Floating LNG (FLNG) is a new type of offshore platform for production, liquefaction, storage and offloading of natural gas. The offloading process of liquefied natural gas (LNG) will use cryogenic loading arms between FLNG and LNG carrier in side-by-side arrangement. The loading arm has many track records in LNG terminals. However, environmental condition of offshore gas field is severer than those of ports. Unexpected large ship motions may occur and affect the offloading operability.

In this paper, the results of the operability assessment for the side-by-side offloading are presented. First, ship motions with liquid cargo in tanks and the free water surface motion in the narrow gap between two vessels are studied by numerical calculation in frequency domain and verified by model test. Then, the limits of environmental conditions for offloading operation are examined by the results of numerical calculation using the criteria for side-by-side offloading. Finally, offloading operability of FLNG and LNG carrier arranged side-by-side in Brazilian sea is evaluated.