Measuring drag of dynamically aged marine biofilms treated with ultraviolet light (UVC)*

The presence of marine biofilms has been shown to cause significant increases in drag on ships and marine vehicles. Previous field experiments have demonstrated the application of ultraviolet light (UVC) results in a considerable reduction in biofilm for both static and dynamic environments. This experiment was designed to address how changes in biofilm treated by UVC modify the drag properties. An epoxy coating was applied to two PVC test plates (10 cm wide x 75 cm long) which were then immersed at Florida Tech’s estuarine field test site.  The panels were dynamically aged in the estuarine environment using an open channel flume (10 cm wide x 300 cm long).  Panels were immersed for approximately one week to accrue biofilm. A select panel was also exposed to UVC (25W, 254 nm) in the flume over the course of the week. Panels were then removed and the biofilm characteristics (thickness, percent cover, microbial community, chlorophyll content) were determined. Associated drag penalties were measured in a separate field deployed flow channel. Results demonstrate the correct dose of UVC can significantly reduce biofilm formation under flow, which results in lower drag penalties. These reduction in drag penalties are discussed in context of full-scale ships and underwater vehicles.