Analysis of Motion in Single-Point Mooring Systems

A mathematical model of the slow motions of ships in single-point moorings is described. The model is used for analysis of stability of equilibrium positions. An analytical criterion for stability relating main system parameters is derived under simplifying assumptions. A numerical example with a 100 000 dwt tanker showed that the effect of wind and current are of equal importance with respect to system stability, and astern propulsion is generally required to avoid stable oscillations. Stability problems in waves have not been found. The effects of time varying excitations are discussed and illustrated by simulation.