Revised by BoatUS editors in April 2012
Copper, or cuprous oxide (a copper compound), keeps marine flora and fauna from growing on the bottom of your boat. Toxicants such as copper, are the key to the effectiveness of these types of antifouling paints. Not all antifouling paints are the same. They contain different amounts of copper, have different ways of releasing the copper, and have different binders (the material which keeps the copper in suspension.)
Amount of Copper
One difference in antifouling paints is the amount of copper the paint contains. Don't be fooled - more isn't necessarily better. The secret to copper's effectiveness is how fast it's released. The percentage of copper a paint contains will give you an idea of how long the paint will last, but remember that binder type, water conditions, boat speed, frequency of boat use, etc. will also affect service life.
Conventional Paint Copper Release
With conventional paints, copper is evenly spread throughout the hard paint film. Once the boat is in the water, the particles closest to the surface dissolve, but the paint itself does not. When the copper dissolves, there is a hole which lets the water dissolve copper further inside the paint. This happens repeatedly until all the copper is gone.
Soluble and Ablative Paint Copper Release
Soluble and ablative paints work quite differently. With these paints, the paint itself slowly wears away as the copper dissolves. This continually exposes new copper. The rate of erosion is determined by a number of factors including the chemical composition of the paint, boat speed, and turbulence. Of course, the thickness of the paint layer determines how long the paint itself will last.