A complete guide to yacht antifouling paint
Written by Michael Henson
Last updated: 19/09/2016
Antifouling paints work by releasing a controlled amount of biocide (such as copper) from the paint surface into the microscopic layer of water immediately next to the hull. It is this layer of biocide that stops the fouling from setting. Modern antifouling paints are purposely formulated to release just the right amount of biocide to keep the surface clean throughout the season, without the need to scrub the hull.
Why use antifouling paint?
There are three reasons antifouling paint should be used:
1) Safety - Heavy fouling growth will reduce the responsiveness of a yacht as well as making it sit lower in the water, due to the extra weight. Fouling can also grow unevenly across the bottom, making the boat off balance, potentially making it uncontrollable. This can have serious implications in challenging weather conditions.
2) To prevent hull damage- Fouling can burrow into hull coatings, opening up the surface and allowing water to come in contact with unprotected metals and fibreglass. This can cause corrosion to metals and blisters in fibreglass through osmosis. These problems are expensive and time consuming to repair.
3) Speed and efficiency - Fouling causes drag, which in turn reduces speed. Therefore, more fuel is needed to drive the boat through the water to maintain the same speed. For racing boats this can make a big difference when competing. An increase in fuel consumption will not only cost more, but will also have an environmental impact due to increased air pollution.
What types of marine antifouling paints are there?
There is a wide variety of paint available to meet all sorts of fouling growth challenges. Below are three of the most common paints.
- Polishing action provides controlled biocide release giving long term performance
- Wears away with use
- Reduced maintenance, due to minimal build-up
- Haul and re-launch without need to repaint
Hard paint (Contact leaching)
- Hard, durable, season-long finish
- Resistant to abrasion and rubbing
- Suitable for fast crafts and crafts on dry moorings
- Scrubable finish
- Fluoro microadditive for speed
- Smooth low friction surface that increases speed, reduces friction, reduces fuel consumption.
Checking if antifoul yacht paint is compatible?
If applying a first coat to a yacht for the first time then it’s vital to make sure to use paint that is compatible with what was on the hull prior.
The first step is to try and establish what the old antifouling was. If unsure, wet the boat and rub the hull to find out whether it’s hard or soft. The general rule is that you can put soft on hard but not hard on soft. However, products have now changed and in the many ranges allow hard on soft.
How to apply antifouling paint to your superyacht
Antifouling can be applied using a brush or roller. Using a small roller is less work on the arm but takes longer to cover the surface area. If a brush is preferred, choose a large width brush; the finish will not be as smooth as a topside paint so the type of brush used is not critical.
- Health and Safety - Before commencing preparatory work, ensure the area is ventilated. Ensure the correct PPE is worn; including nitrile rubber gloves, overalls and a solvent mask.
- Inspection - Check for areas of damage, separation or peeling, or any other indications that the existing coating is not firmly adhered to the substrate.
- Preparation – in good condition - High-pressure fresh water wash, to remove loose antifouling; ensuring all residue and wash water is contained and disposed of. Allow drying. Check for compatibility.
- Preparation – in poor condition - If existing antifouling is cracking, peeling or showing signs of detachment this should be totally removed.
- Masking/tape off - Before priming or applying antifouling, mask off the area to be painted.
- Repair/priming - Repair damage where necessary. Inspect GRP for gelcoat damage and signs of osmosis – treat accordingly. Remember to pay particular attention to drying times and overcoating intervals.
- Application - Mix paint thoroughly with a stirring stick, ensuring that any settlement is mixed in. Apply according to label recommendations, using a brush or roller.
Apply the antifouling at the correct thickness; this may mean an extra coat is needed, depending on application methods and conditions.
Apply an extra coat to leading and trailing edges; e.g. waterline, trim tabs, outdrives, keels and rudders. These areas experience more water turbulence and so more wear on the paint surface.
Follow over coating times and immersion times carefully. Failure to do this could result in detachment, blistering or cracking of the antifouling.
The marine environment is harsh for paint so it must be allowed to dry thoroughly before immersion.