Biofouling

Hull Bio-Fouling and Its Treatment

What is Bio-Fouling?

Vessel hulls need protection against the attachment of marine organisms such as barnacles and algae. The presence of these unwanted passengers is known as bio-fouling. Bio-fouling negatively affects the hydrodynamics of the hull by increasing drag and consequently, it requires increases in engine effort to maintain propulsion speed. This inefficiency increases fuel costs, with estimates as much as an additional 40% and more. Vessels will also require regular hull cleaning at considerable cost.

Anti-fouling

Historically, resin or pitch was used for antifouling. In the 1960s copper-based paints containing mercury oxide and arsenic compounds were in widespread use. The 1970s saw the use of paints containing TBT (tributyltin) and other biocidal coatings.  These use self-polishing co-polymers which gradually leach biocides to kill the attached organisms.

Environmental concerns

However, these chemicals are proven to have had a detrimental effect on the marine environment. Studies have shown that these compounds persist in the water, and pollute harbour bottoms, kill sea life, and enter the food chain. Consequently, there has been much lobbying of nations to clean up their act over several decades. In 2001, the International Maritime Organisation (IMO) banned the use of paints containing TBT and in 2008 it oversaw the complete prohibition on organotin compounds in anti-fouling systems. Nevertheless, most antifouling paints still today slowly release heavy metals and harmful biocides into the marine environment.

Alternatives

Currently, the main alternative to biocidal antifoulings are foul-release coatings, which aim to prevent the settlement of fouling by providing a low-friction surface onto which organisms have difficulty in attaching. However, these coatings suffer from being soft and easily damaged. They are also reliant on vessel speeds sufficient to remove the attached organisms and are most suitable for vessels with a minimum speed of 30 knots. Sometimes light fouling still occurs but is easily removed with high-pressure hoses in annual dry dock visits or divers using rotating brushes.

The Future

Hope exists for the development of natural resistance and natural biocides. Research is ongoing into the properties of marine organisms like sponges and corals that manage to remain free of fouling. Other research is based on the preference of organisms to stick to hydrophobic or ‘water repellant’ surfaces, such as rocks and vessels as opposed to hydrophilic or ‘wettish’ surfaces. Efforts to develop Hydrophilic coatings are being made so that fouling organisms will gain no grip. Other coatings such as those with microscopic prickles have been shown to be useful for antifouling static objects such as buoys. These prickles have been shown to prevent the attachment of barnacles and algae with no harm to the environment, however, they have little application in moving vessels.

Skippers Tip

The writer and sailing guru Tom Cunliffe describes a pragmatic solution for vessel skippers with fouling problems. He recommends a week or 10 days in the Baltic Sea or Dutch Inland Waters to naturally remove hull fouling. He concludes that the cost of a boat trip there or to other inland waters can be offset against the mid-season scrub that you will no longer require.

Related article: Blistering Barnacles.

Acknowledgments:

1. “Anti-fouling systems” IMO paper 2002 http://www.imo.org/en/OurWork/Environment/Anti-foulingSystems/Documents/FOULING2003.pdf
2. ECOTEC-STC Paper LIFE06ENV/B/000362 EC Europa EU Hydrex paper http://ec.europa.eu/environment/life/project/Projects/index.cfm?fuseaction=search.dspPage&n_proj_id=3087&docType=pdf. 31st January 2017.
3. “Yachting Monthly 200 Skipper’s Tips”. Cunliffe, Tom. Wiley Nautical Press 2010.

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