A Study Of Mathematical Model For Yawing At Anchor

Anchoring is an essential procedure to ship transportation. The problem of safety anchoring is concerned with life of seaman, ship and cargo. Consequently, experts and scholars have been paying close attention to it. To enhance the safety of anchoring, a lot of researches have been conducted for many years. There are two main methods of study of mooring safety. One method of research is that of experiment, including experiment on ship and on model, anther is that of theory.In this paper, a mathematical model of five freedom for mooring motions is built to study Safety anchoring: dragging anchor and grounding. It breaks the limitations of old mathematical model .Not only are the surge, sway, yaw considered, but also the heave, pitch and effect of shallow water. The elements, which affected mostly by shallow water, are modified in this paper. The results are of more precision by adopting the latest achievements. Conclusions are drawn by a large number calculation.1 .To large extent, the magnitudes of sway and yaw are affected by the depth of water, so is that of anchor chain tension; The magnitudes of sway and yaw are smaller in the shallows than in the deep, so is that of anchor chain tension;2.To small extent, the magnitude of heave and pitch is affected by the depth of water.3.The magnitudes of anchor chain tension caused by heave and pitch is small. So is the effect on dragging anchor.4.The depth of water, which anchored ship requires, is to large extent affected by heave and pitch . So the probability of grounding of an anchored ship is enhanced.5.The formula which calculate the minimum depth of anchorage for anchoring is presented in this paper. To prevent dragging anchor and grounding, in full loading state the depth between 2d and 1.5d+2Hmax/3 and in ballast state the depth between 2d +1 and 1.5d+2Hmax/3 is proper for ten thousand tons ship.