BEARING ARRANGEMENT FOR LIMITING DEFLECTION OF A TURRET OF A TURRET MOORING DEVICE

Abstract: A turret mooring device consisting of a vessel (2) carrying a turret (3), the turret being connected to the hull of the vessel by means of an upper (4) and a lower bearing arrangement (5), the turret being provided with means for fastening (7) and guiding (8) anchor lines (9) and with at least one fluid line (10) extending downwardly through the turret, wherein the lower bearing arrangement (5) is a slide bearing comprising a slide block having a sliding surface, and a slide plate, the slide block being connected to the outer wall of the turret and the slide plate being connected to the hull of the vessel, a clearance being provided between said slide block and said slide plate such that in case a bending moment exceeding a predetermined value is applied to said turret by said anchor lines relative to said upper bearing arrangement, the deflections of the turret are limited by contact of slide block on slide plate.

Description: !_____ BEARING ARRANGEMENT FOR LIMITING DEFLECTION OF A TURRET OF A TURRET MOORING DEVICE The invention relates to a turret mooring device consisting of a vessel carrying a turret the turret being connected to the hull of the vessel by means of an upper and a lower bearing arrangement, the turret being provided with means for fastening and guiding anchor lines and with a turret cylinder extending downwardly through the vessel moonpool. At least one fluid line is routed through the turret cylinder. Turret mooring devices are for example used for mooring a vessel to a seabed, whereby the vessel can weathervane freely around the axis of the turret, wherein fluid line connections can be made from the vessel via the turret to a wellhead for example. The turret mooring holds the vessel on place under the influence of loads exerted upon the vessel caused by the action of waves, wind and current. Background of the Invention Well known turret mooring devices consist of a vessel carrying a turret vertically positioned within the hull or in front of the bow, wherein the turret is connected to the hull of the vessel by means of an upper and a lower bearing arrangement, the lower bearing arrangement often being situated below water level, the turret being provided with means for fastening and guiding anchor lines and with at least one fluid line extending downwardly through the turret. Commonly, the lower bearing arrangement comprises a contact bearing, such as axial and/or radial roller bearings or sliding bearings. Due to their concept, contact bearings permit only a very slight displacement of bearing members relative to eachother. In case of mooring a vessel to a sea bed by a turret mooring device, the combination of an upper and a lower contact bearing arrangement causes in the turret body both a high rotational torque due to rolling or sliding resistance of the lower bearing arrangement, and a mooring force due to the dimensions and directions of loads exerted upon the vessel by the anchor lines. In practice, the high rotational torque can achieve such a dimension, that the bearing arrangement is inhibited from rotating, thus causing twisting of the flexible riser system located underneath the turret relative to the vessel. Such twisting can cause failure of the riser system and thereby spillage of oil out of the lines extending between a wellhead and the vessel. Sometimes, in turret mooring devices the lower bearing arrangement is omitted for preventing the occurrence of such heavy torques and forces. Obviously, in this case the upper bearing arrangement has a more severe task whereby both the bearing arrangement and its supporting means have to be designed to much higher forces, if it can be designed at all. Moreover, lower bearing arrangements are commonly located below water level. Thus, service and exchanging of parts is hard to do. The object of the invention is to provide a lower bearing arrangement for a turret mooring device which reduces the negative effects of a one bearing arrangement and gives the benefits of a double bearing arrangement to a great extent, wherein easy service and exchange of parts is possible. foliηπ y of the Invention: According to the invention the turret mooring device consisting of a vessel carrying a turret vertically positioned within the hull, the turret being supported by the hull of said vessel by means of an upper and a lower bearing arrangement, the turret being provided with means for fastening anchor lines and with at least one fluid line extending downwardly through the turret, is characterised in that the lower bearing arrangement comprises a slide block having a sliding surface, and a slide plate, the slide block being connected to a wall of the turret and the slide plate being connected to the hull of said vessel, whereas a clearance is present between the slide block and the slide plate for limiting deflections of the turret in case a bending moment is applied to the turret by the anchor lines relative to the upper bearing arrangement which exceeds a predetermined value. During relative easy or normal conditions the turret mooring device operates with only the upper bearing arrangement in use. In case conditions become such that a bending moment occurs in the turret body, thus causing deflection of the turret relative to upper bearing arrangement and the bending moment exceeds a predetermined dimension, parts of the lower bearing arrangement abut eachother, thus limiting further deflection. The clearance provided in the lower bearing arrangement during normal conditions allows non- frictional rotation of slide block and plate with respect to each other, and on the other hand limits deflection in case of extreme bending moments occuring temporarily. As said extreme moments occur only during a very short moment the lower bearing does not really become locked. According to a further aspect of the invention the slide block is shiftably guided within a radial casing connected to the wall of the turret said casing being closed by a closing cover, the axis of the slide block being aligned with respect to the axis of said casing. To enable easy service and exchange of parts the slide block is removably mounted in the casing, which slide block can be shifted out after removal of the cover. According to a further aspect of the invention the casing contains of at least one shock absorbing device for absorbing shocks caused by bumping the slide block against the slide bearing. Obviously, severe loads are exerted upon the slide block when abutting the slide plate. Such a shock absorbing device may be a bumper pad positioned in the casing between the slide block and the closing cover. According to a further aspect of the invention the slide plate is connected to the turret and the slide block to the vessel. Brief description of the Drawings: The invention will be further elucidated referring to an embodiment of the invention shown in the drawings, wherein: Figure 1 shows in sectional side view a vessel carrying a turret vertically positioned within the hull, according to the invention; Figure 2 shows in sectional sid_ view the lower bearing on an enlarged scale in the installed position according to the invention; Figure 3 shows in sectional side view the lower bearing according to figure 2 in a retrieved position. Detailed description of the Invention: In Figure 1 a preferred embodiment of the turret mooring device 1 according to the invention is shown. The turret mooring device 1 consists of a vessel 2 carrying a turret 3 vertically positioned within the hull of the vessel 2. The turret 3 is connected to the hull of the vessel 2 by means of an upper and a lower bearing arrangement ., 5- The lower bearing arrangement 5 can be situated below water level 6. The turret 3 is provided with means 7. 8 for fastening and guiding anchor lines 9« At least fluid line 10 extends downwardly through the turret 3- Through this fluid line may be transported to the vessel. In Figure 2 the lower bearing arrangement 5 of Figure 1 is shown on an enlarged scale in the installed position. The lower bearing arrangement 5 comprises a slide block 11 having a sliding surface 12, and a slide plate support 13 carrying a slide plate 1.. The slide block 12 is supported by the wall 15 of the turret 3 and the slide plate support 13 is connected to the hull of the vessel 2. The slide plate 1. is connected to the hull of the vessel 2 by suitable reinforcement means which form the support 13. A clearance 16 is present between the slide block 11 and the slide plate 1.. In case a bending moment on the turret exceeds a predetermined value, the sliding surface 12 abuts the slide plate 1., thus limiting deflection of the turret 3 inside the hull. The slide block 11 is shiftably supported by the wall 15 of the turret 3 by means of a radial casing 17 closed by a closing cover 18, the axis of the slide block 11 being aligned substantially with the axis of the casing 17- The casing 17 is supported by means of a supporting platform 19. In practice suitable reinforcement means may be applied for connecting the casing 17 to the supporting platform 19 as well as for connecting the supporting platform 19 to the wall 15 of the turret 3. The casing 17 has at least one shock absorbing device 20, such as a bumper pad between the slide block 11 and the closing cover 18, for absorbing shocks caused by bumping of the slide block 11 against the slide plate 1.. In Figure 3 the lower bearing arrangement 5 of Figure 2 is shown in a pulled out position. Corresponding elements are indicated by corresponding reference signs. The slide block 11 is removably mounted in the casing 17 for ease of service and exchanging slide blocks 11. The closing cover 18 may be slidably connected to the supporting platform 19.

Claims: C L A I M S 1. Turret mooring device (1) consisting of a vessel (2) carrying a turret (3) vertically positioned within the hull or in front of the bow, said turret (3) being connected to said hull of said vessel (2) by means of an upper and a lower bearing arrangement (.;5). said turret (3) being provided with means (7;8) for fastening and guiding anchor lines (9) and with at least one fluid line extending downwardly through said turret (3). characterised in that said lower bearing arrangement (5) comprises a slide block (11) having a sliding surface (12), and a slide plate (14), said slide block (11) being connected to a wall (15) of said turret (3) and said slide plate (14) being connected to said hull of said vessel (2), whereas a clearance (16) is present between said slide block (11) and said slide plate (13) for limiting deflections of said turret (3) in case a bending moment, is applied to said turret (3) by said anchor lines (9) relative to said upper bearing arrangement (4), which exceeds a predetermined value. 2. Turret mooring device according to claim 1, wherein said slide block (11) is shiftably guided within a casing connected to said turret (3) the axis of said slide block (11) being aligned with respect to the axis of said casing (17) • _ . Turret mooring device according to claim 2, wherein said slide block (11) is removably mounted in said casing (17) for ease of service and exchanging slide blocks (11). 4. Turret mooring device according to claim 3. wherein said casing (17) has at least one shock absorbing device (20) for absorbing shocks caused by bumping said slide block (11) against said slide bearing (13)- 5. Turret mooring device according to claim 4, wherein said shock absorbing device (20) is a bumper pad positioned between said slide block (11) and said closing cover (18). 6. Turret mooring device according to claim 1, wherein said slide block (11) is connected to the vessel and said side plate connected to the turret.

Inventors: BRAUD JEAN, POLDERVAART LEENDERT, BRAUD, JEAN, POLDERVAART, LEENDERT
Applicants: BRAUD JEAN, POLDERVAART LEENDERT, SINGLE BUOY MOORINGS, BRAUD, JEAN, POLDERVAART, LEENDERT, SINGLE BUOY MOORINGS INC.
Application year: 1995
Main classification: B63B22
IPC codes: B63B21