Fore's partner (3)
I believe the answer is:
aft
'fore's partner' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aft that I've seen before include "Towards the rear at sea" , "Towards the back on board" , "Of ship, fat in the rear" , "near the tail" , "Behind (naval)" .)