Customs duties and the Sunderland coal trade

By 1700 Sunderland was 'noted for its sea coal trade', supplying a 'great quantity of coals' and employing 'great numbers of ships yearly in carrying coals...' Most was transported along the east and south coasts of England and some to Scotland.  Customs duties were collected on all coal shipped out of Sunderland, so quantities were recorded. Some of the lists survive, from which these graphs have been draw.  Even though incomplete and sometimes unclear, the graphs show a dramatic rise in total coal sales over the century, and a matching increase in overseas exports.