The effect of cleaning and repainting on the ship drag penalty

Abstract

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 $k_s\mathrm{}$ 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 $\mathrm{\%}\mathrm{\Delta }{\overline{C}}_f$ and total hydrodynamic resistance $\mathrm{\%}\mathrm{\Delta }{\overline{R}}_T$ during operation. Here the report also discusses two recently reported empirical estimations that can estimate k_s 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 $\mathrm{\%}\mathrm{\Delta }{\overline{C}}_f.$

Keywords:

• Turbulent boundary layer
• skin friction drag
• ship-hull roughness
• roughness estimation

Acknowledgements

The authors thank PT Dharma Lautan Utama for providing access to the Dharma Kencana IX ferry, Dr Marcus Tullberg of Hempel A/S for his assistance in obtaining the hull roughness imprint, and PT Biro Klasifikasi Indonesia for ensuring the safety of the research team.

This paper uses re-analysis data from Nugroho et al. (2021) and they are openly available from the University of Southampton repository at https://doi.org/10.5258/SOTON/D1559.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the Australian Research Council and the Newton Fund for the support of this work. B. Ganapathisubramani is grateful to EPSRC for their support through grant EP/P009638/1. I K A P Utama acknowledges the support from the Ministry of Research, Technology and Higher Education of the Republic of Indonesia under the World Class Professor 2019 Grant scheme: T/42/D2.3/KK.04.05/2019.