Smoothing the way to decarbonisation

THE antifouling coatings on ships’ hulls are unlikely to be the subject of discussion in the local coffee shop. However, those within the shipping industry will know just how complex, and at times contentious, this subject has been for many years.

For a long time there were two main issues: the toxicity of antifoulings in the marine environment and the transmission of alien species around the globe. Addressing them has not been easy because without effective antifoulings, unwanted organisms cling to hulls and travel the globe. These include potentially invasive species that can do immense harm in places where they are not part of the existing ecosystem.

The strongest and most effective biocide used in antifoulings, tributyl tin (TBT), was banned by the International Maritime Organization (IMO) some time ago. Since then, the coatings industry has been very busy developing various antifouling systems that keep hulls clean without harming the marine environment.

While much emphasis has rightly been placed on the invasive species threat, over recent years the importance of maintaining a smooth hull for moving towards decarbonisation has become apparent. Shipowners have always known that hull fouling increases a vessel’s drag through the water and thus increases fuel consumption if service speeds are to be maintained. Now however, reducing fuel consumption is seen as a vital part of reducing shipping’s carbon dioxide (CO2) emissions in the short term.

CO2 is of course a potent greenhouse gas (GHG) that contributes to global warming. The importance of maintaining a smooth and clean hull free from biofouling has been outlined in a new IMO report. The United Nations agency’s publication Analysing the Impact of Marine Biofouling on the Energy Efficiency of Ships and the GHG Abatement Potential of Biofouling Management Measures highlighted that a layer of slime as thin as 0.5 mm covering up to 50 per cent of a hull surface could trigger an increase of GHG emissions in the range of 25-30 per cent depending on a ship’s characteristics, speed and prevailing conditions.

The new report warned that these percentages can be much higher for more severe biofouling conditions, depending on the type of ships and other parameters. It said the perceived impact of biofouling is likely to have been historically underestimated by the shipping community. While anti-fouling coatings remain the main option for preventing biofouling growth, its findings highlighted the “notable potential of biofouling management measures to support the performance of anti-fouling coatings and to reduce fuel consumption of ships”.

In addition to analysing the impact of biofouling on ship efficiency and how current industry practices for biofouling management impact ship efficiency, the study presented results from seven scenarios (or anti-fouling strategies) in relation to a reference of a target vessel (bulk carrier) between dry-docking periods. IMO said its results demonstrate the magnitude of fuel, CO2 and cost savings that can be achieved by keeping the ship as clean as possible from biofouling.

Biofouling management is one important contributor to the overall operational efficiency of ships and should be considered by shipowners to achieve IMO’s Carbon Intensity Indicator, which measures vessel carbon intensity over time. IMO concluded: “Combined with recent surveys on the true level of biofouling prevalent within the shipping fleet, the outcome of this report clearly underscores the importance of biofouling management as an essential component in the toolbox for GHG emissions reduction by the shipping industry.”

This is especially true in the short to medium term, where biofouling management may be used as a means of compliance with IMO carbon intensity requirements, while the development and deployment of other GHG reduction strategies based on new low-carbon and zero-carbon fuels or technologies come to fruition. On the subject of alternative fuels, developments and deployments appear to be coming in thick and fast. In recent months, there has been a surge of reports on the use of biofuels.

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In June, IMO’s Marine Environment Protection Committee published a new Unified Interpretation which accepts marine biofuels to satisfy the requirements of Marpol (The International Convention on Marine Pollution) with regard to emissions of nitrogen oxides. This move has given shipowners the confidence to move to biofuel. Among the latest to do so, North European shipping and logistics company Samskip has signed an agreement with supplier GoodFuels, committing four of its container ships to run on marine grade bio-residual fuels.

Marketed as a drop-in replacement that cuts 90 per cent off CO2 emissions generated by conventional fuel oils, GoodFuels MDF1-100 biofuel is made entirely from sustainable waste streams from the European Union’s Renewable Energy Directive list. It has also earned International Sustainability and Carbon Certification. “Sustainable marine biofuels offer a viable way for Samskip to cut CO2 emissions by 90 per cent so that our ships and freight customers reduce their carbon footprint in the interests of the planet,” said Erik Hofmeester, head of vessel management, Samskip. “It would take the equivalent of 1.7 million trees to offset this amount of CO2 emissions.”

Just how much of the world fleet can be switched to biofuels, or how large those sustainable waste streams could be, remains to be seen. In the meantime, keeping the hull clean seems like a good plan.