During service the ship will experience fouling on hull and propeller.
The degree of fouling depends on many factors; the length of port stay and the service speed at sea; the nature of water in different areas of the world, e.g. salinity, temperature, pH, salts and oxygen concentration.
The ship also experiences different fouling grades on different parts of the hull.
Those parts of the hull exposed to light (usually the sides of the hull) are more exposed to fouling.
The treatment of the hull in between dry docking-periods has importance.
Polishing of the propeller and underwater cleaning of the hull will remove the fouling on these parts, Almeida et al. (2007)