Dull, expert on ketch (7)
I believe the answer is:
prosaic
'dull' is the definition.
(similar in meaning)
'expert on ketch' is the wordplay.
'expert' becomes 'pro' (I've seen this before).
'on' says to put letters next to each other.
'ketch' becomes 'saic' (saic is a type of ketch, a type of boat).
'pro'+'saic'='PROSAIC'
(Other definitions for prosaic that I've seen before include "routine" , "Dull - pedestrian" , "Workaday" , "Lacking poetry" , "Is a crop (anag) - unimaginative" .)