Hail a boat (4)

I believe the answer is:

ahoy

'hail' is the definition.
(I've seen this before)

'a boat' is the wordplay.
'boat' becomes 'hoy' (type of ship or barge).
'a'+'hoy'='AHOY'

(Other definitions for ahoy that I've seen before include "Hello sailor!" , "Offshore hail" , "Nautical greeting" , "Naval call for attention" , "Nautical hail" .)

I've seen this clue in the Sydney Morning Herald.

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