Ocean Thermal Energy Conversion (OTEC) harvests energy from the ocean by utilizing the temperature difference between warm seawater on the surface and cooler seawater by transporting seawater through risers. To ensure the safety of the floating platform, this study examines the hydrodynamics performance of the OTEC floating platform in the various states, including the dismantling states where the moonpool exists at the bottom of the floating platform and in the operating states when the risers are fully attached to the platform. The analysis was conducted numerically based on the Boundary Element Method (BEM), where the main dimensions of the platform and the seawater risers were adopted from the previous study. The results show that the ship with the moonpool has a reduction in the amplitude of the heave, roll, and pitch structural response of 20%, 46%, and 37%, respectively, of the response of the ship without modification, as the moonpool increases stiffness and radiation damping by slowing the water flow around the structure, providing an additional damping effect on lateral and vertical motions. In addition, the pipe configuration resulted in improved longitudinal stability over the entire operating frequency range, with results showing 5%, 95%, and 90% reductions in the structure’s heave, roll, and pitch responses, respectively.