Keeping ship hulls free of marine organisms

Special underwater coatings prevent shells and other organisms from growing on the hull of ships – but biocide paints are ecologically harmful. Together with the industry, researchers have developed more environmentally-friendly alternatives.

If a ship is at anchor for longer periods algae, shells and barnacles begin to colonise it. Every year, this so-called biofouling causes economic losses worth billions of dollars, because biological growth on the underwater surface promotes corrosion.

The deposits increase the roughness of the hull below the waterline, which has a braking effect as the ship travels. Depending on the roughness of the basified bio layer, the consumption of fuel can increase by up to 40 percent. In the case of a large container ship this can result in additional annual costs of several millions.

All the countermeasures used to date have considerable drawbacks; cleaning the hull by sandblasting in a dry dock also removes the painted coating and can only be used every three to five years.

There are effective hull coatings preventing the growing of adhering bio layers, but in most cases using ecotoxic biocides. Both copper ions and synthetic biocides accumulate in the coastal water and in the sediments. For this reason the particularly toxic tributyltin (TBT) has been banned since 2008 and the currently preferred and still permitted copper oxide containing coatings will have to be replaced by non-toxic alternatives in the foreseeable future.

As part of the BMWi-supported project consortium, ''Controlled Antifouling System based on Nanocomposits for Shipping'' (GANaS), researchers at the Fraunhofer Institute for Mechanics of Materials (IWM) in Halle, Germany, have developed a more ecologically-friendly alternative. ''The electrochemically active coating system produces regularly changing pH values on the surface of the hull, explains Professor Manfred Füting of the IWM in Halle who is coordinating the project." "This effectively prevents colonisation without having to use any  biocides."