Drag penalty due to fouling on a high-speed catamaran: a frictional resistance problem

This study investigates the effect of surface roughness on the resistance components of a high-speed catamaran using CFD. While the influence of roughness has been extensively studied for low-speed monohulls, its impact on high-speed multi-hull vessels remains largely unexplored. Unlike previous work focused on monohulls, this research examines the unique hydrodynamic response of the Delft 372 catamaran at a high Froude number (Fr = 0.75). Simulations employ a URANS approach with a roughness-modified wall function, validated against experimental flat-plate and smooth-hull data. The results reveal a fundamentally different roughness–resistance interaction compared to monohulls: increased roughness significantly alters the turbulent boundary layer, causing a substantial rise in frictional resistance—up to 110% at model scale and 70% at full scale under the most severe condition. Critically, in contrast to findings on some monohulls, the wave-making and viscous pressure resistance components remain largely unaffected. Consequently, the total resistance increases by up to 70% (model scale) and 40% (full scale). This finding demonstrates that, for high-speed catamarans, roughness effects are almost exclusively frictional in nature, decoupled from wave-making processes. The study provides new vessel-specific insight into roughness effects at high Froude numbers and offers a simplified framework for predicting performance degradation of high-speed catamarans, with direct implications for hull maintenance and fuel efficiency. The roughness-induced increase in resistance is interpreted in terms of drag penalty, which provides a practical measure of the hydrodynamic performance degradation associated with hull surface deterioration.