Flat-bottomed hauler (4)
I believe the answer is:
scow
'flat-bottomed hauler' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scow that I've seen before include "Flat-bottomed boat for cows" , "Vessel" , "Wide-beamed dinghy" , "Unpowered freight barge" , "ighter" .)