The Triton


Machinery Matters: Don’t let fuel FAME live forever


Machinery Matters: by Larry Rumbol

The words from the musical “Fame” could almost have been written as a biodiesel mantra: “Fame! We’re gonna live forever”. That’s a reality if operators don’t take precautions as microbial growth can exponentially double in size, living forever and, in the briefest instant, grow to triffids in the tank if left unchecked.

FAME is also an acronym for Fatty Acid Methyl Esters. In layman’s language, biodiesel, which under current regulations can be present in regular hydrocarbon diesel fuel from 7% to 30%, depending on where it is bunkered. Biodiesel refers to esters (chemical compounds) derived from vegetable oils such as palm oil, soybean oil, rapeseed oil, animal fats (tallow) and used cooking oil. 

Inevitably, whether diesel is specified as FAME-free or not, FAME will and does creep into the supply chain, particularly as blending is permitted in cutter stocks containing FAME. Adequate controls should ideally be in place that fuels are compliant with Clause 5 of the spec ISO8217 where the FAME should be at a de minimis level. However, not all yacht fuel is or can be bought to this spec.

How bad is FAME?
It is impossible to spot FAME visually as there is no difference between a pure hydrocarbon diesel and a FAME blend except maybe a slight haziness. Ignition and lubricity properties are unhindered.

Yet there are real challenges associated with all levels of FAME in fuel and that is related to its affinity to water. Due to this hygroscopic nature, these FAME diesel blends can contain more water than regular hydrocarbon-only diesel, which reaches water saturation at levels greater than 1,000ppm, whilst biodiesel fuels can reach saturation at less than 100ppm. Thus it is possible to have a FAME/diesel blend that has water above the saturation limit, resulting in what is called “free water”. This can occur even if the FAME and diesel themselves contain only dissolved (not free) water. 

Notwithstanding any of the above, the actual source of water content varies considerably with each of the bio sources.

Due to its hygroscopic nature, FAME diesel blends are more susceptible to biological attack by microorganisms. These organisms grow in the interface between fuel and water in the fuel tanks and are aerobic in nature, consuming hydrocarbons and producing fungi and yeasts that are sludge forming, resulting in filter blockage and ultimately sudden unexpected engine stoppage. Anaerobic species also form, which can cause rapid tank corrosion as they produce sulphur-forming acids with attendant pungent aromas. Left unchecked, the damage can be considerable and irreversible. In some cases the contamination is not evident until a vessel gets into a seaway, which is the worst scenario for engine shutdown.

Laboratory testing immediately upon bunkering is the best practice whilst keeping a sealed, tamper-proof sample that both vendor and recipient have witnessed and recorded. It is also important to avoid the temptation to provide a “good, clean sample” of fuel. Two samples are best; one from mid-tank and one from the bottom at the fuel/water interface (if contamination is suspected) as only this will give a true indication of the severity of the problem. Should microbial growth be proven with a lab report, the remedy is quickly shock dosing with a recognized biocide and a regime of testing and dosing to make sure it is eradicated.

Can’t trust the ticket
FAME, however, is not the sole cause of microbial growth as any water in fuel, especially in warm, humid conditions, will create the perfect nursery for this malady. Condensation in fuel tanks can actually introduce water and the attendant problems so it is not only poor fuel husbandry by a supplier that is always the root cause. Again, regular testing is the key, identifying water, FAME, microbial growth and, of recent importance, sulphur content to ensure the level is within IMO 2020 Sulphur Cap regulations.

Theoretically, a bunker supply note/delivery ticket should be sufficient to satisfy any Port State inspection as to the sulphur level of fuel being used, yet there are well-documented cases of fuel with a higher sulphur than the IMO-specified level being discovered under inspection and $300,000 fines imposed with vessel detention and crew being sent home. This despite a delivery note to the contrary in each case. 

Port State inspectors are within their rights to demand a sample be analyzed if they are not convinced of fuel sulphur levels and that can cause quite some delay. Due diligence is the key here with lab testing and retention of sealed and witnessed fuel samples kept on board until the result is received.

This third-party analysis is a convincing policy for any Port State that care has been taken. This is not only the ultimate safeguard against innocently “getting caught out” but it is normal practice on commercial vessels with which this is a standard operating procedure. There is discussion ongoing at the international level to make this practice standard on all vessels over a certain size. 

Even better if the fuel can be isolated in a tank and not used until the results are received as de-bunkering and resolution with the supplier will be much easier if fuel is proven to be off spec. The very practice of such diligence will also reduce the likelihood of nefarious practices by unscrupulous suppliers.

The aforementioned challenges with fuel are exacerbated by the increased demand on distillate stocks as a result of the IMO 2020 global sulphur limit, which drastically reduced the consumption of heavy residual fuels by commercial shipping. Furthermore, environmental pressure in certain countries is increasing the legalized amount of biofuel that is blended with hydrocarbon fuels, and this will only increase with time. 

A well-organized fuel buying and husbandry program will keep problems at bay for sure – just keep a weather eye open because what used to be “fill up and get going” is no longer quite so simple.

Larry D. Rumbol has 40 years of expertise in marine condition monitoring and is marine business development manager with Spectro | Jet-Care in the United Kingdom, United States and Switzerland. Comments are welcome below.

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One thought on “Machinery Matters: Don’t let fuel FAME live forever

  1. Scott Fenwick

    Thank you, Mr. Rumbol, for your warnings and insights on the “nefarious practices by unscrupulous (fuel) suppliers.” The National Biodiesel Board supports proper fuel handling practices and quality verification for all fuel types. Water (particularly free water) is an extremely important parameter to monitor as noted, since this is an absolute necessity for microbial growth to occur whilst FAME content is not. As more hydrotreating transpires to distillate fuels to reduce the sulfur content, this also affects the water solubility of hydrocarbon fuels. By reducing water solubility, traditional petroleum fuels are almost certain now to contain free water as they are transferred throughout the global fuel distribution system; thus, leading to increased risk for microbial growth. Since you have noted the increased affinity of FAME for water, you should also then agree that biodiesel blends may be the only option for absorbing the existing free water within the fuel distribution system that accumulates.

    Biodiesel is not produced and sold at its saturation level for water content. In fact, the water limit for biodiesel under the EN 14214 specifications is a maximum of 500 mg/kg (ppm) of total water (both dissolved and free), which is well below its saturation level as you are aware. Within the ISO 8217 Marine Fuel specifications, not every grade has limits FAME to “de minimum”s levels. There are several grades that allow for 7% biodiesel (with allowances for legislation mandates to even higher levels) while the “de minimus” level has been increased from 0.1 to 0.5 volume percent. The global technical fuels experts have studied the impacts of biodiesel blended fuels and recognize many benefits.

    Biodiesel has specific performance properties that may attract users. Biodiesel does improve lubricity and ignition values for many fuels around the world. Improved emissions, safer handling, and lower greenhouse gas releases all lead to improved sustainability and engine performance around the world.

    Learn more at

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