Numerical Simulations for Determining Resistance, Trim, and Sinkage Characteristics of a Tugboat

A detailed numerical investigation of the calm-water hydrodynamic performance of an azimuth stern drive (ASD) tugboat is presented. Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations are performed to predict the total resistance, trim, and sinkage over a wide range of Froude numbers at model scale. The free-surface flow is captured using the Volume of Fluid (VOF) method with a high-resolution interface capturing scheme, while turbulence effects are modeled using the SST k–ω formulation. To account for dynamic hull response, the vessel is allowed to move freely in heave and pitch through a Dynamic Fluid Body Interaction (DFBI) approach. A systematic mesh and time-step convergence study is conducted to ensure numerical accuracy and solution independence. The numerical predictions of resistance coefficient, trim angle, and sinkage show good agreement with available experimental data, validating the adopted computational framework. In addition to global performance metrics, detailed analyses of the flow field are carried out, including free-surface wave patterns, hull pressure and skin-friction distributions, and stern wake characteristics at the propeller plane. The results provide physical insight into the resistance mechanisms and stern flow features of ASD tugboats operating in calm water. While employing established numerical methods, the primary contribution of this work lies in providing a comprehensively validated dataset and detailed flow physics analysis for a benchmark ASD tugboat—a bluff, unconventional hull form that remains underrepresented in high-fidelity CFD literature. The validated methodology and flow-field findings support the application of CFD as a reliable tool for tugboat hydrodynamic assessment and design optimization.