Fuel System Surveying

As a marine surveyor, we look at the fuel system to see if it’s safe. Fuel systems on a a gas-powered boat are different than those on a diesel boat because gas is more volatile, and its fumes can ignite when a spark occurs in the vicinity. This is why boat manufacturers are trying – or should be trying – to limit the DC-powered items mounted near the gas tanks. It is also why you don’t use things like an automotive battery charger on a boat. They are cheaper than a marine-grade one, but the marine charger is designed not to spark while under use. The volatility of gas means that a gas engine requires the use of the blower system for at least four minutes to clear the engine space of any vapours before starting the engine. A diesel-powered boat doesn’t require this precaution.

Diesel systems can have their own problems, including leaks.  Diesel leaks are unpleasant and can occur from several places, the most likely being a leak in the fuel tanks.

The likelihood of a tank leak stems from the material the tank was built from, and how it was installed. Early boats often had tanks constructed of steel. They were called “Black Iron” and were easier to make. A steel fuel tank works well on a car, but they are subject to a few other problems in a boat. They are close to water, which keeps the tank cooler than the air; the resulting condensation occurs both inside and outside the tank. If installed right on the hull’s surface, or on a spacer that deteriorates, water can become trapped against the outside of the tank. If that water has some salt content, the tank starts rusting. This is why tanks should be mounted with enough space below and on the sides to allow air to flow past and dry out the inevitable water. Even with a space, you must keep this area clean, so dirt doesn’t build up and trap water against the tank.

Tanks can be built of other materials. Aluminum is one option and can work better, but it is susceptible to electrolysis from differing metals touching it. Stainless tanks are another solution, but we need to watch them for cracks at the welds. Rotomolded Poly tanks are another solution. They can be built tough enough to last a long time. Outboards have been using them for decades.

You will need to monitor whatever tank you have and watch for things that can lead to leakage.

In a survey, we also look at the fuel system from where gas is put into the tank to where the engine injects it into the motor. Most boats have the fuel fill port on a horizontal portion of the deck surface. It’s convenient, but it can become a problem when the O-ring gasket on the cap that should seal the port deteriorates with use. Now, water flowing down the side decks will flow over the fuel port, and some will leak into the fuel line, the tank, and the injectors. Check your fuel cap O-ring.

When you fill the tank with diesel, you are flowing a lot of fluid down a tube to the tank. It must displace the air in the tank, or the pressure will build up and blow the fuel back out of the hose. To help, the manufacturer has installed a vent hose from the tank to the outside, preferably on the side of the hull. This through-hull will have a screen on it.

All hoses deteriorate with use and age, so we must check for this. It’s hard to see from the outside, but if you squeeze a brittle hose, you can hear “crackling” on one that needs replacing. If there is room, we check that two SS hose clamps are on all the connections and that they aren’t rusted.

We check the fuel filter systems to ensure they will trap any contaminants before reaching the engine. We might suggest a dual-Racor filter setup with gauges, so that if you see the restriction on one filter, you can switch filters before the engine stops due to a lack of fuel.

If that occurs, you must bleed the air out of your fuel lines to restart the motor. Some people use an electric fuel pump to help them bleed the system when this occurs. An automotive pump can cause sparking, so look for a marine unit, or mount the pump well away from the engine space.

Diesel engines can be susceptible to a “runaway situation” where they cannot be stopped. For this reason, we look to see if a fuel shut-off valve can be reached without going into the engine space. If possible, it should be close to the tank and well-marked so that everyone can find it in an emergency.

Another convenient item to have on your tanks is a cleanout hatch.  This is a 4- to 6-inch plate bolted to the tank with a rubber gasket. Over time, all diesel tanks will get dirt, water, and microbial growth, which should be cleaned out before it gets to the filters and plugs. Sometimes, you can go through the fuel sender hole, but it can be hard to get your arm through this to scrub out the tank.

Part of any sound fuel system are the detectors required to let you know if a problem is developing. Look into your need for carbon monoxide and/or carbon dioxide detectors and install them as needed.

You should also install a firefighting port on the engine space wall to enable you to discharge a fire extinguisher into that space without opening it fully and letting in too much oxygen. Also consider a smoke or heat detector in the engine room to alert you quickly that a fire has started.