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Fuel Systems 

Why are there so many requirements for fuel systems?

Gasoline is extremely dangerous and volatile. It can go boom at the worst moments ruining your whole day! But it's no joke.

Fuel system regulations have been developed over many years, mainly by the Society of Automotive Engineers (SAE) and the National Fire Protection Association (NFPA).  These have been incorporated into the ABYC standards and the US Coast Guard regulations.

Most fuel leaks occur at a fitting.  So standards were developed to prevent this. Things such as double clamping a hose and using swaged fittings were made primarily to prevent leaking connections.

Hoses that were used in autos were found to be inadequate in boats. Fuel in cars does not stay in the hose very long, but in boats it can sit for months at a time.  This gives the additives and the components of the gasoline itself time to attack the compound of the hose.  So hoses have to be able to resist this.  Alcohol in the fuel leaches out the parafins that make the hose pliable and flexible. So hose was developed that was alcohol resistant. Even so, hose should be checked periodically for cracks, stiffening, becoming very soft and mushy, and replaced. 

Hoses that are exposed to sunlight have to be UV resistant as well.  Hoses used for outboard engines in particular have to be UV resistant because they often are outside exposed to the sun.

Hoses used in some areas on the boat also need to be fire resistant. If a fire gets started the last thing you need is a fuel hose burning through and dumping fuel into the boat, feeding the fire.  So hoses have to resist a fire for 2 1/2 minutes.  Why 2 1/2 minutes? Because if your fire fighting system doesn't put out the fire in that amount of time, you probably won't put it out. It gives you time to get off the boat.

Fuel hose clamps are usually metal, although plastic ones are being used occasionally.  The metal has to be corrosion resistant. So stainless clamps should be used, but all stainless! Many supposed stainless clamps are not.  The little screw that tightens them is not always SS. The clamps corrode and lose their tension, loosening the connection. One of the most common causes of fires is fuel dumped in the boat when fueling up. This is because the clamps on the fuel fill hose have loosened and fuel leaks at the fitting, or the hose falls off.

Metal fuel lines also have problems. Copper in a marine environment deteriorates rather rapidly. Plus that it is subject to galvanic corrosion. So metal fuel lines have to be certain materials such as copper-nickel or nickel copper. Steel lines are also allowed. A big problem with metal fuel lines is vibration. Vibration loosens fittings, and fatigues the metal, resulting in cracks, usually at the fittings. So metal fuel lines are usually kept short, and there are short flexible lines between the metal fuel line and the engine inlet.

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Other fuel system components have the same sorts of problems. Fuel pumps and filters have to be fire resistant and not leak. Fuel filters used in cars don't meet these requirements. If you get a fuel leak in a car the gas goes on the ground. In a boat it goes into the bilge. So components have to meet the same requirements as hoses and tanks.

Fuel tanks need to be of a material that doesn't easily corrode, is fire resistant, and strong enough to last with all the forces that they are subjected to.  Tern plate (a lead tin compound) used to be common on cars.  Unfortunately, it corrodes rapidly on boats. So tern plate is not allowed. Steel needs to be properly prepared and coated to resist corrosion.  Aluminum corrodes if it is constantly wet. It also is subject to corrosion from the inside of the tank due to phase separation of the gasoline and alcohol, and alcohol's tendency to attract water. So it needs to be mounted properly to avoid corrosion. The same goes for any metal tanks. Stainless is a special problem. It too will corrode if wet, so it needs to be mounted where it can be kept dry. It is also subject to crevice corrosion, particularly at the welds. So welds need to be kept to a minimum. All of these materials have to be able to resist shock and vibration, sloshing of fuel in the tanks, and sudden accelerations in all three directions.

One question that comes up often is "why can't I put the fuel pump in or on the tank"?. This is commonly done with fuel injected systems on cars .  It helps to eliminate vapor lock and insures a steady supply of fuel.  However, this means that the fuel line running from the tank to the engine is under pressure. In some fuel injected systems this can be as much as 30 psi. Think what would happen if a leak developed! In a pressurized system this would result in all of the fuel in the system being sprayed into the boat.  I mean all! It would empty the tank.  This is one of the basic laws of physics. So, the fuel pump on a boat is required to be on or within twelve inches of the engine. That way the only line under pressure is the one from the fuel pump to the carburetor or fuel injection system. This line is usually very short, generally about a foot or maybe two on larger engines. The fuel from the tank is sucked to the engine rather than pushed.  If a leak develops, the fuel just stops flowing and the engine quits.  Pressurized lines and fuel systems are not allowed on boats, except for that one short line.

Why not a closed fuel system?  Why does it have to be vented to the atmosphere? Doesn't this add to air pollution?  Yes it does. But for the reasons cited above you don't want a pressurized system. A leak would dump all the fuel into the boat. However, the new EPA Fuel system rules do allow for up to 1 psi in the tank, fill and vent.

So the main purpose behind fuel system regulations is to prevent leaks, thereby preventing fires and explosions.

To add a complication, the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have recently (since about 2001) proposed a series of regulations that would control evaporative emissions from permanently installed fuel systems, and exhaust emissions from inboard gasoline engines.  The  regulations would limit evaporative emissions to 15 grams per square meter of surface per 24 hour period. This is far less than the current 100 for A1 or B1 hose and 300 for A2 and B2 hose.  The same requirement would apply to tanks and vent systems which have always been open to the atmosphere. Because of the safety issues surrounding pressurized systems, the EPA and CARB have agreed not to require closed systems, as are used on cars, but to require a charcoal canister in the vent that would not create back pressure and would absorb fuel vapors.  Plastic tanks would also have to limit the amount of vapor permeated through the tank wall.  The engine exhaust will have a catalytic converter, similar to cars but much smaller in size. Some of these regulations go into effect in 2009, and all go fully into effect in 2010.  As of July 2012 all of these EPA regulations are in effect. See See the Page on environmental rules.

Revised 03/04/2022  ¬© 2007 All rights reserved

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