The anchor is just used for mooring in fairly shallow water. When the ship is on a drilling location, dynamic positioning is used. Six computer controlled thrusters, are used to keep the ship on a drilling location. The vessel is not equipped with the eight anchor windlasses, that would be needed for conventional mooring on a drilling location.

Love looking at these heavy-duty mothers !! What length is the anchor chain on these vessels? They must be a fair length if moored in deep water.