With such a big array of choices for antifouling boat bottom paint, the task of selecting the right one can be daunting. Read on to learn which one is right for your boat!
This column is part of a 2 part series on boat paints. This section will focus on anti-fouling bottom paints where the following section will focus on top paints. We’ll link to the top-side paint section article once it’s ready. Subscribe to Floatways updates so you don’t miss any of the great articles.
Antifouling boat paint is a something that thousands of boaters and sailors worldwide need to consider and learn about. It’s mainly for boat owners that leave their boats in the water for extended periods of time to help prevent the growth of algae, barnacles and other organisms on the part of the hull that is submerged underwater. Most bottom paints reduce growth by releasing toxic materials called biocides at a controlled rate. The idea is that enough biocides are released to control growth but keep environmental contamination to a minimum. Important environmental issues of antifouling paint will be discussed at various points during the article.
There are many different types of paints depending on usage. Since we will be mentioning various specific products from a number of brands throughout this feature, let’s first look at some of the most popular anti fouling paint brands:
Antifouling Boat Paint Brands
- Interlux
- Pettit
- AWLGrip
- West Marine
- Z-Spar
- Rust-Oleum
Types of Antifouling Paints
There are various types of anti-fouling paints, this even across the same brand. The reason for this is because different boats, locations and usage requirements call for different types and formulas. Additionally, budgets and price points can also determine the various formulas a manufacturer offers based on price. One good example of location affecting bottom paint is the state of California. California has very stringent requirements for Volatile Organic Compounds and requires the use of low VOC antifouling bottom paint. Furthermore, apart from looking after the environment and sticking to codes and laws, location affects antifouling paint formula choice based on whether it will be used in fresh or saltwater, and on the temperature of the water, which causes variations in the amount of fouling. A boater in northern climates would likely choose a specific paint if he has to haul the boat out for the winter. A boater in the tropics, where his boat will spend the entire winter in the water, would likely choose something different.
A boater in northern climates would likely choose a specific paint if he has to haul the boat out for the winter.
Some bottom paints like the Interlux Trilux 33 work well across a wide range of surfaces and conditions such as fresh or saltwater. Paints like this are generally good not only for fiberglass hulls, but also for wood or aluminum hulls and other metal underwater parts such as drives and outboards when primed properly. For this reason, and even though they work across a large range of substrates, they are sometimes considered specialty paints.
On the other hand, there are other anti-fouling paints that are a lot more specialized. Many of them are not safe to use on aluminum and oftentimes cannot be left out of water. Meaning that for the paint to remain effective the boat must be left in the water. If you store your boat on the hard, or you transport it on a trailer often between water-time, be sure to select a bottom paint that can be left outside. To further explain this, let’s look at the different types of antifouling paints in a little more detail:
- Modified Epoxy – Hard and durable bottom paint that works well in various types of waters. It’s recommended that a modified epoxy paint with a higher content of copper is used in areas that are more highly susceptible to fouling, such as the tropics. It’s generally a paint that should be repainted often – every 1-2 years. It doesn’t like to be out of the water as it hardens too much and then looses its effectiveness. If you haul the boat out of the water every year for winter you might was well repaint before launching in spring. If you live in warmer climates and the boat stays in the water through winter you might be able to get away with keeping the same paint for 2 years. These paints are hard so unless you strip them before repainting you will end up with thick build up. Modified epoxy paints with low copper content are generally less expensive but are better left for low or medium fouling areas.
- Ablative (also called polishing) – These paints have a moderately hard finish that actually wears away slowly over time. This allows for a fresh and effective layer of copper biocide to always be acting to prevent fouling. Because it wears away the boat does not end up with heavy buildup over time. Some ablative paints are meant to be reapplied every year but others allow a thick application that can be reactivated after cleaning by scrubbing or light sanding and polishing, hence the name. Multi-season ablative paints cost more than modified epoxy paints but can end up costing less in the long run because of the less frequent reapplication. Some ablatives also include slimicides to help prevent growth of algae by preventing photosynthesis. An example of a muti-season ablative paint is Pettit Hydrocoat, which also happens to be easy to clean, less toxic and less smelly because it is water-based. Unlike epoxies, multi-season ablatives are OK out of the water. Ablatives that use Cuprous Thiocyanate, like Pettit Vivid and Interlux Trilux 33 allow for more bright colors than traditional paint. Cupruos thiocyanate paints are safe to use on aluminum boats where the cuprous oxide paints react with aluminum and damage them. Even though Cuprous thiocyanate paints are safe on aluminum boats, owners should still prime their hulls with an appropriate epoxy primer for specifically for use on aluminum.
- Thin Film – These paints are very slick and organisms tend to have a hard time attaching themselves to it. They are used in fresh water and because of their super-slick properties are quite popular on fast boats and racing sailboats. They provide their antifouling protection using a combination of a copper biocide and the paint’s super slick characteristics. A very popular thin film paint is Interlux VC 17m with also contains Biolux, a branded slimicide to slow down photosynthesis and prevent the growth of bio-film which is the initial stage of fouling. It’s a paint that dries super fast as well.
- Vinyl – Vinyl type paints are hard and durable. The coating can be polished smooth to help with speed and fuel efficiency. They are usually also compatible with saltwater but they don’t quite provide the protection that modified epoxies offer. However, they are smoother and slicker so as long as you keep it clean can result in a faster boat. Vinyl paints don’t play well with other types of paints. The hull needs to be cleaned, sanded and prepped well before applying vinyl paint in order to assure good adhesion. Painting over existing vinyl paint with vinyl paint is possible but the existing coat most be very well sanded and cleaned.
- Soft – These types of paints are not as popular anymore. They last more than a season and they will wear away with motion, meaning the more you use the boat the more the paint will wear away. They used to be quite popular in colder climates. Unfortunately, due to the fact that they are very soft, you usually need to scrape it off and clean the hull before applying other types of paints.
The Antifouling Biocides
Anti-fouling paints use various different chemicals called biocides to help prevent the growth of a thin layer of organic material called biofilm, which then leads to the growth of algae. In turn, that leads to barnacles and other little creatures attached to your boat making it really slow, heavy and really ugly. Typically, bacteria creates this slimy biofilm. The biocides (as the name implies) essentially kill such bacteria on contact to prevent the formation of biofilm. As you can imagine, this is not so good for the environment. The dissipation of metal such as copper (one of the most popular biocides) prevents organisms from adhering to the hull. However, there are other biocides that are way more toxic than copper, most of which have been banned. More on that below.
Biocides:
- Cuprous Oxide (an oxide of copper) – Most of the off-the-shelf antifouling paints these days use mainly copper as the main biocide to control fouling. Copper is regarded as less damaging to the environment than TBT (Tributylin Moiety – very toxic) and therefore replaced it as the standard biocide for bottom paints. It’s regarded as safer than TBT but of course there is still quite of bit of debate as to how safe it really is. Even so, more studies and developments are leading to other alternatives in the near future. Due to high concentrations of copper found in harbors by organized studies, there is a big chance of copper also being banned in many areas. While there was a time where TBT was used as the main biocide, copper has been in use for many, many years before TBT. Cuprous oxide is the main biocide used in popular anti fouling paint such as Z-Spar “The Protector”, West Marine PCA Gold, Interlux Ultra and Pettit Trinidad among many others.
- Copper Thiocyanate – This type of copper is sometimes referred to as “white copper.” It’s supposedly cleaner and safer than cuprous oxides and results in paints with better colors. Used in some Pettit Vivid and Interlux Trilux 33 bottom paints. Copper thiocyante is safe to use on metals, including aluminum as long as proper priming of the substrate is done.
- Econea™ – Branded metal-free antifouling additive used by Interlux and Pettit in some of their paints. Claimed to be safer for the environment. Its degradation products are claimed to be biodegradable. Also, paints that use this antifouling agent can be produced in brighter, more vivid colors. One example of antifouling paint that uses Econea is Interlux Pacifica Plus which also happens to use the next biocide mentioned below…
- Zinc Omadine – It is essentially an antibacterial and antifungal agent. When used in antifouling paints it’s basically a slimicide because it helps prevent the collection of bacteria that causes the slimy bio-film that leads to fouling.
- Tributylin Moiety TBT – Mentioned earlier, TBT is very toxic even to larger organisms and therefore banned. – In other words… DON’T USE IT.
The chemicals used in modern antifouling paints that help prevent photosynthesis near the waterline are sometimes known as “slimicides” because they prevent the formation of “slime” (biofilm) that’s usually boosted by sunlight. These slimicides can be found in paints by their trademark names such as Irgarol and Biolux. Call them slimeacide, fungicide or algaecide, the point is they kill the bacteria that causes the growth. The zinc omadine mentioned above would fit perfectly in this bill.
There are of course non-toxic alternatives that create hydrophobic or hydrophilic surfaces. Hydrophobic antifouling coatings create a low friction surface that makes it hard for larger organisms to attach to. The problem is that once the boat is stationary for an extended period of time, a biofilm will cover the hydrophobic chemicals and fouling with larger organisms begins. For this reason, there are some paints that do contain copper in smaller percentages, but make up for that lower content with a slick hydrophobic surface.
Most bottom coatings on crafts in relatively clean, well-flushed marinas on boats that are always in the water should be serviced and cleaned by a professional diver at least once of month. For boats that require clean hulls to go fast, such as racing sailboats this is even more important. Otherwise you’re not going to be winning any races dragging around junk stuck to your hull.
Preventing Blisters
When preparing a hull to be bottom painted it’s a great idea to seal the gelcoat with a protective blister-preventing product. These products help create a sealing layer between the paint and the hull that prevents water to be absorbed into the fiberglass which is the cause of blistering. You can use a product such as Pettit Protect to do this job. Another very popular product for this job is Interlux InterProtect 2000E Barrier Coat System. These products are great for both older and newer boats to help prevent blistering in the first place. By the way, to apply a gelcoat blister protectant you need to REMOVE ALL BOTTOM PAINT and clean with a fiberglass solvent. The hull needs to be bare gelcoat with not a bit of paint for it to bond properly and do its job. Obviously, applying the sealer to a new hull is much easier because the prep work is much less. You just need to completely clean the hull to remove any mold release agents from the factory. You can do that with a fiberglass solvent. Then, sand the gelcoat with 80-100 grit sandpaper to get the surface ready before you can apply the barrier coat.
Tips When Painting
Allow the Correct Drying times – Most paints require a minimum and maximum drying time allowed before launching. Meaning, if you don’t wait enough, the paint won’t be cured enough for the water and if you wait too much, the paint will harden too much and start losing its effectiveness.
Check the Weather and Prepare Accordingly – If you will be doing the prep and painting job outside (as most people would) be sure to check the weather and plan accordingly. Look for a good long window of good weather for final prep work, application and drying time of the paint. Obviously, the cleaning process in the early prep work is not so crucial on a fiberglass boat as opposed to a metal or wooden boat, but once the final stages of prep work are underway, weather conditions become increasingly important. What you will be looking for is logically, no rain, but also knowing the temperature, humidity and dew point of the air is very important.
- Dew Point – It’s important to know the dew point of the surrounding air to be aware of the possibility of condensation over the painted surface as it cools down as the solvents evaporate during drying.
- Humidity – The humidity of the air is important to know as well. Too much humidity in the air can result in the air not being able to evaporate the solvents quickly enough, which equals slower dying times.
- Temperature – Temperature for paint application is a very important factor. There is a temperature range in which paints are formulated to dry and cure effectively. See the instructions and recommendations on the label of the paint you choose to make sure you apply it and let it dry in the optimum temperature range.
- Relatively Humidity – Relative humidity is a measurement of the amount of water vapor present in the air compared to the maximum amount of water that can be held at a given temperature. If the relative humidity is measured to be 50% at 75˚F it means that the air is currently holding half of its capacity to hold water vapor at 75˚F. Air that is completely saturated with water and cannot hold anymore would be quoted at 100% at a given temperature. When humid air contacts a cooler surface, the water vapor in the air, if enough, will condensate (turn into water droplets) – This is the dew point mentioned earlier. Check the label of the paint you choose to see the manufacturer’s recommendation for relative humidity. Typically, if the relative humidity is high, say 80%+, chances of reaching dew point on the painted surfaces are nearly assured. You can measure relative humidity using a hygrometer but local forecasts can also provide enough information.
Other Things to Keep in Mind
Wear protective gear before working. Using a mask, gloves, eye protection and proper skin protective clothing is absolutely essential. Make sure the filters you use for your mask are rated to protect from the chemicals you will be working with. Not all filters are the same.
Don’t sand too early, it can mess up and break the paint film. You want the paint to at least be “through-dry”.
When adding additional coats it’s important to do it at the right intervals. If the paint is too fresh you might damage the coat already applied. Follow the paint manufacturers instructions on how long to wait between coats.
It’s not good to paint in direct sunlight or if the hull is excessively hot. This can be detrimental to the final quality, look and durability of the final paint job.
Before painting over old antifouling, make sure to choose a paint that is compatible with the old paint already on the boat. Most major paint companies have a compatibility chart that shows what paints are compatible with others. If the paint you want to use is not compatible with the one currently on the hull, it would need to be removed.
Different paints have different primer requirements. Check with the paint manufacturer to find out what primer to use and how many coats are necessary.
Before you get started be sure you have all the materials that you need. Take special care to ensure you have enough paint. The last thing you want is to run out of paint before you are done.
Do the research on the best application methods. Applying by hand with a roller is very effective for bottom paints, but application with a spray gun is not uncommon.
Avoid painting transducers with the same anti-fouling you use for the hull. There is specialized transducer antifouling paint such the water-based paint made by MDR.
There is specialized inflatable boat antifouling paint available – Pettit makes one. This is paint that is water-based and specially formulated for use on inflatable rubber boats. It also is OK when left out of the water for extended periods.
Where to buy: Of course, you can buy locally, but not everyone lives in an area that has shops with the options you need. Also, as you have learned above, there are many different types of paints depending on your needs. So here’s an idea. Click on the link below to go to one of the more popular options these days. You can either order that one, or search around the site for options that fit your needs based on the guide above. Also helpful, check out the reviews on specific brands by customers who have bought them.
