Hormoconis resinae found at the bottom of the tank demonstrating a highly contaminated fuel system

Prepare the fuel system for winter and reduce the risk of the dreaded Diesel Bug

For crew preparing a yacht for the winter period the time has come to review onboard systems and preparation for the forthcoming season.

The changes to fuel specification in January 2015 stated all vessels operating within defined Emission Control Areas (ECAs) must use fuel containing no more than 0.10% sulphur or operate with exhaust gas scrubbing systems to limit emissions. As a result of the new regulation, fuel quality has become an even more popular subject matter among crew prompting questions such as; what are we burning?  Are we happy with our onboard fuel management? How clean is our fuel system?  What products do we use to reduce operational risk?

Gone are the days when fuel took care of itself                                                                                                                      


Fuel filter with contaminated fuel

Sulphur is known as a lubricity improver, and may also inhibit microbial growth commonly known as the diesel bug. As environmental legislation is changing the nature of fuels, the risk of microbial contamination is increased and as a result, to prevent engineering implications, it is forcing those involved in its production, distribution and use to review the way they manage fuel quality.

Many different microorganisms can enter fuel at any stage in the supply chain, living in the water phase and feeding off the fuel. Prolonged, heavy contamination is an expensive issue, with the possibilities of causing corrosion and requires expensive mechanical intervention and significant downtime to clean the tank. The majority of operators have concluded that detecting and dealing with the problem by testing early is the efficient, cost effective answer.

How clean is your fuel system?                                                                                                                    

There are a number of proprietary tests on the market to determine the presence of microbial contamination and prior to the winter layup it is a sensible time to consider this option.  Regular fuel testing is the only way we can identify a microbial problem. Conidia’s simple fuel test Fuelstat Diesel Plus will deliver accurate results in ten minutes. Its manufacturer says no special skills are required to use the test, and there is no investment needed for a reader to translate the results.

This test is unlike current growth-based tests which require a minimum of 72 hours to provide any results. It measures the amount of active growth in the sample and provides actions and alert levels.

Even at moderate levels of contamination filter blockage, pump and injector wear plus metering and gauging issues may cause costly operational issues. The fuel system and the fuel may also require both polishing and biocide treatment.

Dr Joan Kelley technical director of Conidia Bioscience advises “It is good practice to monitor a tank by testing after carrying out a biocide, as regrowth can occur if treatment has not been totally successful.  That is, do not just test once but look over a period of a month to see if background levels of organisms increase and such changes would be picked up by Fuelstat”

With the drop in temperature over the winter periods, storing fuel may also add to the risk of microbial contamination. Preventative actions include filling fuel tanks to 100% to help stop condensation forming on the tank walls. The water should be drained from all fuel and water separators regularly; this is often difficult or impossible with many marine instillations which can lead to the build-up of microbial growth at the water/fuel interface within the tank.