The influence of biofilms on skin friction drag.

The contribution of biofilms to skin friction drag is not clearly defined, and as regulations continue to restrict the use of biocides in antifouling paints, they are likely to form a greater presence on ship hulls. This paper reviews the flow regime around a ship's hull, the basics of boundary layer structure, and the effects of rigid surface roughness on drag. A review of experimental studies of biofilms in turbulent shear flows at laboratory and ship-scale is made. The consensus of these studies shows that biofilms increase skin friction drag. Some measurements carried out in turbulent boundary layer flow using a two-component, laser Doppler velocimeter (LDV) are also presented. These results indicate an increase in skin friction for biofilms that is dependent on composition as well as thickness.