Bottom Painting

Written by barrington

Sometimes it’s easy to believe everything was better back in the “good ole’ days.” That certainly seems to be the case with our boat’s bottom paint. There was a sense the antifouling coating we applied to our boat’s underwater surfaces, performed better when they contained a witch’s brew of environmental toxins. Contrary to our fear of anything new and different however, bottom paint manufacturers have been very successful at replacing harmful substances with equal or improved performance.

We remember the toxic coatings of years past working so well and having a long service life, because they contained such high quantities of toxins that no marine life could live on the surface of the paint. Unfortunately, the high concentration of toxins would also leach into the surrounding water and poison other marine life as well.

The negative environmental effects of bottom paint have been improved in two different ways which are often confused with each other. The first is the elimination or reduction of the more aggressive biocides which are overly harmful to marine life. Historically all ships bottoms were red, because red was the color of the highly toxic lead oxide biocide contained in the paint. Bottom paints have also contained biocides of tin or arsenic which are also very toxic to marine life.

Today copper is the most common biocide used in the form of cuprous oxide. Bottom paint manufacturers are seeking and testing replacements for cuprous oxide, because it is strongly suspected all states will have stricter regulations on its use in the near future. Several copper-free alternatives like Econea™ or zinc omadine are currently being used and are showing very promising results. Bottom paint manufacturers have also developed mixes which are able to deliver a reduced amount of biocide to the surface of the paint more effectively, thereby maintaining performance with less toxic biocide content.

The second way bottom paints have been improved is in the elimination of volatile organic compounds (VOCs). Bottom paint manufacturers have developed water based versions replacing the VOC solvents. Water based products are not harmful to the air or atmosphere the way solvent based products are. Water based products also allow easy cleanup with water, eliminating the need for additional solvents typically used for cleanup.

Even in their more environmentally improved versions, bottom paints are still regulated as pesticides, because barnacles and marine organisms attempting to attach to our boat’s bottoms are still “pests” we want to avoid.

How They Work

Traditional bottom paints work by suspending a biocide toxin within a paint resin. The challenge a boater faces today is not finding high quality, environmentally friendly bottom paint, it’s correctly matching the different type of paints to their use and location. There are many variables that must be considered when selecting a suitable bottom paint for a specific application. Variables include — salt water versus fresh water, cold versus warm, active year-round boat use versus seasonal layup.


Ablative Paints: Ablative bottom paints are designed to slowly wear away as a boat moves through the water, exposing fresh biocide as the outer surface wears away. These paints are good for boaters that use their boats often, but are not as advantageous for folks who may not take their boat out more than a handful of times a season.

Hard Modified-Epoxy Paints: Modified- epoxy paints are often called “hard paints,” because they continue to cure and get harder, even after the boat is launched. These paints slowly leach the biocide throughout the paint’s life, regardless of whether the boat is moving or not. This makes them a great choice for boats that may not leave the dock as much as others, but they’re also a good all-purpose paint.

Hard Ablative Hybrid Paints: These relatively new bottom paints offer boaters the advantages of both hard and ablative paints. They’re tougher and more abrasion resistant than typical ablative paints, but retain some of the self-polishing qualities of ablative paints. All good biocide formulations should include a retardant for slime. Controlling soft growth like algae and plant matter requires different ingredients than those used to control hard shell growth. Boats in fresh or very warm water will experience this more than those in cold salt water.

Non-Biocide Hard Finish Paint: Sometimes referred to as “hard-vinyl”, Non-Biocide Hard Finish paints dry to an extremely hard, durable finish that’s tough enough to polish smooth, making them ideal for performance sailboats and high-speed powerboats. The concept behind these paints is for the finish to be so hard and so slick, that marine growth cannot attach itself firmly to the surface.

Secret to Success

Each manufacturer has developed proprietary formulations in the above categories which are unique to them. Success in selecting a bottom paint depends on the following steps:

  • Consult the manufacturers selection charts to match the paint’s features to your specific application.
  • Purchase a high-quality paint from a reputable manufacturer.
  • Whether painting yourself or selecting an experienced boat yard to do the work for you, make sure the existing surface is prepped according to the paint manufacturers specifications.
  • Follow the paint manufacturer’s maintenance guidelines.

The saying “out of sight, out of mind” should not apply to bottom paint. A good quality bottom paint job will save money in fuel consumption in a power boat and a precious few knots of speed under sail. Properly selected, applied and maintained, bottom paint should provide multiple seasons of performance while protecting the investment in your boat.