Fuel Storage ( GAS OIL )

biodieselFuel Storage Increased care is needed in the storage of diesel (gas oil) where this contains biodiesel.


Due to their hygroscopic nature, biodiesel blends can contain more water than ‘normal’ diesel which can result in accelerated corrosion, sediment formation, and filter blocking. All of this can be controlled by good housekeeping and fuel management.

All diesel is contaminated with water to some extent either because it is suspended in the fuel itself or it gets into fuel tanks through faulty seals and vent pipes and from condensation caused by changes in ambient temperature. The latter is a particular problem in common rail diesel injector systems. Because biodiesel is hygroscopic, it exacerbates the problem and biodiesel blends are more susceptible to biological attack by micro-organisms. Aerobic micro-organisms that consume hydrocarbons, such as fungi, bacteria, and yeast, usually grow at the interface between fuel and water in fuel tanks. Anaerobic species can actively grow on tank sides.

Bacterial growth can result in the blockage of fuel pipes and filters and increase the problems of corrosion. Prolonged use of contaminated fuel may result in damage to engines. Bacterial growth can be prevented by eliminating water from fuel tanks and conducting regular checks to ensure that tanks remain free of water. Where a bacterial growth outbreak has occurred, this can be addressed either by emptying and cleaning the tanks, or by tackling the outbreak with biocide additives and filtering.

Biodiesel is a better solvent than ‘normal’ diesel. As a result it may pick up deposits already in fuel systems and in fuel tanks. To prevent those deposits from blocking filters, a one-time replacement of storage tank and off-road equipment fuel filters, outside the regular service interval, after 2 to 3 tank throughputs of biodiesel is recommended. In addition, fuel seals in sight gauges on older fuel storage tanks may be incompatible with sulphur free diesel, irrespective of whether it contains biodiesel, and may require replacing. Users should examine seals and if there are signs of leakage, they will need a one-off replacement of these seals.

The oxidation stability of biodiesel is poorer than that of ‘normal’ diesel. Over time oxidation can precipitate solids with the potential to block filters in fuel distribution systems. To minimise the likelihood of this occurring, it is recommended that users take particular care to ensure a fuel turnover period of once every 6 months and, in any event, no longer than once every 12 months. Bio-diesel blends have a higher Cold Filter Plug Point (CFPP) than ‘normal’ diesel which means it may not flow as well (a phenomenon known as ‘waxing’) in cold weather or stop altogether. However, the fuels made available to the latest standards (BS EN 2869:2010) include additives to prevent waxing and maintain oxidisation stability.

Current advice based on good practice recommends that:

  • fuel in any tank is turned over regularly, at least every 6 months and certainly no more than 12 months;
  • when in use, tanks are kept as full as possible, to reduce condensation, however this must be balance against the amount you use and how long a tankful is likely to last you
  • water must be drained off regularly (although it is rarely possible to remove it all) in order to discourage MBC (micro biological contamination). Consideration should be given to modifying the drain facilities to make them more effective
  • seals and components in the fuel system are inspected and, where necessary, replaced
  • strainers and filters are checked and cleaned more regularly

It is understood that this is easier said than done. Smaller marinas and boatyards may only have one supply tank and may not sell enough fuel to turn it over regularly particularly in the winter months. Many recreational craft are laid up over the winter with full tanks for 6 months or more in some cases. A balance must therefore be struck between the amount of fuel bought and the amount of fuel you use. Where possible you should try to buy diesel that does not have biodiesel in it. But remember that the problems described here also affect ‘normal’ diesel as well, albeit to a lesser extent.

If you are concerned about biodiesel and whether there is something nasty in your tank, test kits are now available, which can identify whether contamination is present and its severity. These have been demonstrated to give quick and accurate results on-site.

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Kill Cord

The kill cord is a red lanyard which has a quick-release fitting at one end and a clip at the other end. When used correctly, the quick-release fitting is attached at the console and the other end with the clip attached to the helmsman. The kill cord is normally attached around the driver’s knee and clipped back onto itself.

A kill cord is coiled in its design to allow the driver natural movement when helming a boat. Should the driver move away from, or be thrown overboard, the kill cord will detach from the console and the engine will stop. The kill cord should always be worn by the driver whenever the engine is running! Should you for any reason not wish to attach the kill cord around your leg, attach it securely to your personal buoyancy aid. In either case it should not foul the steering or gear controls and become a safety risk itself.

The kill cord should always be clipped back onto itself. It should not be clipped onto any item of clothing or attached to any other location where the clip would release from the helmsman rather than detach from the console/control box, as the console end must detach for the kill cord to stop the boat.

It is tempting to use a kill cord that is longer than the item provided by the manufacturer of the engine or boat, allowing you a little more movement, but this could result in the kill cord not doing its job when you really need it. If you need to leave the command position, or you are changing helmsman, you should ALWAYS turn off the engine. The engine should only be re-started when the kill cord has been secured to the new helmsman.

  • Check the kill cord’s condition
  • Check your kill cord works at the start of each day or session by starting the engine and pulling the kill cord to makes sure it stops the engine.

Monitor the kill cord & lanyard for signs of wear

Kill cords should be protected from the elements. Over time extremes of temperature and UV light will harm the lanyard. Kill cords may become stretched or brittle if stored open to the elements. Monitor the kill cord for signs of wear, rust and reduced elasticity, replace as a recommendation once a year to be safe.
When replacing kill cords, purchase a good quality lanyard with a strengthening cord through the middle.

Summary of the RYA advice and recommendations:

  • The RYA recommends that the kill cord be attached around your leg. It should not foul the steering or gear controls.
  • The RYA does not recommend extending the length of the kill cord provided by the manufacturer of the engine.
  • Always check your kill cord works at the start of each day or session and check it regularly for signs of wear.
  • When replacing kill cords, purchase a good quality lanyard with a strengthening cord through the middle.
  • Do not leave kill cords out in the elements. Extremes of temperature and UV light will harm the lanyard in the long term.
  • If your lanyard has a fabric outer sheath, but has lost its spiral tension, it is advisable to replace it as it is possible that the inner strengthening cord may be damaged. 
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