Floating Offshore Wind Turbine (FOWT) is a solution to obtain more significant wind resources while dealing with space constraints for the installation. The structure is subjected to six degrees of freedom, which not only influences the power output performance but also the safety of the structure. Considering this, the present study aims to evaluate the performance of the spar platform with various mooring system configurations in the context of the most extreme environmental conditions in eastern Indonesia. The analysis was conducted using the Boundary Element Method (BEM) via Ansys Aqwa, focusing on the stability and response of the movement following the installation of a mooring system. The RAO analyses demonstrate that the platform exhibits effective damping capability at high frequencies, with notable responses at low frequencies (0.1–0.5 rad/s). In the mooring analysis, the configuration with eight mooring lines exhibits a balanced tension distribution, whereas the configuration with nine mooring lines, characterized by a shorter horizontal span, exhibits the highest tension at 1.4 MN. The mooring variations show varying peak values in PSD, motion response and mooring tension, with a maximum tension percentage of up to 22%.