Speed-Dependent Performance of Ships. The Effect of Fouling

For many decades the performance of ships was optimized at their design speed and con-firmed by ship trials upon delivery to the shipowner, when the hull and all systems are in perfect condition. However, during operation both the underwater hull and the propeller are appended by biofouling and become progressively rough. Roughness constitutes a major resistance component superimposed on the frictional ship resistance and deteriorates its performance leading to increased power requirements and CO2 emissions to retain a specified speed or to a speed reduction at the same power delivered by the main engine ME. Sailing at reduced speed either due to adverse sea conditions, when the excessive dynamic responses of the ship compel the operator to reduce speed, or for fuel economy is a quite common situation, occurring for a major part or even the whole period of charter contracts to reduce the cost of transportation. In this paper the effect of roughness is investigated and the overall performance of a ship at reduced speeds is assessed directly affecting its techno-economic management. Currently the speed dependence of fouling resistance is evaluated only once at the beginning of the charter contract being valid throughout the whole charter period. The study uses full-scale records and CFD calculations available in the literature to demonstrate the effect of fouling in the overall performance of ships.