Sacrificial anodes

A sacrificial anode is a big lump of metal, usually zinc, which is attached to a metal object such as a ship, to inhibit the object's corrosion. The anode is electrolytically decomposed over time while the object remains free of damage. A new anode looks like this:

After three years of electrolytic decomposition, the Africa Mercy's anodes look like this:

One of the many jobs needing to be done whilst the ship is out of the water, is the replacing of the hundreds of anodes that line the hull. Another fascinating blog entry by Olly.