Ships – Mooring device – Having ship-mounted turret
Patent
1999-10-29
2000-12-05
Avila, Stephen
Ships
Mooring device
Having ship-mounted turret
441 5, B63B 2202
Patent
active
061551937
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a vessel for use in the production and/or storage of hydrocarbons, comprising a receiving means having a downwardly open space for receiving and releasably securing a submerged buoy connected to at least one riser, a rotatable connector for connection with the buoy and transfer of fluids, and a dynamic positioning system for keeping the vessel at a desired position.
There are previously known a number of different types and embodiments of vessels for use in the production, storage and transport of hydrocarbons from offshore fields. The known vessels of the type to which the invention relates, are based on the so-called STP concept, wherein the abbreviation "STP" stands for "Submerged Turret Production". For a further description of STP systems reference can, for example, be made to Norwegian laying-open print 176 129 and Norwegian patent 177 778.
The known vessels of the topical type comprise a submerged, downwardly open receiving space which is preferably arranged in the bow portion of the vessel and is arranged for receiving a bottom-anchored underwater buoy for the transfer for hydrocarbons, and a service shaft extending between the receiving space and the deck of the vessel. At the lower end of the service shaft there is arranged a rotating coupling device or so-called connector for connection of the buoy to a pipe system on the vessel. The connector is movably arranged, to be able to be moved away from the shaft to a parking position when it is not in use.
Thus, these known constructions are based on a submerged receiving space (STP space) which is arranged at the lower end of a service shaft, and on a rotating connector which is arranged at the lower end of the shaft. This implies that the shaft will be partly filled with water in connection and disconnection of the buoy, and that the service shaft after these operations must be emptied of water to get a dry access to the equipment at the lower end of the shaft. Even if the STP concept affords great operational and security advantages in relation to previously known solutions, the submerged environment in connection with the receiving space implies that special structural considerations must be taken which complicate some of the structural details.
An object of the present invention is to provide a new solution giving the possibility for structural simplifications, at the same time as it results in an easy access to the structural units, with a view to easy installation and maintenance.
Another object of the invention is to provide a solution enabling the use of the STP concept of the existing drilling or production ships, or other floating production systems, which are provided with a moonpool and are dynamically positioned.
The above-mentioned objects are achieved with a vessel of the introductorily stated type, which, according to the invention, is characterized in that it comprises a moonpool extending through the hull of the vessel from the bottom up to the deck level thereof, and that the receiving means is a unit which is raisably and lowerably arranged along the length of the moonpool, the rotatable connector being arranged at deck level, for direct connection to the buoy when the receiving unit with the buoy has been raised to an upper position at the top of the moonpool.
Thus, the solution according to the invention takes it starting point in the STP concept with a submerged STP buoy and a rotating connector. The main difference resides in that the buoy after pulling-in is mounted at deck level (at the "tank top") instead of in a submerged space at the bottom of the vessel. A presupposition is here that the vessel is kept in position by means of a dynamic positioning system, so that the buoy does not need to be bottom-anchored.
By means of the solution according to the invention there is achieved that a rotating connector is placed at a "dry" place, with an easy access for installation and maintenance. Further, all connections to the connector can be carried out at deck level. The problems connected to the STP space
REFERENCES:
patent: 4321720 (1982-03-01), Havre
patent: 5540607 (1996-07-01), Breivik et al.
Skiftesvik Per
Syvertsen Kare
Avila Stephen
Den Norske Stats Oljeselskap A.S.
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