The effect of cleaning and repainting on the ship drag penalty.

Although the hull of a recently dry-docked large ship is expected to be relatively smooth, surface scanning and experimentation reveal that it can exhibit an "orange-peel" roughness pattern with an equivalent sand-grain roughness height k s = 0. 101 mm. Using the known k s value and integral boundary layer evolution, a recently cleaned and coated full-scale ship was predicted to experience a significant increase in the average coefficient of friction % Δ C ¯ f and total hydrodynamic resistance % Δ R ¯ T during operation. Here the report also discusses two recently reported empirical estimations that can estimate ks directly from measured surface topographical parameters, by-passing the need for experiments on replicated surfaces. The empirical estimations are found to have an accuracy of 4.5 - 5 percentage points in % Δ C ¯ f .