Bottom Paint Essentials Article courtesy of Tim Banse
You already know that without bottom paint dutifully protecting the bottom of a boat that barnacles, zebra mussels, weeds and slime would proliferate dragging down acceleration, top speed and helm response. And that in order to inhibit marine growth we rely on bottom paint. But the big question is with the different types of anti-fouling lining the shelves of marine chandleries which one is the best choice for your boat? The answer is that in order to sort through the many offering it's vital to understand the basic differences between them. Only then can you intelligently pick the right product for your boat and its geographic area of operation. In this story we'll cover the basics and suggest a couple of paints. Unfortunately there isn't room to cover the myriad of brands and offerings.
Let's begin at the beginning. Know that there are two basics types of anti-fouling paint: ablative and hard, each one boasting distinctive properties. Soft ablative paints release biocide at a constant rate throughout their life span, scrubbed away with use much like a bar of soap. One benefit to this scrubbing action is that as the biocide is used up the paint goes away. This characteristic reduces paint buildup, which in turn reduces the amount of surface preparation required before applying a new coat.
Pettit Marine Paint's Ultima SR-60 is an example of ablative bottom paint. It's loaded with copper (60%) and also dual biocides (slime resistant Irgarol) lending multi season protection.
In sharp contrast to ablative blends, hard anti-fouling paints rely on contact leaching. How it works is as simple as the sea is salt. Once the paint dries, the bottom is blanketed with a porous film saturated with biocides. The biocide releases in steadily decreasing amounts. Once exhausted, the hard film remains. Generally speaking, boats with hard anti-fouling coatings cannot be hauled and launched without repainting. One benefit to hard anti-fouling paint is resistance to abrasion. Due to its low drag resistance, hard bottom paint is an excellent choice for high performance boats.
Another Pettit offering is Trinidad SR, a hard anti-fouling, a blend offering multi-season protection thanks to dual dual biocides backed up with a high copper load. Tip: copper content is why gallon buckets of bottom paint are so heavy. Left in the water, a bottom painted with Trinidad SR will enjoy years of protection.
So far we've given examples of ablative and hard bottom paints. How about one that incorporates all the benefits of both ablative and hard paints in one? That would be Pettit's multi-season Vivid offered in a palette of bright colors, including white, blue, green, yellow black and red.
Think whiter whites and blacker blacks. Primary colors can be applied as-is, or blended to create a custom color. Its hard, smooth surface withstands trailering and is easily burnished for lower drag, a godsend on high performance boats. When applied over the recommended priming system Vivid can be used on aluminum hulls and outdrives.
No matter what type or brand of anti-fouling you decide on it's crucial to painstakingly follow directions. Read the label, paying careful attention to the part about surface preparation. At a minimum the existing anti-fouling paint, which provides the foundation for the new paint, must be in good condition, meaning without flakes. Sand the entire bottom with 60- or 80-grit sandpaper, roughening the surface and lending the new paint a foothold. Question: Is this dirty, time-consuming surface preparation a Do-It-Yourself endeavor? Not if you can afford to pay the boatyard to do it.
Make sure the old anti-fouling paint and the new coating are compatible. Consult the manufacturers chart. Thoroughly stir anti-fouling paint before and during application. Usually, the store where you buy the paint will perform an initial shake-shake-shake with its paint shaker. For good reason marine supply stores will only shake cans that have never been opened. That said, even when you stir by hand with a flat wooden paint stick, five or 10 minutes should be sufficient to get all the biocide in suspension. The first few strokes with the stick will be difficult because the heavy compounds settle to the bottom. Be patient. And be sure to scrape down the sides of the can and the bottom to flow all of the ingredients into suspension. Stir the paint frequently during application to prevent settling.
It's absolutely critical that you follow over-coating times and immersion times. In other words, allow the paint to dry thoroughly before applying another coat and before launching. If you don't, you risk the specter of the paint detaching from the hull, and all the time, energy and money you'll have spent will have been wasted. Finally, when finished, dispose of the empty paint cans in an environmentally friendly manner. If you're in doubt about how to do this, any boatyard will be able to tell you the proper procedure. Tim Banse is a marine engines expert and has written about propulsion for Popular Mechanics, Yachting, Motor Boating, Boating Industry and other publications around the world. His current pet project is www.MarineEngineDigest.com, a source for free information about outboard motors, stern drives and inboards. Tim's articles will be seen here and in the iboats.com blog, plus at www.MarineEngineDigest.com.