Hulks

Ships in the Thames used as prisons following the temporary suspension of transportation in 1776. Following the resumption of transportation in 1783 used continually until the mid nineteenth century for those awaiting their sentence.
Found on http://www.oldbaileyonline.org/static/Glossary.jsp

hulks

old ships, many relics of the Napoleonic Wars, their masts removed, anchored in the Thames and the Medway and used as prisons from 1776-1857. The practice started in 1776 when the American war prevented the transporting of convicts to America and conventional prisons were full. Abel Magwitch escapes from a prison ship in Great Expectations.
Found on http://charlesdickenspage.com/glossary.html

hulks

ships in the Thames used as prisons
Found on http://www.encyclo.co.uk/local/21814
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