Applying copper sheathing to a ship's hull.
• (p. pr. & vb. n.) of Copper • (n.) An envelope or covering of copper. • (n.) The act of covering with copper.
Cop'per·ing noun 1. The act of covering with copper. 2. An envelope or covering of copper. 
Coppering was the sheathing a ship's bottom with thin sheets of copper, to prevent the ship-worm eating into the planks, or to keep shells and weeds from accumulating on the surface, and so retarding the vessel in her sailing.