Sailor a foot nearer the stern (5)
I believe the answer is:
abaft
'nearer the stern' is the definition.
(I've seen this before)
'sailor a foot' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'foot' becomes 'ft' (abbreviation).
'ab'+'a'+'ft'='ABAFT'
(Other definitions for abaft that I've seen before include "In the stern half of a ship" , "near end of Titanic?" , "At, near or toward the stern of a ship" , "behind at sea" , "Towards the back (naut.)" .)