One drawing is of Her Majesty on small boat (8)
I believe the answer is:
sketcher
'one drawing' is the definition.
(someone drawing sketches)
'her majesty on small boat' is the wordplay.
'her majesty' becomes 'ER' (Elizabeth Regina).
'on' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'boat' becomes 'ketch' (ketch is a kind of sailing vessel).
's'+'ketch'='sketch'
'er' put after 'sketch' is 'SKETCHER'.
'is of' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for sketcher that I've seen is " Artist".)