Using low current to fight biofouling on ship hulls
If a ship is anchored for longer periods of time, local algae, shells and barnacles colonize its hull and cause biofouling. Biofouling causes large economic losses since its growth on water vehicle hulls causes corrosion as well as higher fuel consumption. While some research groups develop surfaces which deny the initial formation, a group of researchers from Fraunhofer Institute for Mechanics of Materials (Fraunhofer IWM) in Halle came up with their solution for this problem in a form of an eco-friendly coating.
Aside other novel solutions, cleaning the hull by sandblasting in a dry dock removes painted coating and it is usually performed every three to five years. Aside constant maintenance, basified bio layer can increase the fuel consumption by up to 40 percent. Effective hull coatings which prevent the growth of adhering bio layers do exist, but most of those coatings rely on ecotoxic biocides to achieve the desired effect.
Both copper ions and synthetic biocides which are used in such biocides are recorded to accumulate in the coastal water and in the sediments. These reading caused toxic tributyltin (TBT) to be banned since 2008, and the currently preferred and still permitted copper oxide containing coatings are to be replaced by non-toxic alternatives in the foreseeable future.
“The electrochemically active coating system produces regularly changing pH values on the surface of the hull. This effectively prevents colonization without having to use any biocides”, said Professor Manfred Füting, who coordinates the project at the Fraunhofer IWM in Halle.
Although their approach doesn’t use biocides, it does require small amounts of current in order to operate. The researchers painted large area electrodes on an isolating primer coating, and the electrochemical active layer based on a sol-gel paint of NTC (nano tech coating gmbH) becomes modified by electrically conductive particles. In order to increase its effectiveness and adequate distribution of the electrolysis current, a highly conductive interlayer is applied between the isolating primer layer and the active layer.
Current (with density lower than 0.2 mA/cm2) is periodically commutated and interrupted in order to induce preprogrammed and optimized electrochemical process of the electrolysis. It causes enough pH stress near the surface of the hull to prevent the growing on of any barnacles, shells and algae.
Tests with the first prototypes at the Barth shipyard gave promising results. Researchers are testing different configurations to prove their long-term stability against hydrodynamic stress and efficiency to prevent adherence and growth of bio layers.
The electrochemical antifouling by alternating pH values was developed and patented by the project partner bioplan GmbH. The method devised by Fraunhofer IWM researchers is working effectively and independently of marine flora and the kind of sea water, and it could be powered by a photovoltaic module.