This is the time of year where you are planning your next boating season and before you launch your boat, you more than likely will be repainting her bottom. So what to use? Today paint choices are abound, but the main choice is between; Hard antifouling and Ablative antifouling. Biocides/toxins; When a bottom gets fouled the first sign is a slime covering the bottom called biofilm, which then leads to algae growth which in turn leads to barnacles and other creatures attaching to the bottom. To combat this Bottom paints contain biocides, cuprous oxide being the most popular, which are released at a controlled rate.
Level of Toxins Hard paints contain varying levels of biocides which are released slowly on contact with water. Ablative paints generally contain lower levels of toxins but they are released at a more steady rate as fresh paint is exposed. In addition to Cuprous Oxide many paints now include a slimicide to prevent growth of slime. Slimicides can be identified by the names; Irgarol, Biolux by Interlux, and SR Slime Resistance by Pettit.
Cost of bottom paints; You get what you pay for; Biocides and Slimicide, especially copper add to the cost of the paint and are expensive. Cheaper paints can be OK for colder water with fewer nutrients.
Hard Antifouling dries to a hard smooth finish, but is actually full of very small pockets chock full of biocides. Over time these biocides leach out of the bottom paint killing off growth. After a while, the level of available biocides decreases; eventually offering little or no protection. Hard paints when the biocides have leached out look like swiss cheese.
Positives; Hard anti-fouling paints which work on contact with water are ideal for go-fast boats and racing sailboats, and for boats which have divers clean the bottom during the season.
Negatives; Hard paints lose their effectiveness if left out of the water, (copper oxidises) hence you need to launch soon after painting. Each year that you add hard antifouling the build-up increases and at some point you will need to strip the paint.
Types of Hard paints;
Modified epoxy paints; are one-part epoxies hard and durable which work well in various types of waters. It’s recommended that modified epoxy paint with a higher content of biocides is used in warm water and areas that are more susceptible to fouling. Thin Film (Teflon) Paints; are very slick and organisms tend to have a hard time attaching themselves to it. To get a very smooth surface fewer biocides are used. They are generally used in fresh water due to the low levels of biocides. Vinyl type paints are hard and durable. The coating can be polished smooth to help with speed, also have low levels of biocides but are more effective than thin film paints in salt water
Ablative bottom paints
Ablative paints are engineered to gradually wear away as the boat moves through the water. They work by layers of paint rubbing off exposing fresh biocides. One advantage of Ablatives is there is no paint build-up.
Positives; This is the best type of bottom paint for boats that spend time out of the water, because the paint does not lose effectiveness when dry.
Negatives; If you spend most of the time at the dock ablative paints will not work as they need water moving over their surface. Also if you have a fast boat too much paint will be removed leaving you with a bare bottom. Also do not dive on ablative antifouling as you will just scrub it off. Using copolymers like Micron 66 on a displacement cruiser, there are examples of boats covering 10,000 miles on one full application.
Ablative paints include;
Ablative paints, self-polish when the vessel is underway, shedding layers which release new biocides. Copolymer paints, binds the biocide to the pigment within an ablative binder. On contact with water a chemical reaction controls and sustains the release of biocides, before the paint wears off. Copolymers since they do not need water movement can work at the dock. Hybrids are the latest in Ablative paints. They claim to have the qualities of hard paints and ablatives. Sloughing paints are the most inexpensive and lowest performing ablative paints. Sloughing paints are very soft. The paint is lost in visible flakes and are single season use only and utilize a soft rosin binder with low copper content.
Water-based ablatives have become available in recent years, with less odor and easier clean-up.
The future of Bottom paint
Copper free paint & other technology
The Netherlands, Sweden and some locations in Denmark have already banned the use of copper and it is coming to the US soon. Washington is the first State to ban copper starting in 2018, and so the search for good non copper paints is being waged by paint manufacturers. Paint manufacturers believe that ECONEA™, a metal-free antifouling agent may be the future of antifouling paint. Econea, is a pharmaceutical product that has a very rapid half-life, and iit disappears quickly in the water. ECONEA-based paints like Interlux’s Pacifica Plus and Pettit’s Ultima ECO are now available.
Biocide-free foul release coatings are beginning to be available to recreational boaters, similar to products like PropSpeed used on propellers.