Ships – Mooring device – Having ship-mounted turret
Reexamination Certificate
1999-02-15
2001-01-23
Basinger, Sherman (Department: 3617)
Ships
Mooring device
Having ship-mounted turret
Reexamination Certificate
active
06176193
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
This invention relates to vessel turret systems, that is systems that can be used in offshore terminals comprising dedicated vessels, for providing fluid couplings between the vessel and subsea risers/pipelines.
It has been previously proposed to convert a vessel such as an oil tanker into a floating production storage and offloading (FPSO) system by attaching a turret assembly to one end, generally the bow, of the vessel. The turret assembly includes a fluid swivel allowing relative rotation between, firstly, the seabed and associated production risers, mooring chains etc. and, secondly, the vessel itself while maintaining a continuous flow path for production fluids from the subsea well into the vessel. The previously-proposed mounting of the turret assembly has been significantly outboard of the end of the vessel, which has resulted in the turret assembly being exposed to adverse environmental effects, as well as requiring a complex structural mounting arrangement attached to suitable load-bearing portions of the vessel end. Accordingly, once the turret assembly had been fitted, the conversion was effectively permanent, or at least semi-permanent in that considerable work would be required to remove the turret assembly.
SUMMARY OF THE INVENTION
It is an aim of the invention to provide such a vessel turret system which is modular in design and which can accordingly be readily fitted to the deck of a tanker (or other suitable vessel), and also can be removed with minimum effort and cost, so that the vessel can then be used again for its original purpose.
According to a first aspect of the invention there is provided a method of installing a turret system on to an existing vessel, the method comprising the steps of:
removing a portion of the existing structure of the vessel at one end thereof, the removed portion including external plating;
attaching a support structure to an exposed portion of the vessel remaining after removal of the existing structure portion, the support structure including turret support means and metal plating attached to the exposed portion;
attaching a turret assembly to the turret support means of the support structure;
installing fluid piping between the turret assembly and pipework of the vessel; and
cladding the turret assembly for environmental protection thereof.
According to a second aspect of the invention there is provided a floating production storage and offloading (FPSO) vessel, including a turret system installed on a converted vessel, the FPSO vessel comprising:
a support structure attached to an exposed portion of the vessel remaining after removal of a portion of the existing structure including external plating, the support structure including turret support means and metal plating attached to the exposed portion;
a turret assembly attached to the turret support means;
fluid piping between the turret assembly and pipework of the vessel; and
cladding around the turret assembly for environmental protection thereof.
In a preferred embodiment, a framework structure may be attached at the top of the turret assembly, to the weather deck of the vessel. In one arrangement, the turret system is mounted externally of the original end (bow) of the vessel wherein the support structure includes extension structures such as plates attached to the existing decks of the vessel, forming deck extensions. Vertical extension plates may also be provided at each side of the deck extensions, and horizontal stringers may also be attached to the vessel at different levels to the deck extensions. The extension plates and stringers include respective apertures for accepting and retaining the turret assembly. In another arrangement, the turret system is mounted at least partially, preferably at least substantially, within the profile of the original vessel. In this arrangement, the centre splice of the vessel is removed and longitudinal support structure plating is attached in its place. A turret casing is assembled to the support structure plating. Once the turret assembly has been fitted in the turret casing, a manifold structure is attached at the top of the turret casing, and then a fluid swivel is installed over the manifold structure.
Conversion of a vessel such as an oil tanker can be effected readily using these techniques. The resulting vessel turret systems are strong and well-protected against environmental effects. Moreover, the modular nature of conversion designs means that, as well as simplifying the installation process, the turret systems can be readily removed, allowing the vessel to be used once more for its original purpose.
REFERENCES:
patent: 3335690 (1967-08-01), Busking
patent: 3407768 (1968-10-01), Graham
patent: 4254523 (1981-03-01), Kentosh
patent: 4301840 (1981-11-01), Jansen
patent: 5381750 (1995-01-01), Pollack
patent: 0 259 072 (1988-03-01), None
patent: 2 150 517 (1985-07-01), None
patent: WO93/11032 (1993-06-01), None
Basaran Mehmet Ismet
Hawley Philip Raymond
Whitby Ian
Baraona R. C.
Basinger Sherman
Edwards R. J.
J. Ray McDermott S.A.
Marich E.
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