What bottom paint works best for a boat that is trailered between uses?
My 19-foot fibreglass motorboat lives on a trailer and usually comes out after each day's boating in salt water. Occasionally I leave it afloat for a fortnight on holiday. Do I need antifouling, and which type will survive launching and retrieving?
Answer
For a boat launched for the day and stored on its trailer afterwards, clean, unpainted gelcoat is usually the best bottom finish. For longer stays afloat, choose an antifouling explicitly approved for repeated hauling and relaunching, with enough abrasion resistance to withstand your trailer bunks or rollers.
Count the days afloat
Base your choice on the longest continuous spell afloat, rather than the number of trips each season. Fouling takes time to establish. A boat that dries between day trips needs different treatment from one spending several summer weeks on a mooring.
- Day trips: normally leave sound gelcoat unpainted, then rinse and remove slime after recovery.
- Occasional weekends afloat: cleaning after retrieval may still be enough; check how quickly growth develops locally.
- A fortnight or longer afloat: consider antifouling, particularly in warm, nutrient-rich salt water where growth can establish quickly.
These are starting points, not guaranteed fouling-free periods. Inspect the waterline, transom corners and shaded areas first. Slime often appears there before obvious weed or shell growth.
A biocide-free finish may also suit short immersion periods, especially where local rules require it. Restrictions vary by country and waterway, so check what is permitted where you launch. Freshwater and small dinghies can be subject to particularly strict rules.
Check drying and abrasion limits
If you need antifouling, check whether it retains its protection after drying ashore. Look for explicit approval for trailering and repeated launch and recovery, along with details of any treatment needed before relaunching.
A suitable multi-season ablative or self-polishing antifouling gradually wears away, limiting paint build-up. Soft formulations can rub off onto bunks and rollers, leaving bare strips along the hull. Choose a product whose manufacturer specifically supports your use.
Hard antifouling generally resists handling and abrasion better, but hardness alone does not make it suitable. Some conventional hard paints lose antifouling performance if left ashore too long. Others permit relaunching after specified preparation.
Check these points on the product data sheet:
- Suitability for repeated drying and relaunching.
- Minimum drying time before launching and maximum launch interval.
- Suitability for your boat's maximum speed.
- Compatibility with the hull material, primer and existing coating.