NEWS FEATURE: Bio beware

Ethanol and boat engines are far from a perfect match.

NEWS FEATURE: Bio beware
NEWS FEATURE: Bio beware
The Boat Owners Association of NSW (BOA) has issued a consumer guide for boaters in respect to bio-fuels. This follows the State Government mandating the blending of ethanol and bio-diesel with petrol and diesel fuels in a bid to reduce greenhouse emissions and a reliance on imported oil.

The BOA, however, has advised that only ethanol-free petrol and 100 per cent mineral diesel are used onboard, citing a number of characteristics specific to each fuel that makes them unsuitable for recreational boating.

The sale of all ethanol-blended petrol requires labelling with the prefix letter E. Petrol containing 10 per cent ethanol, for example, must be labelled E10. The sale of biodiesel blended diesel, however, only requires labelling if the biodiesel blend exceeds 5 per cent. Diesel with higher percentage blends must be labelled with the prefix letter B so that diesel containing 20 per cent biodiesel, for example, would be labelled B20.

The BOA says the use of ethanol and biodiesel is ideal in applications where the cycle time (the time it takes to burn a tank of fuel) is relatively short — commercial and public transport being good examples. However, both suffer from a short shelf life with fuel breaking down or separating.


According to the group, as stated above, ethanol-blended petrol has a short shelf life, particularly in a marine environment. Ethanol it says is hygroscopic (absorbs moisture) and has a tendency to bind with water molecules, and then separate from the petrol.

"This can occur in a matter of weeks, especially in hot and humid conditions, but is more likely where fuel is stored for longer periods," says the BOA. "If drawn into the combustion chamber of the engine, this ethanol and water combination can bring about engine failure as it has poor ‘burn’ qualities."

As the ethanol and water combination separates from the petrol, a by-product called "boundary-layer" can be created. This by-product is highly corrosive and can damage rubber and plastic components in the fuel delivery system, and even some aluminium and fibreglass fuel tanks. Also, ethanol is a solvent, which can mobilise deposits in fuel tanks and lines that may cause blockage of fuel filters and fuel delivery systems.

While some marine engines are designed for use with ethanol-blended petrol, some components in fuel systems, as well as older engines, are susceptible to damage as outlined above. For these reasons, the BOA recommends ethanol-blended petrol should not be used in boats and options include higher octane rated or premium petrol, and ethanol-free regular grade petrol available from some marinas.


The BOA continues that the addition of "bio" components to mineral diesel reduces the shelf life of the fuel. "Even in concentrations as low as 5 per cent of volume, the blended fuel can ‘breakdown’ in as little as six months," it says.

Breakdown of the fuel can result in accelerated engine wear, poor lubrication, and blockage of oil and fuel filters. For boats voyaging offshore, especially yachts and others which turn over fuel slowly, this can be a serious safety issue.

The BOA notes that biodiesel exhibits poor oxidation stability and is an excellent medium for microbial growth, sometimes called "diesel bug". Diesel bug can itself cause blockages in lines and filters, while rubber and plastic components in the fuel system can be damaged by both aggressive forms of diesel bug, and the solvent properties of some bio-components commonly found in bio-diesel.

For safety and the protection of your engine and fuel system, the BOA recommends boaters should insist that their marine-diesel supplier provide only 100% mineral diesel. "As diesel fuels with up to 5 per cent concentration of bio-components are not required to be so labelled, buyers should always ask the retailer to confirm that diesel fuel for marine use is bio-free," it warns.

Visit for more information.


Want the latest stories delivered straight to your inbox? Sign up for the free TradeBoats e-newsletter.