The Ultimate Antifouling Paint Guide

Antifouling is one of the most important boat maintenance tasks, as without antifouling paint, your boat will be exposed to marine organisms which can, over time, damage your hull. We've picked the brains of our highly experienced team to collate a comprehensive guide covering all of the most important, and most frequently asked questions we've received over time.

Within this blog post we’ll be looking at the following:

If you click on any of the bullet points below, you'll jump to the respective section.

What is antifouling paint?
What are the benefits of antifouling paint?
What are the different types of antifouling paint?
Applying antifouling paint.
- When should you apply antifouling paint?
- How often should you apply antifouling paint, and how long does it last?
- How much does it cost to antifoul a boat?
- How much antifouling do you need?
- How do you apply antifouling paint?
- Antifouling legs, propellers and sterndrives.
How to remove antifouling paint.
Other frequently asked questions.

What is antifouling paint?

Antifouling paint is a specialized type of coating applied to the hulls of boats to prevent the accumulation of marine organisms, such as barnacles, algae, and molluscs on submerged surfaces. These organisms can attach to the hull over time, creating drag and reducing the vessel's performance. Additionally, the growth of marine organisms can lead to corrosion and other damage to the hull.

Antifouling paints typically contain biocides or other chemicals that are toxic to marine organisms. When the boat moves through the water, the paint releases these chemicals, creating a toxic environment that discourages the attachment and growth of fouling organisms. 

What are the benefits of antifouling paint?

There are an array of benefits of applying antifouling which will protect your boat and your wallet! As we touched on above, antifouling prevents marine organisms accumulating on the hull of your boat, creating drag and reducing its speed, thus increasing your fuel bill. Antifouling paint help maintain a smooth, clean hull, optimising your vessel's performance and fuel economy. 

Another benefit of a cleaner hull is extended maintenance intervals and lower maintenance bills. Antifouling paint reduces the frequency of hull cleaning and maintenance. Without antifouling protection, you would need to clean and remove fouling organisms more frequently, leading to increased maintenance costs and downtime.

What are the different types of antifouling paint?

There are two main types of antifouling paint, which are hard and soft. 

Hard Antifouling:

Hard antifouling paints are typically composed of a solid resin matrix that holds biocides, releasing them gradually to deter the attachment and growth of fouling organisms. Hard antifouling paints are known for their durability and resistance to abrasion, as the solid film withstands friction from water flow and contact with the hull. The application of hard antifouling paint results in a relatively smooth finish on the hull. This characteristic is advantageous for boats that require consistent hydrodynamic performance.

Suitable For:
Powerboats, racing yachts and vessels that can achieve speeds of over 30 knots. 

Examples of hard antifouling paints:
Hempel Hard Racing Antifoul 2.5L.
International Ultra 300 Antifoul 2.5L.
Seajet Emperor 034 Antifoul 2.5L.

Soft Antifouling:

In contrast, soft antifouling (also known as ablative antifouling) wear away gradually over time, releasing fresh layers of biocides as they erode. This self-polishing effect helps to maintain a clean hull and optimal hydrodynamic performance. Ablative paints are often used on boats with moderate activity levels.

Suitable For:
Vessels with speeds up to 30 knots, as if the antifouling is used on boats faster than this, it will erode too quickly.

Examples of soft antifouling paints:
Hempel Cruising Performer Antifoul 2.5L.
Hempel Mille NCT Antifoul 2.5L.
Seajet Shogun 033 Antifoul 2.5L.

Applying Antifoul Paint

When it comes to the application of antifouling, preparation is of the upmost importance as applying antifoul paint can be dangerous, if you do not take the correct precautionary steps. You must ensure that you are working in a ventilated space and are wearing the correct personal protective equipment.

Protective equipment we recommend includes:
A mask that covers both your nose and mouth.
Eye protection.
Nitrile gloves.
Overalls that do not leave any skin exposed.

When should you apply antifouling paint?

The timing for applying antifouling paint depends on various factors, including the type of paint used, the climate in your region, and the specific needs of your boat. Ideally, antifouling paint should be applied shortly before launching your boat. This ensures that the protective coating is fresh and effective when your boat is exposed to the water.

If possible, apply the paint within a few days or weeks of launching to minimize the time the hull is exposed to potential fouling. The time in which you can launch your boat after applying antifoul will vary from paint to paint, so we highly recommend looking at the product data sheet beforehand, as this will provide you with all the information you need. Areas such as film thickness, temperature, finish and application tools are covered. If you're browsing any of the antifouling paints we sell, you'll find it at the bottom of the product description under 'Useful Links'.

If your boat is regularly taken out of the water for maintenance or storage, consider applying antifouling paint during these dry-docking periods. Applying antifouling paint while the boat is out of the water allows for proper preparation and application without the constraints of tides.

How often should you apply antifouling paint, and how long does it last?

The frequency of antifouling paint application depends on various factors, including the type of paint used, the local environmental conditions, and how frequently your boat is used. Common practice is to apply antifouling paint annually but in some cases especially in areas with moderate fouling conditions, applying antifouling paint every two years may be sufficient. This approach can be more cost-effective and may be suitable for boats that spend extended periods out of the water. Antifoul paints such as Seajet Shogun 033 state that two thick coats will last two seasons in Northern European waters.

If your boat is used seasonally, such as during the summer months (as is common here in the UK), you might choose to apply antifouling paint before each boating season. This ensures maximum protection during the months in which you'll be out on the water.

This is one of our most frequently asked questions, so we've written a blog post titled 'How often should you antifoul a boat?' which takes a closer look at the subject.

How much does it cost to antifoul a boat?

As has been the common theme in this article, the cost of antifouling a boat will significantly vary from vessel to vessel. One thing that is for certain, is that not cutting any corners in the process of applying antifouling will save you maintenance costs further down the line. If you're having the work done for you, you can expect to pay anywhere from £30-50 per metre. We've written a guide that takes a closer look at the cost of antifouling a boat.

How much antifouling do you need?

To work out the amount of antifouling you require, you will first need to know the surface area of the hull.

If you have a fin keel, the formula is as follows:
Waterline length x (beam + underwater depth) x 0.5.

If you have a long keel, the formula is as follows:
Waterline length x (beam + underwater depth) x 0.75.

Once you have established a number, you will need to know the coverage of the antifoul, which can be found within the product data sheet. You can then use the following calculation to establish the total litres of antifouling required.

Surface Area (m2) ÷ Coverage Rate (m2)/L = total litres of antifouling paint required.

Please Note:
These calculations are for one coat – if you wish to apply more coats, then you will need to adjust the amount accordingly. We have a dedicated article for this subject, titled 'How much boat antifoul do I need?' plus leading paint brands such as Hempel antifoul and Seajet antifoul also have their own paint calculators which are worth checking out.

Links:
Hempel Paint Calculator: https://yachtpaintcalculator.com/
Seajet Paint Calculator: https://www.seajetpaint.com/

How do you apply antifouling paint?

Applying antifouling paint involves several steps to ensure proper adhesion and effectiveness. We take a deeper dive into this subject in our antifoul application blog post, but here is a short guide.

Before applying antifouling paint, inspect the hull for any damage, and repair as necessary. Remove loose or peeling existing paint using a scraper or sandpaper. Lightly sand the entire hull to create a smooth surface, and clean it thoroughly to remove dirt and contaminants. Also be aware that surface preparation will vary depending on the substrate of the hull. Namely, aluminium boats may require special attention during surface preparation.

Mask off areas you don't want to paint, such as the waterline and through-hull fittings. Take precautions to protect the surrounding environment from paint overspray.

Some antifouling paints may require a primer, especially if you're working on a bare hull or do not know what antifoul you're applying on top of. Check the manufacturer's recommendations and apply the primer according to the instructions, allowing it to dry completely.

Choose your preferred application method - brush, roller, or spray - based on the type of paint and your expertise. Apply the recommended number of coats, usually two, allowing each coat to dry thoroughly before applying the next. Pay attention to areas that may be missed and ensure even coverage.

Follow the recommended drying times between coats. Factors such as temperature and humidity can affect drying, so be mindful of environmental conditions. As mentioned earlier, all of this information will be found within the product data sheet.

Clean your tools and equipment according to the paint manufacturer's instructions. Dispose of waste materials in accordance with local regulations.

Antifouling legs, propellers and sterndrives

Propellers, sterndrives and legs are especially susceptible to fouling due to their constant motion through the water, which may not be sufficient to prevent the attachment of marine organisms. As these are hard to reach areas, it is common practice to use spray on antifoulings to protect these crucial components.

Popular antifouling sprays:
Hempel Mille Prop Primer 500ml - suitable for propellers, outboard engines, drive units and small patches on yachts. 
International Prop-O-Drev Antifoul 500ml - suitable for use on outdrives, outboard legs, propellers and sterngear.
TK Antifouling Spray 500ml - suitable for propellers, axels, flaps and gears. 

How to remove antifouling paint

If you're using the same antifoul as previously and your hull is in good condition, you can simply give your hull a good wash and then apply new antifouling over the top - just be sure to check the product data sheet to ensure you don't need to do any light sanding first.

On the flip side, if your antifoul is flaky or has become thin, patchy or damaged, it will be necessary to remove it before applying a new coat for effective protection.

Sanding:

Sanding is a mechanical method that involves using sandpaper or a sander to remove the antifouling paint. This method can be effective but may generate a lot of dust.

Scraping:

Scraping involves using a scraper to physically remove the paint. Be cautious not to damage the underlying surface. This method may require more effort, especially if the paint is thick - but can often be the quickest.

Chemical Stripping:

Chemical stripping involves applying a paint stripper (such as International Interstrip AF or Owatrol Dilunett) and leaving it to lift the paint, before scraping it off. This then makes the task of scraping the paint off far less labour intensive. When using a chemical stripper, you must be very careful that you do not apply too much, as this may take the primer off too. You must also be very careful to check that the chemical stripper is suitable for use on GRP surfaces. For the best results, International recommend working on a small area at a time.

Other Frequently Asked Questions:

How long does antifoul last in a tin?

From feedback from our customers, an opened tin of antifouling can last a good couple of years if resealed properly to ensure no evaporation occurs. Make sure the tin is stored in an environment where the temperature will not fall below freezing.

When re-opening the tin to apply another coat, make sure the paint is thoroughly mixed. If you haven't got enough antifouling left over to complete the job and have purchased more antifoul, use the newly purchased antifoul first, as if there any problems with the antifouling that's been sat on your shelf for a few years, it may cause the newly purchased antifoul on top of it to fail; where-as if you put the old antifoul on top and it does fail, it will not affect the antifouling below it.

How quickly can I launch my boat after applying antifouling?

This will all depend on which antifouling you purchase and in what temperature you apply it, as different antifouling paints dry at different speeds and as a common rule of thumb, the higher the temperature, the faster the drying speed. You will find all of this information within the product data sheet of each antifoul paint. if you're not in a rush, the maximum time is also listed, which is often around 6 months.

My boat is in fresh water, what antifouling do I need?

The type of water in which a boat operates can significantly impact the effectiveness of antifouling paint, influencing the choice of antifouling product. The key factors related to water type that affect antifoul selection include temperature, salinity, and the presence of marine life. Each product will specify which type of water it is most suitable for use in. If you're browsing our range of antifouling paints, you'll be able to use handy filters to only show antifouling paint for the water you keep your boat in.

Where can I buy antifouling paint?

For over 30 years we've been supplying a leading range of antifouling paint from the industry's most trusted brands, including Hempel, International and Seajet. We aim to make your shopping experience as simple as possible, which is why we've included handy colour and water type filters. You'll also find dedicated FAQ's on each product, colour previews and product data sheets. We also offer antifoul value packs, which give you a free roller pack and masking tape when you purchase two or more tins of antifouling.

If you're in the South East of England, why not come and visit our Rochester store? We have one of the largest chandlery stores in the United Kingdom, with thousands of products spread across two floors. Our expert team are boat owners themselves, so are perfectly placed to provide you with any advice and guidance you need. You can also speak to them by calling us on 01634 295 233, or emailing [email protected].

Other useful blog posts:

Antifouling an aluminium boat.
How much boat antifoul do you need?
How much does it cost to antifoul a boat?
How often should you antifoul a boat?
How to antifoul a fibreglass boat.
How to apply antifouling.