"Why so, Bill? I have always understood flotsam to be the debris of a foundered ship - could be so still, surely,
even if washed ashore?"


Anglo-Fr floteson < OFr flotaison, a floating < floter, to float < MDu vloten (or OE flotian), to FLOAT6
1 the wreckage of a ship or its cargo floating at sea
2 odds and ends

var. of JETTISON
1 that part of the cargo or equipment thrown overboard to lighten a ship in danger: see FLOTSAM
2 such material washed ashore
3 discarded things

The way I interpret it, so long as it is afloat, it is flotsam. When it is thrown up on the beach, it becomes jetsam.