I've been looking in a book on naval records at TNA and while it does not give a definition of artificer
per se, I get the impression that an artificer was a master craftsman. (In fact I have an 18th century relative, from a shipwright family, who is mentioned in the Artificer's Records of Deptford Naval Dockyard.) In the 18th century, artificers (civilian officers appointed by the Navy Board) could be warranted as inferior officers at sea. This would have included such craftsmen as sailmakers, caulkers, ropemakers and coopers. This practice died out in the 19th century.
Description books of Artificers 1748-1830 are held in class ADM106.
But since he was appointed by the Board of Ordnance, as Stan says, his line of work involved a bit more destruction than construction.

Nell