This study explores the impact of hull and propeller roughness on full-scale Computational Fluid Dynamics (CFD) predictions for ship performance. As regulatory demands for greenhouse gas reduction intensify, accurate fuel efficiency estimation has become increasingly important. While the ITTC method is commonly used to estimate added resistance due to roughness, it becomes unreliable when low roughness values are measured or when propeller roughness should be considered. CFD offers a more robust alternative by enabling direct integration of roughness effects into simulations. In this work, self-propulsion simulations were performed on the JoRes5 Bulk Carrier using both smooth and rough wall treatments, with and without a Pre-Swirl Stator (PSS). Results were compared against sea trial measurements. The findings show that incorporating realistic roughness models significantly improves the accuracy of power predictions and better captures performance trends observed in trials. These results highlight the importance of advanced roughness modelling in CFD for evaluating energy-saving devices and enhancing the reliability of full-scale performance predictions.