Vessel for laying a pipeline and comprising an A and R means

A vessel (1) for laying a pipeline, the vessel comprising a hull structure (3) comprising one or more floaters (4), a tower (5) defining a firing line (6) when positioned in a pipelaying position, the tower (5) being pivotable relative to the hull structure (3) about a tower pivot axis (7), and an A & R means (8) for abandoning and/or recovering the pipeline, wherein the tower (5) is pivotable about said tower pivot axis (7) substantially independent from the A & R means (8) and the A & R means (8) is configured to operate while the tower (5) is pivoted about said tower pivot axis (7).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No. PCT/NL2007/000327, filed Dec. 21, 2007, the contents of which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a vessel for laying a pipeline, the vessel comprising a hull structure comprising one or more floaters, a tower defining a firing line when positioned in a pipelaying position, the tower being pivotable relative to the hull structure about a tower pivot axis, and an A&R means for abandoning and/or recovering the pipeline. The firing line is the line along which the pipeline is lowered to a seabed. The tower positioned in the pipelaying position defines the firing line. During pipelaying, the pipeline leaves the tower along the firing line.

BACKGROUND OF THE INVENTION

Such a vessel is known from the prior art. During the laying of the pipeline the tower is positioned in an upright position, with an angle relative to the hull structure that is variable. If for one reason or another, the pipelaying operation has to be stopped, for instance when bad weather conditions are forecasted, the vessel has to be prepared for pipe abandonment. This means that the pipeline has to be abandoned from the vessel by positioning the pipeline on the seabed. Furthermore, the tower has to be pivotally lowered towards the hull structure and placed in a lowered position. The pipeline may remain connected to the vessel via for example a cable. Because of the high waves which occur during bad weather, the length of said cable must be such that it provides sufficient clearance between the vessel and the pipeline.

The known vessel abandons the pipeline by means of the A&R means which are provided in the tower. Said A&R means generally comprises reeling means with long cables. During the abandoning operation it is required that the tower remains in an upright position. After the pipeline is positioned on the seabed, the lowering of the tower towards the hull structure and in the lowered position can be started. Said preparation of the vessel for bad weather is a time consuming operation. This is also the case for the preparation of the vessel for resuming an operation, for instance after the weather conditions have improved. For this, the tower has first to be raised from the hull structure to an upright position. After that, the pipeline can be recovered by the A&R means.

This means that the preparation of the vessel for bad weather or for resuming an operation after bad weather is very time consuming. Due to this, costly operational time in which pipeline can be laid is lost.

Furthermore, due to the fact that the preparation of the vessel for bad weather is very time consuming, said preparation has to be started long before the bad weather is expected to arrive. The accuracy of a weather forecast highly depends on the time period in which said forecast is made. This means that a bad weather forecast which is made several hours before the actual arriving of the bad weather is far more accurate than a forecast made one day or more before the arrival of said bad weather. With the known vessel it often happens that due to the a wrong weather forecast, the vessel is taken out of operation and prepared for bad weather, while said bad weather at the end changes of course and does not arrive at the vessel location. Many hours of operational time often lost this way.

SUMMARY OF THE INVENTION

An object of the invention is to provide a vessel which allows a faster preparation of the vessel for bad weather or for operation after bad weather.

The object is achieved by that the tower is pivotable about said tower pivot axis substantially independent from the A&R means and the A&R means is configured to operate while the tower is pivoted about said tower pivot axis.

This has the following effects. For the preparation of the vessel for bad weather, the lowering of the tower does not have to wait until the pipeline is abandoned. For the preparation of the vessel for operation after bad weather, the recovering of the pipeline does not have to wait until the tower is raised in an upright position relative to the hull structure. Costly operational time is saved this way.

Furthermore, it will be clear that by reducing the required time to prepare the vessel for bad weather it is possible to make the decision for such a preparation on basis of a more accurate weather forecast. This means that the risk that the vessel is taken out of operation and prepared for bad weather while said bad weather does not arrive at the vessel is reduced.

In an embodiment of the vessel according the invention, the A&R means comprises a static construction substantially fixed in a specific position. The A&R means are positioned in a position suitable for abandoning or recovering the pipeline, while the tower is pivoted.

In a further embodiment of the vessel according the invention, the A&R means is movable relative to the hull structure and substantially independent of the tower. The A&R means may be pivotable relative to the hull structure about an A&R pivot axis and substantially independent of the tower. The A&R pivot axis may extend substantially parallel with the tower pivot axis. The tower pivot axis and the A&R pivot axis may extend substantial perpendicular to the firing line of the tower. The A&R pivot axis may substantially coincide with the tower pivot axis. The pivotal movement of the tower may define a pivot plane and the A&R means may be pivotable in said pivot plane. Each of these configurations provides a practical and/or constructional advantage.

In another embodiment of the vessel according the invention, the A&R means is configured such that the A&R means is movable between a position in the firing line and a position outside the firing line. When positioned in the firing line, the A&R means may advantageously be used for abandoning and/or recovering the pipeline. When positioned outside the firing line, the A&R means allow the passage of a large structure (like an inline structure) along the firing line. Additionally, when positioned outside the firing line the A&R means may be used in a different function than A&R of a pipeline.

In an embodiment of the vessel according the invention, the vessel comprises a hang off means for hanging off the pipeline, wherein the tower is pivotable independent of the hang off means. The hang off means may for example comprise a hang off table, one or more friction clamps or one or more tensioners. The hang off means may be movable relative to the hull structure and substantially independent of the tower. The hang off means may be pivotable relative to the hull structure about a hang off pivot axis and substantially independent of the tower. The hang off pivot axis may extend substantially parallel with the tower pivot axis. The hang off pivot axis may extend substantially perpendicular to the firing line of the tower. The hang off pivot axis may substantially coincide with the tower pivot axis. The pivotal movement of the tower may define a pivot plane and the hang off means may be pivotable in said pivot plane. Each of these configurations provides a practical and/or constructional advantage.

In a further embodiment of the vessel according the invention, the hang off means is configured such that the hang off means is movable between a position in the firing line and a position outside the firing line. When positioned in the firing line, the hang off means may advantageous be used for hanging off the pipeline. When positioned outside the firing line, the hang off means allow the passage of a large structure (like an in-line-structure) along the firing line.

In another embodiment of the vessel according the invention, the vessel comprises a line up means for lining up the pipeline, wherein the line up means is movable substantially independent of the tower. The line up means may be configured such that the line up means is movable between a position in the firing line and a position outside the firing line. When positioned in the firing line, the line up means may advantageous be used for lining up the pipeline along the firing line. When positioned outside the firing line, the line up means allow the passage of a large structure (like an inline structure) along the firing line. The line up means may be pivotable about a line up pivot axis. The line up means may be pivotable connected to the A&R means.

In an embodiment of the vessel according the invention, the A&R means comprises an U-shaped frame which is at two ends thereof pivotable connected to the vessel. The tower may comprise a U-shaped base which is at two ends thereof pivotable connected to the vessel and wherein the U-shaped frame of the A&R means in may be located inside the U-shaped base of the tower.

In a further embodiment of the vessel according the invention, the vessel comprises a workstation, which is movable between a position in which the work station is located in the firing line to a second position in which the work station is positioned outside the firing line.

The invention also relates to a method of laying a pipeline with a vessel comprising a hull structure comprising one or more floaters, a tower defining a firing line when positioned in a pipelaying position, an A&R means for abandoning and recovering the pipeline, which method comprises the abandoning and/or recovering of the pipeline by means of the A&R means while pivotally moving the tower about a tower pivot axis and relative to the hull structure. The method may comprise the step in which the tower is pivotally lowered to the hull structure while the pipeline is abandoned and/or the step in which the tower is pivotally raised from the hull structure while the pipeline is recovered.

The invention further relates to a method of laying a pipeline with a vessel according to the invention, comprising the steps of positioning the A&R means in a hoisting position, —hoisting an item with the A&R means, and moving the A&R means such that the hoisted item is positioned in the firing line.

The A&R means may be located outside the firing line when the item is positioned in the firing line. The hang off means may be located outside the firing line when the item is positioned in the firing line. The line up means may be located outside the firing line when the item is positioned in the firing line. This is advantageous when the item is a large structure (like an inline structure).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1Aand/or1B show an embodiment of a vessel according the invention, the water line30and the sea bed31. The vessel1is used for the laying of a pipeline2. The vessel1comprises a hull structure3with two floaters4, and a deck34positioned on top of those floaters4. A tower5is positioned at the bow of vessel1. The tower5is positioned in a pipelaying position11in which it defines a firing line6along which the pipeline2is laid. During pipelaying, the pipeline2is constructed from pipe sections and leaves the tower5along the firing line6. The pipelaying position11of the tower5is determined by the pipe departure angle. The tower5is pivotable connected to the vessel1such that the tower5can pivot relative to the hull structure3about a tower pivot axis7. The pivot movement of the tower5is indicated by arrow41. The tower5may be lowered from said pipelaying position to the deck34into a laid down position29. Said pivot movement of the tower5defines a pivot plane (10ofFIG. 2) in which the tower5is pivotable.

The vessel1furthermore, comprises A&R means8which is pivotable about an A&R pivot axis9. The tower5is pivotable independently from the A&R means8. The A&R means is configured to operate while the tower5is pivoted about the tower pivot axis7. Said operation of the A&R means may be the abandoning and/or recovery of the pipeline2. The A&R means8is pivotable relative to the hull structure3and independent of the tower5. The pivot movement of the A&R means8is indicated by arrow42. The A&R means8is positioned behind the firing line6. The position of the A&R means8is adjustable by means of an A&R adjuster32.

The vessel1further comprises a hang off means14for hanging of the pipeline2. The tower5and the hang off means14are pivotable independently from each other. The hang off means14is pivotable relative to the hull structure3about a hang off pivot axis15. The hang off means14is in this figure positioned in the firing line6. The pivotable movement of the hang off means14is indicated by arrow43.

Line up means18are connected to the A&R means8. Said line up means18are pivotable about a line up pivot axis21. Said pivot movement is indicated by arrow45. The line up means18serve to line up a pipe section positioned in the tower along the firing line6. In this figure, the line up means is positioned in the firing line6.

A workstation25is provided for giving shelter to persons working on the pipeline2. Said workstation25is arranged such that it is movable as by arrow44. In this figure the workstation25is positioned in the firing line6. It may be moved along said arrow44to a position outside the firing line.

Due to the specific configuration of the vessel1, it is possible to abandon or recover the pipeline2with the A&R means while pivotally moving the tower5about the tower pivot axis7and relative to the hull structure3. Because of this it is possible to pivotally lower the tower5to the deck34while the pipeline2is abandoned. It is also possible to pivotally raise the tower5from the deck34while the pipeline2is recovered.

FIG. 2shows a view in cross section of the vessel ofFIG. 1. The pivot plane10in which the tower5is pivotable is indicated. The tower5comprises an U-shaped base23. Said U-shaped base23is with two ends24thereof pivotable connected to the vessel1.

The A&R means8comprise an U-shape frame22which is with two ends33thereof pivotable connected to the vessel1. The U-shaped frame22of the A&R means8is located inside the U-shapes base23of the tower5. The line up means18are pivotable connected to the A&R means8. The tower pivot axis7, A&R pivot axis9and hang off pivot axis15coincide.

FIG. 3shows in an enlarged view part III ofFIG. 2. The tower pivot axis7, A&R pivot axis9and pivot axis15are clearly shown is this figure. The tower5, A&R means8and hang off means14can all pivot independently from each other. Although in the drawing all three pivot axes coincide, relatively small height differences may be applied. If the A&R means8is pivotable connected to the tower such that the A&R pivot axis9is located at a relatively small distance above the tower pivot axis7(seen from the view ofFIG. 3), then the A&R means8is substantially movable independent from the tower5even though the A&R means8may be subjected to a small displacement when the tower5is pivoted. The same applies to the hang off means14and the line up means18.

FIG. 4shows an enlarged view of part IV ofFIG. 1during an abandonment or recovery operation. The tower5is shown in the laid down position29but may be raised to the pipelaying position during the A&R operation. The A&R means8is positioned in the firing line6such that the A&R wire38can be lowered or raised following the firing line6. To enable the A&R operation, the line up means18are positioned outside the firing line6. Also the hang off means14are positioned outside the firing line6. During a recovery operation, the hang off means14can be rotated into the firing line6after A&R head39, which is connected to the end of pipeline2, is lifted above said hang off means14positioned in the firing line6.

FIG. 5shows in an enlarged view part V ofFIG. 1while an inline structure35, is positioned along the firing line6. The A&R means8, hang off means17, workstation25and line up means18are positioned outside the firing line6. Because of this, space is created so that the inline structure35can be positioned along the firing line6and lowered, for instance with a travelling block (not shown), such that inline structure35passes the A&R means8, hang off means14, workstation25and line up means18. After passage of the bulky part of the inline structure35the collar46on the stem40of the inline structure can be positioned such hang off means14can be pivoted in the firing line6and under said collar46(shown in dotted lines). Collar46can then be hung off on said hang off means14positioned in the firing line6. The workstation25can be moved in the firing line6and the line up means18can be pivoted into said firing line in order to receive additional pipe sections. In the situation that a pipeline end termination (PLET) is used, the A&R means8can be pivoted into the firing line6for connection of the A&R cable38to the PLET for laydown of the completed pipeline on the seabed31.

FIG. 6shows an enlarged view of part VI ofFIG. 1while an item36is hoisted from the deck34. The A&R means8is positioned in a hoisting position28. In said hoisting position the A&R means8is positioned between the firing line6and the deck34of the hull structure3. The workstation25is positioned in the firing line6. The line up means18are positioned adjacent to the frame of the A&R means8. This way, the item36can be hoisted by the A&R means8and subsequently moved by pivotally moving the A&R means8. It is possible to pivot the A&R means8such that the item36is positioned in the firing line6or in a position past the firing line6.

It will be clear to the person skilled in the art that many different embodiments are possible without departing from the scope of the invention.