Vessel west of region's docks (9)

I believe the answer is:

subtracts

'docks' is the definition.

'vessel west of region's' is the wordplay.
'vessel' becomes 'sub' (sub is a kind of vessel**).
'west of' says to put letters next to each other.
'region's' becomes 'tracts' (both can mean a large piece of land).
'sub'+'tracts'='SUBTRACTS'

(Another definition for subtracts that I've seen is " Deducts, takes away".)

I've seen this clue in The Telegraph.

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