A new coat of paint prevents aquatic life and barnacles from sticking to the bottom of your boat. However, before you start painting, you should prepare the underside of the boat by cleaning, sanding, and priming the keel. Once this is done, you only need to apply 2-4 coats of antifouling paint on the underside. Painting the bottom of your boat once a year will keep it looking good and working for many years.
Part 1 of 3: Baiting the Boat
Step 1. Remove the boat from the water
You must paint the boat on land. You can lift the boat out of the water using a tow hitch attached to a car. Back the trailer into the water via a boat ramp. Ask someone on the boat to gently place the boat on the trailer by lightly pressing the accelerator. Alternatively, you can hire a marina or shipyard to take the boat for you.
Step 2. Clean the bottom of the boat
Use a hose to remove any dirt. If there are hard algae or barnacles on the bottom, take a brush and scrub them. You don't need to use any soap when washing the bottom of the boat.
- You only need to clean the bottom of the boat below the waterline. This is the keel of the boat. Find the boot strip, which is an unpainted edge between the bottom paint and the tops of the boat (which are on the sides of the boat above the waterline).
- To remove stubborn or hardened dirt, use a power washer. You can rent one at a hardware store. A shipyard may also have one on hand that you can borrow or rent.
Step 3. Remove the wax sealer if the boat has never been painted before
New boats will have a wax coating on the bottom. To get rid of it, buy a dewaxing solvent from a marine supply store. Dip a clean cloth into the solvent and rub the wax. Rinse with a clean, damp cloth. It runs the entire keel.
Step 4. Peel off the old paint if the old paint job is significantly damaged
If the old paint job is still smooth, you don't need to remove the paint. If there are bubbles, large chipping strips, or torn chips in the paint, remove the old paint completely. First, apply a chemical paint remover to the old paint job. Use a 2-inch (5 cm) hook scraper to scrape off the paint.
- If you remove the paint, place a tarp under the boat to collect the debris.
- Just lift the paint below the boat's waterline. Don't scrape the paint off the top of the boat.
- If you keep your boat in a shipyard, ask the management if someone can use an electric dynamite on the boat. This tool should only be handled by professionals, but you can remove the paint much faster than doing it by hand. Ask for soda blasting in a fiberglass can or sandblasting in an aluminum or steel can.
Step 5. Sand the bottom of the pot to prepare it for priming
Rub the outside of the keel with 80-grit sandpaper. It should have a dull, "icy" appearance when you're done.
Step 6. Apply the base to the keel with a roller brush
Stir the primer with a varnish. Prime the edges with a brush before filling the center with the roller. Make sure there is an even coat of primer on the keel.
You can buy a good boat primer at a marine supply store or online
Step 7. Sand the primer once it dries
It may take 1 to 2 hours for the primer to dry completely. Use a fine-grit sandpaper to sand the primed surface before you begin painting.
Part 2 of 3: Apply the paint
Step 1. Buy antifouling paint to prevent barnacles and other vegetation from growing
Antifouling paint contains a chemical called biocide, which will kill barnacles, algae, or other growth before it develops on the keel of your boat. There are 3 types of antifouling paint you can buy: ablative, hard bottom, and hybrid.
- Ablative paint is good for slower boats that are in constant use, such as fishing boats or pontoon boats. Ablative paint wears off on its own, preventing you from having to remove the paint later.
- Hard bottom paint is ideal for boats that are fast or not used as often as speedboats. These paints don't wear off very easily, but they are more difficult to remove when you need to apply a new coating.
- There are "hybrid" or "semi-hard" paints that combine the benefits of ablative paint and hard paint. These are good for frequently used powerboats or boats.
Step 2. Stir the paint with a varnish
You can use a piece of wood or a paint stirrer. Stir the paint for at least 5 minutes. If you feel hard chunks on the bottom of the can, press down with the varnish to break them up and keep stirring until the paint mixes evenly.
Step 3. Apply the paint to the keel with a roller
Fill a paint tray about half full with paint. Dip the roller into the paint and spread it against the edge of the tray to distribute it evenly. Start painting at one end of the keel and move slowly to the other. Use a paintbrush to fill in small or difficult areas.
- Don't paint above the waterline. The upper parts of the boat require a different type of paint than the lower part.
- If you need to add more paint to the tray, be sure to stir it into the can first.
Step 4. Sand the boat
The first coat should be dry by the time you finish applying the paint. Take a fine-grit sandpaper and lightly sand the keel of the boat again before adding the next coat.
Step 5. Add a second coat to the boat
Go back to the beginning and use the roller to apply a second coat of paint. This second coat will double the life of the paint job.
- Some paint brands may recommend that you apply 3-4 coats total. If you do, just remember to sand the fin between each one.
- If desired, the top cover can be a different color than the bottom layers. This will help you tell when the paint is wearing off.
Step 6. Let the paint dry for several hours
Drying times may vary depending on the brand of paint you use. Read the paint can to see how long to wait before putting the boat back in the water. In general, it can take several hours or overnight.
Part 3 of 3: Preserve Paint
Step 1. Clean the keel every 4 to 6 weeks
While antifouling paint can help prevent barnacle and algae growth, it may not stop them completely. Make sure to clean up any dirt or growth that sprouts on your new paint job as soon as possible.
- If you used ablative paint, lift the boat out of the water. Use a hose to spray the dirt and scrub the stains with a sponge. You don't need to use soap.
- If you used hard-bottom paint or hybrid paint, you can go underwater. Use your hand or a rag to clean the dirt or algae. You can also hire a diver to clean the boat.
Step 2. Use the boat frequently
Antifouling paints are designed to work best while the boat is moving. The more you use the boat, the more effective the paint will be. If you don't plan on using your boat very often, you may want to store it on land.
Step 3. Reapply the paint once a year using the same paint as before
Mixing paint types can reduce the effectiveness of the biocide. If you used ablative paint before, stick with ablative paint. If you used a hard primer, keep using the hard primer. If you want to switch to a different type, you must completely remove all the paint from the keel.