Silicone Paint Challenges Copper for Cleaner Boat Hulls Test

A new European study is putting fresh pressure on the leisure marine coatings market, after researchers found that a biocide-free silicone antifouling paint delivered the strongest fouling control across several coastal test sites.

The research, led by Chalmers University of Technology in Sweden, compared seven antifouling paints in Swedish, Danish and French waters. Five products contained cuprous oxide at concentrations ranging from 6% to 32% by weight. The remaining two included a biocide-free silicone coating and a copper-free paint based on tralopyril and zinc pyrithione.

Across test locations in Tjärnö, Hundested and Arcachon Bay, the silicone coating performed best against hull fouling. The tralopyril-based product followed closely, while the copper-based coatings also provided protection but did not show better performance at higher copper levels.

That result matters for boat owners, marinas, coatings suppliers and regulators. Hull fouling increases drag, slows vessels and can raise fuel use, making antifouling paint a practical maintenance issue as well as an environmental one. At the same time, many traditional coatings rely on biocides that can leach into coastal waters and sediments.

For manufacturers, the study adds weight to a key product development question: how much copper is needed to deliver reliable antifouling performance? If lower-copper coatings can achieve similar results, high-copper products may face tougher scrutiny in markets where coastal pollution and marine biodiversity are rising regulatory priorities.

Environmental Claims Face Closer Scrutiny

The study also highlights the gap that can exist between environmental positioning and measured environmental impact.

The tralopyril-based coating performed well against fouling and is marketed in some EU countries as an environmentally safer option. However, the study found it created the highest environmental risk among the products tested. Researchers’ modelling suggested biocide release levels several thousand times above acceptable thresholds.

A separate toxicity test, using leachate solutions from painted panels and four marine species, supported those concerns. The tralopyril-based paint showed the highest toxicity, followed by the product with the highest copper content. The silicone coating combined strong antifouling performance with low toxicity, giving it the strongest overall sustainability profile in the comparison.

For the B2B marine sector, the findings point to a more data-driven phase for antifouling paint. Copper-free does not automatically mean low impact, and copper-heavy does not necessarily mean better performance. Product claims will need to stand up to leaching data, toxicity testing and regulatory review.

Adoption will still depend on practical factors. Silicone coatings can require more surface preparation and a compatible primer system, which may affect cost, application time and maintenance routines. That could slow uptake among recreational boat owners used to conventional antifouling systems.

Even so, the direction of travel is clear. Marine coatings that reduce fouling, limit drag, lower toxicity risks and meet tightening environmental expectations are likely to gain attention from marinas, boatyards and regulators. For suppliers, the opportunity is not just to make cleaner claims, but to prove performance under real coastal conditions.