Ships – Mooring device – Having ship-mounted turret
Reexamination Certificate
1999-09-20
2001-01-30
Swinehart, Ed (Department: 3617)
Ships
Mooring device
Having ship-mounted turret
C114S293000
Reexamination Certificate
active
06178910
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a mooring construction having at least one swivel comprising an outer and an inner annular wall defining a ring-shaped central chamber, the walls each comprising an opening which is in fluid communication with the central chamber, one of the walls being connected to a riser extending from a subsea structure to the swivel, the other of the walls being connected to a product supply duct.
DESCRIPTION OF THE RELATED ART
It is known in the offshore technology to support the inner walls of a swivel stack from a gantry, or swivel support structure. The swivel support structure can be placed on an fixed tower resting on the sea bed or can be connected to the vessel in such a way that it bridges the turret In this construction each outer wall of each swivel is supported on the inner walls of the swivel stack. In order to overcome the resistance forces between the inner and outer walls which are created by the high pressure in the central chamber and by the elastic sealing elements between the inner and outer walls, it is known to use drive mechanisms for rotating the outer walls of the swivel in the form of a rigid frame connecting the outer rings and the vessel. The known drive mechanisms are normally placed near the largest diameter swivels near the bottom of a swivel stack. The drive mechanisms have large diameters as they surround the inlet piping connected to the outer walls of the swivels and in view of fatigue problems due to continuous small excursions of the vessel around the turret.
Due to the large mass of the swivel stack, wherein each swivel may weigh up to 20 tons, and the large dimensions of the gantry and the turret, the diameter of which may amount to 20 meters, relatively large displacements between the swivel stack and the turret can occur. In order to take up variations in the spacing between the turret and the swivel, the product piping that is connected to the outer walls of the swivel stack has a relatively complex configuration and comprises a number of expansion loops. In order to accommodate the piping arrangement with the expansion loops, and in view of the large swivel weight, the swivel support structure is relatively large.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a swivel drive arrangement which can be of small dimensions and which allows for a favourable support structure for the swivel.
It is an other object of the present invention to provide a swivel support structure which is relatively small and which allows for relatively little displacement between the swivel and the swivel support structure, in particular between the swivel and the turret. It is again an object of the present invention to provide a swivel support structure which can be used in conjunction with a straight forward configuration of the product piping.
Hereto the mooring construction according to the present invention is characterised in that the inner wall is rotatably suspended from a swivel support structure, the inner wall being further connected to rotation drive means for rotating the inner wall with respect to the support structure. By connecting the rotation drive means to the inner wall of the swivel, the drive means can be relatively small as they only have to surround the centralised piping that leaves the inner part of the swivel. The swivel support structure according to the present invention may be mounted on the turret of a vessel or may be part of a fixed tower construction resting on the seabed to which tower construction a vessel is moored in such a way that it can weathervane.
In one embodiment according to the present invention the outer wall is connected to the-riser and the inner wall is connected to the product supply duct. For this swivel arrangement the connection of the rotation drive means to the inner wall of the swivel, or multiple swivels in a swivel stack, allows the weight of the swivel to be transferred directly to the turret wherein the inner wall is rotated by the drive means to rotate in conjunction with the vessel while weathervaning around the turret.
According to another embodiment of the present invention the inner wall of at least one swivel is rotatably connected to the swivel support structure on the turret via a bearing, the rotation drive means being adapted for rotating the inner wall in conjunction with the vessel. Because the inner wall of the swivel is directly connected to the turret via the support structure, the swivel can be kept better in line with the turret. Deformations between the turret and the swivel are reduced thereby so flat it not necessary to use expansion loops in the product piping and that the pipe layout can be simplified. By means of the rotating support via the bearing, the inner wall of the swivel can be kept accurately in line with the vessel when the vessel weathervanes around the geostationary turret.
The outer wall of the swivel may be connected to the turret so that it can rotate in conjunction therewith. Preferably the rotation drive means for the outer wall are provided in the form of a motor drive. Preferably multiple swivels are used, the inner walls of which are interconnected to form a stack. The inner walls may for instance be connected by means of bolts in a weight-carrying manner whereas the outer walls of each swivel in the stack are independently supported on the inner walls.
In a further embodiment of a vessel according to the present invention the outer wall of the swivel is fixedly connected to the swivel support structure on the turret. In this way the outer wall of the swivel supports the swivel weight. No bearing between the swivel and the turret is necessary in this case. Preferably a multiplicity of swivels is used wherein the outer walls are mutually connected to form a stack. The outer walls of the swivel are for instance connected by means of bolts in a weight-bearing manner whereas the inner walls of the swivel may be interconnected by rotation transfer members to be rotationally coupled. By means of the above construction, the support structure on the vessel for the rotational drive and the product pipes can be largely reduced in size.
REFERENCES:
patent: 5823837 (1998-10-01), Boatman et al.
Single Buoy Moorings Inc.
Swinehart Ed
Young & Thompson
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