How do I choose the best antifouling paint for my boat?
My 10-metre fibreglass cruiser stays in a saltwater marina from April to October, and I mostly sail at weekends. The old antifouling is sound in places but I don't know the brand. Should I use self-polishing or hard antifouling, and how much preparation does it need?
Answer
Choose antifouling to suit your hull material, local fouling and boat use; self-polishing paint is the usual starting point for a cruising yacht, while hard antifouling suits repeated abrasion and many fast motorboats. Check the existing coating first, because even an effective paint will fail if it cannot bond to the surface beneath it.
Check hull and existing paint
Find last season's tin, invoice or boatyard record before buying paint. You need the product name, coating type and, preferably, application date. Colour alone tells you little.
Inspect the bottom after washing. A sound coating that is firmly attached may need only cleaning and the preparation specified by the paint manufacturer. Loose flakes, widespread cracking or thick ridges mean the weak material must come off. Another coat simply adds weight to a failing surface.
- Fibreglass: most conventional yacht antifoulings are suitable over the correct, sound primer system.
- Aluminium hulls, saildrives and outdrives: use a coating specifically approved for that metal and component. Many conventional copper-based hull paints are unsuitable because of corrosion risk.
- Timber: choose a system approved for the timber construction and existing coating. Traditional soft antifouling remains an option on some wooden boats.
If you cannot identify the old paint, ask the new paint's manufacturer for compatibility advice. A recommended tie-coat can sometimes isolate a sound old coating, but it cannot secure loose paint or make every combination compatible.
Match paint to boat use
Self-polishing antifouling gradually renews its surface, exposing fresh active ingredients. It is the usual choice for displacement cruising yachts and many motor cruisers kept afloat through the season. Annual recoating is common, though service life depends on the product, applied thickness and conditions.
Check the product data sheet for a speed limit. Tell the supplier how often the boat moves, too. Some polishing coatings perform less well on boats that sit idle for long periods, and products differ in their ability to protect a stationary hull.
Hard antifouling leaves its binder behind as the active ingredients are released. Its resistance to mechanical wear makes it useful for fast boats, repeated trailer handling and racing hulls that need a smooth, prepared finish. Old binder accumulates, so expect periodic sanding rather than simply adding more coats.
Traditional soft antifouling erodes more readily and is associated particularly with wooden working boats. Switching between soft, hard and polishing systems may require removal and priming. Follow the specific compatibility instructions.