Researchers Test for Hull Coating Replacement

THURSDAY, MAY 25, 2023

A recent study has reportedly tested a silicone-based coating in the Baltic Sea to find a cleaner alternative to hull coatings. Researchers recently tested the performance of these coatings on ship hulls in comparison with the currently used copper-based biocidal coatings.

Scientists have reportedly found that the copper-based coatings can be toxic to “non-target” organisms in the water, specifically hurting high-traffic areas like the Baltic Sea. The study reportedly looked to find a suitable solution for trade ships passing through the area.

About the Research

According to the European Commission, shipping traffic in the Baltic is expected to increase in the coming years due to Europe’s shift from road to sea transport. Researchers state that around 2,000 ships are in the Baltic at any given time and that it has a slow, 30-minute-water-exchange cycle.

Both shipping and leisure vessels occupy the Baltic, with Finnish and Swedish boat parks also housing around 2 million vessels in the semi-enclosed sea.

A separate recent study found that copper-based hulls in the Baltic Sea are reportedly the largest anthropogenic contributors of copper pollution, reportedly making up one third of pollution in the area. Reducing the use of these copper coatings is expected to minimize “environmental contamination from toxic leachable pollutants.”

Antifouling coatings with toxic substances that act to repel or poison certain organisms can reportedly negatively affect non-target organisms as well. Researchers stated that the objective was to assess the environmental sustainability and efficacy of a “silicone-based foul-release coating (FRC), and the market barriers to using it, to evaluate if it could be a viable alternative to the copper-based coatings currently in widespread use.”

To compare the two coatings, the team reportedly painted 15-by-15-centimeter PVC panels attached to metal frames and submerged them 1.5 meters below the surface in July 2020. Researchers also state that two different copper-based biocidal coatings were used, as well as one non-biocidal coating as a control for comparison with the FRC.

This was reportedly done at three marine research stations along the Swedish coast, with one in the Baltic and the other two in Skagerrak, a strait which connects to the North Sea.

To compare each panel, researchers  took photos once a month for later visual assessments of the amount of fouling present and used the Naval Ships’ Technical Manual (NTSM) fouling scale, which ranges from 0-100. On the scale, levels from 10-30 qualify as “soft fouling,” while anything 40 or above is hard fouling.

The team then conducted a literature review of different types of silicone FRCs to access their viability from an environmental perspective. In the review, researchers searched for two aspects of silicone FRCs: their toxicity to aquatic organisms in comparison to copper coatings and the chemical nature and potential environmental hazard of leachable substances.

Researchers also said that to understand market barriers in the region, they interviewed representatives of one local company that was manufacturing silicone coatings for shipping and leisure boat markets. At the time, this company was the only one in the region manufacturing these coatings; however, since then, one more has also launched a silicone coating for hulls.

Findings reportedly showed that the silicone FRC performed “as well as, or better than” the copper coatings at all three sites. While Silicone FRC may be a viable alternative to copper coatings, researchers also say that some FRCs on the market may be more toxic than others.

Additionally, they said that some can contain leachable substances like silicone fluids. Because of this, further research is expected on silicone FRCS though their toxicity in comparison to copper-based biocide coatings is still much lower.

Researchers expect the potential cost savings to be a key motivator for ship owners, though leisure boat owners may be less interested in the transition. To combat this, the authors of the paper push for tighter regulations to encourage companies to launch biocide-free silicone coatings or leisure boats.

Previous Research Report

Last year, in December, researchers found that environmentally friendly alternatives to copper-based antifouling paint were best at keeping fouling at bay on ships and vessels.

A team of researchers from Chalmers University of Technology, the University of Gothenburg and the Swedish Environmental Institute IVL investigated whether biocide-free silicone paints are a viable alternative to copper-based bottom paints to combat fouling.

According to a previous study from Chalmers University, as much as 40% of copper inputs to the Baltic Sea come from antifouling paints on ships and leisure boats. The heavy metal materials reportedly do not degrade in the environment, contaminating water, sediment and soils in marinas, ports and shipyards.

However, despite this impact, the antifouling paint market is “dominated” by copper-based paints, with silicone-based paints in the shipping sector making up just 1% of the market in 2009 and raising to 10% by 2014. For the recreational boating sector, the proportion of boats painted with silicone paint is reportedly estimated to be significantly lower.

The study, which was published in the scientific journal Marine Pollution Bulletin, was carried out over a year at three sites in the Baltic Sea region and the Skagerrak. Black painted surfaces were coated with biocide-free silicone-based paint, while red surfaces were coated with copper-based paint. The white surfaces had no antifouling treatment.

The silicone paint is based on silicone, produced using silicone oxide extracted from sand. The university notes that some silicone paints contain highly fluorinated substances, or PFAS, but the paint tested in the study was fluorine-free.

While the traditional antifouling paint continuously leached copper and other toxic substances, the silicone paint utilized its smooth surface properties to make it difficult for fouling to stick to the hull. The silicone is also self-cleaning, meaning any fouling that does stick is removed as the hull moves through the water.

According to the release, the scientific paper’s collection of ecotoxicological studies shows that silicone paints are significantly less harmful to the environment than copper paints.

Additionally, although the study was carried out over 12 months, the test panels were left at one of the test sites, showing that these results were found to persist over time.


Tagged categories: Asia Pacific; Coating Materials; Coating Materials; Coatings; Coatings Technology; Copper; EMEA (Europe, Middle East and Africa); Environmental Control; Environmental Controls; Environmental Controls; Environmental Protection; Health & Safety; Industrial coatings; Latin America; North America; Ships and vessels; Silicone; Toxicity; Water/Wastewater; Z-Continents

Join the Conversation:

Sign in to our community to add your comments.