The wind is gently picking up past 8 knots, the spinnaker is nicely filled, and the trimaran is accelerating. I take the helm to check that everything is OK: not a single vibration, the multihull is effortlessly gliding through the water. Pure bliss!
Sailing with a clean hull and appendages is not just a matter of maintenance or about fuel consumption, it also guarantees that you can enjoy the sensation of sailing to the full. My reverie is interrupted by the phone ringing - WhatsApp, to be precise. Thanks to Starlink, you can’t get any peace anywhere, even halfway across the Bay of Biscay! But it’s Emmanuel, the editor of Multihulls World... “Hi Brieuc, how’s the delivery going? Listen, I’ve got a favor to ask you...” Basically, after five minutes of discussion, I’ve been given the thorny subject of antifouling for the magazine’s next Forever Green special edition... and I know it’s not going to be an easy task! Let’s start with a quick overview of the various laws that apply before getting to the heart of the matter.
Between Protected and Prohibited
The purpose of antifouling paint is not only to slow down the formation of fouling on a vessel’s hull, but also to limit the spread of invasive species via the hulls of passing boats, a major issue in Europe, particularly in marine protected areas, or in relatively unspoiled areas such as Australia and New Zealand.
The first major measure to regulate antifouling paint appeared in 1998 at the instigation of the International Maritime Organization, a United Nations agency responsible for regulating the safety, security, and environmental performance of international shipping. The IMO is behind the International Convention on the Control of Harmful Anti- Fouling Systems on Ships (AFS). Adopted in 2001 and entered into force in 2008, it bans the use of coatings and paints containing tributyltin (TBT), an extremely toxic and persistent organic pollutant.
In Europe, the framework has been further strengthened, as TBT was banned in 2003 and the Biocidal Products Directive introduced initial regulations for ship repair areas. Only a dozen active substances, mainly copper- or zinc-based, are authorized, following an impact assessment. Since 2018, manufacturers have been subject to marketing authorization and advertising is regulated: the terms “organic (or “bio”),” “safe,” and “non-toxic” are prohibited.
In the United States, measures are targeted and progressive, similar to those in Europe, with a federal ban on TBT since January 2003. Some states have strengthened federal legislation with plans to ban copper in the medium to long term and with strict controls on leachates from haulout areas in boatyards.
In short, the elimination of TBT in the early 2000s forced manufacturers to reformulate their paints and work on improving the “discharge” of the biocide over time. We’re all familiar with conversations in yacht club bars about bottom paints “that don’t work nearly as well as they used to…” As for “fouling release” paints and coatings, since they do not contain biocides, they are currently subject to very few regulations.
The Main Families of Antifouling Products
In reality, the state of the art is quite simple: either you apply a paint that releases biocides designed to kill organisms that seek to colonize your hull (antifouling), or you opt for a paint or coating that aims to prevent them from adhering (fouling release).
There are three main families of antifouling products:
Hard Matrix Antifouling
This type of bottom paint is suitable for fast boats such as powercats, which can be beached or stored on a trailer between trips. It is also used for racing multihulls because they allow for better hull preparation and therefore a better glide through the water. However, it requires frequent cleaning with a sponge to be effective, which is not always easy for large multihulls due the fact that diving to clean hulls is banned in most ports, and also the cost and availability of lifting equipment.
Ablative Antifouling
These gradually release their biocidal agents as the paint layer wears away in contact with water. This is a more versatile product for multihulls that sail irregularly in areas with heavy fouling, such as the Caribbean, or in difficult harbor conditions. To be effective, an ablative, or erodible, coating must be thick enough to remain effective over time.
SPC (Self-Polishing Copolymer) Antifouling Paint
These are the Rolls-Royce of antifouling paints, generally applied by professionals. Unlike conventional ablative bottom paints, the SPC paint film breaks down in a controlled manner through a chemical reaction, even at zero speed. This gradual polishing ensures a constant and controlled release of biocides, resulting in greater efficiency and longer life. Of course, these paints are significantly more expensive, but as we will see later, their widespread use on multihulls could prove to be a sensible choice in the medium term.
How Does Antifouling Paint Work?
Traditionally, antifouling formulations are based on copper precursors which, when oxidized by contact with seawater, are converted into Cu2+, an effective biocide. Fouling release solutions are a non-biocidal alternative to traditional antifouling agents. Rather than killing organisms, they seek to prevent them from adhering to the hull by making the surface smooth, flexible, or slippery. There are two technical solutions: let’s start with silicone paints, which create an ultra-smooth, hydrophobic surface that prevents organisms from attaching themselves permanently. With no biocides, the paint is self-cleaning while under way. On paper, this is the miracle solution, but in practice, it is far from simple: these paints are fragile (their low mechanical resistance can lead to the release of microparticles into the environment in the event of impact or abrasion) and require special equipment for application, as silicone can clog and permanently pollute equipment. As for waste, it is difficult to recycle - once dry, silicone residues are neither biodegradable nor easily recyclable.
Let’s now take a look at technical adhesive films: once bonded to hulls, these coatings prevent organisms from adhering thanks to their physical structure or surface properties. Like silicone paints, this is still an emerging technology that has yet to prove itself over time. Here again, in theory, the advantages are attractive: zero biocides and easy repair or replacement. But the reality is more nuanced: application requires perfect technical expertise, an impeccable surface finish, and durability is subject to the vagaries of boating. Being scuffed by an errant headsail sheet, for example, that has managed to slip under the hull, a collision with a UFO (unidentified floating object), or worse, an invasion of barnacles due to lack of regular cleaning... all of these can quickly compromise the effectiveness of the film. I can speak from experience: I currently sail on a 90-foot aluminum boat equipped with MC Glide coating (the manufacturer is no longer in business). Even though the hull remains particularly clean when sailing, I am seeing more and more tears in the film, and I won’t hide the fact that I dread the day when it will all have to be removed... the operation looks to be complex and costly
“Eco-friendly” Alternatives: Where Do We Really Stand?
When it comes to antifouling paints, the task is complex for manufacturers and researchers working on the subject. It is extremely difficult to find a natural broad-spectrum biocide. A molecule derived from a sea sponge, for example, may be effective against some microorganisms but completely ineffective against mollusks or barnacles.
In reality, we’re still at the basic research stage, although some players, such as the local authorities of the Brittany Region in France, are actively investing in research programs to try to develop more environmentally friendly solutions. From an economic point of view, the cost of regulation, approval of new biocides and obtaining marketing authorizations is a major obstacle to the search for innovative technical solutions.
From a marketing perspective, to give themselves an “eco-friendly” image, some manufacturers offer paints in which copper is replaced by zinc, which, to be honest, does not fundamentally change the environmental impact. Others are trying to pull the wool over our eyes by loudly proclaiming that their products are “TBT-free,” knowing full well that this molecule, as we saw above, has been banned for 25 years...
The technical challenge for manufacturers lies more in improving existing products, particularly by optimizing the release of biocides over time.
With regard to fouling release coatings, technical solutions may be easier to develop in the future due to the absence of biocides. But here again, the cost of implementation and the fragility of the materials remain serious obstacles to their widespread adoption.
Take the example of Finsulate, a fibrous coating made from nylon and polyester, inspired by the texture of sea urchins to limit the adhesion of marine organisms.
While it is popular with some users, others point to its insufficient effectiveness in certain geographical areas or after one season. Ultimately, its synthetic components are not without fault from an environmental point of view.
Alternatives to Traditional Antifouling Paints
Among the emerging solutions, ultrasound stands out for its discreet and innovative approach. Without paint or biocides, this system is based on a physical principle: the emission of high-frequency vibrations that propagate through the hull of the boat and disrupt the settlement of marine micro- organisms. Transducers, fixed inside the hull, create an acoustic environment that is unfavorable to the attachment of larvae. Invisible and silent, this device operates continuously, whether the boat is at anchor or under way. It is an attractive solution, but its technological promise has its limits. Its effectiveness varies depending on the hull construction material – it’s optimal on aluminum or steel, but less reliable on wood or certain composites. And while ultrasound effectively discourages the early stages of fouling, it is no match for established barnacles.
What’s more, installation represents a significant investment, and in most cases, this system does not completely replace antifouling but rather complements it to prolong the cleanliness of the hull between two haulouts.
Another alternative, considered a return to the Stone Age by some and the ultimate solution by others, is permanent copper antifouling: this is a hull coating designed to last for several seasons (up to 10 years), based on a formulation that is very rich in copper (often in powder or leaf form) and a hard, non-ablative structure. Unlike conventional antifouling products, which need to be renewed every season, these products form a stable barrier designed to prevent marine organisms from attaching themselves permanently. To be effective, this type of antifouling must be reactivated by being sanded very frequently, which releases a large amount of copper each time...
Between Ecological Imperatives and Technical Reality
Ultimately, the industry is based on a paradox: protecting the environment while using products that are, by their very nature, harmful to it. Until biotechnology research progresses and offers real alternatives, the best way to limit our impact is to adopt a rational approach to the use of existing products.
Our multihulls are often large vessels that are expensive to haul out of the water. It therefore makes sense to opt for high- quality, more durable antifouling products, even if they are more expensive to purchase. Their longevity can be optimized by storing boats ashore during the winter months or the off-season, which, let’s be realistic, remains a logistical headache for multihulls due to their size.
An interesting alternative is to protect the hull while afloat with systems such as K-REN (see inset). The device may seem difficult to install, but if it avoids costly haulout and doubles the life of the bottom paint, it is well worth the effort.
Finally, another lever for action lies in the quality of the application itself. The days of brushing TBT antifouling onto the family cruiser with a roller on a sandbank between tides are fortunately over. Nowadays, it’s better to call in professionals who will apply the products in the right conditions, with the right tools, on compliant drying pads or haulout areas. This comes at a cost, of course, but it also has real environmental value.
Commercial Vessels vs Multihulls: Different Worlds, Different Scales...
When it comes to antifouling on a global scale, the cruising multihull sector really is a drop in the ocean. The merchant navies of the world now count more than 106,000 commercial vessels, container ships, oil tankers, and bulk carriers, each of which consumes several thousand gallons of antifouling paint per year.
In contrast, cruising multihulls represent less than 30,000 units worldwide, with an average consumption of two and half to four gallons (10 to 15 liters) per haulout. Even assuming a haulout every two years, this represents only a few hundred thousand gallons per year, or less than 0.5% of global volumes.
But let’s not forget that this fleet of multihulls is heavily concentrated in ecologically sensitive areas—tropical lagoons, coral archipelagos, marine protected areas—and that it is our collective responsibility to help preserve these.
United States Federal and Local Regulations Concerning Antifouling Paints
Federal Regulations on Antifouling Paints
Ban on Irgarol
The EPA (Environmental Protection Agency) has formalized a ban on Irgarol (TBT) as an active ingredient in antifouling paints due to its toxicity to marine wildlife and its contribution to coral bleaching. This ban came into effect on January 1, 2023, and applies to the entire US territory, including the East Coast.
Copper-based paints
There is no federal ban on copper antifouling paints. However, the EPA has identified copper as a pollutant of concern for the marine environment. Studies have shown that dissolved copper can harm marine life, leading to the adoption of local regulations in some sensitive areas.
State Regulations
Washington State (West Coast)
The State has introduced legislation to phase out the use of copper-based antifouling paints on recreational boats.
Initially, the ban on the sale and application of paints containing more than 0.5% copper was due to come into force on January 1, 2026.
However, due to the lack of equally safe and effective alternatives, the Washington Department of Ecology has postponed this ban, with it now expected by June 30, 2029.
California (West Coast)
California regulates the use of copper-based antifouling paints by limiting the leaching rate to 9.5 micrograms per square centimeter per day, particularly in sensitive areas such as Marina del Rey and the port of San Diego. The aim is to reduce copper pollution in fragile marine environments.
Boaters in these two states are therefore encouraged to use low-leaching copper paints or to explore more environmentally friendly alternatives.
A Word from the Pros: Lucie Doriez, Director of K-Ren, France
- a large footprint for small wetted surfaces. As a result, the covers are small in relation to the volume of the multihull.
A Word from the Pros: Alex Sastre, Performance Yacht Sales, Miami
“At Performance Yacht Sales, our approach to antifouling is tailored to our local situation in Florida and the Caribbean, i.e., warm waters with heavy fouling. After several years of experience in the field, our go-to product has become Interlux VC Offshore (in classic black), which offers exceptional protection and durability. For demanding owners or racers, we recommend the VC Offshore Regatta version, combined with careful wet sanding to achieve a smooth, high-performance finish for racing.
Interlux, an American brand of the AkzoNobel group, is the equivalent of International, which is well known in Europe. Our application method includes careful sanding of the GRP hull, followed by three coats of primer and three coats of antifouling. This system guarantees optimal adhesion and long-lasting protection. To maintain performance and extend the life of the coating, we advise owners to schedule a professional underwater cleaning every three weeks in summer and every four weeks in winter.
A Word from the Pros: Matthieu Taburet, Director of Nautix, France
At the same time, the company entered the marine coatings market by developing high-quality antifouling paints. Unlike the major players in the sector, who initially developed solutions for shipping, Nautix designed its range exclusively for the recreational boating market and racing sailors. For 30 years, Nautix has been at the forefront of environmental issues related to antifouling paints, thanks to a joint laboratory with the French National Research Agency. Matthieu Taburet, the company’s CEO, welcomed us for a candid discussion:
“Antifouling should be compared to a topical antibiotic, which prevents the formation of the first colonization, the biofilm. The challenge in making a good antifouling product is to release biocides just above the threshold level of effectiveness, so as not to release copper into the environment unnecessarily. The freedom to travel at sea comes with responsibilities, because a dirty hull leads to increased fuel consumption and air pollutant emissions, loss of speed and maneuverability, and a significant increase in maintenance costs. But another aspect that is not talked about enough is the spread of invasive species: 60% of marine species disappear due to introduced species, hence the need to limit their spread via boat hulls as much as possible.”
A Word from the Pros: Franck Vasseur Director of AGL Marine, in Britanny and French Atlantic Coast
Among the flagship products of this new generation, Seajet 038 Taisho is becoming increasingly popular, including as an original equipment product at several major shipyards. This product is recognized by the EPA (Environmental Protection Agency) in the United States as a credible alternative to copper-based antifouling products. It is notably authorized in sensitive areas such as Puget Sound and Southern California, where regulations are among the strictest in the world.
However, its formulation requires professional application, which Franck considers a guarantee of performance: “The quality of the antifouling depends largely on the preparation of the hull,” he insists. He also recommends always applying the antifouling over a primer from the same brand, thus ensuring perfect chemical compatibility.
Finally, to achieve two seasons of protection, Franck is categorical: “You need thickness.” There’s no miracle solution - he recommends at least three coats, paying particular attention to the waterline and appendages.
