It is well known that at the single point mooring or anchoring the slewing motion of a ship is caused by action of the wind or the current. During the slewing, the extraordinary tension occurs in the mooring line when the ship's yaw angle becomes nearly maximum, and incurs, as the case may be, the breakdown of mooring lines or unforeseen drift of anchors. However, there exist only a few published papers related to the slewing motion, and theoretical predictions of slewing motions and tension of mooring lines do not agree well with the observed ones.
In this paper, a new mathematical model is proposed to describe the current forces acting on a ship under the slewing motion, and validity of the proposed model is examined through comparing the ship motions and the tension of mooring line predicted by the present method with those measured at the model experiment performed in the water basin.
Prior to advent of the mathematical model proposed in this paper, the current force acting on a ship during the slewing was experimentally determined in the wind tunnel or the water basin as functions of relative inflow angle of the current.
As the result of examining the prediction through the present method, it is verified that the method proposed in this paper is of a great practical use compared with the previous method, because the proposed method enables us to evaluate various effects of changing the mooring conditions such as ship's displacement, ship's trim, the length of mooring line, current speed, etc. on the slewing motion with ease and with accuracy.