Heretofore, vessel mooring systems have been provided in which a vessel may weathervane about a turret which is normally anchored to the sea floor. The turret is supported for rotation on bearing structures secured to the vessel. Both horizontal and vertical loads are transferred between the turret and the fixed structure of the vessel. Vertical and radial bearing structures have been provided heretofore for transferring the horizontal and vertical loads between the turret and the vessel. For example, U.S. Pat. No. 5,240,446 dated Aug. 31, 1993, shows a mooring system which includes a rotatable turret mounted on the vessel. The turret is supported in a well of the vessel and has a radial bearing structure or assembly. A plurality of radial bearing assemblies are spaced about the outer periphery of the turret and have bearing blocks engaging a support ring about the outer periphery of the turret. The bearing blocks may pivot to fit any uneven adjacent surfaces of the turret.
U.S. Pat. No. 5,359,957 dated Nov. 1, 1994 likewise discloses a turret for a vessel with the turret having fixed radial arms which are supported by both radial and axial bearings. The radial bearings includes rollers or wheels which run against a rail fixed to the vessel. A wedge device moves the rollers in and out in a radial direction. The rollers are mounted in very close relation to each other to limit flexure in the rail section.
Radial bearings react horizontal loadings from the turret structure to the ship structure. Radial flexures and radial deformations must be compensated by the radial bearings. Such radial bearings heretofore have also included Belleville type springs to compensate for radial flexures or deformations in radial bearings for turrets in which rollers on a turret side against a rail fixed to the structure of the vessel. The Belleville springs absorb a substantial horizontal loading with only a relatively small deflection required. However, a disadvantage in the utilization of Belleville springs occurs when a relatively large horizontal loading is being reacted from only one side of the turret with the rollers and rail on such one side in contact, while the rollers and rail on the opposite side of the turret are out of contact as a result of the relatively small travel or deflection provided by the Belleville springs. As a result, once the turret returns or travels back to its neutral center, the horizontal rail and rollers on the opposite side recontact each other but the rollers have to "climb" up the crown of the rail until the rail and rollers return to their original radially centered position. During return to the original radially centered position, the bearing system undergoes or experiences an increased rolling resistance which requires an increased torque in order for the vessel to weathervane about the turret. Thus, a need exists for a spring assembly to take up any slack occurring when a relatively large horizontal loading is being reacted from only one side of the turret which may result in a spacing between the rollers and rail on the opposite side of the turret.
It is an object of the present invention to provide a spring urged radial bearing structure for a turret which remains in contact with the turret during maximum lateral excursions of the turret.
Another object of this invention is the provision of a spring structure for a radial bearing structure including a pair of spring device with one spring device being effective after the other spring device is ineffective thereby to maintain the radial bearing structure in contact with the turret during maximum lateral excursions of the turret.