Recently, computational fluid dynamics (CFD) approaches have been effectively used by researchers to calculate the resistance characteristics of ships that have rough outer surfaces. These approaches are mainly based on modifying wall functions using experimentally pre-determined roughness functions. Although several recent studies have shown that CFD can be an effective tool to calculate resistance components of ships for different roughness conditions, most of these studies were performed using the same ship geometry (KRISO Container Ship). Thus, the effect of ship geometry on the resistance characteristics of rough hull surfaces is worth investigating. In this study, viscous resistance components of four different ships are calculated for different roughness conditions. First, flat plate simulations are performed using a previous experimental study for comparison purposes. Then, the viscous resistance components of three-dimensional hulls are calculated. All simulations are performed using two different turbulence models to investigate the effect of the turbulence model on the results. An examination of the distributions of the local skin friction coefficients of the DTMB 5415 and Series 60 showed that the plumpness of the bow form has a significant effect on the increase in frictional resistance with increasing roughness. Another significant finding of the study is that viscous pressure resistance is directly affected by the surface roughness. For all geometries, viscous pressure resistances showed a significant increase for highly rough surfaces.