Possible biases in wind speed measurements from merchant ships

Wind speed measurements obtained from ship-mounted anemometers are biased by the presence of the ship which distorts the airflow to the anemometer. Until recently this bias had only been quantified for a few well-exposed anemometer sites on individual research ships, whereas the magnitude and even the sign of the bias was unknown for anemometers on merchant ships. Three-dimensional numerical simulations of the airflow over a typical tanker/bulk carrier have been performed to quantify the pattern of the airflow above the ship’s bridge. The accuracy of the numerical simulations has been verified by comparison to wind tunnel studies. Typically, the flow is accelerated by up to 18±6 % or decelerated by 100% depending on position. In practice, an anemometer located above the bridge should be mounted as high and as far forwards as possible.