A review of surface roughness in antifouling coatings illustrating the importance of cutoff length.

Surface roughness (SR) can affect the hydrodynamic performance of antifouling (AF) coatings and influence the settlement behaviour of fouling larvae, which makes it an important parameter in the evaluation of novel coatings. This paper reviews the causes and consequences of SR in the shipping industry, the methodology used for measuring it, and the importance of measuring and reporting it correctly. SR is a parameter that originates from marine engineering, but has been used extensively by marine scientists to characterise novel coatings and to investigate microtopographies that might inhibit settlement behaviour. One of the integral components of the SR measurement is the use of a cutoff filter. This is a short-pass filter that lets the high wave-number components through and thus separates the waviness from the roughness. Depending on the length of this filter, roughness at different levels of magnification can be investigated. Much of the published work on SR of AF coatings makes no mention of cutoff length, so that the results cannot be compared. It is suggested that an international standard is needed and that if more researchers were aware of the significance of stating cutoff length when reporting SR, more interdisciplinary work between biologists, engineers and material scientists would be possible in this field.