Do I need to antifoul my boat?

Winter Boat StorageWhy antifoul?

Antifouling paint prevents a build-up of marine growth on boats. It is most commonly used on the hull, but it can also be used on drive shafts and propellers that are continually in the water too.

Marine fouling starts showing on a boat as a layer of green slime. This green slime is nature’s rich combination of bacteria, plankton and algae and quickly grows thicker. Once the slime is thick enough more of the local environment can enjoy the slime and you will see the likes of barnacles, tubeworms and seaweed attaching. This green feeding curtain is all too familiar on so many boats moored in the harbour.  A layer of green slime can develop in days.

So, why antifoul… The marine growth does the following:-

  1. Increases fuel consumption.
  2. Makes the boat more difficult to manoeuvre.
  3. Affects your top speed.
  4. May make it difficult or impossible to push the boat to plane.
  5. Spoils the aesthetics.

All up you don’t want it growing on the bottom of your boat.

The most common way of cleaning off marine fouling is using a pressure washer. This fast cleaning method works but it can cause damage to fibreglass hulls and RIB tubes. The material in RIB tubes needs special, gentle attention. to avoid damage to seams.

What’s in an antifoul treatment paint?

Basically antifoul is poison to anything trying to latch on to your boat.  The most common type of paint contains biocides, such as copper oxide and xylene and the more expensive paints contain a sophisticated combination of organic biocides and other chemicals.  The marine fouling organisms in seawater are different from freshwater, so most of the paint brands offer different products for salt and fresh water.  The challenge comes when you store and use your boat in both fresh and seawater. I recommend you speak directly with your paint supplier for advice.

Antifoul paint is closely regulated and most countries have their own rules about which biocides can be used and the composition. The upshot is some countries allow stronger antifoul treatments than others.

How do I decide which antifoul paint to use?

Generally, the more expensive, premium antifouling paints offer protection for two years whilst the cheaper ones suggest the paint is applied annually.  However, you will need some local knowledge and boating experience to work out how often you need to antifoul your boat because it all depends on where you keep your boat. If you keep your boat on a river or estuary where treated sewage and nitrate fertiliser from the land gets into the water you have the perfect ecosystem for fouling organisms and you will need to antifoul annually.

Whatever antifoul treatment you use the best way to reduce marine fouling is to regularly use your boat and drive it at high speed.

There are various types of antifoul:

Hard Antifoul: Smooth surface and minimal drag through the water so it won’t be washed off at high speeds.

  • Suitability – fast planing powerboats and RIB hulls
  • Example products: Seajet Coastal, Hempel Hard Racing, International Ultra 300, Flag Performance Extra
  • Drawbacks: to stay effective the antifoul must be scrubbed several times a year. Some marinas have boat scrubbing machines or may offer a lift out and scrub service. After many years of additional antifoul application at some point, you will need to scrape off all the old antifoul and start afresh.

Soft Antifoul (also known as ablative or self-polishing): Designed to slowly erode as the boat is used, getting rid of marine growth.

  • Suitability – relatively slow boats (less than 17 knots). If you repeatedly go over 17 knots the antifoul simply won’t stick. There are some products which claim to hold fast at higher speeds, but be wary.
  • Example products: Seajet Shogun, Jotun Mare Nostrum, Hempel Tiger Xtra.
  • Drawbacks: it easily comes off when you scrub the hull. It’s tricky to work out which is the best product for your boat as there is a large range of softness levels available.

Other specialist products:

  • Specialist primers – this product is for hulls which haven’t previously been antifouled to ensure the antifoul sticks. If no primer is applied the antifoul will come off as soon as the boat goes through the water. All antifoul paint manufacturers also make their own primer too. 
  • Antifoul paint with copper thiocyanate – this antifoul is for aluminium hulls, trim tabs and drive legs. Standard antifoul contains copper oxide and will cause corrosion. Example products are International Trilux 33 and Seajet Emperor.
  • Flexible antifoul paint – this paint is for RIB tubes where they’re permanently in the water. Example products are Polymarine and Gommoguard. There are different paints for Hypalon and PVC tubes.
  • Antifoul paint for propellers – if the boat is being used irregularly you can either coat the prop with synthetic greases, like Prop-Shield, or apply antifoul paint that has been specially developed for propellers. Example products are Marlin Velox and the main paint suppliers will also have their own propeller antifoul formulation.

What are the alternatives to antifoul?

You may hear boat owners complain that antifoul doesn’t work as well as it used to; it’s true. Some of the chemicals in antifoul have been extremely toxic to the marine ecosystem and so as regulations continue to tighten antifoul manufacturers struggle to maintain the effectiveness of the paint.  No-one sets out to pollute the environment, but on balance it’s better to antifoul than to burn a lot more fuel for the same performance.

There are though some viable alternatives:

Coppercoat: A mixture of copper dust and epoxy that is sprayed onto the hull and dries to form a hard surface.

  • Application – requires skill, diligence and time for what is a lengthy preparation. The hull must be thoroughly dried out and checked with a moisture meter before Coppercoat is applied. This may mean for a boat that has been in the water for a long time indoor storage for several months before the Coppercoat can be applied. Most boat owners will appoint an external company to provide Coppercoat so there is a long term guarantee that the Coppercoat will not flake off and allow moisture to be trapped.
  • Cost – Coppercoat is expensive to apply, however, it only needs to be re-done every five or six years, rather than antifoul which needs to be applied every year or two.  You do still need to buff the hull to reveal fresh copper every year.
  • Drawbacks : it’s not very effective on the slime so this still needs to be regularly scrubbed off the boat. Another drawback is the initial high expense.

Ultrasonic Transducers: Transducers are fitted to the hull and the vibrations are proven to reduce the build-up of marine fouling.

  • Application – transducers are unlikely to completely rid your boat of marine fouling, so most suppliers recommend using transducers in addition to regular hard antifouling.
  • Drawbacks : transducers won’t work on composite or wooden hulls because they need the hull to resonate. They also need electrical power so they’re not always suitable for boats away from an electrical source on for example, a mooring.

Nanotech Paint: these paints don’t contain biocides and work by creating a surface that is so hard and slippery that nothing can attach itself.

  • Application – relatively straightforward. Example products are Aquacote and Hempel Silicone.
  • Drawbacks: the hull will still require regular scrubbing, the boat must be regularly driven above 20 knots and sometimes boatyards find lifting and launching boats tricky because the paint makes the boat slippery.

antifoul my boatAlways store your boat ashore and avoid antifouling: small to medium-sized boats can be stored ashore. There are storage costs, but no antifouling means a faster boat and often boats have a better resale value if they haven’t been antifouled.  If you sometimes need to leave your boat afloat for up to a month there are paint products such McLube Antifoul Alternative Speed Polish which temporarily do a good job.

You could keep your boat ashore in a boat park on its own trailer and launch and recover it yourself, but there will usually be a queue on the slipway on sunny weekends. The ideal option is Drystack storage, where the boat is kept inside and launched for you whenever you want to use it – you just turn up, launch and go. Drystack storage also offers better security than most boat parks and if the boat’s stored inside it won’t be exposed to UV rays that cause long-term damage, and you won’t need a cover.


If your boat is going to stay in the water and you’re unable to use it regularly and at a fast speed you will need to antifoul your boat.  As with all maintenance, with some advance thought and action marine fouling need never be a problem. 

Trafalgar Group
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