The International Maritime Organization (IMO) is urging ships to keep its hulls free from slime noting that a thin layer of this can reduce a ship’s GHG emissions by up to 25%.

According to the preliminary findings of a new study on the Impact of Ships' Biofouling on Greenhouse Gas Emissions launched at COP 26 this month, a layer of slime as thin as 0.5 mm 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.  

IMO said biofouling is the build-up of microorganisms, plants, algae or small animals on surfaces and that one of the most significant factors impacting the efficiency of all ships in service is associated with the resistance generated by the underwater area.

It said maintaining a smooth and clean hull free from biofouling is of paramount importance. 

"More severe biofouling conditions can lead to higher emissions, showing the importance of good biofouling management. 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," it added.

To reduce the GHG emissions from the maritime industry the IMO has adopted a series of legally-binding ship design and operational performance indices that must be achieved by individual vessels.

The aim, it said, is to ensure that ship operators consider options to improve the efficiency of their vessels throughout their lifecycle.