Introduction to bio-fouling
Bio fouling is a common condition in which a large number of marine organisms such as barnacles and algae, permanently attach themselves to the underwater areas of marine vessels. This condition increases the frictional resistance of the water against the hull and slows down the speed of the ship. In extreme conditions of bio fouling hundreds of different species of plants, algae as well as hard shell marine organisms including encrusting bryozoans, mollusks, polychaete and other tube worms, and zebra mussels form a layer that can be very thick and can have hanging branches more than one meter long. Within six months of active service a vessel could have up to 150 kilograms of marine life per square meter attached to the hull. This obviously has huge fuel efficiency and bunker fuel cost implications. Even minor volumes of fouling can impact fuel efficiency by up to 40%. Therefore, reducing drag, or skin frictional resistance is vitally important to reducing ever-increasing bunker fuel costs.
To prevent bio fouling we must make the surface uninhabitable or non-attractive for sea organisms. This is achieved either by a smooth/ slippery paint or by adding biocides to the paint.
Copper powder is known to be the most effective and the most environmental friendly biocide for marine paints or antifouling coatings.
Because of copper’s biocidal properties, copper sheet metals and copper compounds have been used for centuries for the protection of the hulls of ships starting the early wooden ships. The growth of friction-causing marine organisms is detrimental. Fouling both reduces the speed of the vessel and increases its fuel consumption. It also increases wear on propulsion systems. The first copper bases antifouling marine paint was made in 1915 by J. C. Hempel (a Danish manufacturer), and such paints have been the standard of the industry ever since. Thus, today, whether the ship is an ocean-going freighter or tanker, a racing yacht, or a weekend sports boat, antifouling bottom coatings have become a necessity.
Copper is the ideal biocide for use in antifoulant paints. it is a naturally occurring substance that is an essential element required for normal growth by all plants and animals. Further, the chemistry of copper can change in the environment, thereby affecting its bioavailability.
According to Dr. Julian E. Hunter of International Marine Coatings, Ltd., copper has been found to be safe to humans and to the environment when used in antifouling paints, and is approved for use by most government authorities throughout the world. It is clearly accepted that the use of copper in antifouling paints is significantly safer to the environment than …
How to select copper powder for antifouling pait?
Weather you are a paint manufacturer or want to try your own recipe of anti-fouling paint, there are a number of factors you must consider.
- Select a fine powder. Generally copper powder mesh 325 (smaller than 44 micron particles) are good to use. Fine copper powder offers a higher bio-availability and distribute easier. Fine copper particles can completely submerge in the layer of paint and you can have a paint with smooth surface. Coarse powder (lower mesh) on the other hand create a rough texture paint that provide a good grip to the sea organisms.
- Don’t look for a high purity copper powder. It’s not necessary for copper to be .9999 in order to function as a biocide. A minimum of 95% purity is enough. The impurities of a good quality copper powder are often copper oxide or other copper salts which all of them biocides as well. The benefit of metallic copper or high purity elemental copper is its slow release.
- Select copper powder with solid spherical or spheroid particles. Powders with irregular, rod shape or spongy particles are not suitable for anti-fouling paints. You can also use flake particles if you like a metallic coppery shine on your paint.
Some of the copper powders you may use for anti-fouling paits are CU301, CU118SP, CU112SP and CU7005F.
Can I add copper powder to an existing paint?
Use pure resin, not existing industrial paints. Technically you can add copper powder to any paint to give it biocidal and antifouling properties. Most paints however have other fillers and pigments that are not needed for your application as an anti-fouling paint. Starting with a high purity base resin allows you to formulate a most effective antifouling paint.
How much copper powder is in antifouling paint?
If you are going to make your own anti-fouling marine paint you may be wondering how much copper powder you should use in your paint. Depending on the type and grade of copper powder you use and method of application you have in mind, your formula may include 40% to 80% copper powder by weight. If you are using a powder with apparent density of about 3 g/cc, then the ratio is most likely close to 80% and if you are using a powder with apparent density of 1, then the ratio will most likely be closer to 40%.
Application of anti-fouling paint
Since you are reading this article you most likely have some ideas on how to apply the antifouling paint you will be making. Almost all methods of painting such as brush, roller, sprayer and even a spackling knife may be used to apply the antifouling paint depending on the area size, conditions of the surface and the viscosity of the paint. I do however offer a few additional advice that might be helpful.
- Never apply the antifouling paint on a bare metal surface. If copper particles come in direct contact with another metal they may form an electrolytic cell and cause corrosion. Always apply one or two coats of high quality primer first. Primer will insulate the surface and prevents electrical contact between the copper particles and the surface you will be painting.
- If the surface is very smooth, first sand it a little and roughen it up so that your antifouling paint can form a strong bound with the surface.
- After the antifouling paint drys, polish the surface. Polishing will expose some copper particles at the surface so that the antifouling properties will be immediate. Repeat polishing every year or every two years to expose more copper particles.
Have questions or suggestions?
If you have questions about this article please feel free to reach me by phone or email. I can also use your help in improving this article. If you have picture of biofouling in marine vessels and installations, please send them to me so that I can use them in this article.