Does the radar paint an image of a 3/4 submerged container? I understand that some 10,000 of them (yes!) are lost from container ships each year.
And I bet they drift well away from the shipping lanes.
If you collide with a ship there is at last a chance that someone on the ship notices, but with a container .... it's adios, baby
Unless you have a full moon and glass seas, someone on watch won't see it either