While at sea or in port, the hull of a ship can be an attractive new residence for all sorts of creatures. The initial slime build-up can then provide a welcome mat for more and more creatures. This 'biofouling' can end up being inches thick and heavy in weight as well as stopping the streamlining of the vessel. The drag caused can result in more fuel being needed to keep the ship moving forwards at the same speed - more cost and more carbon.
Tom Heap meets a new stowaway on ships which will help fight the build up. Paint company Jotun has now developed the Hullskater robot. Monitoring of conditions will alert when the robot needs to be deployed on missions - with its magnetic wheels and high definition cameras it inspects the surface and uses brushes to remove the build up.
With an increasing fleet of ships, Dr Tamsin Edwards from King's College, London also reflects on other measures to keep hulls free of build up and alternative fuels that might help the international fleet reduce its carbon impact.
Listen now on BBC Radio 4
What our experts say
We asked Society Fellow Professor Bharathram Ganapathisubramani from the University of Southampton to offer some observations on the potential of preventing build up of biofouling and improved design on ships in reducing carbon emissions. His points take some of the themes of the programme a step further.
Maritime transport contributes 940 million tonnes of CO2 annually and is responsible for about 2.5% of global greenhouse gas (GHG) emissions. However, detailed information on emissions from ships has not been recorded. In fact, only recently has the EU required (from 1 January 2018), large ships over 5,000 gross tonnage loading or unloading cargo or passengers at ports in the European Economic Area (EEA) to monitor and report their related CO2 emissions and other relevant information.
Overcoming the resistance of the ship moving through water consumes a large fraction of the fuel burn. Up to 90% of the total resistance experienced by ships can come from the hull (in the water). In the presence of fouling, the hull resistance increases dramatically. In fact, even a lightly fouled ship hull experiences over 35% increase in resistance while a heavily fouled hull could experience 100-200% increase in resistance. This increase is entirely due to the growth of barnacles in the ship hull that makes the surface “rough”. The excess power is spent (which means fuel is burned) to overcome this additional resistance penalty of barnacle roughness. Therefore, any reduction in fouling roughness will directly reduce the powering penalty and in liaison with other technologies including decrease in wind resistance, improving propulsion technologies, alternative fuel arrangements which will lead to a decrease in emissions.
Cargo ship in port in Gambir, Indonesia (Image: Tom Fisk/Unsplash)
What are the limiting factors?
Fouling is only a problem for around 50% of ships, so addressing fouling can only reduce fuel consumption for these vessels. Moreover, there is no clear and obvious way to predict the effects of fouling on the resistance. We know it is bad in general and typically when fouling is bad, so is the fuel consumption. However, if we are to get to a point of autonomous routine cleaning, then, we need to be able to predict the resistance of a given hull state. It is possible that some types of cleaning could lead to a worse situation compared to others. In a relatively “clean” state, it is unclear how the arrangement of barnacles/fouling affects the resistance.
It would be ideal to take some information about the spatial arrangement of the fouling and use that in laboratory tests/numerical modelling to then arrive at an estimate of fuel burn for a future journey. Researchers from around the world are now starting to think about this type of approach, so, we are seeing great progress in this front!
What are the co-benefits of reducing biofouling and reducing emissions from shipping?
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Reduction of the transfer of invasive species that can attach to ships’ hulls.
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Proactive cleaning means that ships do not need manual cleaning by hand, which can often release chemical pollutants into the water.
Are there any potential negative impacts of this idea?
Further reading
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Chung, D., Hutchins, N., Schultz, M.P. and Flack, K.A. (2021), Predicting the Drag of Rough Surfaces, Annual Review of Fluid Mechanics, Vol. 53, pp. 439 - 471
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Schultz, M.P. (2007), Effects of coating roughness and biofouling on ship resistance and powering, The Journal of Bioadhesion and Biofilm Research, Vol. 23 (5), pp. 331 - 341
About the series
39 ways to save the planet is a new radio series by BBC Radio 4 developed in partnership with the Society and broadcast in 2021. It showcases 39 ideas to relieve the stress that climate change is placing on the Earth. In each 15 minute episode Tom Heap and Dr Tamsin Edwards meet the people behind a fresh and fascinating idea to cut the carbon.
Programme website
Over the course of 2021, the Society will be producing events and digital content to accompany the series.