I have always believed that if you prostrate on your back and eyeball the bottom of the boat, your view mirrors what a flounder must see in its day-to-day life. But where the flat fish has the good fortune to swim away, you’ll probably be applying a fresh coat of antifoulant paint.
Each time I paint a bottom, I convince myself that I’ll never do it again, only to repeat the process whenever marine growth tries to enjoy a free ride at my expense. I recall old salts in the boatyard telling me about wooden hulls that were launched with soft bottom paint still wet or tacky to promote season-long protection. Today’s antifoulant paints have evolved into various concoctions that deliver yearly and longer protection with prices that match their virility.
Seasonal paints, for instance, leach out biocide or toxicants and lose effectiveness over time, as well as when they’re exposed to the air during dry and winter storage. This means a fresh application is necessary the following season. But because the previous film remains in place, good results also require a careful cleaning and sanding to remove some of the old layer to prep for the new coat to adhere.
The weight of multiple coats of old paint must be avoided to prevent flaking that creates a rough, coarse running surface, which will hinder the effectiveness of the paint and the boat’s performance. The main advantage of a seasonal paint is that it works around the clock whether the boat is used regularly or spends most of its time at the dock.
Multiseason paints have an ablative formula that repels marine growths such as barnacles, algae and slime by incorporating biocide in a paint film that gradually wears away as the boat moves through the water. The ablative paint constantly wears away like a bar of hand soap, and thus retains its effectiveness for multiple seasons, unaffected when exposed to air. By avoiding a buildup of heavy, yearly coats, the surface is burnished smooth for better performance, speed and fuel economy. It may be necessary to slip on a light refresher coat at the waterline or in areas where the paint has worn through, but I have gone longer than five years on some of my boats without the need for a complete repaint.
When applying a multiseason paint for the first time, it is common to start with a different color than the eventual topcoat shade. The forward-thinking strategy is that when you see the color of the undercoat peeking through, it means you have worn out the strength and protection of the topcoat and need a thorough and fresh application.
Paint manufacturers insist that in order for multiseason paints to work as advertised, you need to get the boat away from the dock and let water pass over the bottom. If your boat is a dock queen, ablative paints may not be your best choice. If in doubt, ask the yard’s paint foreman for his opinion based on how much you use your boat.
I am often asked which bottom paint is best, but I maintain that if you are satisfied with what your current paint is providing, the best plan is to stay with it. Changing paints can pose problems if solvents in the paints vary from one formula to another. One solution is to employ a water-based antifoulant paint that can generally be applied over most any paint with no solvent odor, and with simple soap-and-water cleanups.
A thorough bottom job also includes addressing the underwater hardware, such as the running gear. A dubious, though common tradition is to apply a coat of bottom paint to the struts, props and prop shafts, rudders and trim tabs. Many boatyards recommend Propspeed, a biocide-free, foul-release coating in lieu of paint. It provides excellent slime and barnacle protection for a couple of seasons, and its effectiveness is not compromised when boats are removed from the water for repairs or winter layups.
Whichever process you choose, remember to leave clean metal surfaces for attaching zinc anode collars for prop shafts, rudders, trim tabs, keel coolers, and bow and stern thrusters, all to protect the metal from galvanic corrosion.
