There are four main categories of antifouling paints on the market today: Self-Polishing Copolymer (SPC), Fouling Release coating (silicone, biocide free), hard paint (biocide free) and Controlled Depletion Polymer (CDP) with their respective pros and cons.
Self-Polishing Copolymer, SPC
SPC is a self-polishing paint which matches the performance of traditional TBT-based coatings as it is based on a chemical reaction between water and the coating. SPC contains a smaller amount of biocides than CDP and they are also less toxic. The base is copper as in CDP, but the amount needed is only 2/3 of that in CDP. The other biocide used in SPC is generally zinc pyrithione. SPC has a more controlled leakage of biocides over time which reduces the risk of fouling. The service life of SPC is up to five years.
Wallenius experiences from using SPC coating have been positive so far. Surface preparation is easy, because of the thin leached layer which SPC forms. The mechanical properties of SPC are quite good, making it suitable for over-coating with most paint systems on the market. SPC paint has low content of solids which makes several coatings necessary, leading to higher application costs.
Fouling release
Fouling release is an antifouling paint, free from biocides, available on the market. It is normally silicone-based and leaves a surface on which organisms have trouble attaching. The efficiency is dependent on the speed of the vessel; when the vessel increases speed, the organisms fall off.
However, it is rather sensitive to abrasion which means it is easily damaged when the vessel sails through ice or touches the quayside. As fouling release is normally based on silicones there is a problem with recoating the surface with other types of paint. Shipyards have subsequently been reluctant to use this type of paint because of the risk of contaminating adjacent vessels. There is a high initial cost associated with the application of fouling release which makes good planning necessary. A typical vessel to be re-coated with fouling release is a reasonably new vessel in need of a full blast, normally at the time of the vessel’s second special survey, ten years after delivery.
Wallenius has painted several vessels with fouling release paints with varying results. Therefore testing and evaluation of fouling release is still being undertaken.
Hard paint without biocides
There is also another paint without biocides that is extremely hard due to its content of glass flakes. The basic principle of this paint is that organisms may attach to the surface but in that case should not attach strongly because of the hardness. Consequently, this paint needs to be cleaned more frequently than ordinary paints. The problem in that lies in cleaning it in a controlled manner assuring that no foreign species are released into the water (similar to the problem with ballast water). Hard paint is ideal for ice going vessels as the ice automatically and regularly cleans the most fouled areas. Once hard paint is applied, it normally needs very little touching up for a very long time. Some manufacturers suggest that a full repaint is never required.
Wallenius has never painted a full vessel with hardpaint due to the challenges with cleaning.
Controlled Depletion Polymer, CDP
CDP was the first type of tin-free antifouling paint to be released on the market. The coating is reliable for up to three years. Dissolution is slow, similar to the way soap dissolves in water, because of the rosin content, which is slightly soluble in water. The biocides are released by diffusion. The dissolution gradually slows down because of a leached layer formed by insoluble materials at the surface. The roughness of the surface and fuel consumption will therefore increase as time passes. CDP is the coating that has the largest leakage of biocides. Although it is based on copper, it also contains some very strong biocides – generally much more toxic than those found in other types of coatings. The leakage, usually considerable at first, is then reduced because of the leached layer. This also makes CDP more difficult to control than the other types of paint.
Several vessels in the Wallenius fleet has been coated with CDP paint in the past. The environmental aspect together with limited service life and high costs related to preparation of the surface has made Wallenius stop using CDP.
Read about our results and statistics within antifouling