Assessing a sailor (6)
I believe the answer is:
rating
I believe this is a double definition.
'assessing' is the first definition.
(rating is a kind of assessing)
'a sailor' is the second definition.
(British term for a naval enlisted man)
(Other definitions for rating that I've seen before include "Ordinary seaman" , "Sailor - assessment" , "Non-commissioned sailor - classification" , "Sailor - deserving - reprimand" , "Valuation" .)