Boat owners quickly discover that the combination of boat bottoms and water almost always yields a very healthy biology experiment…bottom growth! Although we are not aware of a perfect preventative, modern anti-fouling paints are quite effective and considerably healthier for the environment than their predecessors.
As is typical in our times, the available selection can be confusing. We don’t profess to have the “magic bullet” for preventing bottom growth…however; we can explain the basic choices.
SOFT BOTTOM PAINT
The time-tested, affordable, copper based antifouling paint commonly know as “soft” bottom paint has been all but replaced by modern technology. It is moderately effective, especially in cooler waters where growth potential is less than in warmer climates, as it slowly washes off the bottom of your boat. Depending on how heavy an application is applied and how long your boat is in the water, it may be mostly gone by the time you haul the boat out at the end of the season. Pressure washing the hull all but guarantees a very minimal build-up of paint. If you are on a tight budget, soft antifouling paints may be the way to go. There are two notable downsides to soft antifouling coatings- they are becoming more difficult to locate, and once you commit to using a soft paint you must stick with a soft antifouling paint…or remove all the paint completely before applying a different type of paint. This probably accounts for the lack of popularity, and hence, the difficulty in finding this type of paint.
HARD BOTTOM PAINT
Hard antifouling coatings are probably the most commonly used. They tend to have more biocide (generally, cuprous oxide) in them and are more effective because of that. They tend to go up in cost based on a higher percentage of copper in the paint. As hard paints have a tough surface, which can be burnished in many instances, they make good finishes for the bottoms of racing boats (especially sailboats, where every 1/10th of a knot increase in speed counts!)
This hard surface comes with a cost however—paint build-up over multiple seasons. When you notice areas of paint flaking off the bottom of a boat when it’s in storage during the off-season, you can bet that you are looking at multiple layers of a hard antifouling paint. This flaking is the result of layers of paint build-up and separation of the base coat from the hull. When the flaking gets to be too severe, one must resort to the Draconian practice of removing the existing layers of paint down to the hull surface…either by stripping/scraping or by grinding/sanding. In any event, should you find yourself in this situation…remember, the paint dust is toxic, as are most stripping compounds. Protect yourself…gloves, hat, painter’s suit, and a facemask are a must for this job.
ABLATIVE (POLISHING) ANTIFOULING PAINT
In the last 15 years, ablative antifouling paints have gained in popularity for a variety of reasons. They are designed to “dust off” (think of a bar of soap) the outer surface while still having an ample amount of biocide. This allows ablative antifouling paints to work quite well in most environments, assuming the boat is used on a regular basis and the outer layer’s particles are coming off as designed. The great advantage here is that ablative antifoulings, while generally quite hard to the touch, do not build up thick layers of paint that require removal after a period of time. Most often, a pressure washing at haul-out and a quick wipe down with a solvent prior to recoating is all that is required…no scraping or grinding.
There are single season antifoulings and multiple season antifoulings. The single season product will work well for “a season”— loosely defined as for as long as the boat stays in the water, is used regularly, and the antifouling coating lasts (generally, 12 to 18 months, depending on the thickness of the coating.)
Multiple season ablatives work for well over two years and don’t require the boat to be in the water continuously— that is, you can haul-out at the end of a season, re-launch the following season, etc.— until the paint is wearing away.
A common recommendation is that a base layer of a contrasting color of the same ablative paint be used beneath the final coating. In this way it is easy to see when recoating is required while still maintaining antifouling protection.
SPECIAL PURPOSE ANTIFOULING PRODUCTS
Waxes are an alternative to conventional antifouling paints. These are most frequently used on fiberglass boats moored for short periods of time, or kept on trailers, racks, or lifts.
METAL HULLS
When there is a metal based biocide in an antifouling paint, there is always the possibility of a reaction between the metal in the paint and that of the hull. This is a complex physics problem dealing with the flow of electrons from one metal to another. If the flow is from your hull, guess what? You will soon have holes in your hull. Not good. There is nothing quite so disconcerting as realizing that your beautiful aluminum boat has become a giant sieve and can not be repaired. Simply put, either use an antifouling with no metal biocide (or at least one less noble than the hull material), or apply an insulating barrier between the metal hull (this applies to all in-the-water metals: outdrives, etc.) and the antifouling coating. There are a number of great information sources dealing with this topic. We suggest that you consult them.
ENVIRONMENTALLY FRIENDLY PRODUCTS
To think that a product designed to prevent (read “kill”) growth of living organisms on a boat bottom is environmentally friendly is an obvious conflict. We are dealing with toxins and pollutants—however, there are some that are considerably easier on our ecosystem than others. These are all quite new and the jury is out on most of them. That said, they are growing rapidly in popularity, and they seem reasonably effective. Quite frankly, they will be the wave of the future, if for no other reason than they will be mandated by state and federal environmental regulations.
Most of these products use alternative biocides less toxic than copper and tin– or a “slippery” technology, creating surfaces that growth simply can’t get a good hold on.
Water-based antifoulings, as opposed to solvent-based product with high VOC (Volatile Organic Compound) content, have also made rapid gains in popularity—partially because some of the solvent based products have been legislated as too hazardous for general public consumption, while many manufacturers have developed excellent water based products than can be produced more cost effectively. These products, for the most part, have been around long enough to be proven effective.
If there is a caution with water-based antifouling paints, it relates to wooden hulls. Be sure the hull is dry enough to allow the paint to dry properly prior to launching. If the hull is too damp, the paint may not be cured and will lift off when the vessel is launched. Most wooden hulls, if they have been out of the water for over 30 days, are dry enough to apply water-based antifouling paint
SAFETY
Take all recommended precautions listed on product labels. Be aware of the hazards of fumes, dust or product contact with skin and eyes, and flammability. Many antifouling products and their support products can be very toxic.
COMMON SENSE
Conventional wisdom dictates that one gets what one paints over—so, surface preparation is important. Be sure that you can apply that hot new antifouling paint that you want over the existing paint.
You may want to use a conversion coat over “soft” bottom paint, rather than remove it. If you need to remove the existing paint, do so carefully, being sure not to damage the hull surface. If you have a fiberglass hull, when you are down to the hull surface, consider applying an epoxy based barrier coating on the hull. This will prevent further water migration into the fiberglass. If you have osmotic blistering, now is the time to address that situation. Consult product literature, as this process is well beyond the scope of this advisor.
Be sure the hull surface to be painted is roughed-up and cleaned with a solvent wash, so the paint will adhere properly to the hull surface.
Metal hulls, especially aluminum, should have an insulating barrier coat applied to the bottom prior to application of antifouling paint.
Read the product labels. All antifouling products are not created equal. Manufacturers will stress using specific procedures or their own proprietary products. While shortcuts may be possible as well as non-proprietary products (such a thinners), cheap insurance usually includes following the manufacturer’s recommendations to the letter when prepping a bottom and applying antifouling products. Fixing a failed “bottom job” tends to make one consider giving up boating.
Naturally, always feel free to consult with us here at Hamilton Marine for professional advice regarding antifouling products—or anything else regarding your boat. We will do our best to give you all the information you’ll need to do the job right…the first time.
