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Coppering a ship prevents weeds fouling it, and this improved method prevents the ship's structural bolts from mysteriously rotting away.
Copper sheets fitted to a wooden ship keeps weeds and worms at bay, making the ship faster in the water and longer lasting in service. However, until the advent of a new alloy for making bolts to hold ship's timbers in place, coppering caused the iron bolts to be eaten away. Although nobody understands why the iron bolts fail, experiments have revealed that an alloy of copper and zinc can make bolts of sufficient strength that are immune to the mysterious problem.
Copper sheathing for a ship is not a trival expense, being about six times more expensive than replacing damaged timbers. For those navies who do it, however, the improved performance from not having weed-fouled hulls s well worth the expense. Fancy metalurgy is a small additional price to pay.
Historically, the alloy bolts made coppering a success, so much so that "copper bottomed" bacame a mark of approval: something so (financially) sound it could not possible fail. The method remained in use until the development of anti-fouling paints; even iron hulls get fouled by weeds.