Vessels: most at base, after refit (10)
I believe the answer is:
'vessels' is the definition.
(steamboat is a kind of vessel)
'most at base after refit' is the wordplay.
'after refit' is an anagram indicator (letters refurbished or refitted).
'mostatbase' is an anagram of 'STEAMBOATS'.
I've seen this clue in The Times.
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