Antifouling Your Boat

Liliana Engelhardt | VOLUME 32, ISSUE 3
Antifouling is necessary on boats that are on the water for any length of time
Antifouling – not as much fun as tinkering with the engine or polishing the chrome, but a vital maintenance task nonetheless.

Mention antifouling to a boat owner and you’ll likely evoke much the same reaction as scratching a blackboard does (eek). But despite its ill repute, antifouling is absolutely necessary and well worth the investment.

But what is antifouling and why do hulls foul? Objects left in the water are soon coated by algae (slime) and will eventually be colonised by larger organisms such as barnacles, mussels and seaweeds. This is called biofouling. How quickly and to what extent this happens depends on whether the object is stationary or mobile, as well as the local conditions, which include tidal strength, water temperature, salinity, quality of nutrients and amount of light filtering into the water.

Biofouling on a hull forms a rough surface, which creates drag that slows the boat down, reduces manoeuvrability and impacts fuel efficiency. If the growth infiltrates moving parts and hull openings, these can seize up or block, potentially causing all sorts of trouble.

Antifouling is the ability of specifically designed devices and coatings to remove or prevent biofouling. Antifoul paint is a chemical treatment that’s applied to a hull to make the surface uninhabitable (or at least very undesirable) for aquatic organisms.

Antifouling is necessary on boats that are on the water for any length of time, especially if they’re kept there while not in use. By definition, that’s all boats.


Depending on where your boat lives and how often it’s used, you’ll need to antifoul every six to 15 months. Between appointments, you might also want to scrub/polish or hose off everything below the waterline, including the running gear, anodes and any other bits down there. Some antifoul paints are ‘soft’ ablative coatings, so be sure to follow the manufacturer’s instructions on whether scrubbing/polishing is advised, or even necessary.

Owners of trailerboats, jetskis and OTB craft have an easier job, as they can give the hull a little TLC after each use.

Shane Subichin, GM of Queensland boatyard The Boat Works, says the most common mistake made by boat owners in relation to antifouling is waiting too long to antifoul in an attempt to save money … which actually results in the opposite, as they’ll generally have more issues with the boat, costing more in the long run.

“Cleaning a neglected hull is far more tedious than regular maintenance,” says Shane. “Other issues can also occur when antifouling is neglected, such as engines overheating because of blockages in the raw-water intake, or electrolysis because the anodes can’t do their work – that’s a high risk, especially on alloy hulls and components like sterndrives and saildrives.

“Once the hull is clean and has been correctly treated with antifouling, boat owners are often surprised at how well their boat performs – including fuel consumption, which can improve quite significantly.”

As with any maintenance task on a boat, unless you really know what you’re doing, it’s recommended the antifouling is done professionally. But why?

“To begin with, because an experienced contractor will know what the best product is for your boat, based on what the hull is made of, the type of boating you do, and the conditions where it’s kept – which is why it’s a good idea to choose someone with local knowledge,” says Subichin.

“They’ll also have the right equipment to apply the antifoul – the best option is to apply it with an airless spray gun. Depending on the rollers and brushes, they can leave little ‘pots’, or grooves, that biofouling can grip to the inside of – the smoother the product is applied, the better it will do its job, and a sprayed finish will last longer than a rolled one.”

A professional will also know what else to look for that might otherwise go undetected, such as checking the skin fittings and anodes. Also, removing old coatings requires professional equipment in a controlled, enclosed environment, as this is done by abrasive blasting or with chemical strippers.

Additionally, there are health and safety requirements that may be difficult to fulfil in a DIY situation outside of a controlled environment (unlike a boatyard, which has rules and regulations), such as waste disposal, which must be collected to prevent it from entering waterways or the surrounding ground (check with council regulations if you’re doing it at home). And you’ll need to wear protective clothing to shield against the dust and fumes.

A number of factors will determine the cost to antifoul your boat, including the size of the hull and what it’s made of, the cost of slipping, and what type of coating is needed. Have a chat with your contractor of choice to talk about what they recommend and the cost involved.

Antifouling is of importance from an insurance perspective, too. Club Marine National Claims Technical Manager Phil Johnson says it’s the boat owner’s duty of care to ensure their boat is in proper working order, and claims resulting from incidents on neglected or insufficiently maintained boats – including antifouling the hull – can lead to a claim being denied.

“It can be a real issue when boat owners neglect their boats, no matter what type of maintenance we’re talking about,” says Johnson. “In a broader sense, it’s also an issue if they don’t follow manufacturer’s recommendations on maintenance and repairs on any part of the boat and its equipment – this extends to hull, motors, gearboxes, running gear maintenance and timely antifouling.

“If a claim is lodged, but the boat owner has neglected their boat or undertaken repairs or maintenance that don’t comply with a manufacturer’s recommendations and this has led to the issue occurring, then there’s a fair chance the claim will be rejected.”

Johnson recommends regular inspections and timely antifouling to insure this doesn’t happen.


Very basically, there are two types of antifouling paint: hard coatings, and ablative/eroding coatings (which gradually wear away).

The antifouling effect in most paints is achieved with biocides that are slowly released at the paint surface/water interface. Both types usually contain a form of copper, together with various types of organic biocides that help the copper do its job more effectively. Many countries now regulate these biocides (often called active ingredients) and only allow certain types to be used.

Silicon-based products form a very smooth, non-stick surface where organisms have problems attaching to. It’s worth noting that biofouling will grow on the surface, but the more the boat is used and the faster it travels, the cleaner it will stay. Needless to say, they’re not suitable for boats that aren’t moved much.

Market-leader Akzo Nobel says hard antifoulings, such as its International-brand Longlife and Ultra (both to be replaced by Ultra 2 later this year) are best for very fast powerboats and racing yachts, as they don’t wear away very much over time and are more suitable for regular scrubbing or washing. However, since the paint does not wear away, it slowly builds up in thickness, leading to harder maintenance at the end of the season.

Ablative/eroding antifouling types are suitable for most other vessels, especially for boat owners who list easy maintenance as a priority. By slowly eroding whenever water moves across the hull, they leave a fresh layer of biocides, resulting in minimal coating build-up and reducing the amount of preparation needed for the next season.

Ablative/eroding products include two types: a basic type (including International Awlcraft) that has little ability to control the erosion rate and will microscopically become rougher over time; and self-polishing paints (including International Micron Extra 2), which become smoother with time, have improved control over the erosion rate, and perform for longer periods.

Meanwhile, most copper antifoulings cannot be applied to aluminium hulls, as copper and aluminium react with each other, leading to the aluminium dissolving away. You’ll need a suitable primer and a compatible product – such as International Trilux 33, a self-polishing product that, unlike conventional copper-based antifoulings, comes in a range of bright colours.

And then there are specialty products, such as International’s VC Offshore – specially formulated for race boats (power and sail, salt- and freshwater), it has a fluoro additive that further reduces surface friction and drag.

Another specialty product comes from Kiwi business Oceanmax, which manufactures Propspeed – a foul release coating system for metal surfaces below the waterline. It’s used for propellers and running gear and comprises a two-component etching primer that bonds to the metal substrate, and a clear coat that creates an ultra-smooth outer layer that marine growth can’t cling to. It’s said to work for up to two years in most cases, with some boat owners claiming it to last three to four years.

Oceanmax’s Nona Pederson says while the product is best applied by a trained applicator, Propspeed is available in many marine maintenance centres worldwide for the capable DIYer.

“Feedback from boat owners around the world confirms that Propspeed soon pays for itself, as it reliably keeps the running gear free from biofouling,” says Pederson. “The short story is more speed, less fuel – Propspeed allows the engine to be under a lot less engine load, burning less fuel and giving you more speed. It’s the most inexpensive repower a boat owner will ever undertake.”

Which is a good point … after all, everyone wants to spend less money and more time on the water.


Another issue to consider is boats carrying marine pests to new locations – this can occur locally (say, from your home marina to a bay you visit for the weekend) and internationally (such as by ships arriving from foreign ports).

Abell Point Marina, on Queensland’s Airlie Beach, is located in a marine park and boasts a pristine aquatic environment with an abundance of marine life. The marina is frequented by boats from around Australia and beyond. General Manager Luke McCaul says while most boats utilise antifoul techniques as a method to maintain their hulls, the marina doesn’t have requirements on the use of particular antifouls or to have had a vessel antifouled before entry – a common approach by marinas.

“As we are in a marine park, antifoul actually breaks down the healthy environment of the water quality, including the production of reef and abundance of fish,” says McCaul. “We have reef life growing in our marina that has not even been identified out on the outer reef – this is how healthy the environment in the marina is.

“In our experience, the state of our customers’ vessels is reasonable and within the standards set by Maritime Safety Queensland and AMSA.”

The Australian Government’s Department of Agriculture and Water Resources says the introduction and spread of new marine plants and animals through biofouling can harm fisheries and threaten healthy fish habitats. The department is currently conducting an online survey to better understand boat owners’s antifouling habits, which concludes on July 31. To take part, go to:

Meanwhile, New Zealand’s Biosecurity 2025 system sees new border requirements from May, 2018, that will affect all arriving vessels. Find information here:, or here:

And for requirements for vessels entering Australian waters, go to:


The cost and effort associated with antifouling, as well as possible environmental concerns with biocides, has led to other innovative ways to reduce biofouling.

Marine creatures don’t survive long out of water, so storing the boat in the air is a relatively simple approach. There are several devices that lift boats out of the water to store them, elevated, in a pen. The AirBerth system, for example, can lift boats of up to 45.3ft (13.8m) and 15 tonnes and park them out of the water in the owner’s berth.

Sea pens are another option – the pen’s flexible liner is shrink-wrapped around the hull as the water is pumped out, with a woven roving mesh creating an airgap between the liner and the hull to keep the boat dry.

Float bricks are a nifty way to store smaller craft, with these modular docking systems providing a stable platform high above the waterline.

There’s also a case to be made for ultrasonic or electrolytic systems – such as BarnacleRid, a copper ion anti-fouling system that uses electrodes submerged in the water. The device is said to create an environment around a docked boat that makes it undesirable for barnacles, hard-shell creatures and algae to attach to the hull.

And of course there’s always the option of using a marina’s dry-storage facilities, with the added benefit of qualified staff taking care of your pride and joy for you.

How to-Safety