Fouling control coatings

Marine biofouling can be defined as the undesirable colonization of fabricated structures immersed in seawater by dissolved compounds, microorganisms, plants and animals. Seconds after immersion, the biofouling process will commence with the physical adsorption of dissolved organic matter such as polysaccharides and proteins on the submerged surface (i.e. a ship hull), giving rise to the so-called conditioning film. Marine organisms will also tend to attach to such a surface, where they can make use of the natural movement of the seawater for feeding and waste removal, thus saving energy for other vital processes.

The consequences of biofouling on ship hulls are:

  • High frictional resistance caused by increased weight which results speed reduction and loss of manoeuvrability
  • Higher fuel consumption and thus increased emissions of harmful compounds (SO2, NOx) and CO2
  • More frequent dry-docking equivalent to increased expenses and generation of toxic waste
  • Introduction of invasive or non-native species

To combat marine biofouling, fouling control coatings are used, which are mainly based on one of the two following principles:

  • Chemically active coatings with controlled release of biocides (conventional antifouling)
  • Smooth coatings with low surface energy (fouling release)

The main challenge involved in conventional antifouling is to design a coating system with controlled release of biocides just enough to keep the fouling from settling on the hull. At the same time, the antifouling coating system should provide a smooth, low drag surface over the whole service period, which is typically 3 to 5 years.

The main challenge involved in fouling release coatings is to design a smooth coating surface that remains fouling free without the use of biocides over the entire service period.

The disciplines involved in understanding the working mechanisms of fouling control systems are mainly polymer chemistry, mass transfer and diffusion processes, colloid and surface chemistry and ship hydrodynamics.