Influence of loading condition on the behavior of a moored liquefied natural gas ship

In a recent paper, a verification study was presented of the time-domain mooring simulation program TERMSIM. In that paper, the verification was restricted to the behavior of loaded ships. Extension to the verification of the model for different loading conditions is made in this technical note. For the downtime analysis of a new liquefied natural gas (LNG) terminal, the influence of the loading condition is often neglected and the analysis is only carried out for the loaded ship. This assumption seems valid, because the draft difference between laden and ballast is small for LNG ships. However, prototype measurements of line forces showed quite large increase of mooring forces during the loading process of the ship. This strong dependence also follows from computer simulations presented in this technical note. Large differences in moored ship behavior in swell waves between the loaded and ballasted condition can occur because of a different roll period and ratio between the wave frequency and stiffness of the mooring system.