Toward a boat's back (3)
I believe the answer is:
aft
'toward a boat's back' 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 "behind at sea" , "Astern" , "Towards rear (of ship)" , "Near the stern" , "Near the rear (of ship)" .)