This article follows Part 3 of this series discussing the different antifouling technologies available in the market. In this fourth and last instalment, we take a look at past technologies used in antifouling systems and other non-coating technologies used to protect the hull.
Coal Tar Epoxies
Coal tar epoxies used to be a popular choice as a primer for marine coating systems for ship hulls, but due to the health hazards they pose to those applying these coatings, it is slowly losing its popularity. It is even outright banned in some locations.
Their performance is satisfactory and they have found applications in other areas as well, like pipes tanks in underground service.
Another technology that is no longer used are organotins used a biocide for the biocide-based antifouling paints.
Organotins are a large class of chemical compounds is characterized by at least one Sn-C covalent bond. They are very toxic to marine and freshwater flora and fauna at very low concentration. They have been found to leave long term damage to marine fauna and their use in antifouling systems started to lose its mainstream use in the late 70’s.
They find their way into the food chain by the fish produce we obtain from the sea, they are found dangerous due to the long term immunological effects they bring to mammals.
Other (non-coatings) Ways to Protect the Hull
Impressed current cathodic protection (or ICCP) is another well-known ship fixture that is used to prevent the corrosion of the ship’s hull.
As a vessel glides through the water during normal trade, the static current is generated between the ship’s hull and the surrounding water, the charge generated is countered by the impressed current generated from the machine.
Commonly made of an alloy of zinc, they come in different geometries and weights. These anodes are placed very carefully around the ship hull along the side bottom that protects the hull from galvanic corrosion. They will wear/erode away after a few years of service if installed correctly.
Usually, a combination of marine coatings and non-coatings solutions are the best approach to avoid corrosion in deep-sea trading vessels.