Cargo cast overboard (6)
I believe the answer is:
jetsam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cargo cast overboard</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for jetsam that I've seen before include "Ship's discharge" , "abandoned cargo" , "Material discarded" , "stuff washed ashore" , "Discarded objects washed ashore" .)