The Lowdown On Bottom Paint

By Frank Lanier

While death and taxes may be better known, there's a third certainty in life many boat owners face that's often viewed with just as much trepidation.

Photo of man painting the bottom of a boat
Photo: Frank Lanier

Ever since our first troglodytic ancestor shoved off astride his trusty log, mariners have tried most every concoction imaginable to keep waterborne critters and growth at bay, from mixtures of tar, sulfur, and brimstone, to paints laced with tin, arsenic, pesticides, and even the occasional jar of chili powder. Although environmental concerns have relegated the most noxious mixtures of yesteryear to the dustbin of history, bottom paint still remains a complex topic. Here's a look at what bottom paint is, its application, and how to find the one that's right for you.

What Is Bottom Paint, Anyway?

Bottom paint (aka antifouling paint) is a paint or coating designed to discourage weeds, barnacles, and other aquatic organisms from attaching themselves to (and in the case of wooden boats, eating) the underwater portion of your boat's hull. Bottom paints have traditionally accomplished this by inclusion of a biocide, with copper being the most commonly used today. In general, the more copper or other biocide a paint contains, the more effective (and costly) it is. Copper replaced tin, the previous biocide of choice for decades, now banned in most marine applications due to the environmental damage it caused while leaching into the waters of the world. While copper may still be king, the latest generation of eco-labeled bottom paints utilize little or no copper, a response to the increased scrutiny copper-based paints have received as potential environmental pollutants.

Bottom Paint — Who Needs It?

If your boat stays in the water year round or during most or all of the boating season, application of bottom paint is pretty much the rule. For boats left in the water for short periods of time (that two-week summer vacation, for example) or that are stored out of the water (trailer, lift, dry storage facility), a good coat of wax and regular cleaning are typically all that's needed to maintain a clean hull.

Tip iconA 3- to 4-foot extendable roller handle will save your back and make painting much easier.

If your boat has never been bottom painted and you're mulling over the idea, make sure you understand that once bottom paint is applied, the die is cast, and that periodic bottom-paint application, cleaning, and renewal become a permanent part of the vessel's routine maintenance schedule. Another consideration is that the application of bottom paint in some cases (particularly on trailersized boats) may be viewed as a negative to potential buyers if you decide to sell later on.

What's Your Type?

Despite seemingly endless choices, traditional bottom paints can be divided into three broad groups: ablative, hard, and hybrid paints.

Ablative (aka self-polishing) paints gradually wear away a tiny bit at a time to reveal fresh biocide as your boat moves through the water (think a bar of soap that wears away each time it's used). One advantage to this is that as long as paint remains on your hull, you know it's working to prevent growth (like that soap bar, which may get smaller, yet still lathers up). Another benefit is that as it's constantly wearing away, there's no buildup of old paint, which can be a pain to remove when the time comes. But ablative paints can be less effective if your boat remains idle for extended periods of time, which denies it that self-cleaning action provided by water movement. The flipside to this self-cleaning feature is that ablatives aren't a good choice for fast-moving boats, which would accelerate the ablation process and cause rapid paint loss.

With hard bottom (aka non-sloughing or hard modified epoxy) paints, it's the copper biocide that gradually wears away (rather than the paint itself), allowing the water to penetrate deeper and deeper into the paint until all biocide is depleted. Hard-bottom paints form a tough, hard coating that holds up well and doesn't wear away, making them a good choice for faster boats. They can even be burnished, allowing racers to squeeze every possible bit of speed from their hull. On the downside, when the copper is depleted, the hard, tough coating remains and it can be messy and difficult to remove, particularly if multiple layers of paint have been added over the years. Eventually this accumulated paint reaches critical mass, becoming so thick it begins to crack and peel, necessitating a complete stripping of the hull.

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DIY Or Yard?

The only allure of doing your own bottom job (cleaning, prepping, and applying antifouling paint) is saving money. It's a messy, tedious job that isn't fun by any stretch of the imagination, but it's not rocket science, either. Owners comfortable with DIY projects can do their own bottom job with satisfactory results, as long as they follow the manufacturer's instructions and rules regarding containment of old bottom paint during removal (as well as proper disposal afterward). Many bottom paints are toxic and have to be treated as such; some even require a pesticide license or other special permit to apply. As such, any potential DIYers will need to ensure they're thoroughly familiar with the entire application process and follow all required safety precautions and practices, such as the use of respirators, protective clothing, etc. In addition, many boatyards have their own rules about boaters taking on this chore.

Paying a professional to tackle the job has several advantages. The time and effort required for a bottom job can (and likely will) be greater than many newcomers estimate, particularly if the hull is in need of substantial prep work prior to painting (i.e. removal of old paint buildup, blister repairs, etc.). The possibility of this "unexpected" extra time should be factored in when weighing the savings of a DIY approach versus the yard, as should the ancillary costs of painting equipment and safety gear.


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