Biofuels are renewable fuels derived from biological sources — such as agricultural crops, waste, or residues — and are designed to reduce greenhouse gas emissions. Depending on the production process, biofuels may take liquid, gaseous, or solid form.
Blends
In practice, biofuels are most commonly used as blends with conventional fuels, whereby a proportion of biofuel is mixed with marine gas oil or fuel oil. These blends are typically referred to as BXX fuels (for example, B20 or B30), where the figure denotes the share of biofuel in the mixture.
Drop-in fuels
Biofuels may also be used as drop-in fuels — fully compatible replacements for fossil fuels that can be used in existing fuel systems. Not all biofuels meet full drop-in specifications, however, and fuel quality can vary depending on the feedstock and production process.
Operationally, this means biofuels are not a single fuel type but rather a flexible solution, ranging from low-percentage blends used in everyday operations to higher blends or pure biofuels in more controlled applications. The chosen approach depends on engine compatibility, fuel availability, and specific operational requirements.
Main risks
Biofuels can pose risks to a vessel's engine if they are not properly handled and treated.
A key concern is filter clogging caused by fuel degradation or oxidation, which can produce sludge and sediment that obstruct filters and separators. Biofuels are also more acidic, particularly at higher blend levels such as B100, and can cause corrosion and degradation of piping systems, especially those containing copper, brass, or zinc components. In addition, they can lead to the hardening or deterioration of rubber hoses and seals, potentially resulting in fuel leakage.
The organic components in biofuels can also absorb moisture, promoting microbial and fungal growth within fuel tanks. This, in turn, can cause filter blockage and pipe corrosion.
A further risk relates to cold-weather performance. Owing to their higher cloud point, biofuels can form wax crystals at lower temperatures, which may restrict fuel flow, clog filters, and in severe cases block engine nozzles.
Skuld experience
Skuld has started to encounter claims and incidents linked to biofuel use. Explore the articles to the right, written by our subject-matter specialists, and reach out at any time to connect with our experts.