This disclosure relates to a boat including a hull which forms a closed engine compartment. The compartment is air-tight at and above the water line or draft level which is formed when the boat is overturned in the water. The boat further includes an air inlet duct and an exhaust duct which extend into the engine compartment. Each of the ducts has one end which opens in the compartment above the draft level, and another end which is out of the compartment and below the draft level, thereby forming an air space in the compartment when the boat is overturned.