At sea, no rating is clueless (8)
I believe the answer is:
ignorant
'clueless' is the definition.
'at sea no rating' is the wordplay.
'at sea' indicates anagramming the letters.
'no'+'rating'='norating'
'norating' with letters rearranged gives 'IGNORANT'.
'is' acts as a link.
(Other definitions for ignorant that I've seen before include "Lacking information" , "Lacking knowledge or skill" , "Without knowledge" , "Knowing nothing" , "Uncouth or uninformed" .)