Wave Drift Forces Affecting on Maneuverability Derivatives

Maneuverability in waves is important for the safety of ships and other marine vehicles. Conventionally, the maneuvering experiments are performed in still water at a constant forward velocity. In order to investigate the wave effects on ships steering, a series of towing tests with a Planer Motion Mechanism System (PMM) are carried out in waves in the present work. The ship model is forced to oscillate in horizontal plane at a low frequency when being towed forward at a small constant speed. As an extension of the previous work, the low-frequency oscillation of yaw motion is also considered. Hydrodynamic forces and the displacements of the ship model are measured throughout the tests. Then, the measured data are analyzed by the Fourier analysis to obtain components at different frequencies. By comparing the hydrodynamic forces measured in still water and that in waves, the wave effects on the maneuverability of ships are estimated. The variation of these nonlinear hydrodynamic coefficients against the wave amplitude and wavelength is examined.