The Bug Is Taking Over

You need a large aperture to gain access to all corners of a tank

Following our arrival in the Canary Islands last autumn we watched an endless stream of yachts line up at the pontoon alongside the boatyard, all of them with fuel contamination problems. In my experience, it’s usual to find that in cases like this the outbreak can be isolated to one or two suppliers who have a problem with storage or maintenance – the word soon gets around. But the engineer, who seemed to spend his entire time doing nothing but pump out and clean tanks said no, there was no common source for the fuel, but it was in his view part of a rapidly increasing problem linked to the increasing use of biodiesel blends, as there had been a major spike in the level of boats affected since its more widespread uptake.

What’s Behind It?

Fatty Acid Methyl Esters (FAME) known as biofuels, are now being combined with conventional diesel on a wider scale, and often in increasing amounts. Automotive diesel specification EN590 allows up to 7% of FAME to be incorporated, even though it is known that levels of above 2% are more susceptible to microbial infestation. The reasons behind this microbial problem are varied, but two stand out. The first is that FAME is hygroscopic, and so absorbs water, the principal culprit behind most bug growth, and the second is that it is an excellent nutrient resource for the microbes to feed upon. The effects this can cause are bad enough on the road, but have the potential to be far more serious for those of us who go to sea.

The problems that FAME diesel can cause are well known, and include blocked filters and damage to rubber and plastic components in fuel systems, especially in older engines. Equally, there are cures available in the form of biocides that block the bugs’ ability to feed, or dispersants that remove their critical habitat, water, by lifting it into suspension. Both types can be effective, although it seems that the biocides may have an edge in terms of a short term cure, whilst the dispersants may be more effective as preventative treatments. Some are more quick acting, whilst others can leave residues that may affect your filters, so always keep a couple handy after any treatment other than a simple preventative one.

Prevention Is Better Than Cure

Obviously there are ways to try and avoid this issue in the first place, but depending on where you are it may not be that simple. In the UK, for example, it has been estimated that 75% of all diesel fuel supplied to the marine market will be low sulphur and FAME-free, but that still means that 25% will potentially include FAME. So it will obviously make sense to check on what the local market situation is, and if in any doubt, ask the supplier before putting the nozzle anywhere near the tank. Avoid buying spare fuel in cans from petrol stations, where the likelihood of buying FAME-blended diesel will be far higher. And, just as before, keep your tanks topped up whenever you leave the boat for any length of time to reduce the chance of condensation forming on the tank walls, and so creating the best possible opportunity for the bugs to thrive. And consider using a preventative treatment of biocide or dispersant at every fuel fill up – the cost compared to the cure is small.

Another step is to regularly inspect the contents of your tank, whether or not you’ve had a problem with filters. The best way to do this is via a drain tap mounted as low as possible in the tank(s) so that a sample can be drawn from the very area where problems are going to be the most obvious. Failing that, drawing off a sample via a tube inserted through the top of the tank into the bottom corner can be equally effective. If there’s any sign of contamination, water or sticky deposits, then it’s time to drain off or pump out the bottom section (at least) of the tank until no more contamination is present, then treat with a biocide or dispersant, and change the filters. In really bad cases it will mean pumping out all of the affected fuel for disposal. The tank should then be cleaned  mechanically and with a biocidal system cleaner, as in extreme cases there will be deposits on the tank walls that can cause serious microbial corrosion that will need to be removed – if you’ve got tanks welded into your steel or aluminium hull, think very carefully about this!

But Can You Get At It?

Sadly, all of this is dependent on the builder of your boat having installed at least one of the following: (a) a correctly sited drain plug, (b) a sampling tube, (c) an aperture, (d) a removable inspection plate big enough to allow access to all corners of the tank, or (e) a tank that can be removed without demolishing the boat. Having been on a boat affected by ‘the bug’ which only had (c), I can tell you that cleaning out the tank properly is an impossibility. So with FAME-blends becoming more prevalent, if your boat hasn’t got any of the above then maybe it’s time to think about installing whichever option is the most practical and cost effective in your case. Otherwise you may find yourself joining the queue at the boatyard!

And if you have any experience of diesel contamination problems linked to biofuels, do leave a comment.

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Colin, European Correspondent here at AAC, is a deeply experienced offshore sailor who holds a Yachtmaster licence, and a gifted photographer and talented writer who has added a whole new dimension to Attainable Adventure Cruising. In addition, since Colin and Louise are from England and had their OVNI 435, Pèlerin built in France, they bring a European perspective to our site. You can read more about Colin and Louise and their business at their website.

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