Propulsion system for a boat

A boat comprising:

• a propulsion system including:
• a main mast;
• a plurality of aerofoils connected to the main mast, at least one of the aerofoils being a displaceable aerofoil, the at least one displaceable aerofoil being adapted to be displaced along the main mast between an open position and a closed position;
• wherein when the at least one displaceable aerofoil is in its open position the aerofoils together form a sail of open sail area;
• and
• when the at least one displaceable aerofoil is in its closed position at least some of the aerofoils overlap to form a sail of closed sail area, the closed sail area being less than the open sail area;
• a displacement mechanism adapted to displace the at least one displaceable aerofoil between its open and closed positions;
• at least one of the aerofoils having a solar panel thereon;
• and,
• a stub mast extending along a stub axis, the stub mast being free to rotate about the stub axis;
• the stub mast being connected to the main mast by a stub pivot;
• the propulsion system further comprising a controller connected to the displacement mechanism for controlling the arrangement of the aerofoils, the controller being configured to be programmed with a parameter which is the relative importance of wind power generation and solar power generation, the controller being adapted to detect the wind power generated and solar power generated and control the arrangement of the aerofoils in response to the parameter and the detected wind and solar power generated.