Manacles were used to fasten a person’s hands or ankles.

Until 1782, English convicts were transported to America. However, in 1783 the American War of Independence ended. America refused to accept any more convicts so England had to find somewhere else to send their prisoners. Transportation to New South Wales was the solution. 

(Sydney Living Museums)

If a convict's crime was serious, they might be sent to a distant penal settlement like Port Macquarie, Newcastle, Norfolk Island or Port Arthur.