Your boat’s hull is the perfect surface for marine organisms such as weeds and algae. It also attracts slime and mussels.
Marine growth can cause hull drag, which increases fuel consumption and reduces boat speed. Barnacles can cause pressures to build up on the hull of a boat, especially smaller fiberglass ones.
The removal of barnacles and marine growth can be a laborious and unpleasant process. This is why many boaters use antifouling. It is a biocide which kills all marine growth on the hull.
Antifouling Paints Containing Biocides
Tin was the most popular biocide in anti-fouling coatings for many years. Tin is toxic and therefore banned by the EPA. Copper has been used as a biocide for bottom paint since then, and it’s a common ingredient in Antifoul Paint for Boats to prevent marine growth on hulls.
Copper biocide anti-fouling paints
Include a copper-based biocide such as cuprous oxide, or cuprous thiocyanate. Cuprous oxide has a lower effectiveness and cannot be used with aluminum. However, cuprous thiocyanate can be used to kill marine growth on aluminum surfaces.
Zinc biocide paints anti-fouling
Zinc pyrithione is a biocide that works very well against algae and fungus. It is effective in removing slime, plant growth and algae but not as good against mussels or barnacles.
Copper paints are toxic and expensive in proportion to their copper content. Copper-based bottoms paints are still in use, but concerns over their impact on the environment has led some marinas ban boats that have copper-bottom paint.
Zinc paint is a good protection against UV rays, which can damage gelcoat and fiberglass. It’s also safe to use on aluminum hulls and sterndrives. While zinc-based bottom painting isn’t quite as effective as copper paint, it’s not as environmentally harmful as the latter.
Nonmetallic Biocide
As the environmental impact of metal-based antifouling coatings is becoming more apparent, the shift to non-metallic alternatives for biocide is underway. The copper-free biocides are less toxic and require lower biocide concentrations. Paint manufacturers offer bottom paints containing an anti-slime substance.
Which biocide should I choose ?
When choosing an antifouling paint, it is important to take into consideration the biocide content.
If algae and slime is a problem in your area, you may want to use a zinc-based biocide. However, an area notorious for barnacles might require a bottom paint containing copper. It is also important to take into account local laws and regulations. If you are mooring your boat in a place that does not allow copper biocides then your only option is to use zinc or non-metallic antifouling paints.
Antifouling Paint Types
Ablative antifouling paint
Even after curing, it remains relatively soft. The outermost layer slowly wears away due to the fact that it does not fully harden. Remove the part of the paint that has already released biocide. This reveals a new layer.
Hard antifouling paint
It forms a hard, solid layer on the surface it was painted. When it comes in contact with water, the biocide is activated. The biocide is released without any movement or motion. It gets consumed before the paint. The hull must be repainted once the biocide has been depleted.
What type of paint should I choose?
It is not easy to choose an antifouling coating based on the biocide. Hard bottom paints require more frequent reapplication and have a shorter biocide life span than ablatives. They are more durable, and they don’t wash off. Hard paint is better for boats or speedboats that are often driven at full throttle. Ablative paint has the advantage of clearly indicating when a hull must be repainted. It wears off completely. Boat owners often choose ablative paints with a color that is different from the hull’s to tell when they need to repaint. Ablative antifouling is also beneficial because it doesn’t build up old paint layers and only needs to be repainted once the old coat has worn away.
Antifouling Epoxy and Copolymer Paint
Epoxy antifouling paint
Paints with a hard finish that cures to a solid surface and releases their biocide slowly. These paints tend to have a higher content of cuprous. Epoxy antifouling paint is more durable than ablative paints because it forms a hard, shell-like surface.
Copolymer antifouling paint
Paints with a softer texture that are made using the ablative technique. The copolymer paint formula is designed to release the biocide in a controlled, steady rate. This makes it extremely durable. A standard ablative bottom paint can last for up to three years, while an ablative standard paint is expected to last 18 months.
What is the best paint base to choose ?
Consider the pros and cons for each paint type to determine which one is right for your boat. The biocide in a hard-bottom paint can become permanently inactive after prolonged exposure to air, but copolymer is not affected by long “drying” periods.
Copolymer paint is a better choice for a boat to be stored over the winter. A hard epoxy paint will be better than a copolymer paint if the boat is regularly subjected to wear and tears, such as when it bottoms on shallows.
