How to sail faster, use less fuel, and reduce boat maintenance
Harvey M. Chichester, Durall Manufacturing
Growth on the bottom of a boat can reduce its efficiency by as much as 10%. Once fouling has established a hold on a boat hull it will rapidly spread or “colonize” the surface. Prevention is therefore better than the cure of having to remove the fouling by scraping.
Fouling can pose a safety risk. Heavy fouling growth reduces responsiveness of the craft. The added weight of the fouling can make the boat sit lower in the water than intended. This can have obvious implications in heavy weather conditions.Furthermore, fouling can damage the boat. Prolonged growth of certain types of fouling can damage the substrate of the hull. For example, the natural glues which organisms use to attach to the hull can damage wood and fiberglass. Fouling can also clog water intakes and cause damage to the engines.
Fouling also causes drag. As drag is increased, fuel consumption increases and speed is reduced even to the point where a planing hull may not be able to get on plane. For racing boats, this can be the difference between winning and losing a race.
The best preventive measure is to coat the hull with a specially manufactured boat bottom paint designed to inhibit growth and barnacle attachment, to provide a reduction in friction with the water, and to protect the hull for a long time. The benefits of coating the bottom are less fuel use, faster sailing or motoring, the ability to clean the hull by pressure washing rather than scraping, and less long term maintenance with better resale value.
Antifouling boat bottom coatings are not meant to be cosmetic or decorative. The best boat bottom coatings incorporate the large polytetrafluoroethylene (PTFE) molecule which produces a drag coefficient smoother than ice. One implementation, fluorourethane was originated by the U.S. Naval Research Laboratories (NRL) in the early 1970s. It was a combination of a fluorocarbon (Teflon™) molecule with a urethane molecule. The material was unique in that it provided a surface with approximately the same coefficient of friction as the Teflon®, was hydrophobic, UV resistant, and at the same time provided an abrasion resistance four times that of Teflon. The fluorourethane was originally tested on several ship hulls for the U.S. Navy. One boat tested was a harbor tugboat in Chesapeake Bay. The coating lasted 11-1/2 years compared to a conventional hull coating which lasted only 18-24 months. Of major interest was the fact that no rust or corrosion occurred under the coating.
The best coatings also employ copper. Copper has been protecting boat bottoms from growth since the 1700s when Britain’s Fast Ships, like the Cutty Sark, raced from the Orient to England with cargoes of fresh tea. While tin and other biocides have been used on boat bottoms over the years, the proven standard still relates to the level of copper used. Yet copper is not the only determining factor of how well an antifouling paint will perform. The resin-binder system, the material that holds the paint together, is equally important. In addition to holding the paint together, the resin-binder system determines how fast the copper and other biocides are released. The resin-binder system should be carefully tailored for the amount and type of copper used to obtain maximum efficiency. The amount of copper affects the life of an antifouling coating but the sophistication of the resin-binder system to hold and release copper is far more important to the effectiveness of the antifouling effect. The best antifouling boat coatings release biocide at a nearly constant rate throughout their lives. If the resin-binder is correct, lesser amounts of the highly efficient copper biocide are needed to deliver the best possible performance.
Antifouling coatings will retain their antifouling properties as long as the coating is on the hull. Sanding between coats will add to the longevity of the bottom jobs. By sanding the bottom you can get more coats to adhere and forestall the day when too many coats means that you must remove all the antifouling coatings from the surface and start over. The boat bottom should always be sanded before an additional coat even if it has just been power washed.