This paper explores ship dynamics through numerical investigation using Smoothed Particle Hydrodynamics (SPH). To enhance the performance of SPH simulations, we implement the Dummy Particle Condition (DPC) floating-fluid interaction scheme in our numerical model, substituting the original Dynamic Boundary Condition (DBC). The accuracy of the updated model is validated by conducting a series of two-dimensional (2D) benchmark tests. Subsequently, based on both DBC and DPC, we simulate three-dimensional (3D) ship motion in a series of regular waves, including low and high waves, and compare the simulation results with model test data. It is demonstrated that, compared with the original DBC, the DPC floating-fluid interaction scheme effectively enhances SPH simulation performance in terms of ship dynamics for all wave conditions. Then, the correlation between simulation accuracy, wave height, and particle size in SPH is quantitatively discussed, and a clear relationship is observed for DPC results.