Cox, perhaps, sits with nice blue on bottom of boat (9)
I believe the answer is:
scientist
'cox' is the definition.
(Brian Cox is a scientist)
'sits with nice blue on bottom of boat' is the wordplay.
'with' means one lot of letters go next to another.
'blue' is an anagram indicator (blue can mean a mistake).
'on bottom of' says to take the final letters.
The final letter of 'boat' is 't'.
'sits'+'nice'='sitsnice'
'sitsnice' with letters rearranged gives 'scientis'.
'scientis'+'t'='SCIENTIST'
'perhaps' acts as a link.
(Other definitions for scientist that I've seen before include "`Tis nicest kind of specialist" , "It's insect, strangely, this learned person knows about" , "Researcher - boffin" , "entomologist maybe" , "Person conducting experiments" .)