The Bottom Line on Bottom Paint for Coastal Georgia Boaters Keith Gates, Paul Christian and Keren Giovengo University of Georgia Marine Extension Service 715 Bay Street Brunswick, GA 31520 Many of us just leave the dirty work of choosing bottom paint for our vessel to our local boat repair yard. This is probably a good choice, since most yards know just what type of paint is best for coastal Georgia waters and specific boat construction materials. However, we should also be aware of available choices and what bottom paints are most environmentally friendly. In addition, cost of the paint, how long it will last, boat hull preparation, boat use and long-term economics should concern the boat owner. This publication will examine some bottom paint issues and help you determine which paint is best for your particular application. Discuss the available options with your boat yard and/or retail store when purchasing bottom paints (Figure 1).
Figure 1. Adding bottom paint (http://www.sleepingwithoars.com/Pictures/Bottom%20Job%2010.jpg)
Vessel Marine Fouling In Southern US Waters Anyone who has spent anytime boating in coastal Georgia’s estuarine waters is aware of the large variety and vigorous growth of fouling organisms that readily attach to the bottom of any boat left in the water (Figure 2). The growth robs the vessel of its speed and /or fuel efficiency. Faced with a huge fouling problem, what is the best approach for boaters who plan to leave their
Figure 2. Coastal Georgia fouling organisms (http://crd.dnr.state.ga.us/assets/images/195.jpg) vessels in the water for even short periods of time? Many boaters apply antifouling paint to the boat’s hull to reduce fouling. The other approach is to remove fouling organisms by frequent mechanical scrubbing (Figure 3). Antifouling paints typically contain heavy metals that deter the growth and accumulation of fouling organisms. A once popular ingredient, Tributyl tin (TBT), was shown to be toxic to marine life even at low concentrations, causing sex changes in whelks, oyster deformations, and bioaccumulation in the food web. In October 1987, EPA prohibited the use of TBT containing paints for all non aluminum vessels under 65 feet. TBT bottom paints can still be used on aluminum hulls in coastal Georgia, but they must be applied by a certified boatyard. Remember, copper based bottom paints should never be used on aluminum hulls. The two metals react in salt water, causing severe electrolytic corrosion. As a more environmentally friendly TBT alternative, biocide-free silicone paints are suggested for aluminum hulls. For our rich-productive southern waters, it appears that copper containing antifouling paints are the only currently available practical alternative to frequent mechanical hull cleaning. Neither the US EPA nor Georgia EPD restricts the use of copper containing antifouling paints. However, elevated copper levels in the environment can negatively affect growth, development, feeding, reproduction, and survival at various life stages of: mussels, oysters, scallops, crustaceans, and sea urchins. High copper levels also change the types of phytoplankton found in marina waters. The boater’s challenge is to select the least toxic bottom paint that will effectively prevent or reduce fouling.
Figure 3. Diver cleaning vessel hull (http://www.patriotdiving.com/images/hull.jpg). There are basically two types of bottom paint that discourage marine growth: 1. Ablative or soft paints and 2. Hard paints. Hard paints contain varying levels of copper biocides which are released slowly. Soft or ablative paints generally contain lower levels of copper that are released at a “steadier” rate or more rapidly if the paint is scrubbed, rubbed, or removed by water flow. The impact to Georgia’s aquatic environment overtime is similar for the two paint types, although ablative paints can release larger copper concentrations over short time periods. Non toxic coatings without copper are the most environmentally-friendly option. They contain Teflon or silicone to produce hard slick surfaces that deter fouling. However, these paints are neither presently widely available nor work all that well in Georgia. Antifouling paint discourages the growth of barnacles, weeds, oysters, and other water life on the submersed hull of your boat. If your boat is wooden, it can also prevent marine borers from the eating the wooden hull. If your boat remains in the water year-round, scrape and recoat the bottom with antifouling paint at least every couple of years. Inspect the bottom of wooden boats regularly. The following describes some of the main types of bottom paints available on the market today: Ablative (soft): An ablative paint gradually and constantly wears away to reveal a new surface of copper biocide. It wears from both the chemical reaction with the water and the scouring action of water on the hull. If your boat covers large distances at fast speeds, you can expect to lose a lot of ablative bottom paint. It has two big advantages: as long as the paint remains, it’s 100 percent effective, and it retains its biocidal properties no matter how long the boat is out of the water. Most ablative paints are expensive because they need a minimum of two coats,
preferably three. The paint surface smoothes with boat use, decreasing the amount of drag and fuel consumption. Sloughing (soft): Sloughing paint is similar to ablative paint in that it constantly erodes. However, it is less refined and seems to slough off in coarse flakes rather than disappear discreetly. It uses a softer binder than ablative paint, which translates as less costly. Sloughing paint quickly loses its effectiveness when exposed to air. Modified epoxy (hard): With modified epoxy antifouling paint, it’s the copper that wears away, not the paint. Copper particles in the epoxy gradually dissolve and allow the water to penetrate deeper and deeper until all the copper biocide is used up. Scrubbing epoxy paint reinvigorates the surface, but gradually loses its potency when left out of the water. Although the paint film builds up over the years and occasionally must be removed, an arduous and messy job, epoxy antifouling paint is a good choice for boats left in the water year-round. Vinyl (hard): Similar in action to epoxy, vinyl antifouling paint develops a hard smooth finish that can be burnished for a racing vessel. Like epoxy, it is non-ablative and it loses efficiency out of the water. Vinyl paints must be applied with care, powerful solvents can soften other undercoats, causing them to bubble. Vinyl paint with a Teflon film is smoother than traditional vinyl bottom paint, decreasing drag and fuel consumption.
Carefully follow the manufacturer’s instructions for the proper application of any type of paint. Pay particular attention to required hull preparations before applying the paint. There is no easy answer to the question about which bottom paint is best! If you use your boat infrequently then hard bottom paint may be best. If you keep your boat in the water all the time and do not use it much, then a soft or ablative paint is usually best. However, if you keep your boat in the water all the time (or most of the time) and use it often, then a hard paint may be the best choice. The following chart provides some options to consider as we strive to protect Georgia’s coastal marina waters (Figure 4) (Table 1).
Figure 4. Coastal Georgia marinas (http://crd.dnr.state.ga.us/content/displaycontent.asp?txtDocument=815)
Table 1. Comparison Table of Maintenance Requirements for Hard & Ablative (Soft) Bottom Paints Maintenance Needed Frequency of Repainting
Every 1 to 3 years depending on the thickness of the original application and use of boat Light sanding is generally all that is needed prior to application of new paint
A single coat is applied annually.
Air Quality. Fumes (volatile organic compounds) that are harmful to human health and air quality are released whenever solventbased paints are used. Use water-based paints whenever practical or available
Annual heavy sanding to improve adhesion & prevent build up. If you choose light sanding the resulting build up will need to be blasted or stripped off periodically.
Pressure washing will remove some of these soft paints
Pressure washing will remove fouling growth and possibly paint chips. Very little pigment should be released
Underwater Hull Cleaning
Ablative paints should not be cleaned in the water!
Hard paints may be cleaned by divers if it is done carefully & properly.
Debris. Use the following techniques to keep debris out of the water: - Collect dust created by sanding with a vacuum sander or in tarps. - Blast or strip paint in an enclosed area where debris can be easily captured. - Send collected debris with your regular trash to the landfill. - Encourage any boatyard to follow these pollution prevention practices. Release of Biocides. Boatyards are required by law to remove visible solids from pressure washing wash water before returning it to local waterways. - Solids from hulls painted with hard paints are easily collected in filter cloth, settling basins or even in hay bales. - Inform your boatyard if you have ablative paint. They need to use minimal water pressure, just enough to remove growth but not the paint flakes. Release of Biocides. Be aware that colored plumes (of the paint) should not be visible in the water when hull is being cleaned. If noticed, cleaning should be stopped, allowing paint debris to be removed. - Hard or slick paints may be cleaned while a vessel is in the water as long as care is taken to use the least abrasive material that is practical. - Ablative (soft) paints should not be cleaned in the water. Scrubbing will release paint (or chips) and its associated biocide.
Restrictions on the Use of Marine Antifouling Paints Containing Tributyltin and Copper A White Paper Prepared by Stephanie Showalter, Director Jason Savarese, Research Counsel October 2004 (Updated August 2005).
Environmental Policy Conflicts on the Horizon: Vessel Antifouling Paints, Coastal Water Quality, and Invasive Species Leigh Taylor Johnson and Jamie Anne Gonzalez, California Policy Research Center, University of California, Research Serving California © University of California, August 2006.