Thalatta is a Thames sailing barge, built in Harwich, Essex, in 1906 and rebuilt in St Osyth in 2012. She is 90 feet (27 m) long and 26 feet (7.9 m) across the widest part of the deck. Like all Thames barges, she is flat-bottomed and has leeboards instead of a keel. She spent some of her life ketch-rigged and some of it spritsail-rigged. She is now permanently spritsail rigged, and has a mainmast and topmast that, together, are about 90 feet (27 m) high, and a mizzen mast. Thalatta has had two periods with an auxiliary engine and two without. She carried cargo for sixty years and was then converted for use as a sail training ship in 1966. She was completely rebuilt between 2006 and 2012 at St Osyth with assistance from lottery funds.

A Thames sailing barge is a type of commercial sailing boat once common on the River Thames in London. The flat-bottomed barges, with a shallow draught and leeboards, were perfectly adapted to the Thames Estuary, with its shallow waters and narrow tributary rivers. The larger barges were seaworthy vessels, and were the largest sailing vessel to be handled by just two men. The average size was about 120 tons and they carried 4,200 square feet (390 m2) of canvas sail in six working sails. The mainsail was loose-footed and set up with a sprit, and was brailed to the mast when not needed. It is sheeted to a horse, as is the foresail; they require no attention when tacking. The foresail is often held back by the mate to help the vessel come about more swiftly.