Diesels Afloat co-author Callum Smedley takes a detailed look at the workings of a yacht's fuel system

A yacht’s fuel system comprises everything from the boat’s fuel tank to the engine’s fuel injector or injectors. There are two distinct parts of the fuel system: that installed by the boatbuilder and that attached to the engine. The tank, primary filter and all the pipework to and from the engine are designed and installed by the boatbuilder. From the lift pump onwards, it’s a complete unit from the engine manufacturer.

On older boats, you may find modifications to this part of the system, so investigate yours thoroughly to see if you need to bring it up to scratch. One of the biggest problems is leaking pipes, usually caused by vibration. Generally, however, apart from routine servicing and wear and tear, there should be little trouble from the fuel system. The main job is to simply supply the engine with clean and water-free fuel.

Red diesel

The fuel itself is a hydrocarbon that mainly comes from crude oil. We usually call it diesel oil or ‘red diesel’ (with no duty to pay), but its proper name is marine gas oil. Apart from having red dye added to it, to identify that it is duty-free, marine fuel is very similar to road diesel fuel, often called ‘white diesel’ (on which duty must be paid), used in cars, lorries and buses.

Your boat’s diesel engine will run perfectly fine on either fuel, but white diesel contains biodiesel which can clean out your fuel system due to its higher solvent content. Cleaning out the fuel system may sound good, but the dirt released has to go somewhere, so it ends up in the fuel filters. The fuel filters will remove the dirt effectively but it means they will have to be changed much more often. In any case, it’s always a good idea to carry extra filters on board.

Copper pipework

The pipework in a yacht’s fuel system is most often made from copper. However, over time it can become hardened and brittle, especially if it isn’t supported or clipped properly to the vessel, making it much more likely to crack, which, in turn, can lead to a loss of fuel into the bilges or the pipework failing completely. Fuel in the bilges is never a good idea, because of fire and pollution. If the fuel piping was to fail completely the engine would stop, and it shouldn’t be re-started until a full repair is carried out with the system completely bled of air – one reason why commercial vessels are now starting to use stainless steel pipes.

Flexible pipework

When an engine is mounted on flexible mounts, flexible fuel pipework (hoses) should be used, and it’s vital that the correct grade of hose is used. The suitable grades are;

BS EN 853 rubber covered wire braided reinforced hydraulic type
BS EN 856 rubber covered spiral wire reinforced hydraulic type
ISO 7840 fire-resistant flexible oil fuel hose.

Normally, there will be text on the hose indicating that it is suitable for fuel.

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