Cargo thrown overboard (6)
I believe the answer is:
jetsam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cargo thrown overboard</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for jetsam that I've seen before include "Rubbish on shore thrown from ships" , "Goods thrown overboard from ship in distress" , "Unwanted material thrown overboard" , "Discarded cargo" , "Goods thrown overboard and washed up on shore" .)