Coal was brought to the harbour from the coalfields south and west of the village on wagonways which traversed the area in all directions. Ships were loaded from staithes in front of the Kings Arms and from coal chutes down the side of the new 'cut'. Lighter bottle ships were loaded in the shallowest part of the harbour from the quay below the present concrete bridge. With these two entrances to the harbour and piers both sides extending out to sea, the 'cut' was a success and in 1777 one hundred and seventy seven ships sailed out of the harbour with a total 48,000 tonnes of coal; the 'cut' could also be sealed off at both ends at high tide to serve as a dock to allow loading to continue at all times of the tide and day.

Coal continued to be shipped from the port but the Salt Laws of 1797, and a lack of orders for copperas had closed both these industries by 1828. A cry for better shipping facilities by the colliery owners, in 1848. finally led to major improvements to Blyth and Northumberland Dock on the Tyne, which had been funded by corporate bodies such as the River Commissioners rather than one individual family as at Seaton Sluice. The coal trade was finally ruined in 1862 following the Hartley (Hester) Pit disaster. The Bottle works closed in 1870 and Seaton Sluice went into decline.