When you do not ventilate your boat after fueling what happens to the gas fumes?

The boat could blow up. Gasoline fumes are very explosive. That is why boats are required by law to have ventilation for the engine room. If there are fumes and there is a spark from something electrical then the boat could explode. Always ventilate after fueling for at least 4 minutes, and make sure that electrical equipment on the boat is UL listed as ignition protected. That means it won't ignite any gas fumes. Always check for fumes with your nose before starting the engine.