This work covers an experimental study of the drag resistance of different painted surfaces and simulated large-scale irregularities, viz. dry spraying, weld seams, barnacle fouling and paint remains. A laboratory scale rotary set-up was used to determine the drag resistance, and the surface roughness of the samples was determined by means of two different stylus-based methods, one having a 1.6 mm ball stylus (giving the macro-roughness) and the other having a needle type stylus (giving the micro-roughness). It is demonstrated that, in the case of ideal painted surfaces (low macro-roughness), the micro-roughness is much more important than the macro-roughness. On the other hand, the study also indicates that larger scale irregularities have a much greater influence on the drag resistance compared to measurements of the paint system alone.
Erik Weinell, C., Olsen, K. N., Christoffersen, M. W., & Kiil, S. (2003). Experimental Study of Drag Resistance using a Laboratory Scale Rotary Set-Up. Biofouling, 19(S), 45-51. https://doi.org/10.1080/0892701031000072118