What backfire flame arrestor requirement applies to inboard gas motors not exposed to the atmosphere above the gunwale?

• A. A spark arrestor is acceptable instead of a backfire flame arrestor.
• B. No backfire device is required for inboard motors.
• C. A CG-approved backfire flame arrestor is required for inboard gas motors not exposed to atmosphere above gunwale.
• D. Only for outboard motors.

Answer: (C)

The rule focuses on preventing ignition from engine backfires when the air intake is in an enclosure and not open to the atmosphere above the gunwale. Gasoline engines vent vapors and can backfire into the carburetor. If the engine compartment isn’t vented to the outdoors, that backfire flame could ignite vapors inside the boat, so a Coast Guard–approved backfire flame arrestor on the air intake is required. That device is specifically designed to stop flames from entering the intake, reducing the risk of fire or explosion in enclosed spaces.

So the correct requirement is that a CG-approved backfire flame arrestor is required for inboard gas motors not exposed to the atmosphere above the gunwale. The other options aren’t correct because a spark arrestor isn’t a substitute for a backfire flame arrestor in this situation, backfire devices are required in this scenario, and the rule isn’t limited to outboard motors.