Above: Copper-free bottom paint colors are brighter than copper bottom paints
Copper-Based Antifouling Paint
The active ingredient in antifouling paints is referred to as a biocide. Copper is one of the most common biocides used in the recreational marine industry. A biocide typically prevents the growth of hard fouling organisms such as acorn barnacles and zebra mussels.
In general, an antifouling paint will be more effective if it has a higher copper content. Commonly, the higher copper content is also reflected in the price of the paint.
Every boater looks for different properties in a bottom paint. Traditional cuprous oxide-based antifoulants are effective, but the colors are not very bold and vibrant, and the true color is not evident until after immersion in water. Cuprous thiocyanate-based antifoulants are available in bolder, more brilliant colors. Whites and brighter colors show more true.
Copper-Free Antifouling Paint
Copper is effective, but it's not environmentally friendly because its byproducts do not break down, and are toxic to marine life. Environmental regulations in certain states have forced many boaters to stop using paints with copper biocides.
Common copper-free biocides include Econea™ and zinc pyrithione. Econea takes on the same role as copper biocide to prevent hard shell fouling, and zinc pyrithione is an algaecide that prevents slime and weed fouling.
Econea (tralopyril) is more environmentally friendly because it breaks down quickly, and the breakdown products are biodegradable, and don't persist in the marine environment. It also takes less Econea to prevent biofouling, compared to copper-based paints. In fact, antifouling paints made with just 6% Econea are just as effective as antifouling paints containing 50% copper.
Copper-free antifouling paints also do not leave a patina at the waterline showing the greenish appearance that can be seen with copper-based antifoulants.
In addition, copper-free paints generally can be hauled and relaunched without worrying about having to abrade before relaunching.