In the 18th century the Royal Navy began using copper sheathing to protect their ships from teredo worm, also known as shipworm.
What causes teredo worm?
Species of teredo worm occur in all seas and are most prevalent in warmer waters. They cause great damage to the bottoms of wooden ships by boring through all the timbers below the waterline. Originally, the only protection ships used to combat teredo worm was a thin layer of plank laid on a coating of tar and hair, but this covering was itself susceptible to teredo worm.
When was copper sheathing first used?
Experiments with copper sheathing were first carried out in 1761, when the frigate HMS Alarm was sheathed with the material prior to a two-year voyage to the West Indies. The Alarm was chosen because she was in such poor condition due to teredo worm having taken a significant toll on her hull.
Was the use of copper sheathing successful?
Yes, it kept the hull clean but there was the problem of corrosion by the galvanic action of the copper on the iron bolts, which secured the main frame and the planking. This rendered the bolts nearly useless. This problem was solved in 1783 when orders went out that copper and zinc bolts should replace iron bolts. From there on, copper sheathing became widespread across all ships in the Royal Navy.
Copper sheathing was an important technological innovation, as not only did the copper afford protection against teredo worm, it kept ships relatively free from weed, thus improving their sailing performance.