Evaluation of delamination resistance and corrosion protection of fouling release coatings for bronze propellers

Abstract Fouling Release coatings are a new generation of coatings used for bio-fouling control in propellers of pleasure boats. In this study, the combination between these organic coatings and sacrificial anode cathodic protection is studied. Pleasure boats generally operate at low speeds and on irregular basis, spending long periods moored in port. These conditions can promote aggressive fouling on bronze propellers impairing corrosion resistance and operational efficiency. Fouling-release paints work by creating a weak bond between the coating and biofouling, which can be easily broken by hydrodynamic forces. However, cathodic delamination might occur when sacrificial anodes are employed in combination with organic coatings. This is one of the main failure mechanisms for organic coatings in seawater, leading to weakening or complete loss of adhesion at the coating-substrate interface. Standard testing protocols are generally developed for large ships, which operate under entirely different conditions—namely high cruising speeds, continuous operation, and regular maintenance. This work employs an electrochemical procedure to assess cathodic delamination in coated bronze panels. The coatings are multilayer systems consisting of a two-component epoxy primer and a silicone-based topcoat, both formulated by the company Marlin S.r.l. The coating morphology of samples with various epoxy primers combined with a fouling release topcoat were characterized via SEM. Accelerated cathodic disbonding tests in artificial seawater at -2 V vs Ag/AgCl were carried out to evaluate the resistance to delamination of the coatings, barrier properties were assessed through Electrochemical Impedance Spectroscopy (EIS).