Protected by Sir Humphry Davy

In 1824, Sir Humphry Davy, on contract to the Royal Navy, discovered the principle of cathodic protection for the mitigation of natural corrosion processes. He was searching for a method to prevent corrosion of the copper-clad wooden hulls of English ships. He attached billets of zinc to the copper of the HMS Samarang and observed that the zinc would corrode to save the copper. Today, over one and one-half centuries later, corrosion engineers are still using this same method of preventing corrosion damage by applying this same zinc anode cathodic protection to steel ships around the world.

Whenever different metals are placed in a conductive liquid you create a battery. If you connect these pieces of metal together, current will flow. The current will be removing metal from one of the metal pieces according 'electrolysis'. If this piece is the zinc in your flashlight battery that is good, but if one of the pieces is your propeller it is bad.

The newly installed zinc anodes you see here, all around the propellers of the Retriever, are called 'Sacrificial Anodes'. Zinc is used because it has a higher voltage in the water so the current will be more inclined to flow from it than from the propellers. To complete the electrical circuit, the zinc anodes must be connected to the items they are intended to protect.

Next docking period, most of this material will be gone, giving us an indication that the system of Sir Humphry Davy still works. The anodes will be gone instead of our precious propellers.