The Best Way To Apply Bottom Boat Paint

Painting the bottom of your boat is a critical task if you store your boat in the water for any part of the year. A clean hull is safe, fast, and efficient, while a fouled bottom will reduce your boat's speed and cost you more at the fuel dock. This article will provide a step-by-step guide on how to put bottom paint on your boat, ensuring a smooth and efficient process.

Choosing the right bottom paint

Type of Bottom Paint

The two main types of bottom paint are hard bottom paint and ablative bottom paint. Hard bottom paint is a durable, modified epoxy paint with a higher ratio of pesticides, typically copper. It is suitable for boats that remain stationary or have minimal movement in the water. Ablative bottom paint, also known as self-polishing bottom paint, is a newer technology that is softer and allows the coating to wear off at a controlled rate, exposing a fresh layer of paint with active protection. This type of paint is ideal for boats that are frequently used or trailered.

Boat Usage and Storage

Consider how you use your boat and where it is stored. If your boat remains in the water year-round, a hard, high-copper-content modified epoxy paint may be more suitable as it continuously releases biocides upon contact with water. On the other hand, if your boat is frequently used and trailered, a copolymer ablative paint might be a better option as it does not lose its antifouling ability when exposed to air.

Regional Considerations

The type of bottom paint you choose may also depend on your regional location. For instance, boats in coastal areas with higher sunlight exposure may require bottom paint to deter rapid marine growth. Additionally, certain regions may have specific guidelines and regulations for bottom paint to meet eco-friendly standards.

Hull Material

The type of bottom paint you select should be compatible with the material of your boat's hull. For example, aluminum hulls require a specific type of paint that does not contain cuprous oxide to prevent galvanic corrosion.

Previous Paint

If you are recoating your boat, it is crucial to ensure compatibility between the new paint and the existing coat. Refer to paint compatibility charts to determine the right choice. If the old paint is incompatible or in poor condition, you may need to remove it completely and start with a fresh surface.

Performance and Aesthetics

Consider the performance characteristics and aesthetics of different bottom paints. For instance, copolymer ablative paints offer multi-season protection and efficient copper usage, while paints containing ECONEA as a biocide provide a brighter range of colors. Choose a paint that aligns with your priorities in terms of protection, speed, and appearance.

Preparing the boat

Step 1: Choose a Suitable Work Area

Select a spacious area with good ventilation, ideally an open-air location like a boatyard or marina. If you are working indoors, make sure the space is well-ventilated to dissipate paint fumes. Lay down a large tarp or drop cloth to protect the surrounding area from paint spills and debris.

Step 2: Stabilise the Boat

Use jack stands and blocks to securely support the boat. If your boat is on a trailer, you may need to lift it off and position the stands and blocks accordingly. Ensure the boat is level and stable before proceeding.

Step 3: Clean the Hull

Start by power washing the hull to remove any dirt, loose paint, grease, or marine growth. For heavier fouling, use a strong acid-based bottom cleaner, but be sure to wear protective gear, including eye protection, a respirator, and rubber gloves. Once the hull is clean, allow it to dry completely.

Step 4: Sand the Hull

Sanding the hull creates a rough surface for the paint to adhere to. Use 80-grit sandpaper and a sanding block or a dustless DA sander to lightly sand the entire bottom of the boat. Pay extra attention to high or uneven areas, aiming for a smooth finish to minimise underwater drag. Be cautious around through-hulls, transducers, prop shaft struts, and other metal parts to avoid damage. After sanding, wipe down the surface with a solvent wash and a clean rag.

Step 5: Tape Off Areas Not to be Painted

Use a suitable masking tape, such as 3M's 2090 Scotch Blue Painter's Tape, which can be left on for up to 60 days. Start taping from a natural breakpoint, creating a smooth, even border. Tape around metal parts, transducers, prop shaft struts, and through-hulls to avoid galvanic corrosion.

Step 6: Gather Your Painting Tools and Supplies

Ensure you have the necessary tools and supplies for the painting process. This includes your chosen bottom paint, appropriate thinner and solvents, paint trays, roller frames, solvent-resistant rollers, paintbrushes, drop cloths, rags, tack cloths, paint buckets, stirring sticks, and personal protective equipment (PPE).

Step 7: Check Weather Conditions

While you can't control the weather, try to pick a favourable time when temperatures are in the recommended range for painting (50°–85°F) and humidity is below 65%. Avoid extremely cold, hot, humid, or windy conditions, as these can impact the quality of the paint job.

Using the right tools

To put bottom paint on a boat, you will need the right tools. The first step is to select the right bottom paint for your boat. If you are painting over an existing coat of bottom paint, you must ensure that the new paint is compatible with the old paint. Choose a paint that suits your boat's usage and the type of paint previously applied. Softer paints, for instance, can be applied over harder paints, but not the other way around.

Next, you will need to prepare the boat's surface. This involves removing old paint, dirt, grease, and marine growth. Power washing, brushing, or scraping are effective methods for cleaning the surface. After removing loose paint, wipe down the surface with a solvent wash and sand it with 80-grit sandpaper. If there is a barrier coat, exercise caution to avoid sanding through it. Repeat the solvent wash and clean the surface with the thinner recommended by the paint manufacturer.

Once the surface is prepared, it's time to select the appropriate masking tape. Choose a "long-mask" tape designed for bottom painting, which can be left on the surface for an extended period. Tape as close to the existing boot stripe as possible, creating a smooth and even border. Remember to tape around metal parts such as transducers, prop shaft struts, and through-hulls to prevent galvanic corrosion.

For painting, use the right accessories based on the type of paint chosen. Avoid spraying, as it involves serious toxic hazards. Instead, opt for rolling, which works best for most bottom paint applications. Use a solvent-resistant roller cover or a solvent-resistant foam roller for thin-film paints. You will also need chip brushes of various sizes to cut out around the masked areas and the waterline.

Before painting, stir the paint thoroughly and pour it into a paint tray. Roll the paint evenly from one end of the boat to the other. Apply extra coats in areas of turbulence, such as the bow, rudder, and leading edge of the keel. Follow the manufacturer's recommendations for drying time between coats and the maximum time the painted surface can be left out of the water.

Selecting a suitable location

Weather Conditions

It is best to apply boat paint when temperatures are in a moderate range, such as 50°–85°F, and humidity is below 65%. These conditions ensure the paint dries and cures optimally. If you don't have a temperature-controlled space, plan your project around the forecast to get as close to these conditions as possible.

Well-Ventilated Area

Bottom paints often contain solvents and toxic chemicals, so adequate ventilation is essential. Choose an outdoor location or a well-ventilated indoor space to protect yourself from inhaling toxic fumes.

Surface Protection

Bottom painting can be a messy process, so it's important to protect the surface underneath the boat. Consider using a large tarp or drop cloth to cover the entire work area. This will catch any paint drips or spills, making cleanup easier and preventing damage to the ground or floor beneath.

Accessibility and Maneuverability

Select a location that provides easy access to all parts of the boat's hull. If you need to move the boat, ensure you have the necessary equipment, such as jacks, stands, and blocks, to raise and support it safely. Additionally, consider the ease of reaching different areas of the hull during painting. You may require extension poles for rollers or brushes to reach higher sections.

Environmental Compliance

Before choosing a location, check for any environmental regulations or restrictions specific to your area. Some places may have rules regarding the disposal of old paint and the use of certain types of paint due to their impact on the aquatic environment. Ensure you comply with these regulations to avoid fines or legal issues.

Safety Considerations

Bottom painting can be a hazardous task, so prioritize your safety and that of those around you. Select a location away from high-traffic areas to minimize the risk of accidental contact with hazardous materials. Ensure the area is well-lit and free from obstacles that could cause trips or falls. Have a first-aid kit nearby in case of any accidents.

Applying the paint

Before you start painting, ensure you have the right paint accessories for the type of paint you are applying. Spraying is not recommended for DIYers, as it involves serious toxic hazards. Instead, use a roller, and for most bottom paint applications, a 3/8" nap solvent-resistant roller cover is the best match. Thin-film paints are too runny for such a heavy nap and are best applied using a solvent-resistant foam roller cover or by spray with an airless sprayer.

Make sure to get a few sizes of chip brushes to cut out around the masked areas and at the waterline.

Paint manufacturers’ instructions will give single-coat square foot coverage and recommend the number of coats needed for optimum protection. Don't try to economize on paint by thinning it excessively (most bottom paints are applied unthinned) or by spreading it too thin. Ablative paints, in particular, must be thickly applied. Apply extra coats in areas of turbulence, such as the bow, rudder, and leading edge of the keel.

Have the paint shaken just prior to application. This will make stirring the copper back into solution much easier, because it will settle into a thick mass at the bottom of the can, making stirring a real chore. After thoroughly stirring the paint, pour it into the paint tray and roll the paint evenly from one end of the boat to the other.

As you choose your paint and schedule your haulout, consider how much drying time you should allow between coats and how long the new paint can be left out of the water. Drying time between coats can vary from ten minutes to 16 hours or overnight, depending on the paint. For example, Teflon-based VC-17m has a drying time of ten minutes, while Trilux 33 has a drying time of 16 hours or overnight. For proper planning, it is important to check the manufacturer’s recommendation in advance, both for the drying time and for the recommended number of coats.

Once the paint is dry, remove all masking tape and clean up the area. Be sure to properly dispose of the old paint and any solvents used for clean-up.

Frequently asked questions