Vapors from gas and leaking propane or butane are heavier than oxygen and will quickly flow into the bottom parts of a watercraft. These vapors can collect in the bilge and are highly explosive. As required by the U.S. Coast Guard, all recreational boats that use gasoline engines for mechanical power, propulsion or electrical generation should be fitted with a ventilation system.

It is the boat owner’s responsibility to keep the boat’s ventilation system in operating condition at all times. Proper maintenance includes making sure all openings are free from blockage, ducts and ducting are not blocked or torn, and blowers work appropriately.

The U.S. Coast Guard Ventilation Standard applies to all boats built on or after August 1, 1980. Every boat built after this date should display a label that confirms the inclusion of an appropriate natural or powered ventilation system.

Natural Ventilation System

A natural ventilation system is mandatory for each boat compartment that has a permanently-installed gasoline engine or fuel tank and an electrical component, has openings between it and a compartment that requires ventilation, or that contains a non-metallic fuel tank.

The components of a natural ventilation system include:

• A supply opening (duct/cowl) from the outside air or from a ventilated compartment
• An exhaust opening into another ventilated compartment or an exhaust duct into the air

Each supply opening or duct should be located above the normal accumulation of bilge water and each exhaust opening or duct must originate in the lower 1/3 of the compartment.

Powered Ventilation System

A powered ventilation system is required to be installed for each boat compartment that has a permanently installed gasoline engine with a cranking motor for remote starting.

The powered ventilation system is made up of one or more exhaust blowers, and each intake duct for each exhaust blower should be in the lower 1/3 of the compartment. The duct should also be above the normal level of bilge water.