Ships – Anchoring arrangement
Patent
1989-11-06
1991-10-08
Basinger, Sherman
Ships
Anchoring arrangement
114230, B63B 2150
Patent
active
050544152
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a mooring/support system for marine structures. In this specification marine structures include submerged structures or structures which float or are supported above or near the surface from the sea bed, and include both mono-hull and semi-submersible type ships, barges, oil or gas drilling and production platforms and vessels, towers, fish nets, pens, or devices which may support communications and radar equipment, navigational aids, or any equipment needed to be positioned at sea. Reference herein to a ship or vessel is accordingly to be taken as meaning any marine structure.
The oil and gas industry in particular have a need for positioning operational ships in a specific location relative to the sea bed so that operations such as drilling for oil or gas, recovering and processing the oil or gas, mining and exploring the ocean or its sub-surface can be achieved. The ships or platforms would hold all the equipment necessary for completing such operations. In addition they would hold the equipment needed for communications and radar operations navigational aids, etc.
When such shipping is used in the production of oil or gas for example, it is essential to control the location of the ship during all environmental conditions within strict tolerances which are required by the characteristics of the connection for the flow of oil and gas between the ship and the sea bed. The limitation may be because of mechanical or operational restrictions.
It is known to anchor a mono-hull or semi-submersible ship using single or multiple conventional chain link or wire cable anchor lines extending downwardly from the ship in one or several directions, the anchor lines being connected to anchors in the sea bed. A riser system, which may be flexible, semi-rigid or rigid, is used for connecting the operational equipment onboard ship to sea bed equipment such as the wellhead of a subsea oil well for example. Turret mooring is provided on a mono-hull type ship to receive the mooring chains and risers while allowing the ship to rotate about the anchorage to take into account tides, winds, currents, etc, without twisting the anchor lines and risers. Uni-directional shaped ships, such as semi-submersibles, can be moored in a fixed orientation because the environmental forces act the same in all directions on the vessel; therefore these types of ships do not need a turret.
Another known marine structure used in the oil and gas industries is the tension leg platform (TLP) which is a semi-submersible type vessel that has post-tensioned anchoring tendons extending substantially vertically from the bottom of the hull to anchor points in the sea bed. This type of platform relies on considerable lateral movement to develop the horizontal restraining force it needs to stay near location. The magnitude of this movement depends on sea depth and weather conditions.
With guyed tower type structures which extend downwardly and engage with the sea bed, lateral support for the top of the tower is provided by flexible guy lines which are fixed to the upper portion of the tower and which are inclined and extend downwardly to the sea bed anchors. There can be several levels of guys.
Self supporting structures are founded on the sea bed, supporting operational platforms above the sea thereon with a structure which diverges outwards and engages with the sea bed. The structure is made of steel or concrete or a combination of both to provide the necessary strength and rigidity. Normally these platforms support the drilling or process equipment above the sea and extend down to the sea floor. The risers, and other connections to the wells are usually contained in the support structure.
In yet another known system in which the ship is dynamically positioned, the ship remains on station during all weather conditions utilizing a position monitoring device which determines the ship's exact location. The monitoring device is connected to a computer controlled propulsion system which repositions the ship
REFERENCES:
patent: 2986888 (1961-06-01), Borrmann et al.
Basinger Sherman
Brahan Thomas J.
Marshall Industries Limited
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