Choosing an antifouling: eroding, hard, biocide-free, compatibility

Weed, barnacles, mussels: within a few weeks, an unprotected hull gets covered in growth that slows the boat down, pushes up fuel consumption and can block the water intakes. Antifouling is the paint that limits this fouling. On the shop shelf, the tins all look alike; yet they do not all do the same job. This guide helps you choose the one that suits your boat and the way you sail. The paint manufacturer’s technical data sheet and the boat builder’s manual always have the last word.

1. Questions to ask first

The right antifouling depends less on the brand than on how the boat is used. Write down your answers before going to the shop or calling the yard:

• Speed: a cruising sailing boat or a slow motor cruiser do not have the same needs as a fast motor boat.
• Time spent in the water: afloat all year, afloat for the season only, or on a trailer or in dry stack between outings.
• How often you go out: a boat that sails often does not wear its paint like a boat that sits at the pontoon for weeks.
• The harbour: drying out at low tide, strong currents, fresh or brackish water (estuary, locked harbour) all change how well products work.
• The plans: an ocean crossing or a winter in the tropics calls for longer-lasting protection.
• What is already on the hull: the type of the old antifouling matters as much as the choice of the new one (see part 3).

2. The main families

• Eroding (or self-polishing): its resin slowly dissolves in the water as the boat moves, which renews the active surface. It does not build up from year to year and keeps the hull smooth. It is the usual choice for a cruising boat that sails regularly. On the other hand, it is not recommended for fast boats, boats that rarely go out, or harbours that dry out or have strong currents, where it wears away too quickly.
• Hard (hard matrix): its resin does not dissolve; the biocides are released on contact with the water and the coating stays in place. It withstands rubbing, copes with drying out, suits fast boats, boats kept ashore between outings and long passages, and can be sanded smooth for racing. The downside: the coats build up over the years, and one day the hull has to be stripped back.
• Semi-eroding: a compromise between the two, for mixed use.
• Biocide-free products: silicone-based coatings do not kill organisms, they stop them from attaching for long; the growth comes off with speed or gentle cleaning. They mainly suit boats that go out often, or that spend little time in the water. Applying them often requires a hull stripped back to bare and specific primers. As Figaro Nautisme points out, “biocide-free” does not mean “maintenance-free”.
• “Seasonal” antifoulings: the cheapest, for short-term protection. They can be enough for a boat that is only in the water for the summer, as long as you accept repainting every year.

3. Compatibility with the old coating

Most conventional antifoulings can go on top of one another, but not all. Silicone or PTFE (Teflon) products accept nothing on top of them: to go back to a conventional antifouling, the hull has to be stripped. Likewise, moving from a thick hard antifouling to another product may require careful sanding and a coat of tie-coat primer. If you do not know what is on the hull, ask the yard to check, or apply a universal primer following the data sheet.

It is one of the most useful pieces of information to keep: the brand, the product reference, the colour and the date of the last application. The next yard, or the next owner, will need it.

4. Special cases

• Aluminium hull: only products intended for aluminium, without copper oxide. A copper antifouling on aluminium causes corrosion.
• Outdrives, saildrives, propellers and shafts: these metal parts need specific products, often in spray cans, applied on their own primer. A copper hull antifouling on an aluminium outdrive quickly damages it.
• What is never painted: the anodes (otherwise they no longer protect anything), the depth and speed transducers unless their manufacturer names a product, and the through-hulls the manual says to leave bare.
• A hull with a problem: if the bottom shows blisters, deal with that before repainting — see blisters on the hull: osmosis or not.

5. Reading the label: what the law says

Antifoulings that contain biocides come under the European Biocidal Products Regulation (No 528/2012). Each product must now obtain a marketing authorisation, issued in France after assessment by Anses, the national health and environment agency. A product without a valid authorisation can no longer be sold or applied. When buying:

• check that the label carries an authorisation number;
• read who the product is intended for: some are reserved for professionals, others remain available to private users with specific protection instructions;
• follow those instructions: gloves, goggles, a suitable mask, covering clothes, and no dry sanding of old antifouling without dust extraction and respiratory protection.

Antifouling work itself is regulated: in France it is done on a boat-maintenance area or slipway equipped to collect wash water and residues, never on a beach or foreshore, where discharging harmful substances is an offence under the Environment Code. In many harbours, the rules also forbid scraping or cleaning the hull while afloat: ask the harbour office. Paint flakes, tins, brushes, tarpaulins and gloves go into the bins provided by the harbour, following its sorting instructions. Other countries have their own rules.

6. How much paint

The coverage is written on the tin; Figaro Nautisme notes that it is generally between 7 and 10 m² per litre per coat. Work out the area of the underwater hull (the paint manufacturer’s data sheet often gives a formula by type of boat), multiply by the recommended number of coats, and add an extra coat on the areas that wear most: the waterline and the leading edges of the keel and rudder. Also respect the time between coats and the minimum time before relaunching given by the manufacturer. For the budget of the whole job, see how much a haul-out and antifouling costs.

7. Doing it yourself or using a yard

Putting another coat of eroding antifouling on a sound hull is within reach of a careful boat owner, on a maintenance area and with the right equipment. A change of family, stripping, an aluminium hull or taking the hull back to bare before a silicone coating are rather jobs for a professional, who has dust extraction or soda-blasting equipment and the products reserved for professionals. The full haul-out process, and what to check while the hull is out of the water, are covered in haul-out and antifouling. To find a yard near your port, see the map of professionals.

The Hullteam logbook keeps the antifouling reference, the date of each haul-out and the yard’s invoice in one place — see which proofs count when you sell.

Sources

Pages consulted in November 2026 (in French).

• Choisir sa peinture antifouling, quelle matrice pour quel usage du bateau ? — Bateaux.com
• Bien choisir son antifouling — Figaro Nautisme (February 2025)
• Graphène, silicone, AMM : la grande mue de l’antifouling — Figaro Nautisme (July 2026)
• Réglementation biocides : les antifoulings Nautix validés par l’Anses — Bateaux.com (March 2026)
• Guide sur les bonnes pratiques de carénage — Iroise Marine Nature Park (2017)