BACKGROUND OF THE INVENTION

In shallow waters, pipelay is primarily done by an â€œS-Layâ€ method, which means that the welding is done along the deck of a flat barge and then the pipe bends down to the ocean floor in a sort of â€œSâ€ curve. The pipe bends down on a radiused stinger and then naturally curves back to horizontal as it reaches the ocean floor. In deeper water, the forces on the stinger and the size of the required stinger make it more favorable to weld the pipe together in a near vertical position and have a single bend at the ocean floor. The forms a â€œJâ€ in the pipe and gives it the name of the â€œJ-Layâ€ method.

Offshore deepwater pipeline laying systems are characteristically limited to high cost specialty vessels due the combination of loads and positioning required to accomplish the pipelaying. J-Lay pipelay systems are characteristically complicated and require special connections to the vessel. This makes a costly specialty custom vessel an appropriate investment. As the custom vessel is an appropriate investment, investment in onboard dynamic positioning also becomes an appropriate investment.

Dynamic positioning is using the propellers to actively hold the vessel in position, in contrast to passively holding the vessel in position with anchors and anchor lines.

A pipelay system such as the Flex J-lay Tower described in U.S. Pat. No. 6,776,560 provides the unique ability to be simply mounted on a flat and economical barge. Such a barge or vessel would typically not have dynamic positioning available. The barge or vessel could then be positioned along the pipeline route by one or more service boats which can provide the dynamic positioning capability. The service boats would be connected to the barge or vessel by the connections of this invention.

Such service boats have previously been connected to vessels of this type by a rope, which provides only an axial tension. If the service boat wants to provide a force on the vessel in any direction other than straight along the rope, the service boat must move radially around the connection point on the vessel to another position. The service boat could then pull in that direction only.

An appropriate mechanical connection would have the ability for the service boat to push or pull the vessel. When the service boat has a horizontal bow thruster, it can provide a sideways force on the connection, and therefore on the vessel. By combinations of axial thrust and sideways bow thrusters, the service boat can impart a force on the vessel in any horizontal direction.

A complication to a mechanical connection between the vessel and the service boat is that the larger vessel and the smaller supply boat will characteristically have different periods of vertical motion. As one is going up, the other will be going down at some times during operations.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is to provide a system for improved dynamically positioning a vessel by mechanically connecting one or more dynamically positioned service boats to the vessel.

A second object of the present invention is to provide 3 degrees of rotational freedom on the mechanical connection between the vessel and the one or more service boats.

A third object of the present invention is to provide one degree of axial freedom for normal operations.

Another object of the present invention is to provide a second degree of mechanical freedom when desired.

Another object of the present invention is to allow the service boat to exert a sideways force on the vessel.

Another object of this invention is to allow the service boat to exert a push or pull on the vessel in any direction

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view of a j-lay system on a barge and of a supporting pipe barge, each having service boats connected by connections of this invention for dynamic positioning.

FIG. 2 is a view of a portion of the pipelay barge and a service boat with the connection of this invention between.

FIG. 3 is an enlarged view of the joint between the central connection member and the pipelay barge.

FIG. 4 is an enlarged view of the joint between the central connection member and the service boat with dynamic positioning.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a pipelay vessel 1 with a j-lay tower 2 mounted on the deck 4. A pipe supporting mechanism 6 is shown with a portion of the pipeline 8 suspended in the ocean water. Service boats 10 and 12 are attached to the pipelay vessel 1 by links 14 and 16 respectively.

Side thrusters 18 are provided near the bow of the service boats 10 and 12 which enable the service boats to provide a lateral force on links 14 and 16. Various combinations of lateral and axial forces from the service boat to the vessel allow the service boat to impart forces in any direction to the vessel.

An additional barge 20 is shown in a position to re-supply the pipelay vessel 1 with pipe or other supplies. A third service boat 22 is shown attached by link 24.

Referring now to FIG. 2, link 14 is shown between vessel 1 and service boat 10. Pivoting joint 30 is shown engaging funnel 32 which is mounted to vessel 1 at 34. The mounting can be prepared and permanently affixed to the vessel 1, can be removeably attached, or can be magnetically attached.

Pivoting joint 40 is shown engaging funnel 42 which is mounted to service boat 10 at 44. Portion 46 of the mounting can be prepared and permanently affixed to the vessel 10 and portion 48 can be bolted to portion 46.

Link 14 has a main axial member 50 and a structure 52. Cables or chains 54 and 56 connect between structure 52 and service boat 10 to restrict rotational movement in the plane of the surface of the ocean, restricting the two vessels to a single degree of axial freedom relative to each other. When an extra degree of axial freedom is desired, tension can be released on cables or chains 54 and 56. Buoyancy material 58 is shown generally within the structure 52 to make the structure 52 positively buoyant.

Cables or chains can be installed on the opposite end of the link and attached directly to the vessel to restrict the degree of motion on the opposite end of the link.

Referring now to FIG. 3, pivoting joint 30 is shown in greater detail. Central member 60 is pivoted horizontally relative to main axial member 50 about a vertical pin generally located at 62 (not shown). Motor 63 can be powered to rotate central member 60 about the vertical pin located at 62. Stab 64 is pivoted vertically relative to central member 60 about a horizontal pin generally located at 66 (not shown). Stab 64 lockingly engages funnel 32 to connect to vessel 1 and can rotate about the centerline of the stab. Cylinder 68 can be used to position the stab 64 when the stabbing connection is made. Vertical pin at 62, horizontal pin at 66, and stab 64 provide 3 degrees of angular freedom.

Referring now to FIG. 4, pivoting joint 40 is shown in greater detail. Central member 70 is pivoted horizontally relative to main axial member 50 about a vertical pin generally located at 72 (not shown). Motor 73 can be powered to rotate central member 70 about the vertical pin located at 72. Stab 74 is pivoted vertically relative to central member 70 about a horizontal pin generally located at 76 (not shown). Stab 74 lockingly engages funnel 42 to connect to service boat 10 and can rotate about the centerline of the stab. Cylinder 78 can be used to position the stab 74 when the stabbing connection is made. Horizontal pin at 66 vertical pin at 76, and stab 74 provide decrees of angular freedom.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.