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Anti-Fouling Paints and Coatings

Anti-fouling paint, bottom paint or hull coatings are paints applied to the hull of boats to discourage or prevent the growth of organisms that attach to the hull. There are algae, mollusks including zebra mussels and barnacles, wood boring worms plus other critters that love to make the hull their home. These organisms can seriously affect the performance of a boat. They can also damage the hull.

barnacles are one of the creatures that colonize boat hulls

Photo of barnacles, one of the creatures that attach themselves to boat hulls, by MichaelMaggs

Although preventing growth on the hull is the primary goal of anti-fouling paints they are often formulated to help prevent corrosion and protect the hull as well. Some anti fouling coatings help smooth the hull and improve performance.

Historical Note

When Capitain Cook was getting his Endeavour ready, one of the steps that was taken to protect the bottom from the wood boring worms was to cover the hull with a heavy tar covered felt. This was nailed on. Here is my page on protective tar finishes.

Later before before modern anti-fouling paints were developed, wooden boats might be covered with copper sheets or later with a special brass called Muntz metal, to help reduce fouling. As well cleaning and scraping the hull was a regular activity. Barnacles, zebra mussels and seaweeds are quick to colonize a clean hull.

Modern Anti-fouling Coatings and Paints

Anti fouling preparations all aim at reducing or preventing things from attaching themselves to a hull but there are many ways of accomplishing this.

Many modern anti-fouling paints contain toxic materials that are gradually released and essentially poison any growth organisms. This is the case for Copper based finishes Copper is the most common anti fouling additive. It actively works to prevent fouling.

Muntz Metal an Interesting Story

Muntz metal (also know as yellow metal) is a kind of brass containing about 60% copper and 40% zink. It also contains traces of iron.

It was developed and promoted by A Birmingham metal worker called George Frederick Muntz, in the early 1800's.

Muntz metal replaced copper sheathing which had been used before to protect hulls. Not only was it an effective antifouling coating because of the copper content, but it was only about a third of the price of pure copper.

muntz metal used as anti fouling coating on cutty sark.

It's most famous use was probably as the protective sheathing used on the Cutty Sark.
Photo by Cmglee, Wikimedia Commons

I have a page on some research I did on Brass

Copper Based Anti Fouling Paints

Most manufacturers offer a version of paint containing copper. Copper has a long history of being effective as an anti fouling substance. Its antimicrobial/algaecidal properties help prevent biofouling. It is quite effective and relatively non-toxic.

Researchers attribute copper's antifouling properties, to copper's ability to retard or prevent colonizing by fouling agents because it releases toxic copper ions. These prevent attachment of the micro organisms. Copper provides a separating layer that is corrosive to spores and juveniles or encrusting organisms.

An interesting aside is that brass and copper table tops remain much more bacterial free than stainless steel. This is interesting for hospitals and other health facilities that struggle with unwanted infections.

A great deal of research is being done to develop anti fouling alloys. One of the major push is for aquaculture. Bio-fouling in this industry is a major cost and this is a powerful motivator.

Anti fouling of boats has been a major concern throughout history and keeping critters off the hulls is an ongoing struggle.

Copper used in anti fouling boat coatings can be imbedded in many different types of substrates. Copper is found in boat enamels, epoxy coatings and in urethane matrix. The type of paint used helps determine the characteristics of the coating.

Copper based antifouling paints can be recognized by the weight of the paint (the can feels really heavy) or by a separate package of copper that needs to be added and mixed in before the paint is applied. Typically copper based coatings have either a red-pink colour or have a deep dark colour, often green or blue. If a dried copper paint is sanded, it will show the typical copper metallic shine. Some paints contain "white copper" and come in vivid colours and white. Zink is usually added to help improve the action of the copper since white copper is generally not considered as effective at preventing growth as its red cousin.

Some copper based coatings can cause electrolysis and galvanic corrosion.

TBT (tributyltin) was a commonly used biocide, but is mostly illegal for most common purposes because of its toxicity.

Epoxy based Copper Anti Fouling coatings

When epoxy is used as the matrix for the paint, Copper is slowly exposed as the outer layer gets oxidized. Because it is a slow process and less copper is released, epoxy based copper anti fouling coatings manufacturers claim to be more environmentally friendly than other copper based coatings. The major advantage is the long life of the coating, often exceeding 10 years. Preparation must be meticulous. Maintenance is minimal after application. Often a quick clean and occasional abrasion with fine sandpaper to expose new copper is all that is required.

Because epoxy is hard and resists corrosion it is a very successful matrix that can last for many years with little maintenance. The disadvantage of this finish is that it is lot of work to remove when it becomes necessary to re do the coating. Full protection is often recommended with respirators, mask and suits.

Some so called hard coating such as copper-epoxy paint need to be re-coated if the boats are removed from the water. I've seen large patches of coating flake off in the winter after haul out. At that time the finish surface was good but after drying out it peeled off.

The following table is a brief survey of Epoxy matrix with copper anti foul coatings currently offered. It is not intended to be all inclusive and * I have not verified the claims of the manufacturers. So take this information as a general comparison and a place to start your own research.

Manufacturer and Coating Name Description Life Notes
AMC Coppercoat Epoxy based carrier with copper powder added. Copper oxidizes to cuprous oxide then to cupric hydrochloride. This is eventually washed away revealing fresh copper. Not subject to galvanic corrosion because of epoxy carrier is an effective insulator.* 10-12 yrs. Success depends on proper application and preparation of surface. Also the outside occasionally needs to be lightly abraded to expose new copper according to various forum entries.
Home Made Epoxy with Copper Powder added There are many stories of individuals mixing copper powder with epoxy at a ratio of about 1 kg of copper powder to 2 litres of epoxy. The mixture needs to be continually mixed because it settles. Riskier alternative but much cheaper. This might be illegal in some places because anti-fouling coatings are controlled by law. 8 yrs. Preparation is essential.
Boat Craft Pacific Cop-R-Bote Contains a suspension of copper particles in a modified Bote-Cote epoxy system. It coats the hull in a tough sheath of copper metal. Cop-R-Bote is non-ablative and therefore non-polluting, and is economical as it avoids the regular re coating required for all conventional anti fouling. Available in Australia. 5-10 yrs. Preparation is key to success as in other epoxy based finishes.
Sea Hawk Tropikote Sea Hawk offers several different formulation. This is a copper/epoxy anti fouling coating.Sea Hawk Tropikote Blue Gl 2142GL Multi years Sea Hawk has a finish selector app.
Reactive Resins Copperplus The research has resulted in the discovery of a unique non-toxic additive that makes the epoxy micro-porous. The sponge like epoxy binder is mechanically very strong and it does not trap the copper but allows it to easily leach from the entire thickness of coating to the surface, where it forms a protective film that deters fouling. A hardener has been developed which enables Copperplus to be applied at any temperature. The combination produces a coating that is flexible and abrasion and impact resistant. Mechanical damage is easy to repair. Small areas can be re-coated by hand while larger areas can be spot blasted and re-coated. Up to 10 yrs. Long pot life. Un-used portion can be kept in refrigerator overnight.
I question the "non toxic" claim. Copper is toxic. The low release of copper in epoxy makes it LESS toxic than regular copper bearing paints however. (C.D.)

Other Anti Fouling paints containing Copper

Urethane is also often used in Copper bearing finishes. Sometimes other additives are also included. Urethanes can be 1 or 2 parts and some can last as long as the epoxy formulations. Again the surface must be prepared and the finish applied with great care.

Many other preparations and paints are available. They tend not to last as well but are much less expensive. Rosin is a common ingredient. They often contain copper as well.

The term ablative comes up regularly and merely refers to a paint that gradually wears away thus exposing new biocide to keep the anti fouling surface active. A thick coat is required which gradually wears off. An example of an ablative paint is Interlux Botomkote ACT and XXX. These tend to wear away in areas of more frictions such as leading edge of boat and keel. More modern formulations of ablative anti fouling paints contain copolymers and wear off at more controlled and predictable rates. Examples such as Pettit Horizon and Interlux Micron CSC Quart - 5580Q - Blue are ablative paints with copolymers.

Environmental concerns

The very qualities that make copper an effective anti fouling additive to paints make it a toxic pollutant to desirable species. Different paints leach out copper at different rates and anti fouling coatings are being designed to minimize leaching and reduce environmental impact.

There has been pressure by environmental groups to reduce the use of copper in bottom paints and preferably eliminate it completely for this reason. As alternatives are developed it is likely that copper bearing bottom paints will eventually be banned.

Some Copper Free Alternative Anti Fouling Paints

Because of the environmental impact of copper based paints it is preferable to look to alternatives if at all possible. Many new technologies are currently being developed.

ePaint has a line of antifouling paints that are copper free.Its EP200 has won the Practical Sailor magazine 2011 Editors' Choice for superior antifouling performance.

EP-2000 utilizes sunlight in the water column to generate hydrogen peroxide around the hull, deterring biofouling.

There are a couple of boats in my club that have switched to ePaint. When we hauled out for the winter we all watched with envy as the spotless white boat floated over us. Epaint works very well but has been difficult to get. As of this spring it was mostly a special order here in Toronto. I definitely plan to switch over to EPaint.

They also offer a zink based non fouling paint.

Aquaguard has a waterbased anti fouling paint. Link is to eMarineMart Co

Teflon has been used as a paint additive to make boat bottom ultra slick and prevent or reduce fouling. One example among several is the Interlux VC Offshore anti fouling boat bottom paint.

Another approach to anti fouling is to make it extremely difficult for organisms to attach themselves to the hull. One way is to make the hull very sleek and slippery. Intersleek 700 by Interlux is an example of such coating. This is a silicone based coating. Teflon is another material that has been used successfully. Interlux has Intersleek 900. These coatings do not actively repel and kill organisms. Instead they make it extremely difficult for the organisms to securely attach themselves. Furthermore the coatings make it much simpler to push off unwanted growth and clean the hull because any attached organism can be easily dislodged. The more you use your boat the cleaner it stays because organisms get scraped off by the motion of the boat.

ECONEA is an antifouling agent called Tralopyril. It can be found in Interlux Pacifica plus (Interlux Pacifica Plus Dual Biocide Antifouling Boat Bottom Paint BLUE QUART) and Pettit's Ultima Eco (Pettit Paint Co. Ultima Eco Multi-Season Ablative - Blue Gallon)). In tests it has been as effective as red copper. It does not cause galvanic corrosion and it degrades rapidly. At this point there is not a great deal of information on the toxicity of Tralopyril. No huge red flag has yet been raised though.

This page is a result of research I'm doing on antifouling coatings. It meanders a bit and will be edited and improved as I do my research.

email me if you find mistakes, I'll fix them and we'll all benefit: Christine