<p>This study investigates the resistance performance of a catamaran in regular waves using the Reynolds-averaged Navier–Stokes (RANS) method. Uncertainty analyses were conducted and validated against model test results to ensure the reliability of the numerical approach. The research explores the effects of various factors, including speed, wave orientation, wave height, and wavelength, on the resistance characteristics of catamarans equipped with different appendages in regular waves. At high speeds, the catamaran with a bow-wing configuration exhibited distinct behavior in terms of total resistance, sinkage, and trim angles compared to other setups. Notably, the full-wing configuration demonstrated the smallest fluctuations in sinkage and trim angles. The study also found that total resistance, sinkage, and trim responded uniquely to changes in wave orientation, with the bow-wing configuration showing particularly notable characteristics. Moreover, increased wave height, except for the bow-wing configuration, resulted in higher total resistance for the bare hull, stern-wing, and full-wing configurations. The methods and findings presented in this paper provide valuable theoretical insights to enhance the understanding of catamaran performance in wave environments.</p>