Before and after the removal of fouling
Marine life grows on the undersides of ships (hulls) while they are immersed in water. This is called hull fouling. It is also likely that biofouling will affect sea-chests, pipes, toilet outlets, propeller shafts, fishing gear etc. Fouling marine life includes limpets, barnacles, mussels, crabs and algae. They will travel on ships from their native environment to foreign marine environments.
Ships travel faster through water and consume less fuel and therefore release less greenhouse gasses when their hulls are clean and free from the biofouling. Just a small amount of fouling can lead to a fuel consumption increase of up to 40%.
Ships hulls not protected by anti-fouling paint may gather 150 kg of fouling per square metre in less than six months of being at sea. On a very large crude oil tanker with 40,000 square metres underwater area, this would add up to 6,000 tonnes of hull fouling.
In the early days of sailing ships, arsenic was used to coat ships' hulls to stop hull fouling. Then DDT was used in the 1940’s. During the 1960s new anti-fouling paints were developed using a chemical called tributyltin (TBT) and by the 1970s, most ships were using TBT. The paints were very effective but they were also toxic to animals and plants.
Environmental studies began to show evidence that chemicals from tributyltin (TBT) paints remained in the water and sediments, killing other marine life and possibly entering the food chain. TBT was shown to cause shell deformations in oysters and sex changes in whelks and even can affect polar bears.
Anti fouling paints containing TBT are now banned.