Some Simulator Studies on the Directional Stability of Ships under Manual Steering

Abstract

Derectional stability and steering control of a ship can not be concluded merely by defining the dynamic behaviour of a ship itself; rather, it is the problem of the dynamics of a closed-loop feed-back system which is composed of a ship, steering gear and a human or mechanical helmsman.The control behaviour of human helmsmen is highly complicated and its modelling is not an easy matter, yet the closed-loop analysis on steering control under manual steering is of great interest, since every ship is operated in that manner in narrow and crowded water where steering control is of vital importance.In this aspect, the introduction of a real-time, analogue simulator will be useful. The present paper relates to this kind of simulator studies with particular emphasis on course-keeping performance of dynamically unstable ships under manual steering.Some of the results are discussed, including the “limit-cycle” steering which appears unavoidably in course-keeping of unstable ships and the effect of the time scale factor L/V on the ease of steering of unstable ships, where L denotes ship length and V, ship speed. A brief description of the facilities is also given.