CoatingsXperience is a bi-monthly column on informed commentary on the coatings industry.
By Cynthia A. Gosselin, Ph.D., The ChemQuest Group
In 2022, marine coatings were an $8.7 billion market, with a growth projection of 5–7% through 2028.1 However, there is a lot more to marine coatings than great aesthetics. At approximately a 64% share, anti-fouling/fouling release coatings were the largest portion of the marine coating market, followed by anti-corrosion and self-cleaning/self-polishing coatings. In addition, marine coatings have special and specific functionalities to protect watercraft above and below the waterline. Finally, marine coatings are specially formulated to be easily cleaned.
The two most significant drivers for the growth of the marine coatings market are transportation of goods by sea and recreational sailing. Unlike relatively new, speedy, expensive air shipping, transportation of goods by sea is a centuries-old tradition. To this day, it remains the preferred method for heavy or bulk products. Interestingly, it is also the most cost effective and it tends to have a lower carbon footprint and emission standards. Additionally, safe harbors are widely available almost everywhere there is water, making it a practical and accessible choice.
Recreational or leisure boating is the second largest driver of the marine coatings market. Whether for routine maintenance, hull cleaning, racing efficiency, fuel economy, or craft longevity, marine coatings are top-of-mind for large- and small-craft owners. In both the shipping and recreational categories, shipbuilding and repair are enjoying a resurgence in the post-COVID market.
With all these factors contributing to the growing demand for marine coatings, it’s essential to understand what they are and why they’re so vital. Simply put, marine coatings are broadly defined as waterproof protective layers that are applied to surfaces exposed to or immersed in fresh, brackish, or saltwater. Boats, ships, ferries, small watercraft, and marine structures such as offshore oil rigs and bridge structures employ some kind of marine coating both above and below the waterline.
A wide variety of coating chemistries can be used depending upon the specific substrate and service application, with the exception of unsaturated polyester resin (the type often used in fiberglass). Most marine coatings contain varying degrees of volatile organic compounds and can be applied by brush, spray, roller, or any other convenient method.2
Topside boat paints are usually 1K or 2K polyurethanes, buffable 2K polyurethanes, or alkyd marine enamels that protect the boat from UV damage. Bottom boat paints are antifouling coatings designed to reduce the attachment of aquatic organisms to the hull. Bottom paints include ablative and hard coat paints as well as primers. These types of coatings are best removed with paint removers especially designed for these chemistries.
The inability to escape the effects of biofouling beneath the waterline is one of the main reasons for the strength of the antifouling paint sector. Many boats and ships sat idle during the COVID-19 pandemic and exacerbated the problem, especially in relatively still, warm waters. Sitting idle in the harbor allowed the bottom of watercraft to accumulate barnacles, tube worms, algae, sea squirts, and slime.3 While this is a natural aquatic process, it is one of the most significant hurdles for boat and ship owners alike—particularly when speed and fuel economy are compromised. The commercial reason for using antifouling paints is for improving the flow of water passing the hull, and thereby maximizing fuel economy.
When a hull is covered by only 10% barnacle fouling, 36% more power from the engine is required to maintain the same speed through the water and could be responsible for 110 million tons/year of excess carbon emissions and $6 billion of addition fuel cost in the international shipping industry.4
Even recreational sailing is affected. Tapio Lehtinen was racing the 2019 Golden Globe non-stop, around-the-world race when he was almost stopped dead in the water. Racing furiously with his rival, he surprisingly noticed that he was being left behind. Thinking something had happened to his propellor, he dived in to check. To his dismay, barnacles were growing all over the hull. He did finish the race, but 110 days behind the winner. Barnacles had encrusted the entire bottom of the hull, stealing his speed. More had colonized on his self-steering blade, causing it to shear off when the load became too massive.5 Whether recreational or commercial enterprises, billions of dollars are spent every year to increase the usefulness, fuel economy, and longevity of watercraft by reducing biofouling.
Besides the economic and convenience factors, biofouling presents another important ecological concern. Marine life hitchhiking along the bottom of a boat can be the mechanism for translocating invasive species to the wrong ecosystem, far from natural predators.
Striped zebra mussels are a species native to the Caspian and Black Seas of Russia and Ukraine that have been distributed by ships as invasive species in Ireland, Italy, Sweden, Spain, the United Kingdom, and the United States. Root-like threads of protein called “byssal threads,” enable the zebra mussels to adhere very tightly to hard surfaces (like boat hulls, native mussels, and rocks). They colonize rapidly in the absence of natural predators, filter out algae needed by the “locals,” and are the succubus that attaches to and incapacitates native mussels. The zebra mussels form dense clusters that cut off water flow, clog pipes, and damage equipment. Their sharp edges can injure swimmers, and the infestation may lead to the devaluation of the boat. Since the 1980s, the Great Lakes in the United States have been struggling to eliminate this nuisance that just came along for the ride.6
Because of all the ship and yacht traffic, the Mediterranean Sea has more than 800 identified invasive species. In one audit of leisure vessels sailing through that area, 71% of leisure vessels were harboring at least one non-native species.7
Despite the problems plaguing biofouling of hulls, the landscape for marine coatings is moving toward sustainability measures and stricter environmental regulations. Copper-based, biocide-boosted antifouling paints have been the dominant performers in reducing biofouling. However, the effect of these paints does not segregate itself to affecting only those aquatic hitchhikers that attach themselves to the hull. Rather, cuprous oxides carrying biocides leach into the water, where they ultimately settle at the bottom of the sea or lake, also poisoning oysters, welk, clams, and other bottom-dwelling organisms.
Marine coatings manufacturers are now emphasizing improved sustainability along with operational performance factors of reduced power demand, lower fuel consumption, and carbon emissions. Manufacturers have had to become more cognizant of the environmental effects of biofouling agents because of the push by the regulatory agencies resulting from harbor contamination studies conducted during pandemic idle time.
Earlier, paints that contained the organitin biocide tributyltin (TBT) were banned on January 1, 2008, by the International Maritime Organization. For more than 40 years, TBT had been used successfully to boost the performance of cuprous oxide through controlled release. The problem with this effective method was that TBT would leach out of the paint, damaging the aquatic hitchhikers and contaminating the surrounding water. Once there, it would accumulate at the bottom, affecting the endocrine systems of shellfish. This led to abnormal developments, such as female snails taking on male sex characteristics, and severe deformities in oyster shells, making some beds almost extinct.
Since the TBT biocide ban, the number of effective biocides that meet regulatory requirements has decreased substantially. As a result, self-polishing copolymers (SPC), controlled depletion polymers (CPD), and foul release (FR) coatings are gaining popularity. Right now, the biocides in SPC and CPD are evenly dispersed in the matrix and not bound to anything. Release occurs when the matrix erodes (polishes) or by dissolution when water penetrates the paint film. These reactions are relatively uncontrolled and could lead to premature dissolution or over-leaching. Research is underway to find a way to attach the biocide molecules to a polymer carrier. Using hydrolysable covalent bonds could control the release rate of the antifouling constituents— mimicking the long-lived controlled performance of TBT.3
It is clear that a totally different strategy will be needed in the future to satisfy ultimate environmental concerns and regulations in harmony with antifouling performance characteristics. On the one hand, something is needed that will keep marine organisms from damaging and compromising marine craft below the waterline. On the other hand, even the most hardened industrialist agrees that the solution must keep from damaging everything else in its wake.
Nanotechnology that mimics the surface texture of algae that inhibits attachment of marine organisms is one outside-the-box thought. But this is still in the research stage and not yet available for mass production.8
There is one other approach that uses a totally different point of view and has proven commercially and environmentally successful. Ninety studies have been completed that pass the EU regulation Biocides Product Directive 98/8/EC (BPD) governing “biocides.” Regulating bodies in Japan (CSCL and JPMA), Korea (NIER), and China (MEP, Order 7) have also approved this material, and notifications have been provided to other relevant shipping regions.
Rather than using the typical paradigm of killing off the barnacle hitchhiker (and ultimately everything in the vicinity), an attempt was made to modify the attachment mechanism of the larvae.
Instead of using metal oxide biocides, medetomidine, a mammal anesthetic, was added to bottom paint. When exposed to medetomidine leaching out from a wet coating, the cyprid larvae of the barnacle species Balanus improvises were repelled from the surface. How? Medetomidine in tiny concentrations stimulates a receptor in the larvae causing hyperactive swimming behavior. Instead of settling down on the surface, the legs move at 100 kicks/minute, forcing it to swim away from the bottom of the boat. The effect is reversible. As the barnacle larvae move away, the kicking stops. This makes it impossible for the organism to attach to the surface.9
Since 2016, a thousand governing-body-approved commercial ship applications of this “biocide” were used successfully in several different biofouling paint formulations. This may be the first marriage of true environmental sustainability through benign influence on organisms and the desired performance from an antifouling marine paint.
About the Author
Cynthia A. Gosselin, Ph.D., is director at The ChemQuest Group, ChemQuest Technology Institute, ChemQuest Powder Coating Research. Email: firstname.lastname@example.org.
- IMARC Impactful Insights. “Antifouling Paints and Coatings Market: Global Industry Trends, Share, Size, Growth, Opportunity and Forecast 2023-2028.”
- “Marine Coatings Selection Guide: Types, Features, Applications | GlobalSpec.” https://www.globalspec. com/learnmore/materials_chemicals_ adhesives/industrial_coatings_ sealants/marine_coatings#.
- Koch, S. “Invasive Zebra Mussels.” National Park Service, April 2, 2021. https://www.nps.gov/articles/ zebra-mussels.htm (accessed July 27, 2023).
- “Sustainable Antifouling by Controlled Release from Polymer-Bound Selektope.” ITECH-Technical-Paper_ November-2022-1.pdf, November 2022, selektope.com (accessed July 27, 2023).
- Strickland, K. “Tapio Lehtinen’s Barnacle Blight.” Yachting Monthly, May 22, 2019.
- “The 5 Most Common Marine Fouling Organisms and the Effect They Can Have on Your Boat.” Electronic Fouling Control, Antifouling Tips, June 21, 2023.
- Rotter, A.; et al. “Non-indigenous Species in the Mediterranean Sea: Turning from Pest to Source by Developing the 8Rs Model, a New Paradigm in Pollution Mitigation.” Front. Mar. Sci., 2020, 7, Marine Pollution Section, March 24, 2020.
- Kumar, S.; et al. “Nanocoating is a New Way for Biofouling Prevention.” Front. Nanotechnol., 2021, Environmental Nanotechnology Section, Nov. 22, 2021.
- “About Selektope® – A Sustainable Biocide Used in Antifouling Coatings.” https://selektope.com/ about-selektope/ (accessed July 27, 2023). When exposed to medetomidine leaching out from a wet coating, the cyprid larvae of the barnacle species Balanus improvises were repelled from the surface.