The fuel tank in your boat needs to be durable and stand up to moisture and, in some cases, salt air. The tank also needs to meet all safety requirements and contain the fuel under varying conditions, so having a custom tank made for the boat is sometimes the best solution.
Fuel Tank Construction
If you are going to use a custom fuel tank in your boat, there are are some things that you need to be aware of, and the tank needs to meet the safety requirements of the US Coast Guard and the National Marine Manufacturers' Association (NMMA). Any reputable marine tank builder should know these rules and regulations, but since the tank is going in your boat, you are ultimately responsible for ensuring the tank meets the code.
The material for new tanks is often aluminum because it is incredibly corrosion-resistant, but in some situations, tanks made from polyethylene plastic are used in boats as well. The material it is made from is not regulated, as long as the tank is not leaking and meets the safety requirements.
Every fuel tank must have a vent in the tank that vents away from the cabin if the boat has one. The vent allows the fuel in the tank to expand and contract naturally without over-pressurizing the tank. It is normal for gasoline to expand in the heat and contract in the cold, so even if you are just sitting out on the lake, the warm weather will cause an expansion in the tank, and cooler evenings will let it contract. The vent allows this to happen safely.
While older boats may have open vent systems that vent to the air, new standards require that the vent from the tank have a carbon canister incorporated so that any hydrocarbons venting from the tank filter though the carbon filter material and are not allowed to escape into the air.
When building a custom tank for a boat manufactured after 2011, the builder must incorporate a fluid limit valve in the tank. This valve allows air to escape the tank when you are filling it will fuel, but once the fuel reaches the level of the valve, the valve closes, and the fuel will back up the fill tube and trip the valve in the fill nozzle to shut off the flow of fuel.
The system works almost identically as the system in cars that stops you from overfilling the tank and is intended to keep gasoline in the tank, not on the deck or in the water. If the valve does not close or is missing from your new custom tank, it will be difficult to tell when the tank is full, and the result could be a fuel spill that you may be financially responsible for.
To find out more, contact a company that can work with you to create a custom marine fuel tank.