A weatherproof ventilation system that provides protection from rain and waves entering the hold of a boat or ship while allowing fresh air to reach areas below the deck. The adaptable weatherproof ventilation system is positioned over a hatch and includes a flexible structure, a support structure, a flat bottom section, a folding baffle, and a removable baffle. The weatherproof ventilation system has an opening and arrangement of baffles that is adjustably controlled by the folding baffle and the removable baffle. The weatherproof ventilation system can also comprise one or more loops, one or more elastic cords, a skirt, first and second poles, and one or more snaps, zippers, straps, buckles, and ropes for attachment of the weatherproof ventilation system to the deck of the boat or ship.