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Cruising | Sustainability

The future of antifouling, and why it is changing

Antifouling paints and biocide agents that protect boats from fouling from marine organisms are increasingly restricted by new laws aimed at protecting the biodiversity of our seas. And that is sparking exciting new innovations from ultrasound to robot cleaners and paint that can emit UV light.

  • Effective antifouling reduces fuel consumption, CO2 emissions and maintenance costs
  • Laws are eliminating antifouling substances toxic to aquatic organisms
  • Antifouling is still needed to prevent non-native species being carried to areas where they can become invasive
  • The future of antifouling will be much more eco-friendly and includes robot cleaners, dry sailing, ultrasound and UV lights

Why antifouling for boats is necessary


He had been at sea for months in the Golden Globe non-stop round the world race when Finnish sailor Tapio Lehtinen realised something was wrong with his boat. “I was sailing neck-and-neck [with a rival] across the Indian Ocean when suddenly he started to get away. I thought perhaps a fishing line had caught in the propeller, and dived over the side during a calm spell to investigate,” he said.

“It was not a rope or net, it was barnacles growing all over the hull. When I saw them, I knew my race was over.”

Lehtinen carried on, but he finished the race 110 days behind the winner. The extreme fouling had encrusted the whole underwater body of the boat, at first slowing and then choking off his boat speed. Barnacles had colonised his Windpilot self-steering blade as well, and when it couldn’t cope with this permanent massive increase in load it eventually sheared off.


Fouling affects all boats

Tapio Lehtinen’s experience is a particularly dramatic illustration of how severe a problem fouling can become, and at what cost. Biofouling affects all vessels of all kinds. Without an effective or adequate coating to repel them, aquatic organisms will attach themselves to immersed surfaces and accumulate there. This process happens more rapidly when a vessel is stationary and in warm water or nutrient-rich coastal areas, where pleasure boats spend a majority of their lives.

Even a modest amount of fouling on the hull of a motorboat will affect its performance and fuel consumption. Fouling increases fuel consumption, which leads to greater CO2 emissions. When it affects water inlets and engine cooling pipework, it can cause higher maintenance costs and even breakdowns and safety at sea issues.

Biocides are increasingly being controlled


For all these reasons, biofouling is something that owners of vessels of all sizes, from the smallest motorboat to the largest container ship, want to avoid. However, the use of biocides in marine coatings is increasingly being controlled, restricted or outright banned by regulatory bodies around the world as they seek to protect the aquatic environment from toxic and long-lasting harmful effects to marine organisms and human health.

Products containing TBT, or tributyltin, a biocide widely used on craft for over 40 years, has been banned for many years. This poisonous chemical was found to accumulate in the food chain, affecting the development of invertebrates, then marine mammals such as whales, dolphins and sea otters, and eventually entering the human diet. Alarmingly, scientists found evidence that TBT could remain in the environment for up to 30 years.


The EU drives development

Today, the EU’s REACH programme (Registration, Evaluation, Authorisation and Restriction of Chemicals) and the Biocidal Products Regulation (BPR) introduced in 2013 define which chemicals can be used in products sold in EU countries, while ensuring a high level of protection for humans and the environment.

Currently, there is a transition arrangement for the use of active substances that were available on the market, or used in biocidal products, in 2013. An ongoing review is evaluating and assessing ingredients that can be used for an updated regulation to be harmonised across EU countries. The EU is a major driver of product development worldwide, as it accounts for 70% of the world pleasure boat market. Along with regulations that apply in Australia and New Zealand, these are expected to be the most stringent in the world.

The spread of non-native species


The long delay in concluding the EU review reflects how hard it is to strike the right balance between antifouling efficacy and sustainability. Although the Commission wants to reduce the harm chemicals can cause, it is also very concerned about preventing the translocation of invasive species.

Marine organisms that can grow in ships’ ballast water or on their hulls can easily be transported from an area where they naturally belong to another where they have never previously existed. Just as we see on land, introduced species may outcompete native species. This has already happened in several areas of the world. It is very real and irreversible threat to global marine biodiversity.


Recreational boats spread new species too

“Translocation of species is a big problem,” says Eivind Berg, head of regulatory affairs at Jotun. “In Norway now we have sea vomit (didemnum vexillum), a colonising species originally from Japan, though for now only on the west coast. And there are big changes on the beaches, too. There used to be no Pacific oysters, you didn’t see them 10 years ago, and now they are everywhere, they have totally taken over and blue mussels have become rare.”

In terms of a global threat, pleasure craft are not seen as a major contributor to the problem but, says Berg: “What yachting can do is to spread species further along the coast that have already invaded. So, for example, in Southampton short sea traffic and yachting might bring something up the coast to Scotland.”

Berg uses this as an example, but there are even more pressing problems elsewhere. A recent study concluded that the Mediterranean is the most invaded sea in the world, with around 800 identified invasive aquatic species. In one sample, 71% of leisure vessels were carrying at least one non-indigenous species.

The delicate balance of species


“In the past, all boat owners just wanted to keep their boats clean of fouling to reduce emissions and increase performance. But now it’s been recognised that a fouled boat disrupts the delicate balance of species,” agrees Dr Julian Hunter, head of sustainability at the International Council of Marine Industry Associations (ICOMIA).

“The EU have been very clear in their Green Deal, their overarching environmental policy, that they wanted to restore biodiversity in all EU waters and they are managing very carefully the potential for translocation of species on pleasure craft. But at the same time, we’ve got a set of environmental safety regulations by another part of the EU Commission driving for less and less harmful biocidal systems.

“So they are in the midst of this full evaluation of the traditional way of preventing fouling on pleasure boats and commercial boats, but are struggling to come to understand or to come to an agreement on how to assess it environmentally. Some member states want a complete prohibition of any biocidal release and then there are other parts of the EU who say they really need these products. So we are in an interesting situation.”

Hans Slegtenhorst, a senior product manager at Akzo Nobel, agrees: “The different laws are not working together and our challenge is to find solutions that fit with all these different frameworks. We are working with ICOMIA to find the balance. We might not get rid of current antifouling completely, but we are looking at where are we happy to use biocide-free products and where not.”

Like all manufacturers striving for more effective products, Akzo Nobel is exploring innovative paint solutions using very different technologies. Future options could look very different.



While the ingredients that will be allowed are being assessed, manufacturers are positioning themselves. In the past, conventional antifouling paints would commonly contain a blend of several active substances, but the latest EU legislation is due to restrict the use of these co-biocides, or boosters, so that any given product may contain just one active substance.

Hempel is proceeding on the assumption that copper will be prohibited and have already stopped all products containing it. Jotun, in contrast, argues that copper is right for the job.

“We know everything about using copper-based antifouling and that is why we think yacht paints based on copper biocides are still an ideal solution for yachting. It is an essential nutrient for all organisms living in the marine environment and all organisms apart from the extremely primitive ones have mechanisms for regulating copper levels; it’s called homeostasis,” explains Eivind Berg of Jotun.



It is thought that certain species are sensitive to copper biocides and copper-based antifouling has been banned in some European countries. But it is also recognised that the greatest impact is when concentrated copper scrapings are allowed to enter the water, rather than from the slow leaching of an antifouling coating in the water.

“A very small fraction of copper entering the environment is anthropogenic [from pollution],” Eivind Berg argues. “More than 90% is natural river run off from the weathering of bedrock. We use a lot of copper on roofing and on pipes, and what we use in antifouling is less than other human uses.

“But even then, human use is a tiny fraction of the natural input and only 1% of it is bioavailable because it binds to organic material present in the water at bigger molecules that are not available to marine life. They cannot absorb it or ingest so therefore when some try to estimate the contamination potential of copper it is extremely important to take into account the bioavailable fraction, and there are models to do that.”



“A good thing about copper is that when it leaches out as a copper ion it has high toxicity and is very efficient as it leaves the antifouling paint but it is very short living. So it affects the microlayer that envelops the hull but detoxification occurs when it goes further into the water column because it binds into other molecules that are not bioavailable and becomes harmless quickly.

“So,” Berg adds, “we love copper, at least for recreational craft. Copper type paint can do the job and we don’t see the environment consequences being a concern. If you do have an extremely enclosed marina with small tides and low water exchange you may get concentrations of copper that are not healthy for organisms in that manmade environment. But you may choose to call these parking spaces where we have already changed the environment to a great extent.”


In the other corner is Hempel, which has eliminated copper from its product range. “I have no doubt that we are moving towards a copper free future and I am certain it will be banned or disappear from the market in the foreseeable future,” says Thomas Olsen, yacht marketing director of Hempel.

“Scandinavia and Germany are being really aggressive in getting rid of copper and can ban on environmental impact or human health risks. I think the first area to be hit will be DIY applications and we see in a lot of countries in Europe talk of getting rid of it. But similar things are happening in the US as California is looking at copper sediments in the marinas which don’t break down quick enough, also Florida and Washington where there are pristine waters.

“From a Hempel perspective we have been looking into this for the better part of 10 years, which is why we have two products that are biocide-free and two years ago we stopped all products containing copper. I know some are pushing for copper-based paints but we are going the other way. The alternatives are here, they work.”

A viable alternative to self-eroding copper-based paint is Coppercoat a solvent-free water based epoxy resin mixed with copper powder that has a low leaching rate. Although more expensive than traditional one-season antifouling, Coppercoat claims to offer fouling protection ‘for a decade or more’.

Innovations on the horizon


Legislation has already changed the face of antifouling, and will continue to do so, so many companies are scanning the horizon for future alternatives to traditional painted coatings. What might these be?

“The market is very, very different today than it was 10 years ago,” says Dr Julian Hunter. “Not only is there less and less biocide release but we are also seeing a new approach, with products such as non-stick effects using the same chemistry as bathroom sealants. Ultrasound is also being heavily pushed, using a transducer that emits ultrasound through the hull generating microscopic bubbles through the paint. But there is no one size fits all, and boatowners really have to have a selection to choose from.”



One of these alternative concepts is a special adhesive wrap applied to the hull that has a prickly surface to repel the growth of organisms. Finsulate is the brainchild of Dutch materials scientist Rik Breur, who took his inspiration from the spiky surface of sea urchins. The fibre wrap consists of nylon microfibres arranged on a substrate like small needes on one side, and a self-adhesive film on the other. It is applied to underwater surfaces like rolls of carpet.

When in the water, the constant movement of the tiny prickly nylon spikes, which are packed closely together, creates an unattractive surface for biofouling. The fibres have also been tested to ensure that they don’t fall off as microplastic pollution and the system is warrantied for five years.

“Boat owners want environmentally friendly products that are non-toxic but it's also suitable for large cargo ships and ferries,” says Breur. “Over years of evolution nature has already solved all kinds of things that we can learn from.”



Silicone coatings are another alternative, such as Hempel’s biocide-free Silic One, based on a combination of silicone and hydrogel. This produces a very smooth surface that organisms find it harder to attach to. “These rely on weak adhesion between the coating and fouling species, and a certain amount of movement of the vessel is needed for self-cleaning so generally they are better for boats that are doing more than 8 knots and high activity,” says Julian Hunter.

Hempel also produces a coating that combines the smoothness of silicone with fouling-preventing biocides in a single coat. “The silicone tech we are using with Hempaguard-x7, silicone with a small amount of biocide but reduced by 80-90%, is better at keeping growth off and the surface you get is way more slippery,” says Hempel’s Thomas Olsen.

The long-term environmental impacts of silicone are, however, not yet fully understood. Silicone is a non-biodegradable substance. The toxicity and bioaccumulation potential of polydimethylsiloxane, the backbone of silicone coatings, has been reported to be low, but some researchers have questioned the long term effects of the release of such non-degradable substances.



A different approach to the problem of fouling is in-water docks, or slip liners. Products such as the DockyDock Boat Hull Covering the SeaPen Dry Dock are permanently rigged at a marina berth, and a boat is driven into it. In the case of the DockyDock cover, sea water is pumped out of the cover, while the SeaPen is made to be able to dry float a boat. Both products act like a dry dock, and are suited to small or medium sized motorboats, but not sailing yachts with a keel and rudder.



One solution that is becoming more common is in-water hull cleaning or hull grooming. Autonomous cleaning robots are a future solution already being adopted by established coatings manufacturers. Jotun’s HullSkater inspects and removes fouling non-abrasively without damaging the antifouling coating, and is designed to be used with the company’s SeaQuantum Skate coating.

The HullSkater robot is kept onboard in a portable station which has a launch and recovery ramp and can be used both in harbour and at anchor. The system can also be remotely operated from shore. There are, however, challenges with this approach too, as hull cleaning is not allowed in some waters or ports.

Dry stacking and dry sailing has been an around for decades, and is becoming more commonplace driven by demand. During the pandemic, there was a huge increase in people wanting to spend time on the water, which outstripped the availability of moorings and marina berths. So stacking systems and dry sailing, where your boat is launched on demand, has taken off. When their boat is stored out of the water, owners can forgo antifouling altogether.



Ultrasonic antifouling systems are another potential solution, using the same technology operated for decades in the food, brewing and hydroponic farming industries – and indeed in shipping. Sonihull is market leader in this field. 

Its system produces multiple bursts of ultrasonic energy in a range of targeted pulse frequencies, which are transmitted by a transducer to the hull. The ultrasound produces a pattern of increasing and decreasing pressure on the surface.

In process called non-inertial cavitation, microscopic bubbles are created during the reduced pressure cycle and imploded as the pressure increases. This microscopic agitation has a cleansing effect which destroys algae and stops barnacle and mussel larvae from embedding themselves. It comes into its own in protecting fouling in water intakes and propellers and it can be used alongside other antifouling systems.



A totally new product currently in development and soon to come on the market is a ceramic combined with a pharmaceutical material from the biomedical sector. The developers realised that coatings used in replacement heart valves were designed to prevent anything sticking to them and so would have good antifouling properties. They are non-toxic, at least to humans. Static plate tests are ongoing.

Another potentially revolutionary technology is being explored jointly by manufacturer Akzo Nobel and Netherlands technology giant Philips. They are seeking to combine a paint scheme with UV LED lights. UV light emitted from a coating surface could totally prevent biofouling accumulation.

“We are in the very early stages of this, and maybe it will be 4-5 years before it can be commercialised - if it can be commercialised,” says Hans Slegtenhorst of Akzo Nobel.  “We make a transparent film and Philips make an electrical circuit in it using UV LEDS of a millimetres or less. But it is very complex and difficult and we are in the middle of trying to find solutions. If we can make it work it could be a gamechanger in the future.”

Preserving the purity of the seas


The challenge of preserving the purity of our coastal waters and oceans is a complex one. Harbour and marina design come into play as well, something that the ICOMIA Antifouling Working Group is studying.

Factors such as marina overcrowding, water depth and water exchange volume all have an effect, and conditions have been shown to vary greatly between different locations. Ultimately some guideline recommendations may need to be available for marina development projects taking all these into account.

Boatyards and commercial facilities also have an important part to play their in collecting, filtering and properly disposing of antifouling waste residues when boat are being pressure washed or sanded on land.



Some argue that boat owners themselves may need to adopt a different mindset to protect our waters. “In the future we need a mind change,” says Hans Slegtenhorst. “Currently boat owners want something that works but doesn’t impact their time. That is one of the largest barriers to transitioning to biocide-free products.

“We may need to do a little bit more work on our boats. For example, we might need to go into a cleaning process twice a season. We really need to start that change and I think we have a responsibility to take consumers with us on this journey.”



The new generation of antifouling options beginning to emerge in the market is much needed. In future, the appropriate choice will be based on how you intend to use your boat. If you are going out occasionally at the weekend, perhaps your boat doesn’t need to lie permanently in the water at all. Maybe your boat’s value justifies more expensive, eco-friendly systems such as UV lights or a special wrap.

And should you have an ambition to cross oceans or sail for months at a time, like Finnish single-handed sailor Tapio Lehtinen, there will still be effective paints that you can apply yourself, but they will not be so harmful to the creatures we share our seas with.

Elaine Bunting
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