1968 Volume 1968 Issue 124 Pages 51-72
The main aim of this report is to make clear the effects of finite water depth and finite water channel width on ship manoeuvrability both qualitatively and quantitatively.
For this object, the forced yawing technique, by which the author has measured the coefficients of the equations of motion in last four years with enough accuracy, was used to measure the effects of the restricted waters on each coefficient, to say, acceleration, static and rotary derivatives. Besides these coefficients, the two more coefficients which are representative of the effectiveness of the presence of the channel walls, are measured by the straight tow test with variation of the position of the ship in the water channel. In the following, they will be called as the asymmetric hydrodynamic iorce coefficients.
From these results of experiments, the manoeuvrability of ships, specially the course keeping quality, are discussed in detail. According to them, it can be said that in certain circumstances even a ship which is stable in deep water, becomes unstable in a specific range of water depth, but in more shallow water, the ship returns to be more stable rather than in deep water.
The asymmetric hydrodynamic force coefficients play a significant role on determination of the course keeping quality in narrow water channels. In the most wide and deep channel that was examined in this investigation, that is W/B=6 and H/d=1.9, the ships are unstable in the course keeping quality. But it can be concluded that the unstable quality can be improved by simple automatic steering-by directional control system.