Speed Dependence of Hull Fouling on Ship Performance

The operational profiles of both commercial and naval ships encompass a range of speeds below the service speed. On the way to estimating their performance at these speeds, the varying effect of hull roughness should be quantified. Roughness constitutes a significant resistance component superimposed on skin frictional resistance, which deteriorates ship performance by increasing power requirements and CO2 emissions to retain a specified speed or, equivalently, by reducing attained speed at a given power. This paper exploits the single available full-scale records of a naval combatant and the Computational Fluid Dynamics (CFD) calculations for a well-known containership to compose a methodology to derive the speed dependence of fouling on ship performance at reduced speed based on the respective effect at service speed. Sailing at reduced speed, either imposed by the charter contract for fuel economy (slow steaming) or due to adverse sea conditions, resulting in excessive ship dynamic responses and/or added resistance in waves, is a quite common situation, occurring for the whole period of charter contracts or a significant portion of it, respectively. This study concluded that the roughness effect reduces drastically with speed, supporting shipowners to compose a more reliable charter contract and shipping companies to derive a realistic dry-docking plan.