Estimation of wind, waves and fouling effect on ships from full scale and hindcast data

Abstract

Assessment of vessel performance requires estimating various types of added resistance to the calm water resistance, with the most significant caused by the presence of wind, waves and fouling of the hull and propeller. In this paper, the performance prediction system VESPER is applied to the estimation of added resistance for two fleets, one of bulkers and one of containerships. Firstly, the bias and error of measurements from ship-mounted anemometers is investigated. The measured wind speeds were corrected for the anemometer height and compared with hindcast data. Two different pairs of anemometer heights and wind shear exponents were used and the Mean Bias Percentage Error (MBPE) between the anemometer and hindcast data was evaluated. The study showed an overestimation of wind speed from the anemometers due to flow acceleration by the presence of the superstructure and the ship itself. The acceleration was higher for containerships compared to bulkers. Also, for both fleets the acceleration was higher for side winds. Additionally, the change of the average Confidence Interval of the calculated total added resistance is presented after applying corrections for wind, waves and currents, using both the above wind data sets with and without corrections. For both fleets, the effect of fouling was calculated significantly higher compared to the effect of the weather. Finally, the SPAWAVE method was applied to quantify the effect of waves, which, relative to the total added resistance, was calculated stronger for the bulkers compared to the containerships, while the effect of the wind was similar between the two ship types.