PULL IN - PAY OUT MOORING SYSTEM AND METHOD OF USING THE SAME

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable. BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to methods and apparatus for mooring floating platforms More specifically, certain embodiments of the present invention relate to systems for tensioning mooring lines that are connected to a floating vessel

Multi-leg mooring systems generally include a plurality of mooring lines extending outward from a floating platform to a plurality of anchors set into the seafloor. Each moonng line comprises a short length of chain extending from the vessel and connected to a long length of mooring line running to the anchor. Common procedures for anchoring the vessel include extending (pay out) the chain segment from the vessel so as to connect the chain segment to the mooring line that is connected to the anchor, which has been previously set at the seafloor. The chain segment is then pulled into (pull in) the vessel until the proper tension is generated in the mooring line.

Once the mooring line has been tensioned, the chain is fixed to the vessel so as to maintain the tension in the mooring line This procedure is repeated for each mooring line until the vessel is securely moored. In order to tension the next mooring line, the equipment used to handle the chain is relocated to the next line and set up for use One key component of the handling equipment is the large pull-in winches that are used to pull the chain segments and generate the proper tension m the mooring line Many vessels are equipped with fewer pull-m winches than mooring lines and therefore the winches have to be moved between lines during the mooring procedure. Moving the pull-in winches increases the time needed for mooring as well as increases the difficulty in making later adjustments of the mooring system, such as relocating the vessel within its watch circle. When relocating a vessel within its watch circle, separate mooring lines are payed out or pulled in to change the position of the vessel This process can be time consuming when the mooring lines can only be adjusted one line at a time.

Thus, the embodiments of the present invention are directed to mooring systems that seek to overcome these and other limitations of the prior art.

SUMMARY OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention include a mooring method for a moored vessel that comprises a first chain stopper that is fixed to the vessel and is operable to selectively

couple an upper chain to the vessel. A chain tensioner is coupled to the vessel and is operable to pull the upper chain. A second chain stopper is fixed to the vessel and is operable to selectively couple the upper chain to the vessel. The chain tensioner engages the upper chain at a location between the first chain stopper and the second chain stopper. Thus, the embodiments of present invention comprise a combination of features and advantages that enable substantial enhancement of mooring a floating vessel. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed understanding of the present invention, reference is made to the accompanying Figures, wherein:

Figure 1 is a partial schematic view of a vessel having a mooring system designed in accordance with embodiments of the invention; Figure 2 is more detailed view of the vessel of Figure 1;

Figure 3 illustrates a first phase in a mooring operation using a mooring system designed in accordance with embodiments of the invention;

Figure 4 illustrates a second phase in the mooring operation of Figure 3; Figure 5 illustrates a third phase in the mooring operation of Figure 3; and Figure 6 illustrates a fourth phase in the mooring operation of Figure 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness.

Referring now to Figure 1, mooring system 10 for vessel 12 comprises a plurality of mooring lines 14 coupled to subsea anchors 15. Each mooring line 14 comprises lower chain

16, main mooring line 18, and upper chain 20. Lower chain 16 of each mooring line 14 is coupled to a subsea anchor 15. Main mooring line 18 is coupled to lower chain 16 and extends upward through the water to upper chain 20, which connects to vessel 12.

Referring now to Figure 2, vessel 12 comprises fairleads 22 A-B, chain stoppers 24A- B, chain lockers 26A-B, and chain tensioner 28. Chain tensioner 28 and chain lockers 26A-B are located close to a centerline of vessel 12. Chain tensioner 28 can be any device that can

apply tension to the chain, such as a chain jacks, chain windlasses, and chain capstans. Fairleads 22A-B and chain stoppers 24A-B are disposed on or near the sides of vessel 12. Fairleads 22A-B redirect and laterally secure upper chain 20 as it comes in contact with vessel 12. Chain stoppers 24 A-B releasably engage the upper chain 20 Upper chain 20 is a continuous length of chain that is connected to each mooring line

14A, 14B. From mooring line 14A, upper chain 20 is guided by fairlead 22A upward to chain stopper 24A, which releasably engages one or more links of upper chain 20 so as to effectively fix the chain relative to vessel 12. Upper chain 20 passes from chain stopper 24A to chain tensioner 28 and then to chain stopper 24B. Upper chain 20 passes from chain stopper 24B through fairlead 22B and connects to the opposite mooring line 14B.

Chain lockers 26 are disposed on either side of chain tensioner 28 to store any slack lengths upper chain 20 between the chain tensioner and either chain stopper 24A-B. In certain embodiments, chain lockers 26 may be receptacles built into the hull of vessel. In other embodiments, excess chain may simply be suspended below the decks of the vessel in catenary loops or on a support vessel adjacent to the vessel.

Figures 3-6 show a mooring operation using mooring system 10 as described in Figures 1 and 2. A first phase of the mooring operation is shown in Figure 3. Anchors 15 are set in the seafloor at predetermined locations. Lower chains 16 and main mooring lines 18 are connected to anchors 15 and are suspended by buoys 30. The installations of anchors 15 and the pre-positioned portions of the mooring lines 14A-B are often performed by a specially designed installation vessel 32 or other service vessel before the arrival of floating vessel 12.

Once floating vessel 12 is on location, upper chain 20 is payed-out from the vessel by releasing chain stopper 24A and pulling the chain with installation vessel 32. Upper chain 20 is pulled from chain locker 26A until the end of the chain can be coupled to mooring line 14A by installation vessel 32, as is shown in Figure 4. Chain tensioner 28 is then activated so as to pull-in upper chain 20 until the desired tension is achieved in mooring line 14A. Chain stopper 24A is then engaged with upper chain 20 to fix the chain relative to vessel 12 and maintain the tension in mooring line 14A. During tensioning, excess chain can be disposed in chain locker 26B or may be simultaneously payed-out to a second mooring line 14B by installation vessel 32, as is shown in Figure 5. Chain tensioner 28 is then activated in the opposite direction so as to pull in upper chain 20 until the desired tension is achieved in mooring line 14B. Chain stopper 24B

is then engaged with upper chain 20 to fix the chain relative to vessel 12 and maintain the tension in mooring line 14B.

Referring now to Figure 6, once mooring lines 14A-B have been fully tensioned, chain tensioner 28 can be relocated to another pair of mooring lines 14C-D. The procedure is then repeated until each pair of mooring lines is fully tensioned. In some embodiments, each pair of mooring lines may have its own chain tensioner therefore eliminating the need to relocate the chain tensioner.

Thus, the mooring system 10 described above provides faster installation than conventional systems. Mooring system 10 allows upper chain 20 of one mooring line to be pulled-in while simultaneously paying-out the upper chain that connects to another mooring line. This can eliminate the need for a special pull-in winch and saves time because as one line is being tensioned, the chain for the next mooring line is being payed-out. The system may be further enhanced by using a multi-speed chain tensioner that allows the initial low tension pull-in to be carried out faster. In certain embodiments, vessel 12 may also be able to relocate by adjusting the tension in mooring lines 14. By pulling-in and paying-out select mooring lines 14, vessel 12 can be repositioned at any location within its watch circle. A vessel may be relocated within its watch circle in order to drill multiple wells. With conventional mooring systems and vessels, this operation is done by pulling in and paying out separate mooring chains on separate windlasses. Mooring system 10 simplifies this relocation process by enabling the simultaneous pulling-in and paying-out of at least two mooring lines at one time. Thus, when one end of an upper chain is pulled in, the slack portion is fed into a chain locker, a catenary loop, or onto a support vessel, and then payed out on the other side of the vessel.

The preferred embodiments of the present invention relate to apparatus and systems for mooring a floating vessel. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. In particular, various embodiments of the present invention provide mooring systems for floating vessels. Reference is made to the application of the concepts of the present invention to mooring a semi-submersible vessel, but the use of the concepts of the present invention is not limited to these applications, and can be used for any other applications including other moored floating vessels. It is to be fully

recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.

The embodiments set forth herein are merely illustrative and do not limit the scope of the invention or the details therein. It will be appreciated that many other modifications and improvements to the disclosure herein may be made without departing from the scope of the invention or the inventive concepts herein disclosed. Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.