoil elements are arranged in an array so as to together form a cambered shape; at least two of the aerofoil elements are configured to rotate to thereby reverse the camber of the cambered shape; and the aerofoil elements are configured to be positioned such that slots (17, 18) are formed between the first aerofoil element and the second aerofoil element, and between the second aerofoil element and the third aerofoil element, the slots being configured to regenerate airflow over the suction side of the aerofoil elements. a first aerofoil element; a second aerofoil element; and a third aerofoil element; wherein: each of the aerofoil elements is rotatable about an axis (10x, 11x, 12x) and has an aerofoil section with a centre of area which is closer to its leading edge than its trailing edge; the aerofoil elements are movable to a configuration in which flow from the trailing edge of one of the first or third element is directed toward the leading edge of the second element, and flow from the trailing edge of the second element is directed toward the leading edge of the other of the first or third element; the aerofoil elements are arranged in an array so as to together form a cambered shape; at least two of the aerofoil elements are configured to rotate to thereby reverse the camber of the cambered shape; and the aerofoil elements are configured to be positioned such that slots (17, 18) are formed between the first aerofoil element and the second aerofoil element, and between the second aerofoil element and the third aerofoil element, the slots being configured to regenerate airflow over the suction side of the aerofoil elements. each of the aerofoil elements is rotatable about an axis (10x, 11x, 12x) and has an aerofoil section with a centre of area which is closer to its leading edge than its trailing edge; the aerofoil elements are movable to a configuration in which flow from the trailing edge of one of the first or third element is directed toward the leading edge of the second element, and flow from the trailing edge of the second element is directed toward the leading edge of the other of the first or third element; the aerofoil elements are arranged in an array so as to together form a cambered shape; at least two of the aerofoil elements are configured to rotate to thereby reverse the camber of the cambered shape; and the aerofoil elements are configured to be positioned such that slots (17, 18) are formed between the first aerofoil element and the second aerofoil element, and between the second aerofoil element and the third aerofoil element, the slots being configured to regenerate airflow over the suction side of the aerofoil elements.