This paper investigates the hydrodynamics of an floating liquefied natural gas (FLNG)–liquefied natural gas (LNG) offloading system in a side-by-side configuration using potential flow solver AQWA. The system is moored by an internal turret mooring system allowing itself to weathervane under external disturbances and is designed to operate in a sea environment close to that on the coast of Western Australia. Initially, validations are presented for the computed wave loads, representative motion responses and mooring loads. The results are compared against experimental data and those gathered from literatures. Time domain analyses are carried out for the FLNG–LNG system coupled with hawser, fender and mooring systems under the combination of wind, current and waves. The relative motions between the FLNG and LNG in the horizontal plane as well as the mechanical loads on the hawsers, fenders and moorings are computed. Furthermore, the effects of varying hawser pretension and stiffness on the hydrodynamic performance are investigated.