Dynamics of Ship Anchor-Lines in Waves and Current

The motions and dynamic stresses in a ship anchor-line are determined for the case of single point mooring of a ship to an anchor on the sea bed. The effect of regular long-crested waves and steady current, uniform with depth, on the mooring cable is considered, along with the movements of the upper terminal point of the cable, resulting from the motions of the ship in surge, heave and pitch, and the lifting or laying down of cable on the sea-bed. A condition of the problem is that the cable has zero angle of inclination at the bottom at all times. From the geometry of the system, the statics of the problem and the properties of the mooring line, selection is made of the necessary cable diameter to provide any nominal factor of safety. Solutions of the cable motions and dynamic stresses are obtained by two methods, one of which is rigorous, the other approximate. The complexity of both solutions requires the use of high speed digital computers and finite-difference techniques.