Towards biomimetic air retaining ship hull surfaces - AIRCOAT and its experimental and computational validation methods

Air lubrication has a high potential to reduce skin friction of ship hulls. Active air lubrication system are already available on the market and initial results could show significant long-term energy savings of 4 %. The EU project AIRCOAT (Air Induced friction Reducing ship Coating) aims to develop a passive air lubrication technology inspired by Salvinia molesta, a floating water fern that forms a permanent air layer when submerged in water. AIRCOAT will technologically implement this natural phenomenon to produce a biomimetic hull surface with a high potential to significantly reduce the frictional resistance of ships. The air retaining surfaces based on the Salvinia effect rely on a complex micro- and nanostructured surface with hydrophobic and hydrophilic characteristics. Transferring such characteristics onto sea going ships (e.g. container ships) - which are the largest maritime macrostructures - and demonstrating its effectivity within a three-year project is an ambitious task that involves a well-defined validation method. The AIRCOAT project does this by means of combining experimental and numerical methods to upscale results from laboratory prototypes to application of full-scale solutions in operational environments. Small- and large- scale laboratory experiments will investigate the air retaining and friction reducing capabilities of the surface. Visualisation techniques will be used to determine the phenomena occurring at the ship-air-water interface. In parallel a set of numerical studies at different levels (small, large and full scale) will be carried out to estimate the drag reduction for a sea going ship virtually coated with AIRCOAT. This contribution will introduce into the AIRCOAT project, elaborate on biomimetic air-retaining surfaces and outline the validation concept developed to quantify potential friction reduction.