Copper sheathing and the British slave trade

British slave traders were early and rapid adopters of the new technique of sheathing ships’ hulls with copper. From the 1780s this innovation increased sailing speeds of British slave ships by about a sixth, prolonged the ships’ lives by at least a half, and reduced the death rates of slaves on the middle passage by about half. It was, above all, the fall in death rates, and possibly the improved condition of surviving slaves, that made the investment so compelling. Copper sheathing may have paid for itself in a single voyage, even though it was usually good for several. By the 1790s few slave ships, even if making only a single voyage, were uncoppered. These results confirm that copper sheathing was one of the major improvements in shipping productivity before the use of iron and steam in the mid-nineteenth century.