Sail-drive propulsion system for boats

A boat propulsion system equipped with sail-drive transmission comprising

• a drive motor (M) coupled to a sail-drive transmission equipped with a drive shank (1) carrying a propeller shaft (3) for a propeller at a distal end, and
• a supporting and sealing flange (2), apt to be engaged in a correspondingly shaped opening of a boat's hull, to which said drive shank (1) is attached,
• wherein
• said supporting and sealing flange (2) has an upper and a lower side and consists of a main portion (2a), to which said drive shank (1) is attached, and at least an extension portion (2b) provided with at least one through opening (6a, 6b) into which a corresponding nozzle (8) is engaged, which nozzle is provided with
• an ejection section (8b), arranged on the underside of said flange (2), with an exit channel having an axis oriented substantially horizontally so as to produce a thrust in a different direction from that produced by said propeller,
• an inlet section (8a), located on the upper side of said flange (2), connected to a pressurized water supply pipe from at least a pressurization pump (9) connected to a water loading inlet.