Drag penalty causing from the roughness of recently cleaned and painted ship hull using RANS CFD

The issue of global warming makes energy savings on ships compulsory. One of the biggest causes of energy waste is the increase in friction resistance due to the hull roughness that makes not hydraulically smooth. The process of cleaning and repainting the ship hull turned out to make a roughness that can provide a drag penalty. An investigation using a resolved Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) approached to assess the increase in ship resistance from a recently cleaned and painted ship hull roughness are reported. The rough surface was obtained through surface imprint during its annual dry-docking and digitized via a laser scanner. A roughness geometry that was obtained from the scanning was prepared for the CFD simulations. The results for two ships show that such surface would cause an increase in friction resistance of the full-scale ship by 33%-35%, which corresponds to an increase in the ship’s total resistance by 7.5%-28%. The type of ship that is mostly affected by the roughness is a ship with a higher frictional resistance ratio (lower Froude Number) compared to residual resistances, where most of them are large ships.