Antifouling guide
The right underwater coating is essential for a well-maintained boat. A good antifouling protects the underwater hull of your boat and prevents fouling from settling on the surface. It therefore helps to maintain speed and manoeuvrability and contributes to lower fuel consumption.
Important parameters when choosing an antifouling are The type of boat:
- The sailing and travelling speed: Do you own a fast or slow boat? How often do you sail during the season?
- The hull material: most antifoulings can be applied to primed materials such as plywood, GRP and steel without any problems, but not every antifouling is suitable for aluminium hulls and solid wood (e.g. clinker-built boats)
- The geographical location of the berth: Is your boat moored in salt or fresh water, in warm or cold waters, in flowing waters like rivers, in the South Seas or just on land?
- Existing layers of paint: What antifouling has been used previously, are you due for a rebuild or are you the lucky owner of a new yacht? Environmental protection and legislation in the area where the boat will be used: If you want to visit the Netherlands, for example, you may only use a product with a separate "Holland approval"
There are three different types of antifouling: self-eroding antifouling, hard antifouling, and thin-film antifouling.
An environmentally friendly alternative are biocide-free underwater paints and coatings that work without organic biocides and copper or that work physically, e.g. via their surface structure.
Self-eroding antifouling paints
Self-eroding antifouling paints have a soluble resin system with active components that repel or prevent fouling. After activation in the water, the layers of antifouling are broken down in a controlled manner so that there is always a fresh and active layer of biocides on the surface. This ensures a high level of effectiveness during the sailing season, a smooth surface and reduces the build-up of thick layers of antifouling on the hull. In the next season, the new coat can be applied directly after thorough cleaning and without intermediate sanding.
Self-eroding antifouling paints
Self-eroding antifouling paints have a soluble resin system with active components that repel or prevent fouling. After activation in the water, the layers of antifouling are broken down in a controlled manner so that there is always a fresh and active layer of biocides on the surface. This ensures a high level of effectiveness during the sailing season, a smooth surface and reduces the build-up of thick layers of antifouling on the hull. In the next season, the new coat can be applied directly after thorough cleaning and without intermediate sanding.
Self-eroding antifouling paints
Content: 0.5 Liter (€0.00* / 1 Liter)
Content: 0.5 Liter (€0.00* / 1 Liter)
Hard antifouling paints
Hard antifouling paints have a resin system with a high content of water-insoluble components that make the surface hard and abrasion-resistant. The high proportion of bioactive substances and their constant release into the water ensure a high degree of protection against fouling. Due to its hardness and resistance, the antifouling is ideal for fast motorboats, trailer boats and tidal waters where boats can fall dry. Wet sanding the surface with fine sandpaper can be used on regatta boats to create a smooth finish for more speed. As the active ingredients wash out over the season, the surface should also be wet-sanded before the annual repainting to achieve good adhesion for the new coat.
Hart-Antifouling
Thin-film antifouling paints
Thin-film antifouling paints do not work by releasing active substances into the water, but rather through the very smooth surface, which makes it difficult for organisms to adhere. The smooth non-stick surface is created by a PTFE additive. The effect is sometimes supported by biocide components like copper, which are incorporated in the binder. The smooth surface ensures extremely low frictional resistance in the water and thus ensures higher speeds and lower fuel consumption. Thin-film antifouling paints are also characterised by a very fast drying time.
Thin-film antifouling paints
Biocide free underwater coatings
Biocide-free underwater paints and coatings do not use any biocides currently classified as harmful to the environment (e.g. copper). There are biocide-free coatings that are based on colophony and zinc oxide which have a similar effect to self-polishing antifouling paints and can be applied in the same way. Biocide free hard coatings do not contain zinc oxide and are more suitable for trailer boats that are not permanently in the water.
A special group of biocide free coatings are hydrogel and silicone-based coatings. These coatings work through physical properties of the surface. Non-reactive polymers form a so-called hydrogel layer between the hull and the seawater, creating a micro-rough surface which is perceived as water by microorganisms and causes them not to attach to the surface. The silicone makes the surface extremely smooth and flexible, causing microorganisms to easily fall off when the hull travels through water. Biocide-free underwater paints and coatings are particularly suitable for inland waters with low fouling pressure and for areas where biocide-containing antifoulings are banned. In other waters, such as the North Sea and Baltic Sea, these coatings may be less effective against fouling than coatings containing biocides. Regular inspection of the hull during the season and cleaning with a sponge will help to minimise the build-up of fouling in these cases.
Biocide free underwater coatings
Content: 0.7519 Liter (€0.00* / 1 Liter)
How many coats of antifouling paint do I need to apply?
The number of coats of antifouling depends on the product used, the speed of the boat, the composition of the water and the climatic conditions of the area. Most manufacturers provide a recommendation in the product data sheet on how many layers you will need to paint. As a rule, at least two coats of antifouling are required initially. One coat is usually sufficient to renew the protection.
When do I need to renew my antifouling coating?
We recommend renewing the antifouling annually to ensure adequate protection against fouling. When the boat comes out of the water in autumn, the underwater hull should be cleaned as thoroughly as possible, preferably with a high-pressure cleaner.
If the surface is intact:
- Clean the surface with HEMPELS Pre-Clean and fresh water, for example, and remove any non-adhering paint (sand the transitions lightly if necessary).
- Allow the underwater hull to dry.
- Apply one or two coats of the same antifouling.
If the surface is damaged:
If necessary, treat and prime the surface with filler as follows:
- Wet sand the underwater hull with 100 - 240 grit sandpaper or dry sand with the MIRKA sanding discs and an extraction system.
- Clean the underwater hull, e.g. with HEMPEL's Pre-Clean and fresh water.
- Allow to dry.
- Where necessary, fill and prime with suitable products.
- Apply additional primer coats to smoothed and levelled areas to lock in the filler.
- Allow the underwater hull to dry completely before applying primer and antifouling.
- pply one or two coats of antifouling.
If the underwater hull needs to be rebuilt:
- Sand the old antifouling completely down to the primer or scrape off the antifouling and sand the surface smooth afterwards.
- Clean the underwater hull, e.g. with HEMPEL's Pre-Clean and fresh water.
- Allow to dry.
- Apply primer coats according to the product data sheets.
- Apply one or two coats of antifouling.
Roller or brush - how do I apply antifouling?
Applying antifouling with a roller is usually the quickest method for large areas. High-quality foam rollers or a short-fibre mohair roller create a high-quality surface. Brushes are suitable for difficult and rough surfaces, as well as small repairs and hard-to-reach areas.
You can achieve an even surface if you work criss-cross, i.e. both horizontally and vertically, on an area that is not too large. If you are working with a brush, the final brush strokes should only be light and vertical. We generally recommend the use of high-quality rollers and brushes to prevent the rollers from swelling too quickly due to the solvent and the brushes from losing hair.
Roller and brushes
In what weather can I apply antifouling?
Always follow the manufacturer's recommendations, which you can find on the product data sheets. We generally recommend applying antifouling at temperatures between 10 and 25 degrees. The humidity should not exceed 65%. Only paint your underwater hull when it is completely dry. Due to temperature fluctuations and high humidity, condensation often forms on the underwater hull in spring, in which case you must not apply the antifouling under any circumstances. Also avoid direct sunlight on the surface to be painted and do not apply the antifouling.
I do not know which antifouling has been applied to my boat
If you do not know which antifouling has been used when buying a used boat, you can carry out a test to determine it. Wipe the hull surface with a damp sponge. If the sponge changes colour, it is usually a self-polishing antifouling. If no colour remains on the sponge, it will be a hard or thin film antifouling. In the case you don't know which antifouling has been used prior, you can apply a coat of barrier primer, e.g. SEAJET 015 Underwater Primer or HEMPEL Underwater Primer, and only then the selected antifouling. Also follow the manufacturer's recommendations from the technical product data sheet of the new antifouling.
I would like to change to a different antifouling product, what do I need to consider?
If you want to use a different antifouling product, you should first find out which antifouling is on the hull and whether it is compatible with the new antifouling. Most manufacturers publish so-called compatibility charts that show whether the old antifouling can be painted over directly with the new antifouling or if e.g. a barrier primer is required to provide adhesion for the new coating. Processing instructions for changing products can also be found in the technical product data sheets, which you can find in our download area in our webshop or on the manufacturers website.
When do I need to renew my antifouling coating?
There is no general answer as to how long antifouling paint remains effective, as its effectiveness depends on several factors:
- type of antifouling (read the recommendations in the product data sheet)
- thickness of the coating applied
- the speed at which the boat is travelling
- the temperature of the water
- micro-organisms present in the water
- the general condition of the underwater hull (does the colour hold, is it nice and smooth)
To optimise the effect, a new layer of antifouling should usually be applied every year. It may also be sufficient to simply brush out the antifouling, as the antifouling usually wears off more quickly at the waterline, rudder and keel.
TOPLICHT tip for self-eroding antifouling paint: When completely recoating the underwater hull, it can be wise to first apply a coat of hard antifouling after sealing with an epoxy primer (e.g. HEMPEL Light Primer) and only then apply 2 coats of self-eroding antifouling in a different colour. This can save work and money, as it is only necessary to apply new self-eroding antifouling when the colour of the bottom layer becomes visible.