Green’s Dictionary of Slang

floating academy n.

[SE floating + academy n. (4); run-down or part-derelict ships, no longer seaworthy, were recycled as prison ships, moored in the Thames estuary]

the prison hulks.

[UK]Scots Mag. 1 July 8/2: Mignam [...] as well as other defenders, know what they have to depend on if they once enter on board the floating academy.
[UK]G. Parker View of Society II 141: The Floating Academy. This is a new insititution.
[UK]Oxford Jrnl 7 Sept. 1/2: The above Gang have lately been discharged from that Sink of iniquity the Floating Academy at Woolwich.
[UK]Grose Classical Dict. of the Vulgar Tongue n.p.: The floating academy, the lighters on board of which those persons are confined, who by a late regulation are condemned to hard labour, instead of transportation.
[UK]Caledonian Mercury 20 Oct. 2/3: Mr Duncan Campbell, the Master of the Floating Academy at Woolwich.
[UK]Lex. Balatronicum.
[UK]C.M. Westmacott Eng. Spy II 212: You see the floating academy as is kept a purpose for ’em, said he, pointing to the receiving hulk for the convicts.
[UK]Egan Finish to the Adventures of Tom and Jerry (1889) 140: Many of them [i.e. convicts] [...] had spent a few years on board of the floating academy.
[UK]Lloyd's Wkly Newspaper 7 Jan. 5/3: The prisoners [...] are marched to the quarter-deck of the Hulk [...] then ordered 'forward' under the forecastle of this floating academy.
[UK]Flash Dict. in Sinks of London Laid Open.
[UK]Hotten Sl. Dict.