Useless sailor emptied latrine after panic at sea (9)
I believe the answer is:
incapable
'useless' is the definition.
(I've seen this before)
'sailor emptied latrine after panic at sea' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'emptied' means to remove the middle letters.
'after' says to put letters next to each other.
'at sea' indicates anagramming the letters.
'latrine' with its centre removed is 'le'.
'panic' with letters rearranged gives 'incap'.
'ab'+'le'='able'
'able' put after 'incap' is 'INCAPABLE'.
(Other definitions for incapable that I've seen before include "lacking ability" , "Unable, incompetent" , "Extremely drunk" , "helpless" , "Hopelessly drunk; incompetent" .)