Rust and corrosion: enemy of shipping
When you immerse metal in a conductive liquid such as water, a small electric current is created that causes corrosion or rust. This is a problem for ships. With ships, the hull, rudder and keel are especially vulnerable. Corrosion can cause pitting there. Even under the paint layer, the steel may gradually begin to dissolve. At best, this causes loss of efficiency; at worst, it causes serious rust leaks.
Not every type of metal rusts at the same rate. High-quality metals such as stainless steel, bronze or gold corrode less quickly than ordinary steel or aluminium.