The majority of Department of Defense (DoD) and service vessels use copper-containing ablative antifouling coatings in order to control the accumulation of biofouling on underwater hulls. Fouled vessels suffer an increase in drag resulting in increased fuel use and exhaust emissions, and may also serve as vectors for introduction of non-indigenous species. However, control of biofouling by copper-containing coatings also comes with an environmental cost associated with discharge of copper to the water column. Environmental regulations, together with fleet-specific practices and policies, threaten the continued use of and increase the cost of using copper-containing antifouling coatings. Copper-free antifouling coatings solve several environmental and regulatory problems. These coatings significantly reduce copper-laden waste streams in dry dock, leaching of copper from the coating while in port, and discharge of copper from in-water hull cleaning events. The US Navy has qualified two copper-free antifouling coating systems for fleet use, but limits application to vessels requiring no more than a three-year service life. The largest obstacle to widespread transition of copper-free antifouling coatings to DoD and service fleets, and realization of the associated environmental benefits, is validation of a 12-year service life application that would render these coatings suitable for use for all DoD and service vessels.
The objective of the project is to demonstrate longer service life applications (up to 12 years or Application 3 in MIL-PRF-24647D) for the Navy qualified copper-free ablative antifouling hull paints and to transition them for use across all DoD and service platforms. In particular, and in order to predict service life, the project will 1) quantify coating ablation/erosion rate under dynamic conditions and during operations, 2) quantify coating response to in-water hull cleaning, 3) provide a comprehensive assessment of coating performance on relevant in-service vessels, and 4) develop a business case for copper-free coating technology.
The copper-free ablative antifouling coatings are based on a soluble matrix chemistry similar to the copper-containing ablative coating systems already approved across all DoD platforms for up to a 12-year service life. The copper-free coatings contain the EPA-approved biocides Econea™ (Tralopyril) and zinc pyrithione. These biocides are characterized by short degradation times in seawater, and low toxicity of breakdown products. Preliminary investigations indicate that the efficacy of these coatings against biofouling organisms is comparable to that for copper-containing ablative antifouling coatings.
This program will accelerate the transition of copper-free ablative antifouling coatings, and will validate their application across all platforms and services. Environmental benefits include reduction of Notices of Violation associated with the use of copper-bearing coating systems in dry dock, compliance with current and anticipated environmental requirements, and lower cost to manage dry dock waste streams. In addition, these coatings may provide an enabling capability for improving fuel efficiency of DoD vessels by opening the possibility for increased frequency of in-water hull cleaning. This approach to reducing fouling-associated drag, fuel use, and exhaust emissions would likely not be allowed for the copper-containing ablative coatings currently in use, due to limits on copper inputs. (Anticipated Project Completion - 2016)