Towboats (4)
I believe the answer is:
tugs
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">towboats</span>' is the definition.<br/ ><span class="explanation-format__explanation">('tug' can be a synonym of 'towboat')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tugs that I've seen before include "Pulls in a jerking manner" , "Pulls hard" , "Tows" , "Yanks" .)