Copper-containing ablative antifouling coatings are used on the overwhelming majority of military vessels in the United States (Army, Coast Guard, Military Sealift Command, and Navy). These coatings function reasonably well in terms of controlling biofouling and physical performance, but their continued widespread use is being challenged by an array of environmental requirements. Additionally, with an increase in the number of aluminum-hulled vessels in use by military fleets, there is an increasing demand for copper-free alternatives due to the risk of galvanic corrosion. In response to these environmental and operational requirements, and at the start of this project, two commercial products had already been qualified by the Navy for three years of service or less (Application 1 per MIL-PRF-24647E). The objective of this project was to more fully characterize the performance of these two commercial copper-free ablative coatings with the aim of accelerated transition across all the Department of Defense and service platforms.

Technology Description

The combined results of the base project assessments supported the qualification of two copper-free ablative coating systems to the Navy’s performance specification MIL-PRF-24647E for seven years of service life (Application 2 per MIL-PRF-24647E). This step enabled copper-free ablative coating use on aluminum-hulled vessels (Independence-class littoral combat ship and the Spearhead-class expeditionary fast transport) where, under separate funding, improved performance over legacy coatings (fouling release and a hard/durable fouling release coating respectively) were documented.

Demonstration Results

The better-performing coatings reduced maintenance (cost of cleaning; management of copper waste streams in dry dock), reduced reliance on in-water cleaning thus enhancing operational capability (lowered risk to vessel speed, range), reduced copper inputs, and enhanced operational efficiency (fuel) and readiness. The extended monitoring part of this project was designed to determine whether transition to longer service life applications (up to 12 years; Application 3 per MIL-PRF-24647E) were warranted. Through about seven years of service, the copper-free ablative test coatings performed about as well as legacy copper ablative coatings, with some exceptions. After this time, a slightly higher accumulation of hard biofouling was observed on test versus legacy coatings.

Implementation Issues

The ESTCP extended monitoring task indicated that performance of copper-free ablative coatings was similar to, but did not exceed, that of copper-containing ablative coatings. Given all of the project data, the Naval Sea Systems Command technical authority supports extending qualification of copper-free ablative coatings for a service life of 12 years or less as long as appropriate risk mitigation steps are taken. These may include a) requiring an additional topcoat of paint, and b) informing the maintenance community of the potential risk of more rapid coating performance degradation (versus legacy coatings). When these coatings are qualified as Application 3, they have the potential for use on all service/military craft.