@Livesinafield: "I think 3km is a lot I'm sure a 6kt current can't move 20kilos of metal that's sat in the sand"
At 6kt that distance represents about 20 minutes - if one of two pieces sinks straight away after surface impact and disruption, and the other floats for 20 minutes before sinking carried by a current flowing at that speed, that does not seem particularly unrealistic?