Fouling
Fouling on surfaces – a natural phenomenon
When a surface comes into contact with seawater, it changes very rapidly. Dissolved organic compounds, which exist naturally in the sea, adhere to the surface within a few minutes. Within a few hours, unicellular living organisms, such as bacteria and unicellular algae, colonise the surface, which has become smooth and slimy. After a week or more, the surface will be colonised by a variety of microorganisms, algae and animals. There are about 4000 marine species, which can and will colonise different surfaces in the marine environment.

What is the problem with fouling, and how big a problem is it?
Fouling on ships increases the surface roughness of the hull, which then increases its frictional resistance when the vessel moves through the water. The increased resistance leads to greater fuel consumption. The costs of increased fuel consumption are substantial – after six months, a ship without any antifouling can have 40% greater fuel consumption to maintain normal speed. A medium-sized ship with a 20% increase in fuel consumption and 250 days under way per year would have increased annual fuel costs of about SEK 3 million.

To prevent fouling, over 80000 tonnes of antifouling paint are used every year – with a total market value of € 1 billion. The total cost of fouling is significantly higher. The US Navy faces annual costs resulting from fouling of its ships of over € 1 billion, including maintenance costs and the costs of increased fuel consumption.

The environmental problem is evident and serious. Increased fuel consumption leads to higher emissions of the greenhouse gas carbon dioxide, nitrogen oxides, sulphur oxide, hydrocarbons and particles. In addition, there is new scientific evidence suggesting that fouling can play an important and undesirable role in spreading marine species from their natural areas of distribution to new areas where they can constitute a threat to the ecological balance, becoming what are called “alien species”.

There is a trade off between the adverse effects from fouling and the adverse effects resulting from the use of antifouling paints that are toxic to the marine ecosystem.