The short answer is that there is no perfect bottom paint, but there are a few things to consider in order to help select the right one for a given application.
- Cost: Typically, antifouling paints with higher percentages of biocide are more expensive. Other properties that add to the cost of an antifouling paint include multi-season effectiveness, the ability to self-polish even when the boat is not moving through the water, and slime-fighting algaecides.
- Water type: Is the boat going to be used in salt, brackish or fresh water? Is the fouling light, moderate, or heavy where the boat will be kept? The more copper or biocide an antifouling paint contains, the more effective the paint will be. Copper-free paints containing Econea have also proven to be comparably effective on hard fouling organisms like acorn barnacles. However, if slime and algae are a problem in your area, you'll want a paint boosted with an algaecide such as zinc pyrithione (this applies to copper-free biocides, too) or Irgarol.
- Water temperature: Typically, more biofouling occurs in waters that are warm and still, rather than colder waters where water flow is unrestricted.
- Substrate: Bottom paints are only designed to be applied to specific substrates. Some are designed for wood, fiberglass, or primed steel, while aluminum boats and aluminum outdrives and other underwater metals require antifouling paints that don't contain cuprous oxide due to galvanic corrosion.
- Environmental restrictions: Restrictions regulating VOC (volatile organic compound) and copper content in some areas of the country require the use of antifouling paints that are water-based (instead of solvent-based) and/or copper-free to preserve and protect the marine environment.
- Boat usage and frequency of use: How often do you use your boat? Do you have a speed boat, or do you have a slow-moving sailboat? Short boating seasons are OK for a single-season antifouling paint, but if you enjoy a longer boating season, it is probably more economical, and effective, to buy a multi-season paint. If you trailer your boat, consider a harder ablative antifouling paint.
- Compatibility with the previous layer of paint: If your boat has antifouling paint on it, you need to know whether the new antifouling paint is compatible with the previous antifouling paint. As a general rule, if you don't know what the previous paint is or you know that it's incompatible with the new antifouling paint, remove it completely before applying any new paint.