Boats must now use the same reduced sulphur fuel as road vehicles. Red diesel previously supplied for marine use was too high in sulphur.

Although this legislation only refers to inland craft, faced with the complication of two types of marine fuel some suppliers will opt for the very simple solution of just dying road fuel red for all marine use – simplifying their production and distribution.

Road fuel contains a proportion of biodiesel which is not good for marine use as it provides a medium in which diesel bugs flourish. Fuel sits for long periods in boats and bugs grow in tanks that have even a small amount of water in them – either from accidental ingress or from condensation.

Bio fuel also has detergent and solvent properties, not a problem for modern engines, but is corrosive on seals and pipes in many older boats.

Some suppliers are producing a fuel especially for seagoing marine use that is bio free. You will often hear this referred to as ‘FAME free’ which is short for Fatty Acid Methyl Ester or biodiesel. It does not mean that this is the red diesel offered at the pump. The retailer may opt for the dyed road fuel, particularly at locations serving a mix of inland and seagoing boats and of course at any inland fuel stop.

Check at the pump. If it is FAME free then fine, but if you have to buy bio fuel there are precautions you should take.

General Advice

  • Check tanks for water regularly – those without drains may need modification
  • Drain off water from separators/filters and change filters after every 2-3 tank fills
  • Turnover fuel in tanks every 6 -12 months
  • Consider fitting dual filters with simple switchover in case one blocks
  • Stop water getting in – keep the tanks topped up minimising the condensation on which they thrive and make sure deck filler seals are sound.
  • Use a fuel additive that disperses water and doses against the bacteria that cause fuel bug. We supply one of the most effective on the market.

Fuel Additives

  • MARINE 16 COMPLETE. Regular dosage protects against fuel contamination and maximises efficiency. 

    For complete protection with biodiesels, ulsd and any diesel type. Prevents the growth of diesel bug. Combats all of the effects of using biodiesel and ultra low sulphur diesel. Gives lubricity, cleaner easier starting, reduces emissions, improves fuel consumption and reduces fuel line and injector deposits to zero. Suitable for all diesel engine types and all diesel fuels.

    Diesel Fuel Complete 100ml treats 100 litres of fuel.

  • MARINE 16 DIESEL BUG TREATMENT. One off treatment for contaminated fuel. Marine 16 Diesel Bug Treatment incorporates a highly effective diesel fuel preservative for the control and prevention of microbiological contamination in diesel fuel and is approved for use by Mercedes Benz AG, NATO, DAF and is used by Shell in the Netherlands to prevent/control microbiological contamination in fuels. Just 100 ml of Diesel Bug Treatment will provide preventative treatment for up to 2000 litres of fuel. The product is added direct to fuel and effectively treats the entire fuel system, from tank to combustion chamber, forming a contamination suspension which is entirely removed from fuel tank, pumps and injectors in one operation via the combustion process. If contamination is already present, the treatment rate can be adjusted to suit – for example, if contamination is mild (evidenced by the presence of small, stringy slime elements) then one 100ml bottle per 500 litres of fuel will usually suffice. If contamination is severe and blockages have occurred, then a Shock Treatment rate of 100 ml to 100 litres should be used.


Over heating and water restrictions can be a real problem for boat owners, but there is a way now for you to help maintain your engines water system with the help of RYDLYME Marine. RYDLYME Marine is formulated to meet the demands of today’s water systems. It is non-corrosive, non-hazardous, and biodegradable.

With the reduction of labour and operating costs, downtime, and no installation costs, accompanied with the heavy duty cleaning power, RYDLYME Marine keeps your vessel at sea generating revenue.

This safe and simple solution effectively dissolves rock-like scale deposits that contaminate your water-cooled marine equipment. RYDLYME Marine is used at ambient temperature and then circulated to bring the solution in contact with the accumulated minerals. The reaction results in a slight foaming or bubbling action, indicating the deposits are actually dissolving into solution, and then simply water flush away! These scale deposits, along with zebra mussels and tigershells, damage your equipment and reduce your water system performance. Historically, these problems have been addressed via harsh acids, mechanical methods, ion exchange, polyphosphates, permanent magnets and electronic conditioning. If your vessel is heat exchanger cooled, keel cooled, or radiator cooled, try RYDLYME Marine and ride the waves with maintenance superiority!