A Thames sailing barge was a type of commercial sailing boat common on the River Blackwater, Maldon, the River Crouch, Burnham and of course the River Thames in London in the 19th century. The flat-bottomed barges were perfectly adapted to the The Blackwater, The Crouch and the Thames Estuary, with its shallow waters and narrow rivers. The barges also traded much further afield, to the north of England, the South Coast and even to continental European ports. Cargoes varied enormously: bricks, mud, hay, rubbish, sand, coal and grain. Due to the efficiency of a Thames barge's gear, a crew of only two sufficed for most voyages, although by today's standards it would have been hard physical work at times. The vast majority of barges were wooden hulled (although a significant number were also built in steel), between 80 and 90 feet (25 to 30 m) long with a beam of around 20 feet (6 m). The hull form was as distinctive as their rig, being flat-bottomed with a degree of flair to the sides and plumb ends. The stern was a transom, shaped like a section through a champagne glass, on which was hung a large rudder. The hull was mainly a hold with two small living areas in the bow and stern, and access was through two large hatchways, the smaller before the main mast and a much larger aperture behind. They were usually sprit sail rigged on two masts.
Most had a topsail above the huge mainsail and a large foresail. The mizzen was a much smaller mast on which was set a single sail whose main purpose was to aid steering when tacking. The rig also allowed a relatively large sail area on the upper part of the mast, to catch wind when moored ships, buildings or trees blocked wind on the water's surface. Sail areas varied from 3000 to 5000 square feet (300 to 500 m²) depending on the size of the barge.