How to find and apply the right antifouling for your boat Treating your hull, especially the area below the waterline with antifouling, is especially important to ensure long-lasting, worry-free boat use and great performance. A well-maintained underwater hull ensures easier maneuvering, more safety and lower fuel consumption. In this guide to antifouling, we answer the most frequently asked questions about underwater painting and boat antifouling. Do you already know which antifouling you want?

What is antifouling? Why should I use antifouling? What happens without antifouling? To prevent fouling, mussel and snail growth, it is unavoidable to treat your boat with antifouling in the spring. This applies to all boats that are in the water for a longer period of time. The underwater coating prevents organisms, such as barnacles, but also zebra mussels, and plants, such as algae and mud, from nesting on your hull. Most antifoulings contain biocides, such as copper, to prevent these deposits. However, there are also other products that are more environmentally friendly, such as SILIC ONE products from the Hempel brand. The top three reasons why you should paint your boat with antifouling and what would happen without antifouling:

The boat glides through the water easier and faster! Deposits and contamination make your boat heavier and the frictional resistance increases. This directly affects the maneuverability and speed of your boat.

Easy steering maneuvers! Contamination of the propeller, bow thruster or steering gear can have dangerous consequences. The boat’s response time to steering maneuvers is longer than usual. In the worst case, it can lead to complete failure.

Lower fuel consumption! Due to the 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 benefits 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 contamination.

Provides better boat control. • Save fuel through lower resistance in the water. Do I need antifouling for my trailer boat? If you own a trailer boat and take it out of the water after every use, you don’t necessarily need to use antifouling. Nevertheless, you should regularly clean your underwater hull and clean your boat with a steam jet after each use. If your boat is in the water for several days, we recommend treating the underwater hull with antifouling. The antifouling on my boat is still in good condition. Do I have to reapply? 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 layers and more on the thickness of the layer. To apply a new layer, follow these steps:

Clean the underwater part of your hull with fresh water. For best results and to remove loose antifouling particles, use a pressure washer.

Sand the old antifouling in slightly wet condition.

Rinse off the sanding dust with a suitable product (eg International Super Cleaner). Just rinsing with water is not enough in this case, because the fine abrasive particles will settle in the sanding grooves, which affects the effectiveness of the antifouling.

Repair any damage or minor imperfections where the antifouling has come off. A step-by-step guide can be found in this Video

If you use the same antifouling that you have used before, you can easily start applying antifouling. One layer is sufficient to renew the protection. I bought a new boat.

Do I still need to apply antifouling? Absolute. New boats generally need a coat of antifouling. A new boat with a GRP hull that comes directly from the yard has a layer of wax for protection. This must be completely removed before applying the antifouling. My boat has never been treated with antifouling. How do I apply antifouling? In general, all materials should be completely free of grease, dust and moisture before applying primer and then antifouling. Super Cleaner works perfectly for degreasing. Dirt, oil, wax and grease residues are a thing of the past. Before applying antifouling, prime your surface. International Gelshield 200, a fast drying epoxide primer, is especially suitable for GFRP boats. International Interprotect or International Primocon is a reliable product for aluminum, lead, steel and wooden surfaces. Please also refer to the product data sheets regarding the intervals between layers.

After cleaning and priming: Start by applying your antifouling. Even if the antif ouling is in good condition, a new coat should be applied at the end of the season.

New boats, straight from the yard, should also be treated with antifouling. • Thoroughly degrease, remove dust and dry before the first treatment.

Trailer boats only need to be treated with antifouling if they have been in the water for several days.

Hard or soft antifouling – which antifouling do I need? Hard antifouling, as the name implies, forms a hard surface and is especially suitable for fast motor boats, trailer boats and boats in dry marinas

Self-polishing antifouling, also called self-eroding antifouling, has a polishing effect. Both antifouling and growth are slowly eroded as the boat moves through the water. This type of antifouling is perfect for sailboats

Slow polishing / semi-polishing antifouling prevents the formation of thick layers and is suitable for fast boats. The smooth surface is created by the addition of PTFE and thus also results in higher speeds and less fuel consumption. In addition, no thick layers of paint are built up

Polishing Antifouling for propellers and drives

For propellers, there is special antifouling that usually comes in an aerosol, which makes application a lot easier.

How to choose the right antifouling

Many types of antifouling are made for boats made of GRP, wood and steel. The choice of anti-fouling paints for stainless steel and aluminum boats is somewhat limited. Watch out!

How fast you sail your boat and how often or for how long is also an important factor in choosing the best antifouling

Where the boat is, eg in which waters, is important when choosing antifouling for your boat. In some waters there are more underwater organisms, in others less. Fouling varies with temperature, sunlight, salinity (salt or fresh water), current and water quality, so different types of antifouling are more or less appropriate depending on these factors.

It is also important to note that not all antifoulings or the ingredients used in their formulation are allowed in every area, water or land. For example, many antifoulings are banned in the Netherlands and parts of Scandinavia. Tip: Wherever you are, the Mediterranean, the Baltic or Lake Constance, you can always find out which antifoulings are particularly suitable.

Antifouling over other layers

Since subsequent coats of antifouling must match existing coats, you are limited in your choice of antifouling unless existing coats are completely removed. I have bought a new boat and I am not sure which antifouling has been used before If you are not sure which antifouling has been used before, perhaps because you have bought a used boat, you can first apply a coat of barrier primer (eg International Primocon) and then the antifouling.

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

Completely remove existing antifouling, e.g. Interstrip AF.

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

quantities for your substrate.

To determine how much antifouling is needed, you must first calculate the entire surface area of ​​your underwater hull. This varies slightly depending on whether you own a motorboat, a short keel boat or a long keel, as you can see in this table from the manufacturer International: The practical yield (m² per liter) of the different antifouling products is stated in the respective product data sheets that you can find on our website. The required amount in liters can be calculated with the formula: total surface area / recommended coverage of the paint concerned.

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

As mentioned above, antifouling contains biocides and other substances that can be dangerous to humans. We therefore recommend that you read the product labels carefully and, if necessary, protect yourself with clothing or other equipment when using antifouling. When sanding, use protective gloves, safety glasses and suitable mouth/nose protection with particle filter. We recommend wearing overalls to protect the exposed skin and your clothing.

What items and tools do I need when painting antifouling?

To make applying antifouling an easy and quick process, you need the right equipment and tools. Think of rollers and brushes for applying antifouling, masking tape for masking the areas to be treated, but also suitable thinners or cleaning agents for cleaning your brushes and equipment. If the old antifouling is no longer in good condition, you may have a scraper, a good grinder with matching accessories or a product to remove 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. For International VC Offshore EU and International VC 17m only, the manufacturer recommends roller only application. Using a roller when applying antifouling is usually the fastest method for large areas. The quickest, but not necessarily the most perfect result is to apply with a lamb hair or short fiber mohair roller, as these can absorb more paint. Using a foam roller takes a little longer, but the result is a smoother surface and higher quality. Brushes are perfect for difficult and rough surfaces, as well as for minor repairs and hard-to-reach areas. Using a brush in these areas allows more paint to be absorbed. An even surface is possible when you paint back and forth, both horizontally and vertically over a not too large area. The final brushstrokes should be light and applied vertically. It is important to clean the brush approximately every 30 minutes as paint residue can dry out on the brush and create an uneven surface.

We generally recommend the use of high quality brushes for antifouling application to prevent fine bristles from sticking to the freshly painted hull.

Overview of articles & tools for applying antifouling

• The required amount in liters can be calculated with the formula: total surface / recommended coverage of the relevant antifouling.
• You need the right protective clothing: Gloves, safety glasses, mouth-nose protection with particle filter and possibly protective overalls. • The right tools make the job easier: rollers, brushes, tape, brush thinner, paint scraper and sander.
• You can apply antifouling faster with a roller, but brushes are suitable for rough surfaces and hard-to-reach places. Follow the manufacturer’s instructions.
• Move back and forth in a cross to get an even surface.