What is missing from the Flotsam/jetsam explanation is that jetsam was intentionally thrown overboard,not only in the specialised circumstances of war, but in other situations where the safety of the ship was compromised and often buoyed up or otherwise marked for later recovery, and therfore remained the property of the ship, flotsam was stuff that floated free from a wreck and was Treasure Trove if washed ashore and therefore the subject of a crowners (Coroners) court in the UK,who would decide ownership. If it hadnt been " dissappeared" by beachcombers.