No one can quite explain yet why there was a 30-foot wooden ship from the 18th century buried beneath Ground Zero, but the theories abound. One of the leading possibilities is that the ship was used as landfill material, as suggested by the deliberately sawed off beams, at a time when developers sought to extend the shoreline of Manhattan into the Hudson. But speculation as to the ship’s original function suggests that it sailed the Caribbean, probably as a commerce vessel. (Archaeologists deduced this from evidence of tiny marine organisms.) One theory that is apparently being ruled out is the original suggestion that it may have been a whaling ship.