The MARPOL Annex VI amendments to limit sulphur content in bunker fuel oil did not threaten to impact the superyacht industry, considering most yachts already use low-sulphur fuel. However, the fact that the sulphur content of fuels is and will reduce further is already literally leaving its mark on some yachts. Lloyd’s Register has reported rising incidences of severe corrosion in fuel tanks and possible clogging of dispensing systems, which will only increase as sulphur content is limited further.

Sulphur essentially helps fight bacteria, meaning the reduction of sulphur content in fuels has seen the increase of bacteria proliferation, in combination with condensation and additives. Diesel fuel also suffers from microbial growth problems when water is present in the tank: fungus, mould and different kinds of bacteria live in the water and use the diesel fuel as a food source.

Photographic evidence of corrosion on the fuel tank of a recently-delivered yacht due to bacteria proliferation, courtesy of Lloyd’s Register.

The secretions from these tank pests have a detrimental effect on fuel quality and contribute to equipment problems on board. “Due to bacterial presence, the fuel systems will generate problems, such as choked fuel filters and erratic engine operation,” explains Engel de Boer, yacht segment manager at Lloyd’s Register.

In the past, sulphur acted as a natural biocide, but since there's nothing to prevent bacterial growth in low-sulphur fuels, biocides are used to treat the fuel and prevent microbial growth. However, Lloyd’s Register has also reported that corrosion can be increased by overdosing products with biocide.

It is, of course, easier to prevent these problems than it is to repair them after they happen. Lloyd’s Register advises that costly repairs and time delays can be avoided by ensuring timely fuel oil bunkering analysis.

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