Accurate prediction on the hydrodynamic coefficients of offshore structures with large horizontal surface is critical in offshore installation operation, especially when crossing splash zone. The structures may encounter various wave condition and experience significant impact force which leads to unexpected impulsive load on the hoisting system and limitation of the operation window for offshore installation. This paper aims to determine the impact of the slamming coefficient on splash zone crossing modelling, through a series of time domain simulations for perforated plate under different sea states. The slamming coefficients are determined by the unsteady Reynolds-Averaged Navier-Stokes (URANS) solver of STAR-CCM+, combined with the recommended value from design code DNV-RP-H103. With the obtained coefficients, the lowering operation of perforated plated is simulated in OrcaFlex. The result indicates that the slack probability is underestimated using the recommended slamming coefficient from DNV code for offshore structures with a large horizontal surface such as perforated plate in this study. In addition, the influence of passive heave compensator (PHC) is investigated through a series of deployment simulations for the perforated plate with and without PHC. Based on the results, the existence of the PHC is critical for installation operation at the wave period from 3 to 10 seconds in order to achieve a satisfactory factor of safety.