IMO study: Slime-free hulls reduce GHG emissions

The preliminary results of a new study by Global Industry Alliance (GIA) for Maine Biosafety, an initiative addressing biofouling management, have revealed that removing slime from ships’ hulls reduces greenhouse gas emissions (GHG) emissions by up to 25%.

Barnacles ship fouling (Source: IMO/Lena Granhag)

The GIA launched the report on the preliminary findings of the study on the Impact of Ships’ Biofouling on Greenhouse Gas Emissions during the United Nations Climate Change Conference – COP26.

The findings indicate that a layer of slime as thin as 0.5 millimetres covering up to 50% of a hull surface can trigger an increase of GHG emissions in the range of 20% to 25%, depending on ship characteristics, speed and other prevailing conditions.

Biofouling is the build-up of of microorganisms, plants, algae or small animals on surfaces that can lead to the introduction of potentially invasive species to new environments.

According to the International Maritime Organisation (IMO), one of the most significant factors impacting the efficiency of all ships in service is associated with the resistance generated by the underwater area.

Therefore, maintaining a smooth and clean hull free from biofouling is of paramount importance, the study shows.

With a light layer of small calcareous growth (barnacles or tubeworms), an average length container ship can see an increase in GHG emissions of up to 55%, dependent on ship characteristics and speed.

In order to reduce the GHG emissions from the maritime industry, IMO adopted a series of legally-binding ship design and operational performance indices that must be achieved by individual vessels. The aim is to ensure that ship operators consider options to improve the efficiency of their vessels throughout their lifecycle.  

The report clearly shows the importance of good biofouling management. It illustrates how the perceived impact of biofouling is likely to have been historically underestimated by the shipping community“, IMO concluded.

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