Bottom paint

Anti-fouling bottom paint is a specialized covering applied to the hull of a boat, designed to slow the growth of organisms that would attach to the hull and affect performance and durability. Other types of coatings can act as a barrier against corrosion on metal hulls, or improve water flow past the hull of a high-performance racing yacht.

In the days of the clipper ships, sailing vessels suffered severely from the growth of barnacles and weed on the hull which, left unchecked, reduced the maximum speed of the ship and also its ability to sail upwind -- both of which affected profitability. Thin copper sheets were nailed onto the hull in an attempt to prevent this. A visible example of this may be seen on the clipper Cutty Sark preserved as a museum ship in dry-dock at Greenwich in England.

In modern times, paints are formulated with toxic copper compounds or other special chemistry which impede growth of barnacles, algae, and other such organisms. Since such a barrier ablates slowly, it must be renewed periodically.

Some innovative bottom paints that do not rely on copper or tin have also been introduced. These products have been developed in response to the increasing scrutiny that copper based ablative bottom paints have received as environmental pollutants. One brand, epaints, is used by the US Coastguard on all of their vessels and works by producing hydrogen peroxide in the presence of light.