Green’s Dictionary of Slang

1. to transport a convict.

1859		Matsell Vocabulum.
1882		Sydney Sl. Dict. (2 edn) 1: Boat - Originally to transport - the term is now applied to penal servitude.
1895		Mirror of Life 26 Jan. 3/1: In the old days, when a man was transported he was ‘boated’.

2. to sentence to penal servitude; thus in the boat, sentenced to penal servitude.

1865		Leaves from Diary of Celebrated Burglar 12/2: George Whittaker alias Snags the ‘wire’ who left the ‘star’ with Bill Frenchy (soon afterwards ‘boated’ or a ‘dummy’ on Westminster Bridge).
1882		Sydney Sl. Dict. (2 edn) see sense 1.
1891		J. Bent Criminal Life 222: He would rather be twice ‘boated’ (that is, sent into penal servitude) than once ‘bashed’.

3. to move a convict from one prison to another.

1950		Goldin et al. DAUL 31/1: Boat, v. (P) 1. To transfer a convict to another prison.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Boat: To transfer out of a prison, as in ‘on a boat.’.