Finding & applying the right antifouling

How to find and apply the right antifouling for your boat

Treating your hull, in particular the area below the waterline with antifouling, is especially important to ensure long lasting and carefree use of your boat and great performance. A cared for underwater hull results in easier manoeuvring, more safety and lower fuel consumption. In this guide to anitfouling, we answer the most frequently asked questions about underwater painting and boat antifouling. Already know which antifouling you want?

Here you get directly to our large selection of Antifouling »

What is antifouling? Why should I use antifouling? What happens without antifouling?

In order to prevent fouling, mussel and snail growth, treating your boat with antifouling in the spring cannot be avoided. This is true for all boats that are in the water for a longer period of time. The underwater coating prevents organisms, such as barnacles as well as zebra mussels, and plants, such as algae and mud, from settling on your hull. Most antifouling contains biocides, such as copper, in order to prevent these deposits from happening. However, there are other products that are more environmentally-friendly, such as SILIC ONE products of the brand Hempel.

without antifouling

The three most important reasons why you should paint your boat with antifouling and what would happen without antifouling:

1. The boat can glide easier and faster through the water!

Deposits and fouling make your boat heavier and the frictional resistance increases. This directly affects maneuverability and the speed of your boat.

2. Easy steering maneuvers!

Fouling on the propeller, bow thruster or steering gears can have dangerous consequences. The response time of the boat with regard to steering maneuvers is longer than usual. In the worst-case scenario, this can lead to complete failure.

3. Lower fuel consumption!

Due to increased frictional resistance of the hull in the water, more fuel is needed. This results in unnecessary costs and more CO2 emissions.

Overview of the advantages of antifouling

  • Protects against fouling, mussels and barnacles on the hull.
  • The boat glides better and faster through the water.
  • Protects the propeller, bow thruster and rudder system from fouling.
  • Makes for better steering of the boat.
  • Save fuel due to lower resistance in the water.
Trailorboat antifouling

Do I need antifouling for my trailer boat?

If you own a trailer boat and take it out of the water after each use, it is not necessarily required to use antifouling. However, you should still regularly clean your underwater hull and steam-jet clean your boat after each use. If your boat remains in the water for several days, we recommend to treat the underwater hull with antifouling.

The antifouling on my boat is still in a good condition. Do I have to re-apply?

If your antifouling is in good condition at the end of the season, we still recommend a new coat of antifouling at the beginning of the new season. However, the effectiveness of the antifouling depends less on the number of coats, and more on the thickness of the coat. For applying a new coat, follow these steps:

  1. Clean the underwater area of your hull with fresh water, for best results and in order to remove loose antifouling particles, you should use a high-pressure cleaner.
  2. Sand the old antifouling in slightly wet condition.
  1. Rinse off the sanding dust with a suitable product (e.g. International Super Cleaner). Rinsing with water alone does not suffice in this case, since the fine abrasive particles will settle in the sanding grooves, which will affect the effectiveness of the antifouling.
  2. Repair damage or small blemishes where the antifouling has come undone. A step-by-step guide can be found in this Video.
  3. If you are using the same antifouling you have previously used, you can simply start with applying antifouling. For renewing the protection, one coat is sufficient.

I' ve bought a new boat. Do I still need to apply antifouling?

Absolutely. New boats will generally need a coat of antifouling. On a new boat with a GRP hull that comes directly from the shipyard has a layer of wax to protect the hull from damage. This must be completely removed before applying the antifouling.  

Apply antifouling

My boat has never been treated with antifouling. How do I apply antifouling?

In general, all materials need to be completely grease-, dust- and moisture-free prior to applying primer and then antifouling. For degreasing, Super Cleaner works perfectly. Dirt, oil, wax and grease residues are history. Before you apply antifouling, you need to prime your surface. International Gelshield 200, a fast drying epoxide primer, is especially suitable for GFRP boats.

For aluminum, lead, steel and wooden surfaces, International Interprotect or International Primocon is a reliable product. Please also consult the product data sheets regarding intervals between coats. Following cleaning and priming, you can start applying your antifouling. Watch the following video for helpful tips regarding priming of your underwater hull.

Overview of when and how to apply antifouling

  • Even if the antifouling is in good condition, a new coat should be applied at the end of the season.
  • New boats, straight from the shipyard, must also be treated with antifouling.
  • Before the first treatment, degrease, dust and dry thoroughly.
  • Trailer boats only need to be treated with antifouling if they remain in the water for several days.

Hard or soft antifouling - which antifouling do I need?

Slow polishing / semi polishing antifouling prevents build-up of thick layers and is suitable for fast boats. INTERNATIONAL Trilux 33

Thin-film antifouling works by means of an extremely smooth surface, due to which adhesion of organisms is much more difficult. The smooth surface is created by adding PTFE and thus also results in higher speeds and less fuel consumption. In addition, no thick layers of paint are built up. SEATEC GTI 30

Antifouling for Propellers and drives For propellers, there is special antifouling that usually comes in a spray can, making application a lot easier. This special spray antifouling protects your propeller or drive reliably from fouling. Some propeller antifoulings are not applied with a spray can, but with a spatula. Hempel Prop NCT, International Trilux Prop-O-Drevor Jotun Aqualine Optima

Use biocide-free antifouling and protect the environment. Avoid biocides in antifouling paints and ensure a toxic-free underwater hull coating for your boat and a sustainable solution for boating.

Overview of types of antifouling

  • Hard antifouling: Ideal for fast motor boats, trailer boats and boats in dry marinas.
  • Self-polishing antifouling: Ideal for sailing boats as it has a polishing effect.
  • Semi polishing antifouling: Ideal for fast boats.
  • Thin-film antifouling: Has a very smooth surface, making it harder for organisms to attach. Results in higher speed and lower fuel consumption.
  • Antifouling for propellers and drives: Protects your drive from fouling.

Factors to consider when choosing antifouling:

1 Material

Not all antifoulings are suitable for every hull material. Many antifoulings are designed for boats made of GRP, wood and steel. For stainless steel and aluminium boats, the choice of antifouling paints is somewhat limited. Information on the antifoulings can be found on the corresponding products, the manufacturer's pages or product pages.

2 Speed

How fast you sail your boat and how often or for how long is also an important factor in choosing the best antifouling. Information about what speed the antifoulings are particularly suitable for can be found in the product information.

3 Areas of use:

a. Where the boat is situated, ie. in which waters, is important when choosing antifouling for your boat. In some waters there are more sub-aquatic organisms, in others there are fewer. Fouling varies depending on temperature, sunlight, salinity (salt or fresh water), current and water quality, so different antifouling types are more or less suitable depending on these factors.

b. It's also important to note that not all antifoulings or the ingredients used in their composition are permitted in every area, body of water or country. Many antifoulings are banned in Holland and parts of Scandinavia, for instance.

Tip: Wherever you are, either the Mediterranean Sea, Baltic Sea or Lake Constance, you can always find out which antifoulings are particularly suitable and which should or must not be used when you are there. Certain regulations and guidelines exist and apply in some cases. Look into the local legislation.

4 Antifouling over other layers

Since subsequent layers of antifouling should match existing coats, you will be limited in your choice of antifouling unless existing layers are completely removed.

I've bought a new boat and I'm not sure which antifouling was previously used

If you're unsure which antifouling was previously used, maybe because you've bought a used boat, you can first of all apply a coat of barrier primer (e.g. International Primocon)and afterwards the antifouling. If you decide to use a different antifouling, please consult the compatibility chart below or contact us for more information.

antifouling table

* Unknown antifouling; ** Bad condition

Wet sand existing antifouling,rinse with fresh water and allow to dry. The new antifouling can be applied afterwards.

Remove existing antifouling completely, e.g. Interstrip AF

Apply a coat of sealing primer, e.g. Primocon®. Afterwards, apply your new antifouling.

I would like to use a different antifouling than last year. Is my new antifouling compatible with the old product?

International banner

Cruiser Bright White
becomes Cruiser 200

  • Polishing antifouling suitable for freshwater and saltwater
  • Improved resistance to colour fading
  • A selection of bright colours including true white
  • Suitable for aluminium
  • Low VOC content

Micron Extra EU
becomes Micron 350

  • Powerful SPC antifouling for multiple seasons
  • Improved performance
  • Improved paints
  • Micron 350 has a lower VOC content

Cruiser Uno EU
becomes Cruiser 250

  • Provides protection for one year
  • Suitable for sailboats and motorboats (up to 25 knots)
  • Improved paints

Ultra EU
becomes Ultra 300

  • High-performance hard antifouling
  • Improved paints
  • Hard, long-lasting finish
  • Suitable for polishing and wet cleaning
  • Low VOC content

How much antifouling do I need? Formulas for calculating the correct amounts for your surface.

In order to determine how much antifouling is needed, you first of all have to calculate the entire surface of your underwater hull. This varies slightly, depending on whether you own a motor boat, a short keel or long keel boat, as you can see in this chart from the manufacturer International:

The practical yield (m² per liter) of the different antifouling products is specified in the respective product data sheets that can be found on our website. The required quantity in liters can be calculated with the formula: total surface / recommended coverage rate of the respective paint.

Motorboat sketch
Short keel sketch
Long keel sketch

Key

LÜA = Length over everything ● LWL = Length water line ● B = width ● TG = draft ● F = freeboard ● 1 foot = 0.3 meters ● 1 meter = 3,281 feet ● 1 square foot = 0.098 square meters ● 1 square meter = 10,764 square feet ● 1 gallon = 4,545 liters ● 1 liter = 0.219 gallons

What type of protective gear do I need when working with antifouling?

As mentioned above, antifouling contains biocides and other substances that may be dangerous to humans. This is why we urge you to carefully read the labels of the products and protect yourself as necessary with clothing or other equipment when using antifouling.

Please use protective gloves, safety goggles and a suitable mouth/nose protection with particle filter for sanding work, with protection against solvent vapours when applying antifouling and primer and for any processing of paint and antifouling: In order to protect exposed skin and your clothing, we recommend wearing an overall.

What items and tools do I need when painting antifouling?

In order for antifouling application to be an easy and quick process, you need the correct equipment and tools. This includes rollers and brushes for applying antifouling, masking tape for taping the areas to be treated, as well as suitable thinners or cleaners for cleaning your brushes and equipment.

If the old antifouling is no longer in good condition, you might need a paint scraper, a good grinder with matching accessories or a product for removing the old antifouling.

How do I apply antifouling? Should I use a brush or a roller?

Both application methods are suitable for most antifouling products. It is only for International VC Offshore EU and International VC 17m that the manufacturer recommends application with a roller only.

Using a roller when applying antifouling is usually the quickest method for large surfaces. The quickest, but not necessarily the most perfect result, is application with a lamb hair or short-fibred mohair roller, since these can soak up more paint. Using a foam roller takes slightly longer, but the result is a smoother surface and a higher quality.

Brushes are perfect for difficult and rough surfaces, as well as minor repairs and difficult to reach areas. When using a brush in these areas, more paint can be absorbed. An even surface is possible when you are painting back and forth as well as horizontal and vertical over an area that is not too large. The final brushstrokes should be light and applied vertically. It is important to clean the brush about every 30 minutes, since paint residues can dry on the brush, and these result in an uneven surface. We generally recommend use of high-quality brushes for applying antifouling in order to avoid fine brush hair sticking to the freshly painted hull.

Small tip from our SVB experts: "Hold your brush at a 45° angle to avoid visible brushstrokes"

Overview of items & tools for applying antifouling

  • The required quantity in litres can be calculated with the formula: total surface / recommended coverage rate of the respective antifouling.
  • You'll need the right protective clothing: Gloves, goggles,mouth-nose protection with particle filter and possibly a protective overall.
  • The right tools make the job easier: rollers, brushes, tape, thinner for the brushes, paint scraper and sander.
  • You can apply antifouling more quickly with a roller, but brushes are suitable for rough surfaces and hard-to-reach areas. Follow the manufacturer's instructions.
  • Stroke back and forth in a cross to achieve an even surface.

FAQ

That depends on several factors, e.g., sailing and motor speed, the types of estuaries/waters your boat is used in and the climatic conditions. We generally recommend applying a soft antifouling in three layers and a hard antifouling in two layers. Since the number of coats varies from product to product, you can find more information regarding the correct application in the product data sheets that are available on our website. As a rule of thumb, it is better to apply more antifouling than needed, especially in areas with more abrasion (water line, rudder blade and keel). If you are uncertain how many coats of antifouling you should apply, do not hesitate to contact our customer service.
How often antifouling needs to be reapplied depends on the condition of the existing antifouling. How long the antifouling lasts depends on the thickness of the antifouling layer and the type of underwater coating used. Sailing speed, temperature and water also affect how long the antifouling will protect your boat. This means there's not really a general answer to the question "How often should I renew my antifouling". In some cases, you might get away with a simple antifouling touch up. However, for lasting protection, a new layer of antifouling should usually be applied annually.
An unopened can of antifouling pretty much has no expiration date but is at least good for a year. An opened can should be used up completely if possible. If you are unable to do so, airtight packaging will allow for longer stability of the product.
The drying time very much depends on the respective product. Please refer to the product data sheets for the respective products on our website or contact our customer service.
Antifouling is usually not thinned. If it has thickened, however, you can thin antifouling paint so that it is easier to brush. Be careful though, because if thinned too much, it won't be as effective. Antifouling thinner is used to clean tools and to remove spillage marks. Before using thinner, find out whether it is suitable for your antifouling. If you have any further questions, please do not hesitate to call us.
Specific regulations with regard to the private use of antifouling are in place in the Netherlands. The use of antifouling products that contain biocides is only allowed if you are in possession of a special authorization number. An authorization results in relatively high costs for the manufacturers. SVB does not sell an antifouling that is approved in the Netherlands. Approved antifouling products are easier to locate directly where you live. Of course, you can always use antifouling that does not contain any biocides, such as Hempel‘s Silic One.
If you want to apply antifouling in Scandinavia, make sure you are well informed about local legislation. In Sweden, for example, you can obtain lists of permitted antifouling agents from a government testing centre.
Express shipping of antifouling and other paints and varnishes is unfortunately not possible since these products are considered hazardous goods and cannot be shipped airfreight.
The antifouling temperature should be between 10 and 30°C and the humidity should not be above 65%, since humidity could affect drying of the product. Never apply antifouling in direct sunlight or when the underwater hull has been warmed by the sun. Try to avoid applying antifouling when it’s windy.
We recommend application a few weeks prior to going to water or as close as possible since the active ingredients of the paint already begin to diffuse shortly after application. In that case, antifouling might lose its protective features, if it is applied too early.