An increase of underwater hull surface roughness will increase the hull frictional resistance of the ship while sailing. This will result in additional power requirements with increased fuel consumption leading to increased costs to maintain the ship’s service speed.

Hull surface roughness is divided into two types – physical and biological (fouling) – each with their own micro- and macro characteristics, King (1982).

– Macrophysical roughness: plate waviness, plate laps, welds and weld quality, mechanical damage and corrosion

– Macrobiological roughness: animal and weed fouling

– Microphysical roughness: steel profile, minor corrosion and coatings condition.

– Microbiological roughness: slime fouling

The initial hull roughness when the ship is delivered from dry dock is therefore dependent on the quality of work on building the ship and the quality of the bottom paint. Townsin (1986) has analysed the increase of average hull roughness (AHR) on ships over a period (1976 -1986) and Schultz (2007) has published an analysis of fouling influence on the added resistance.

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