Investigating the impact of inhomogeneous roughness on the drag of a planing craft assisted by numerical simulation

Using unsteady Reynolds-Averaged Navier-Stokes (uRANS) simulations, this study investigates the effects of surface roughness patterns on the hydrodynamic performance of a planing hull. By analyzing homogeneous and inhomogeneous roughness configurations, including "step-up" (SMH) and "step-down" (HMS) patterns, the study evaluates their impact on total, frictional, and residual resistance, as well as dynamic lift, sinkage, and trim. The results show that homogeneous high roughness (HHH) leads to the highest total and frictional resistance, along with increased sinkage and trim, while residual resistance decreases compared to smoother configurations. In contrast, inhomogeneous roughness results in lower resistance penalties, with HMS consistently exhibiting lower resistance than SMH. This contradicts previous studies on flat plates and displacement hulls, where step-down roughness increased resistance. The difference arises from the non-zero pressure gradient on the planing hull, which causes higher frictional resistance in aft segments than forward segments, influencing roughness effects. These findings highlight the significant role of pressure gradient variations in shaping the effects of roughness distribution on planing hull performance.