Failure analysis of antifouling paints on ships hull

Abstract

Fouling on ships hull occurs due to the attachment of barnacles, mollusks and other aquatic organisms on the underwater area of the hull. This leads to increased drag, fuel consumption, resulting in unscheduled dry-docking. Recent advances in antifouling (AF) paints, in general, offer protection against fouling in about 95 % of the vessels immersed surface. However, the remaining area which amounts to 5% or less of the total area does get fouled. Although this level of fouling has marginal impact on the routine performance of the vessel, it is a predominant vector for the transmigration of invasive species which is a serious environmental concern. Virtually all ocean going vessels are coated with antifouling paints, predominant among them are “Self polishing coatings”. These coatings depend on the shear forces on the hull surface caused by the motion of the vessel for the paint to “polish” away and release a biocide at a predetermined rate that results in the hull to be essentially fouling free. Currently hulls are coated with a uniform layer of antifouling paints. However, computational fluid dynamics (CFD) analysis conducted on various types of vessels have indicated that there are certain “hotspots” where shear stresses and therefore the polishing rates are exceedingly high which would polish the AF paints at a much faster rate and ultimately result in the failure of the AF coating. The analysis also indicates that these hotspots primarily depend on the profile of the vessels, its speed and its draft. The current practice of a uniform coat of AF paint does not take into account the fact that there are certain areas of the vessel where the polishing rates are excessive. A possible solution to this issue is to first identify these hotspots and suitable paint schemes/formulations are to be applied in these areas. Such painting schemes would prevent the premature failure of the AF coating in general and significantly reduce the risk of transmigration of invasive species.