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.
Gas fumes will stay in the bottom of the boat.
Unusually nothing happens. BUT a build-up of fumes is possible under the right conditions. That along with an ignition source (engine starter motor etc..) can cause a catastrophic explosion. Use the blower while fueling and before starts IAW your owners manual.
You have a high risk of blowing up you boat.
Ventilate the engine compartment, if enclosed.
You need to ventilate your boat after refueling to disperse any build-up of flammable fumes - especially petrol (diesel is less dangerous). Any petrol fumes sinking into the bilges could be ignited by a spark from an electrical switch, or when smoking.
There is the danger of accumulated fumes catching fire if there is a spark when an electrical device is switched on.
There will certainly be vapour from the fuel present and lighting of any naked flame could cause an explosion of this vapour.
Gasoline and propane fumes are most likely to accumulate in the bilge of a boat, which is the lowest compartment of the hull where water collects. It is important to regularly inspect and properly ventilate the bilge to prevent the build-up of flammable vapors.
While you are tied to the dock and fueling your boat, passengers should remain safely on the dock or in a designated area away from the fueling operation. It's important to keep them clear of potential hazards associated with fueling, such as fuel spills or fumes. Additionally, ensuring that passengers are not on board minimizes the risk of accidents or ignition sources during the fueling process. Always follow local regulations and safety guidelines regarding fueling operations.
You should open windows and hatches when fueling your boat to ensure proper ventilation and minimize the risk of accumulating harmful fumes. This is particularly important when using gasoline, as vapors can be dangerous. Always ensure that the area is well-ventilated before starting the fueling process, and keep them open until the fueling is complete and the area is safe. Additionally, it's advisable to turn off any sources of ignition while fueling.
extinguisher
A huge explosion.