Mooring system for stabilizing a vessel, a vessel, method for stabilizing a vessel and use of a mooring system

The present application is a continuation of pending International patent application PCT/DK2007/000566 filed on Dec. 21, 2007 which designates the United States and claims priority from Danish patent applications PA 2007 00296 filed on Feb. 27, 2007 and PA 2006 01701 filed on Dec. 22, 2006, the content of which is incorporated herein by reference.

The invention relates to a mooring system for stabilizing a vessel for handling offshore structures, a vessel, a method of stabilizing a vessel for handling offshore structures and use of a mooring system.

Vessels for transportation and mounting of offshore structures to be installed on offshore locations are known in the art.

As it is often desired to maintain the vessel in a substantially fixed position during loading/unloading and/or during mounting of said offshore structures, it is a challenge of the vessel to overcome its motion due to wind, waves and current. Different vessels and methods have been suggested for this purpose.

European patent EP 1 220 775 B discloses a vessel for transporting and mounting windmills on previously built structures on the seabed. The vessel comprises at least four vertically elevational support legs mounted in consoles connected to the hull for the support of the vessel on the seabed.

German patent DE 100 21 163 B discloses a vessel comprising four vertically elevational support legs, two by two connected to lift tanks. The lift tanks can be elevated to contact with the seabed whereby the vessel can be lifted above the waterline with its lift tanks resting on the seabed.

A disadvantage of the described vessels is that they are sensible to seabed conditions due to seabed penetration when jacked up. Furthermore rigid vertically elevational support legs are used which in its construction is a relatively complicated set-up.

International patent application WO 2004/046467 A discloses a composite converted vessel for performing drilling operations while supported on a bottom of a water body. The vessel comprises a floating drilling rig component and a support barge component. The barge component comprises a ballast system including pumps that is able to ballast the vessel to rest on the bottom of a water body. Furthermore the barge component comprises a substantially planar bottom.

A disadvantage for the described converted vessel is that it is a complicated and non-flexible setup regarding the construction of the support barge component that must be specific designed to the drilling rig component to which it supports.

It is an object of the invention to provide technique without the above mentioned disadvantages and to simplify the construction of the vessel and hereby increase its operational reliability and capability and flexibility. Furthermore it is an object to preserve the ability of a vessel according to the invention to maintain it in a substantially fixed position during loading/unloading and/or during mounting of offshore structures.

The invention relates to a mooring system for stabilizing a vessel for handling offshore structures where said system comprise at least one mooring unit, connection means for connecting said mooring unit to said vessel, and tractive means for stabilizing said vessel by establishing permanent tension in said connection means. Furthermore said tractive means comprises means for lowering said connected vessel\'s position in relation to the water level.

By vessel is meant any types of boat, ship, craft or the like that is suitable and/or can be arranged for the purpose of handling offshore structures.

By mooring unit is meant a unit that is not a part of the vessel and is free to operate in relation to the hull of said vessel. For various embodiments the mooring unit can be mobile or established at a fixed position.

By tractive means is meant means that is able to establish tension in attached connection means. Tractive means also comprises means that is able to regulate and/or dynamically control the established tension in the connection means.

By the terms permanent tension is meant that the tension in said connection means is applied without interruption when said mooring system is in use but the tension force can be altered, controlled, regulated and/or adjusted during use i.e. the tension force is not constant in relation to time.

By stabilizing said vessel in relation to the present invention is meant that the vessel can be held in positions in such a way that the influence on the movement of the vessel in all directions due to environmental parameters such as waves, tidal, current and/or wind is minimized.

By lowering the vessel\'s position in relation to the water level it is ensured that especially the impact of environmental parameters such as waves on the vessel movement in e.g. vertical direction is reduced.