Abstract: A universally stable oil-well-ship turret (1) has a circumturret cylinder (2) with an inside periphery sufficiently greater than an outside periphery of a turret cylinder (7) to allow vertical positioning of the turret cylinder within the circumturret cylinder in opposition to variations from verticality of the circumturret cylinder in response to effects of wave and weather conditions on a marine vessel in which the circumturret cylinder is positioned rigidly. A plurality of horizontal and vertical bearings (10, 11) are pressure-cylinder actuated to maintain horizontal attitude of a turret flange (8) from which the turret cylinder is extended downward vertically into the circumturret cylinder. Sensor-responsive automation that is self-checking for reliability, selective manual operation and computer controls (52, 54) are provided. Appropriate redundancy and backup are provided for all systems, components and features. A use method is described.

Abstract: A controlled-pressure multi-cylinder riser tensioner has a plurality of preferably six control-cylinder units (1) with proximal ends (2) attached pivotally to a bottom surface of an operational floor (3) and distal ends (5) attached pivotally to a riser-tensioner ring (6). Pressure lines (20, 38) in communication with opposite ends of the control cylinders lead to sources of pressure (46, 47, 48, 52, 53, 62, 63) that are separately controlled. Stroke length of the control-cylinder units is typically 50 feet. Projection of the control-cylinder units downwardly into a moon pool (9) avoids their obstruction of work space on an operational floor (3) of a vessel (4). Positioning pneumatic and hydraulic machinery (10) below deck with tubing leading to the control cylinders lowers center of gravity for marine stability. An over-capacity for tensioning the marine riser with a portion of the control cylinders inactive or incapacitated increases reliability.