TIME-VARYING DRIFT FORCES IN CROSS SEAS: MEASUREMENTS AND THEORY

This paper presents a novel method to determine experimentally both mean and time-varying drift forces. This method is applied to measure the low frequency forces in cross-sea conditions. A brief review is given of the theory for determining the second order forces acting on a moored vessel in directional seas. Whereas in previous experimental work only means drift forces could be determined, this study shows that time-varying drift forces can be measured with reasonable accuracy. Surge and sway forces and yaw moments are measured for a 2000,000 DWT tanker subjected to cross waves in 82.5 m water depth. Comparison between measured and theoretical values is reasonable.