Impact of Surface Roughness on Interference Resistance in Delft 372 Catamarans

Surface roughness from marine biofouling significantly compromises catamara performance, yet current models fail to predict its speed-dependent interference effects, a critical gap in sustainable vessel design. This study employs validated Reynolds-averaged Navier-Stokesbased computational fluid dynamics with the k-ω Shear Stress Transport turbulence model to quantify hydrodynamic impacts across Froude numbers ranging from 0.1 to 0.8. Four different biofouling conditions were systematically analyzed, with rigorous experimental validation against towing-tank data. Key results demonstrate that heavy fouling increased total resistance by 35% at Fr 0.8 versus hydrodynamically smooth surfaces, yet paradoxically generated favorable interference, IF = -0.08, through turbulence-mediated wave suppression. Conversely, hydraulically smooth surfaces exhibited peak detrimental interference, IF = 0.15, at Fr 0.5 due to constructive wave reinforcement. Concurrently, the heavy slime surface reduced inter-hull wave amplitude by 14.5% at Fr 0.5, while expanding the wetted area by 1.24%. The findings address the biofouling paradox by demonstrating that surface roughness facilitates a net reduction in resistance at Fr ≥ 0.65, challenging traditional beliefs regarding the uniformly negative impact of fouling. This study presents the inaugural predictive framework for strategic fouling management, emphasizing bow and midship interference zones, thereby addressing a significant gap in hydrodynamic prediction within realistic operational contexts.