Antifouling is a special protective coating for the underwater area of ​​boats. It prevents growth such as algae, barnacles and mussels from adhering, which increases the flow resistance and impairs the performance of the boat. The protective effect keeps the boat more efficient, reduces fuel consumption and protects the underwater hull from damage. Antifouling is available in different versions: self-polishing , hard or biocide-free . The choice depends on the type of boat, its use and the type of water. For a lasting effect, antifouling must be renewed regularly, as the protection wears off over time.

Please use our antifouling configurator to find out in 7 questions which underwater paint you need.

Antifouling works in two different ways: through chemical agents or through physical barriers . Biocide-based antifouling gradually releases active agents that prevent microorganisms from adhering. Self-polishing antifouling wears away continuously in the water, releasing a fresh layer every time. Hard antifouling, on the other hand, forms a solid layer that releases less active agent but is more abrasion-resistant. Biocide-free coatings use extremely smooth surfaces or physical barriers to make adhesion more difficult. Both methods ensure that the boat stays clean and performs well.

The choice of the right antifouling depends on your boat type, speed and area of ​​use. For sailing boats and slower motor boats, self-polishing antifouling is suitable, which wears off evenly in the water and releases fresh protection. For fast motor boats and trailer boats, hard antifouling is ideal, as it is abrasion-resistant and will not be damaged when slipping or traveling at high speeds. In inland waters or environmentally critical areas, biocide-free coatings are recommended, which are environmentally friendly and make regular cleaning easier.

Please use our antifouling configurator to find out in 7 questions which underwater paint you need.

Self-polishing antifouling is continuously worn away by movement in the water, releasing new active ingredients. It is suitable for boats that are used regularly and experience less abrasion due to high speeds. Hard antifouling forms a solid layer that releases fewer active ingredients and is particularly abrasion-resistant. It is ideal for fast motorboats or trailer boats that are frequently taken out of the water. The advantage of hard antifouling is its durability and robustness.

Biocide-free alternatives offer environmentally friendly protection and are based on physical properties, e.g. extremely smooth surfaces that make it difficult for organisms to adhere. Silicone or Teflon-based coatings are among the best-known biocide-free variants. These solutions are ideal for boats in inland waters or environmentally critical zones. However, they require regular cleaning as they do not offer active protection against fouling. Another advantage is the longevity of the coating with proper care.

Yes, primer is essential to ensure that the antifouling adheres properly. When repainting or on new substrates such as GRP, wood, aluminum or steel, 3-5 coats of Seajet 117 Epoxy Primer should be applied. This protects the hull from moisture and osmosis. If you are switching from an old antifouling to Seajet products, first check the Seajet compatibility table . If the products are not compatible, apply Seajet 015 adhesion promoter . The adhesion promoter ensures a stable bond between the old and new paint.

The number of coats depends on the type of antifouling. For self-polishing antifouling, 2-3 coats are recommended for optimal protection. Changing the color between coats helps to better monitor wear. Hard antifouling, which remains on the hull as a solid protective layer, requires 1-2 coats per year . For biocide-free coatings, at least 2 coats should be applied, as these products are based on physical protection. For all variants, thorough preparation with primer is important to ensure adhesion and longevity of the paint.

Prepare the underwater hull thoroughly: clean, sand and apply a primer (eg Seajet 117 ) if necessary. Use brushes or rollers to apply the antifouling evenly. Work in at least 2-3 coats and observe the drying times between coats. With self-polishing antifouling, it is advisable to apply the coats in different colors. Protect yourself with suitable protective clothing and apply the antifouling in dry weather and at moderate temperatures (10-25 °C).

Yes, you can paint over antifouling, but the compatibility of the products is crucial. Check the Seajet compatibility table beforehand. If the new antifouling is compatible with the old one, it is sufficient to lightly sand the surface and apply a new coat. If the products are incompatible or there is major damage, you should apply a bonding agent such asSeajet 015. If the antifouling is very worn, it is advisable to completely remove the old antifouling and create the basis for a new build using a primer such as Seajet 117 .

Removing old antifouling may be necessary if it is peeling, cracking or if you are switching to a new product. There are several methods:

1. Sanding: Carefully remove the antifouling using sandpaper or a sander. Wear protective clothing and a breathing mask.
2. Stripping: Special antifouling removers chemically dissolve the coating. Observe the safety instructions.
3. Sandblasting: This method is particularly effective, but should only be carried out by professionals in order not to damage the material.
   After removal, prepare the hull thoroughly for a new coat of paint.

A primer such as Seajet 117 Epoxy Primer acts as a base coat and creates a protective layer between the hull and the antifouling. It improves the adhesion of the paint and protects the hull from moisture, corrosion and osmosis. Primers are essential when repainting or when the old antifouling has been removed.

A bonding agent such asSeajet 015 is used when the existing antifouling is not fully compatible with the new product. The bonding agent ensures a stable bond between the old and new layer without having to completely prepare the hull. Always check the Seajet compatibility table before applying!

Self-polishing antifouling should ideally be refreshed with at least one new coat every year . For easy control, we recommend applying each coat in a different color . This way you can immediately see when the antifouling has worn off and where touch-ups are needed. Hard antifouling also requires regular maintenance and should also be renewed annually to ensure optimal protection.

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To check whether your antifouling needs to be renewed, check the underwater hull when craneing or launching the boat. Look for the following signs:

1. Visible growth: Algae, barnacles or mussels adhere to the surface.
2. Peeling layers: If the antifouling shows cracks or comes off, it must be removed and replaced.
3. Primer showing through: With multi-coloured antifouling, the next layer is visible – this is a clear indication that repainting is necessary.

Even if everything looks good on the outside, it is recommended to repaint it once a season to ensure protection.

Since most boats are not taken out of the water during the season, you can clean the underwater hull in two practical ways:

1. With a long handle and sponge/brush: Special telescopic rods with sponges or brushes allow you to clean the underwater hull from the dock or boat without getting into the water.
2. Diving down: If the weather is suitable and you have the right equipment (diving goggles, sponge or soft brush), you can clean the underwater hull directly in the water.

Regular cleaning prevents growth from becoming too embedded and extends the life of the antifouling. However, be careful not to use sharp tools to avoid damaging the coating.

If the antifouling is damaged during the season, it is usually not necessary to crane the boat straight away, as long as the damage does not extend to the primer or the hull. Small areas of wear and tear or local weak spots do not usually affect the protection so severely that they endanger the entire season.

In such cases, you can continue to use the boat and repair the damage after the end of the season. As soon as the boat is out of the water, clean the underwater hull, lightly sand the damaged areas and apply new layers of antifouling. Immediate action is only necessary if larger areas are affected, leaving the hull unprotected, or if there is a significant growth of fouling.

For salty waters, where the growth of algae and mussels is particularly intense, antifouling containing biocides is best. Products such as self-polishing antifouling continuously release active ingredients and renew themselves as the boat moves in the water. Hard antifouling is recommended for faster-moving boats, as it is abrasion-resistant and can withstand high loads. We particularly recommend Seajet 033 for most saltwater areas. Annual renewal is particularly important here.

For aluminum hulls it is important to use a specialized antifouling , as many conventional biocide-based antifoulings contain copper, which causes corrosion. Use a copper-free antifouling , such as Seajet 034A , which has been specifically developed for aluminum hulls (that's what the A after the 034 stands for). In addition, the hull should be primed with an epoxy primer such as Seajet 117 to create a protective barrier. This will prevent galvanic corrosion and ensure that the antifouling adheres and protects optimally.

Otherwise, all biocide-free coatings are suitable for aluminum because they do not contain copper.

Antifouling should ideally be applied at temperatures between 10 and 25 °C . At lower temperatures, the product dries more slowly, which can reduce the protective effect. If you are working in spring or autumn, make sure the weather is dry and allow enough time for drying between coats. In cold regions, it is advisable to work on the boat in a hall or in a sheltered place. Always read the manufacturer's instructions for the optimal application temperature.

Growths such as algae, mussels and barnacles significantly increase drag , which greatly affects the performance of the boat. A hull covered in growth can reduce speed by up to 30% and dramatically increase fuel consumption. In sailing boats, growth has a particularly negative effect on maneuverability and speed. Regularly applying antifouling keeps the hull clean and hydrodynamic, improving the efficiency of the boat and reducing operating costs.

Antifouling should generally be renewed once a year , especially before the season in spring. Self-polishing antifouling wears off through movement in the water and should be applied at least once per season . With hard antifouling, a refresher coat is often sufficient to maintain protection. Regular inspections of the underwater hull are essential to detect damage or heavy growth at an early stage.

A new build is necessary if the old antifouling has been completely removed or the hull needs to be recoated. For a 10m boat (water length) the material costs are around 1000 euros . The following are required:

• Primer (e.g. Seajet 117 Epoxy Primer ): It protects the hull from moisture and osmosis. Cost: approx. 700 euros for 20 liters (for 5 layers).
• Antifouling (e.g. Seajet 031 self-polishing ): Two to three coats offer optimal protection. Cost: approx. 200 euros for 10 liters.
• Tools and accessories: rollers, brushes, sandpaper and covering material. (without machines) Cost: approx. 100 euros .

In addition, there may be costs for removing the old antifouling, e.g. by sanding or stripping. Professional removal costs around 15-25 euros per square meter , which for a 10m boat means around 300-500 euros . Rebuilding is an investment in the long-term protection of your boat. But it can also be done easily yourself.

Always store antifouling products in a cool, dry and well-ventilated place . The ideal storage temperature is between 5 and 20 °C . Avoid direct sunlight or frost as this can affect product quality. Opened containers should be sealed hermetically and used within a few months. Keep the products out of the reach of children and ensure that they do not come into contact with food or drinking water.

Antifouling can easily be applied yourself with a little preparation. The key is careful preparation:

1. Clean the underwater hull thoroughly.
2. Sand the surface lightly.
3. If necessary, apply primer or adhesion promoter.
4. Use a roller or brush to apply the antifouling evenly in 2-3 coats .

For larger boats or heavily damaged hulls, it may be advisable to hire a professional to ensure a perfect result.

Seajet is part of Chugoku Marine Paints Ltd. (CMP) , one of the world's largest manufacturers of coatings for marine and industrial use. CMP has a global network with 105 locations in 35 countries and brings decades of experience in developing high-quality products.

Seajet products are manufactured in a state-of-the-art factory in the Netherlands . This production facility uses the latest technology with renewable energy: 1190 solar cells and geothermal energy ensure sustainable energy supply. Emissions have been reduced by up to 95% , while occupational safety and environmental protection are given the highest priority.

Since the 1990s, Seajet has been providing innovative antifouling coatings, topcoats, primers and paints. The product portfolio combines innovation, quality and environmental responsibility to offer optimal solutions for boat owners worldwide.