Fouling-release of barnacles from a boat hull with comparison to laboratory data of attachment strength
Artikel i vetenskaplig tidskrift, 2010
Fouling-release of various life stages of barnacles was measured from two silicone-based products and a reference Plexiglas (PMMA) surface on a boat hull. From a standard PDMS polymer and a commercial fouling-release coating (Veridian (R)), removal of permanently attached cyprids was efficient whereas removal of newly metamorphosed barnacles was low. The PDMS polymer also demonstrated very low release of juvenile barnacles, indicating significant adhesion to this product. In comparison, Veridian (R) showed higher release of juveniles but similar low release of newly metamorphosed barnacles. Thus, we suggest that coating performance is best evaluated using newly metamorphosed barnacles. The efficiency of fouling-release coatings is commonly tested in a laboratory environment. For barnacles, the adhesive strength can be tested by mechanically shearing or pulling the organisms off the surface. The link between such mechanical testing and the coatings actual performance on a ship hull is however poorly investigated. We calculated the stresses imposed on barnacles by flow and the release data from the present study were compared to earlier measured tensile adhesion strength of barnacles on PMMA and PDMS. The release of permanently attached cyprids was much higher than expected from the tensile strength tests. One likely explanation is that the difference in applied force angle in the laboratory and on the boat hull result in different detachment failure modes. For newly metamorphosed and juvenile barnacles the results from the hull release experiment and the tensile strength measurements were more compatible. We also evaluate and conclude that the imposed forces calculated from mean velocities in the boundary layer better explain detachment of barnacles than forces resulting from instantaneous high velocity sweeps. (C) 2010 Elsevier B.V. All rights reserved.
TURBULENT CHANNEL FLOW