What was the purpose of the cooper sheathing?

Copper sheathing is a practice of protecting a under-water hull of a ship or boat from the corrosive effects of salt water and bio fouling through the use of copper plates affixed to the outside of the hull.
 
It was pioneered and developed by the Royal Navy during the 18th century.

Hope this helps.

The answer would be west.

Ataxation measure enacted to raise revenues for a standing british army in america