Systematic cleaning and evaluation of exposed fouling control coating systems using a novel laboratory scale automated underwater cleaning system

Underwater cleaning is becoming increasingly important in biofouling prevention besides the development of novel fouling control coatings. This study introduces a laboratory scale self-designed automated underwater cleaning system (AUCS) with a digital force sensor which is able to achieve force monitoring during the cleaning process. Spot test and line test across the test panel was conducted to test the repeatability and accuracy of the AUCS. Spot test provided a new method to evaluate the brush stiffness regardless of brush types (e.g. sizes, materials, length of bristles, etc.) and showed the error of repeatability of AUCS within 0.6 N. Line test proved that normal force mainly depended on the deformation of brushes in vertical direction instead of rotation speed or moving speed of brushes and the error of accuracy of AUCS was within 1.5 N. The effects of brush type and cleaning frequency were investigated in details according to fouling resistance and cleaning efficiency on an epoxy coating (EP), a soluble copper-based antifouling coating (Cu-AF) and a silicone-based fouling release coating (Si-FR) by the AUCS. Results from the field testing at the CoaST Maritime Test Center (CMTC) showed that EP panels cleaned by rubber brush performed better fouling resistance property and cleaning efficiency compared with those cleaned by nylon brush. Additionally, better fouling resistance property and cleaning efficiency of EP panels were obtained with biweekly cleaning. Cu-AF panels cleaned by nylon brush performed better fouling resistance property and cleaning efficiency compared with those cleaned by sponge brush over the cleaning period. Cu-AF panels with biweekly cleaning exhibited higher fouling resistance compared with monthly cleaning while the cleaning efficiency was more depended on brush types. Si-FR panels were outperformed compared with Cu-AF and EP during the underwater cleaning period. However, for the first 3 cleaning months, Si-FR panels with underwater cleaning showed poorer fouling resistance compared with panels without cleaning. Additionally, Si-FR panels cleaned by sponge brush gave lower cleaning efficiency with extension of cleaning period and cleaning interval compared with Si-FR panels cleaned by nylon brush.