Hull surface condition plays an important role for ships performances for new-built ships as well as ships in operation since the drag penalties due to hull roughness are substantial. It is a standard practice that ship design is based on performance evaluation by model testing of ship models with hydrodynamically smooth surface and the increase of resistance for new build condition is added by roughness correlation allowance based on empirical formula. Surface roughness effects beyond the new build condition are seldom considered in the design process. The question is whether hull roughness affects the flow characteristics to such extend that it influence with the resulting design. This is especially important for propellers or energy saving devices which are operating around the stern of the ship where the roughness effects on flow characteristics are most pronounced. This paper will discuss some practical questions related to the effect of hull roughness, both in terms flow characteristics, power increase and impact on ship design and operational practice.