Ventilation
All boats that use gasoline for electrical generation, mechanical power, or propulsion are required to be equipped with a ventilation system. A natural ventilation system consists of a supply duct from a ventilated compartment, or from a compartment that is open to the atmosphere and has an exhaust duct to the atmosphere.  Each exhaust and supply opening or duct must originate in the lower one-third of the compartment and must be above the normal accumulation of bilge water.  A natural ventilation system is required for each closed compartment in a boat that: Contains a permanently installed gasoline engine. Has openings between it and a compartment that requires ventilation. Contains a permanently installed tank and an electrical component that is not ignition protected. Contains a fuel tank that vents into that compartment; or Contains a non-metallic fuel tank.
A powered ventilation system is required for each compartment in a boat that has a permanently installed gasoline engine with a cranking motor for remote starting.  A powered ventilation system consists of one or more exhaust blowers.
In open boats, gasoline vapors may be dissipated through exposure to the open atmosphere.  Therefore, open boats are exempted from ventilation requirements.