A vessel that is used to produce hydrocarbons from an offshore well commonly includes a turret that is moored to the sea floor. The vessel hull is rotatable about the turret so the hull can weathervane about the turret with changing winds, waves and currents. The turret can lie in a moon pool in the hull or can lie outboard of the hull such as beyond the bow of the hull. Risers that extend up from about the sea floor to the turret, have upper ends connected to a fluid swivel on the turret. It is common to provide a drilling/workover rig on the hull. The rig supports a tubular drill string that is used to drill wells in the sea floor. A second and later wells may be drilled while risers from previous wells continue to carry hydrocarbons up to the vessel. After wells are drilled and risers installed, the rig can continue to be used, as to support a string of tubing that is used for servicing the wells, as to clean away wax buildup.
One problem encountered in such use of a rig, is that tubing extending down from the rig has to be brought back up when the vessel weathervanes. Otherwise, the string extending down from the rig on the weathervaning hull could eventually wrap itself around the risers. Actually the string could damage the risers when first beginning to rub against them. It would be desirable if a rig was available on the vessel that could drill and/or perform workovers without the requirement for raising the string every time the vessel weathervanes by more than several degrees.