Buoys – rafts – and aquatic devices – Buoy – For mooring a vessel
Reexamination Certificate
2000-02-01
2001-11-13
Morano, S. Joseph (Department: 3617)
Buoys, rafts, and aquatic devices
Buoy
For mooring a vessel
C114S230120
Reexamination Certificate
active
06315625
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a vessel comprising a turret extending vertically within the hull of the vessel, the turret having a cylindrical turret wall with an upper part and a lower part and an annular attachment element which is rotatingly connected to the lower part of the turret wall for the connection of one or more anchor lines for mooring the vessel to the sea bed, the lower part of the turret wall being located at or near keel level, wherein the upper part of the turret wall is located at a position which is below the level halfway between deck level and keel level.
From U.S. Pat. No. 5,266,061 a vessel is known comprising a large diameter turret wall that extends from deck level vertically downwards into a moon pool located near keel level. Within the fixed turret wall, a lower turret section is rotatingly connected. The lower turret section comprises a chain table which is connected to the sea-bed in a geostationary manner. Risers, which extend from a sub-sea structure such as a well head, enter the turret through the chain table and extend into a central shaft extending up to deck level, the central shaft being rotatable together with the chain table within the turret wall. During weathervaning of the vessel, the outer turret wall will rotate together with the vessel around the geostationary chain table, the lower part of the turret and the central shaft accommodating the product pipes.
Providing a large diameter turret wall inside the vessel, the diameter of which may amount up to between 15 and 20 meters, is an extensive operation which may cause a structural weakening of the vessel and which requires separate reinforcements. Futhermore, once a vessel is provided with such a large turret construction for conversion of a tanker to a floating production, storage and offloading vessel (FPSO), it can not easily be rebuilt and brought back into its original state as a transport tanker.
From U.S. Pat. No. 5,237,948 a vessel is known comprising a mooring system. Herein the chain table is fixed to a rigid shaft connected to the hull of the vessel. The chain table is rotatably supported on a flange on the shaft. This construction has as a disadvantage that the known chain table will be susceptible to bending moments which can be directly transferred to the bearings.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a relatively simple weathervaning construction on a vessel for connecting to a sub-sea oil structure during hydrocarbon exploration activities, which can be relatively easily converted back to its original state. It is a further object of the present invention to provide a vessel with a turret construction which is of low cost, and which can be easily accessed during installation and on conversion. It is another object of the present invention to provide a weathervaning mooring construction which has a large resistence against bending moments.
Thereto a vessel according to the present invention is characterised in that a shaft extends from at least the upper part of the turret wall towards deck level for accommodating a product pipe which is connected to a sub sea structure, the diameter of the shaft being substantially smaller than the diameter of the turret wall, wherein the lower part of the turret wall extends along substantially the whole height of the annular attachment element, the attachment element being supported by an upper and a lower bearing, one of the bearings being an axial bearing, the other bearing being a radial bearing.
By providing a relatively short turret wall within the lower half of the vessel, a relatively simple structure is formed which can during hydrocarbon exploration effectively function as a turret structure, and which can be easily installed and removed from the vessel. As the topmost part of the weathervaning construction is formed by the shaft with a relatively small diameter for accommodating the product pipes, relatively little structural weakening of the vessel occurs, and little useful storage space inside the vessel is occupied. As the annular attachment element, such as a chain table according to the present invention is along its full length supported by the turret wall by means of an axial and a radial bearing, a structure is obtained which can adequately take up the bending moments exerted by the mooring chains or cables, without the risk of deformation of the bearings and subsequent failure of the chain table to rotate. After use of the vessel for hydrocarbon exploration, for instance when the hydrocarbon well has been depleted, the part of the turret wall close to keel level can be removed, for instance by cutting through the turret wall, but preferably by means of a releasable coupling. Preferably the lower part of the turret wall extends below keel level such that the attachment element, such as a chain table, can be easily accessed for installation or removal. It is however possible to accommodate the chain table completely within a recess in the hull of the vessel, such that it is projecting below the outer circumference of the vessel.
Preferably the height of the turret wall is relatively small and the upper part is located relatively close to keel level, such as at a distance of between 0.1 and 0.5 times the distance between keel level and deck level. The diameter of the shaft substantially corresponds with the diameter of at least one product pipe for allowing rotational movement of the product pipe within the shaft. Near deck level, the product pipe is connected to a swivel which connects a horizontal product pipe in a rotatable manner to the product pipe extending in the shaft of the vessel. It is however also possible to mount the swivel near or at the turret position by lowering the swivel through the shaft from deck level. In that case the diameter of the shaft is made large enough to accommodate the swivel.
In a preferred embodiment of the vessel according to the present invention, the turret wall comprises an upper and a lower bearing, each bearing having a radially extending flange with an axial bearing surface and an axially extending part forming a radial bearing surface, the axially extending part of the upper bearing being fixedly connected to the lower part of the turret wall, the radially extending flange of the upper bearing being fixedly connected to upper part of the turret wall, the flange and the axially extending part of the upper bearing being mutually connected in a releasable manner.
By decoupling the upper bearing part, for instance by means of bolts, the lower part of the turret according to the invention including the attachment element can be easily be moved. With the releasable bearings according to the invention it is also possible to exchange the lower part of the turret for instance after damage to the chain table, or for use with a differently configured chain table that is adapted to specific operating conditions at different locations.
REFERENCES:
patent: 3590407 (1971-07-01), Bratianu et al.
patent: 5025742 (1991-06-01), Urdshals
patent: 5237948 (1993-08-01), Hvide
patent: 5266061 (1993-11-01), Poldervaart et al.
patent: 5305703 (1994-04-01), Korsgaard
patent: 5346314 (1994-09-01), Perratone et al.
patent: 5755607 (1998-05-01), Boatman et al.
patent: 0 259 072 (1988-03-01), None
patent: 2 150 964 (1985-07-01), None
patent: 2 150 517 (1985-07-01), None
patent: WO 96/14237 (1996-05-01), None
Morano S. Joseph
Single Buoy Moorings Inc.
Wright Andy
Young & Thompson
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