Seat wrecked by sailors aft (6)
I believe the answer is:
astern
'aft' is the definition.
(I've seen this before)
'seat wrecked by sailors' is the wordplay.
'wrecked' indicates an anagram.
'by' means one lot of letters go next to another.
'sailors' becomes 'RN' (abbreviation for Royal Navy).
'seat' with letters rearranged gives 'aste'.
'aste'+'rn'='ASTERN'
(Other definitions for astern that I've seen before include "State of S central US" , "Toward the tail of a vessel" , "following behind vessel" , "Towards a ship's rear" , "Behind at sea" .)