Person drawing vessel in Home Counties river (8)

I believe the answer is:

sketcher

'person drawing' is the definition.

'vessel in home counties river' is the wordplay.
'vessel' becomes 'ketch' (ketch is a kind of vessel).
'in' indicates putting letters inside.
'home counties' becomes 'se' (Home Counties in the South East of England).
'river' becomes 'r'.
'ketch' put into 'se' is 'sketche'.
'sketche'+'r'='SKETCHER'

(Another definition for sketcher that I've seen is " Artist".)

I've seen this clue in The Times.

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