Ships – Mooring device – Boom type
Patent
1986-12-17
1988-04-05
Basinger, Sherman D.
Ships
Mooring device
Boom type
141387, B63B 2100
Patent
active
047351675
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The field of the invention relates to offshore mooring/loading systems for temporarily moored tankers.
DESCRIPTION OF THE PRIOR ART
In the past, offshore mooring/loading systems for temporarily moored tankers were limited to operation in ice-free areas. These systems were mounted on compliant structures and all made use of conventional soft line mooring arrangements. These structures were usually single purpose loading terminals that required a separate production-storage facility and typically transferred the crude from the production to loading facilities through submerged pipelines or the like. The crude oil was transferred from the loading facility to the tanker via suspended or floating oil lines. One such system is discussed in the May 1983 issue of Ocean Industry Magazine on page 12.
There has been little development in designs for mooring/loading systems for arctic areas. One of the known designs for arctic use included a storage terminal structure having an oil handling apparatus mounted to the structure with a center swivel. This system was not useful for production platforms, since the topside equipment necessary for a production structure made the use of a 360.degree. swivel impossible. Furthermore, even where such systems were practical they required a submarine pipe network from the production platform(s) to the terminal loading platform(s).
Other systems have included a suspended perimeter trolley oil delivery system for transferring crude from an oil producing terminal to a moored vessel. These systems are developed for ice-free areas. Although such systems enabled the tethered vessel to drift somewhat circumferentially about the oil production terminal, a full 360.degree. weather vaning capability was not achieved. One inherent llmitation in such prior systems was due to the weight of the crude delivery hose when full of crude. Any systems which required paying out and taking up long lengths of hose filled with crude were limited by the capability of the equipment to deal with such great weight.
The known systems described employed a soft catenary mooring line rather than direct contact between a loading/mooring boom and the vessel to be loaded. The use of a soft mooring line limited the load capacity of the mooring systems and required the moored vessel to use continuous astern power to keep off the loading structure.
BACKGROUND OF THE INVENTION
The apparatus of the present invention is designed to facilitate the berthing and loading of a shuttle tanker from a fixed non-compliant offshore production/storage terminal, especially in a severe arctic environment. It is desirable to allow the connected tanker to weather vane without limit to either direction around the offshore production/storage terminal. By permitting the moored vessel to weather vane around the terminal the mooring loads are greatly reduced by taking advantage of the natural sheltering provided by the terminal structure. Furthermore, the telescoping boom arrangement of the present invention provides a compliant connection between the tanker and the platform to further reduce mooring loads by permitting first order motions of the tanker. First order motions are high frequency low amplitude oscillations of the tanker due to environmental conditions.
Typically, offshore bottom founded production/storage gravity structures designed for arctic service have a general conical profile below the water level and have base diameters as large as 600 feet and more. These structures may be placed in offshore locations with water depths of 60 feet or more. Typical ice capable tankers used to load crude oil from such production/storage terminals can be as long as 1,100 feet or more. The design of a mooring system must take into account the environmental conditions anticipated when ice conditions appear as well as open water conditions. Typically open water conditions are of a dynamic nature and tend to introduce large amplitude motions while the magnitude of the applied forces is relatively small. Ice conditio
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"Cylindrical Semi Can Produce in 300-Meter Water Depths", Offshore, Jan., 1984, pp. 59 and 60.
"Offshore Loading Ready for Deepwater Fields", Ocean Industry, May, 1983, pp. 12-14.
"Assembly Set for Articulated Tower", Offshore, Apr. 1983, p. 138.
"Concrete Manotower for 600-ft Waters", Ocean Industry, Apr. 1983, pp. 143-145.
J. C. Bruce and K. J. Charpentier, "A Satellite Terminal System for the Artic", Offshore Technology Conference, May 1983.
Manoudakis Costas P.
White Geoff C.
Basinger Sherman D.
Brian Watt Associates, Inc.
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