Are you a boat owner? Do you understand the importance of antifouling your watercraft? Selecting the right antifouling for your boat is critical to ensuring you keep it maintained and seaworthy.
Having the latest model outboard motor or sails and rigging is pretty useless to you if you have half of the Great Barrier Reef growing in the bottom of your boat.
Fouling on the hull reduces the performance of your boat. Even the smallest amount of fouling creates drag in the water, reducing the speed and handling of your watercraft. So, how do you antifoul your boat?
This post unpacks everything you need to know about this vital maintenance task.
- What are the Different Types of Fouling?
- How Do I Remove Old Fouling?
- Method 1 – Dry scraping
- Method 2 – Chemical Strip
- How to Prepare the Boats Keel for Antifouling
- Do I Need to Prime My Hull Before Antifouling?
- How Do I Apply Antifouling?
- Which Is the Best Roller to Use for Antifouling?
- How Do I Paint Under Cradle Pads?
- How Do I Paint a Boot-Top Line?
- What Type of Anti-Fouling Formula Do I Need?
- How Do I Mask a Straight Line?
- Tips for Anti-Fouling Stern Gear and Propellers
- Wrapping Up
What are the Different Types of Fouling?
Fouling, otherwise known as “biofouling,” is the term for the accumulation of organic matter on the hull of your boat. The hull can provide a happy home to plants and organisms like coral.
This fouling occurs on all submerged surfaces, just jump into the water at the dock and take a look at the underwater structure. You’ll see all types of biofouling growing around the beams.
There are two categories of biofouling, macro, and micro-fouling. Macrofouling is the larger pieces of organic matter like mussels, barnacles, squirts, and tubeworms.
Micro-fouling includes microscopic organisms like bacteria, slime, and algae.
How Do I Remove Old Fouling?
If the bottom of your boat is coated with fouling and in terrible condition, you owe it to yourself to strip the fouling and recondition the hull. Leaving the fouling on the vessel damages the structure of the hull and reduces the watercraft’s performance.
Antifouling your boat is a tremendous task requiring skill and effort and plenty of time. Most boat owners shudder at the thought of having to recondition their hull, and many decide to let the professionals handle the hassle of the job for them.
However, if you’re on a tight budget, you’ll have to antifoul; your boat yourself. While it’s not the most pleasant experience, you’ll learn a lot during the process. DIY fouling requires a systematic and patient approach to the project.
You can use one of the two common antifouling methods for reconditioning your boat. Choose the process that suits your boat and your budget.
Method 1 – Dry scraping
Dry scraping the hull is the most common and probably the most effective method. However, it’s also the most labor-intensive method of the three. When using the dry scraping method, your success with your project depends on the tooling you use for the job.
You have three tool options for the dry scraping method. There’s the traditional push-scraper, the Bahco pull-scraper with a tungsten blade, and the triangular scraper.
Each of them has a different effect on the dry scrapping method.
The Bahco tungsten scraper provides you with the best performance, followed by the triangular scraper. It’s critical that you keep the blades sharp during the process to reduce the effort needed in scraping the hull.
Top Tips for Scraping
Before you start scraping, round off the edges of the scraper blades to prevent them from damaging the gel coating on the hull.
Use a file to keep the blades sharp while scraping, and lay down some plastic sheeting or a drop cloth to catch the fouling and paint.
Method 2 – Chemical Strip
Scraping is hard work, and we think it’s a better idea to let chemicals take care of your antifouling duties. A chemical strip offers you an effortless way to recondition the hull. However, it’s important to use a chemical stripper safe for use on GRP surfaces.
We used “Marine Strip” as our preferred chemical solution. You’ll find Marine Strip in chandleries, and it’s relatively inexpensive. However, the stripper requires around 12-hours to penetrate the fouling. Apply it to the hull and leave it overnight.
The viscosity of the stripper is somewhat thick, preventing it from running off the hull. Wait until the paint on the hull starts to change color before stripping away the paint and fouling using a stripping blade.
You’ll find the paint and fouling come off the hull like butter, making for a super-easy stripping. Remove all the points, right down to the primer. You also have the option of using a high-power pressure washer to strip away the paint and fouling.
Top Tips for Chemical Strips
If you’re leaving the stripper on the hull overnight, we recommend you cover the hull with cling film to prevent the stripper from gassing off and drying. Working with chemicals is dangerous. Make sure you have the right PPE for the job. Pick up some gloves and overalls and a pair of safety glasses to protect your eyes.
Paint the stripper onto the hull using a wide paintbrush with synthetic bristles. In areas of the hull with thick fouling layers, you might need to use multiple applications to get through all the organic matter.
How to Prepare the Boats Keel for Antifouling
Boats with steel keels are challenging to restore if the fouling starts eating into the surface. You’ll find there are pucks over the keel that reduce the performance of your boat. Remove the paint and tackle the rust and corroded areas of the keel.
You can use a wire brush attachment mounted to a grinder to remove the fouling and strip the keel down to the bare metal. Shot blasting the keel is also an option for an easy finish. After you complete the strip, apply a rust remover like “Fertan.”
Wipe off all the rust and make sure the keel is clean and dry before you start the reconditioning process.
Fill all the pucks on the keel with a solvent-free epoxy filler material. We recommend using epoxy over a polyester filler if you’re working on anything below the waterline.
After you finish the foiling, let it cure and coat the keel with an epoxy primer. The keel root is the most common area where fouling and corrosion start. Make sure the keel structure is firm by wiggling it with your hands. If it feels loose, then you’ll need to consult with a professional to see if the bolts are loose.
Do I Need to Prime My Hull Before Antifouling?
Yes, priming your hull is necessary before painting if you want a long-lasting finish with the best protection for your boat.
Tie-coat primers ensure the antifouling sticks properly to the keel and hull. If you’re just painting over the old paint, you’ll need to check that the two types of paint match
so they don’t cause a chemical reaction that ruins the paint. Fortunately, most modern paint formulations are compatible with each other.
If you’re stripping back to the gel coating on the boat, we recommend you use a primer for the best results. If you’re painting over flaky areas, you’ll need to prime these areas before painting. Scrape the damaged paint away and feather the edges of the affected area with fine sandpaper to ensure the repaired area blends into the rest of the hull.
Specialist antifouling formulations contain Teflon, allowing for a friction-free surface for racing boats. However, these fouling’s are not compatible with other paints and primers.
How Do I Apply Antifouling?
After you finish the prep work for the hull and keel, it’s time to get down to the business of antifouling your boat. We recommend you apply the antifouling in the late afternoon or the early morning when air temperatures are low, and there is less moisture in the air.
Place a plastic drop cloth on the floor to catch any overspray and prevent dust from rising to stick to the paint as it dries. Most antifouling products require two coats for the best results. If you’re painting in cold weather, we recommend keeping the can of paint inside a warm room overnight.
This strategy allows the paint to flow better, reducing the need for spreading while making it easier to work within a sprayer.
Follow this step-by-step process for epic results when you’re ready to apply the antifouling.
Stir the paint well using a stick. The biocides in the formulation will settle to the bottom of the tin. Stirring helps to blend them into the rest of the paint formulation. We recommend stirring until you think it’s properly mixed, and then keep going for another minute or two for certainty.
Don’t mix new batches of paint in an old tin. You might experience an adverse chemical reaction changing the color or the consistency of the paint.
Pour a small amount of the paint on the roller tray at a time to prevent drop, and secure the lid on the tin before you start painting.
Draw chalk lines at one to two-foot intervals to help you systematically apply the paint, preventing you from going over areas twice, saving your paint. The chalk lines disappear under the paint without causing any problems with the adhesion of the antifouling.
Use a fine-tipped brush for painting around the stern gear and the transducers. If you want the smoothest finish possible, have someone follow you with a pad to remove any dribbles and smooth out ridges.
If you have paint left over, apply a coat to the waterline and the leading edges of the keel and rudder. These high-wear areas can benefit from antifouling protection.
Make sure you paint around the cradle pads properly.
Which Is the Best Roller to Use for Antifouling?
While we prefer using a paint sprayer for the best results with the job, we realize you might not have access to one of these machines. If that’s the case, you’ll have to resort to the old paintbrush and roller technique.
We recommend using a sponge roller or mohair roller compatible with gloss paints. Avoid using rollers designed for use with emulsion paints as they will deteriorate quickly and leave fluff on the hull that’s as bad as the fouling, ruining the finish.
For the best results with your antifouling, we recommend choosing a smaller-size roller with a long handle. This roller makes it easier to handle the paint but adds more time to the task.
How Do I Paint Under Cradle Pads?
Painting under the cradle pads is a great idea if you have enough paint. However, it’d be challenging for most boat owners, requiring the correct technique. The best method is to paint around the pads and then get the yard to move the boat before you paint the area.
How Do I Paint a Boot-Top Line?
Painting a boot-top line adds to the visual aesthetic of the boat. If you find that your hull looks slightly yellow at the end of the season, try raising the antifouling level and boot top by a few inches.
What Type of Anti-Fouling Formula Do I Need?
You have several options for paint. Hard antifouling’s like Trilux from International keep the boot line free from any fouling buildup. Unlike many other paint formulations, this antifouling doesn’t contain any copper oxide. Therefore, the paint won’t oxidize on the boat at the waterline.
Standard gloss paint is also an option, and it looks great when it’s dry, providing a shiny effect. However, it’s less resistant to fouling. It’s also important to note that boat owners leaving their vessel in the water may experience bubbling in the paint below the waterline.
How Do I Mask a Straight Line?
There’s nothing worse than finishing your painting job to find the boot-top has a wobbly line. If you want a straight boot line, the key is to take your time and mask the line before you start painting.
When masking the line, use high-quality tape that prevents the paint from creeping under the taped area. Mask the line while standing on scaffolding or stepladder to bring you up to eye-level with the boot line.
You can also have a friend stand back and direct you with your linework, keeping it straight. Pull a long length of tape and lay it while keeping your eye on the line to ensure its straight., You’ll have better success with this method than applying it in short strips.
After you finish your linework, take a few steps back to examine the line and ensure it’s straight.
Tips for Anti-Fouling Stern Gear and Propellers
You have several options for antifouling stern gear and propellers. Adding a highly polished finish to the stern gear and props ensures there is little chance of fouling accumulating in these areas.
You can choose to buff out the metal to a polished finish or apply a hard coat of specialized propeller paint. Send the parts off to the machine shop for professional polishing if you want the best results and a mirror finish that stays fouling-free.
Prevent drips by keeping a rag and thinners on hand to remove them before they have a chance to set and ruin your paint job.
Don’t apply your antifouling vigorously or stretch it further than you should. This approach will possibly damage the primer.
Remember to patch the area around the propeller supports when your boat is in the slings, or ask if they can hold your boat in the slings overnight.
Use masking tape to seal where the overalls expose your wrists. Getting antifouling on your skin is annoying, requiring extensive cleaning to remove it.
Before starting the antifouling process, ensure you complete a thorough inspection of the hull for signs of damage or wear. If you discover any problems, such as osmosis, you’re going to need a professional to handle the repair before you start antifouling.
Repair any surface defects in the hull while the boat is out of the water. Boats with cast-iron keels might have surface pitting on the metal. Fill it with epoxy and smooth it out before you lay the primer.
Using a car epoxy-based body filler is an affordable option. If you have a race boat, you’ll need to spend some time ensuring your keel has a perfectly symmetrical shape, offering you’re the best aerofoil functionality.
It’s a pain in the back to keep bending down to pick up the paint tin or fill the roller tray. Reduce the pressure on your back by placing the cans on a foldable table next to your working area.
Spend some money on a flat-blade paint stirrer. Using a screwdriver will take forever to mix the paint, and using a stick might result in wood shards getting into the paint, ruining your finish. Failing to mix the paint properly means that it won’t stick, reducing the service life of the antifouling.
Before you dip your roller into the paint, wrap the roller pad in a layer of masking tape and pull it off to remove all the small hairs that may end up sticking to the hull.
Keep some wet wipes on hand to remove any paint that splashes onto your skin. Don’t let the paint dry; it will take days to remove it.