Antifouling FAQ

Antifouling is a coating for surfaces below the waterline. It reduces the attachment of algae, barnacles and other fouling. Common types include self-polishing and hard biocidal antifoulings. Biocide-free products are offered as underwater coatings or foul-release systems.

The right solution depends on hull material, cruising area, speed, use and the existing coating. The antifouling configurator brings these details together.

Biocidal antifoulings release authorised active substances at the surface in a controlled manner. Self-polishing products slowly wear away during use, while hard antifoulings form a more abrasion-resistant matrix.

Biocide-free systems work without biocidal active substances. Eroding resin systems, hard coatings and smooth silicone surfaces have different modes of action and maintenance requirements.

The key factors are hull material, maximum speed, cruising area and fouling pressure, whether the boat is moored or trailered, and the type and condition of the existing coating. A product may only be used on approved substrates and in a compatible coating system.

Use the configurator for guided selection or the comparison table to compare products directly.

Self-polishing antifouling erodes slowly during use, keeping the surface active in a controlled way. It reduces the build-up of thick old coatings, but must only be used up to the approved speed.

Hard antifouling forms a more abrasion-resistant matrix and, depending on the product, is suitable for fast or regularly trailered boats. It does not polish itself away; cleaning and sanding may be required before later coats.

Biocide-free alternatives contain no biocidal active substances. They include eroding one-component coatings, hard two-component coatings and silicone foul-release systems.

These systems differ considerably in coating build-up, cleaning, repair and suitable use. Check the complete system and its maintenance instructions, not only the product name.

Not always. On a sound, compatible existing coating, careful cleaning and preparation may be sufficient, depending on the product. A suitable primer or barrier coat is required on bare substrates, for corrosion or osmosis protection, on unknown existing coatings or between incompatible systems.

The required primer and number of coats depend on the hull material and intended function. Check the compatibility table and the technical data sheet.

The number of coats is product-specific. Many antifoulings require two coats for first application; one coat may be sufficient for maintenance on a sound, compatible existing coating. Some hard antifoulings require two to three coats.

Biocide-free systems have their own specifications: Seajet 021 EKO, for example, is applied in two coats, while the Bioclean system consists of two coats of Tie Coat and two coats of Clear Coat. The current technical data sheet is always decisive.

1. Support the boat securely and cover the work area so sanding dust and paint residues are contained.
2. Remove fouling, dirt and loose coatings; check the existing coating and compatibility.
3. Clean, sand and fully dry the substrate as specified in the data sheet.
4. Apply the correct primer in the specified system if required.
5. Stir the antifouling thoroughly and apply it with suitable tools in the specified number of coats.
6. Observe overcoating and launch times.

Wear the personal protective equipment specified in the safety data sheet and provide adequate ventilation.

Yes, if the existing coating adheres firmly and is compatible with the new product. Clean and prepare the surface exactly as specified in the data sheet. The compatibility table shows whether direct overcoating is possible or a barrier coat is required.

Flaking, cracked or unknown coatings must be removed back to a sound system. A primer cannot repair poor adhesion.

Old antifouling can be removed mechanically with a scraper and low-dust sanding system, or with a paint stripper approved for the substrate and coating. Abrasive blasting should be left to specialists.

Sanding dust, stripper and paint residues must not enter soil or water. Use extraction, ground sheeting and the prescribed personal protective equipment, and dispose of residues according to local rules. Check first whether gelcoat, wood or metal imposes special restrictions.

Primers perform different tasks depending on the product: adhesion to bare substrates, corrosion protection, barrier action or osmosis protection. One example is the two-component Seajet 117 Epoxy Primer.

An adhesion or barrier coat connects a sound existing coating to the new system or separates unknown or incompatible coatings. Seajet 015 can be used for this in suitable systems. Selection and coat number depend on the substrate and data sheet.

Inspect the coating when the boat is hauled out and before every season. Renewal frequency depends on the product, film thickness, time afloat, use, cruising area and fouling pressure. Annual maintenance is common for many seasonal products, but it is not a universal rule for every system.

Renew the coating when the specified minimum film is no longer present, significant fouling develops or the surface is damaged. A contrasting first coat can act as a wear indicator on self-polishing products. Follow the technical data sheet and the permitted maximum time before launching.

More information

Inspect the underwater hull when lifting or launching the boat. Action is particularly needed where there is heavy fouling, worn-through areas, a visible control coat or primer, cracks, blisters or flaking.

Distinguish between normal consumption of the antifouling layer and an adhesion problem in the underlying system. Loose layers must be removed back to a sound substrate. If the coating is still closed and sufficiently thick, cleaning and a maintenance coat may be enough, depending on the product data sheet.

Preferably clean the underwater hull after haul-out at a designated wash area where wash water and coating residues are collected. Whether in-water cleaning is permitted and suitable for the coating depends on local regulations, marina rules and the product.

Biocidal self-polishing antifoulings must not be scrubbed aggressively in the water: this can remove the active layer and release material. Follow the specific maintenance instructions for hard or foul-release systems that are expressly designed for cleaning, and use only approved soft tools.

First assess the depth and extent of the damage. If only the antifouling layer is locally worn, repair can often wait until the next haul-out. If primer or hull is exposed, the system continues to flake, or metal or laminate is damaged, the boat should be hauled out promptly and inspected properly.

For repair, remove loose edges, prepare the sound area according to the data sheet and restore primer and antifouling in the original coating system. Professional assessment is advisable for unknown systems, blisters or corrosion.

Salinity alone does not determine the product. Consider local fouling pressure, hull material, boat speed, time afloat, use and the existing coating. A high-performance antifouling approved for the application may be appropriate in heavy fouling; depending on the material, a hard antifouling may suit fast or frequently trailered boats.

Seajet 033 Shogun is intended for heavy fouling but not for aluminium. Seajet 034 Emperor A, for example, is approved for aluminium. The configurator accounts for these differences.

Use only products that are expressly approved for aluminium in the technical data sheet. Copper-containing coatings may be unsuitable, but the specific product approval is decisive, not simply whether a coating is labelled biocidal or biocide-free.

Seajet 034 Emperor A is suitable for aluminium. Bare or damaged areas require a fully compatible, sufficiently closed primer system, for example Seajet 117 Epoxy Primer applied according to its data sheet. Avoid direct contact between dissimilar metals and also inspect drives, sacrificial anodes and electrical isolation.

Apply only within the temperature range stated in the technical data sheet. Both substrate and air temperature matter and can differ considerably. Cold conditions extend drying and overcoating times.

The substrate must be dry and free from condensation. Consider humidity, dew point, ventilation and the minimum and maximum intervals between coats and before launching. Allow sufficient reserve for changing weather.

Fouling increases surface roughness and therefore hull resistance. Possible effects include lower speed, higher energy or fuel consumption and changed handling. The extent depends on the type and amount of fouling, hull shape, speed and propulsion.

Inspect not only the hull but also propellers, shafts, saildrives, rudders and cooling-water intakes. A suitable, intact coating system and product-specific maintenance help to limit fouling.

Material costs depend on the coated area, specified number of coats, coverage of the selected system, required pack sizes and current product prices. A complete rebuild may also require several primer coats, antifouling, cleaners, abrasives, masking and protective equipment, depending on the substrate.

The quantity calculator estimates the underwater area. The configurator uses it to calculate the recommended system and suitable pack combinations. The result is a planning aid; hull shape, application losses and actual consumption can change the quantity required.

Store products in their tightly closed original containers as specified on the label and safety data sheet: cool, dry, frost-free, protected from direct sunlight and in a suitable, well-ventilated area. Keep them away from ignition sources, food and drink and out of reach of children.

Mark the opening date on part-used containers and check condition and shelf life before reuse. Two-component products have a short pot life after mixing; mixed residues must not be returned to the original container. Dispose of unusable residues and empty containers according to local rules.

DIY application is possible if the workplace and local rules permit it and you can safely assess the substrate, coating system and protective measures. You need stable boat supports, containment and dust control, suitable personal protective equipment and enough time for the specified intervals.

A professional should handle unknown or extensively flaking existing coatings, suspected osmosis, corrosion, damaged laminate, abrasive blasting or spray application. The number of coats is product-specific and must not be set universally at two or three.

We focus on Seajet so that antifouling, primers, thinners and topcoats can be selected as clear, compatible systems. Technical data, compatibility information and specific coverage figures are available for these products and form the basis of the configurator and quantity calculations.

This focused range also supports informed advice on coating build-up, application and later maintenance. The individual product must still be suitable for your hull material, cruising area and use profile.