In situ measurements of diatom adhesion to silicone-based ship hull coatings

Diatoms are tenacious fouling organisms and have been observed to remain on ship hull coatings at speeds in excess of 30 knots. This study was designed to investigate the adhesion of diatoms to three fouling release ship hull coatings, Intersleek 700 (IS 700), Intersleek 900 (IS 900), and Hempasil X3 (HX3) and one reference coating Dow Corning 3140 (DC 3140), that were exposed at a static immersion test site. The coatings were subjected to water jet testing to determine biofilm adhesion and the subsequent pressures needed to remove specific diatom species. Differences in community composition were observed among coatings in the pre and post water jet evaluation. All diatoms were removed from HX3 after 0.08 MPa; however, the pressure required to completely remove biofilm and diatoms on DC 3140, IS 700, and IS 900 varied. Biofilm removal pressure ranged from 0.08 to 0.40 MPa on DC 3140, 0.16 to 0.40 MPa on IS 700, and 0.08 to 0.40 MPa on IS 900. Significant differences were observed among coatings for removal pressure, as well as initial diatom abundance; however, differences were dependent on the sampling date. The diatom genera which required the highest pressure for removal from the fouling release coatings were Achnanthes, Amphora, Cocconeis, Navicula, and Synedra. The results show differences in the adhesion strength of diatoms to different fouling release coatings and highlight those species, which have the potential to contribute to biofilms remaining on ship hulls once a vessel is underway.