Integrated chain-wire rope mooring system

Abstract

An integrated chain-wire rope mooring system is comprised of a mooring line consisting of a chain attached to an anchor at one end and permanently coupled to a wireline at the other end which is wrapped around a drum. A windlass wildcat is positioned preferably adjacent to the drum so that it can be driven and controlled in unison with the drum. An interior sheave is positioned inside or in the vicinity of the chain locker and in the path of the mooring line between the wildcat and the drum. The sheave is sufficiently below the drum to allow the wireline to maintain continuous contact with the sheave such that an acceptable fleet angle is maintained.

Description

BACKGROUND OF THE INVENTION

With offshore drilling progressing to waters beyond the Continental Shelf, there is an increasing need for improved mooring systems that are especially adapted for deep waters beyond 300 meters. While a chain has great mooring advantages, when it becomes too long, it also can present certain disadvantages due to its excessive weight: a very long chain requires a greatly reinforced chain locker; because of the heavy weight of chain, a mooring line exclusively of chain takes on too steep an angle near the water surface, thereby imposing an inferior restoring force in the horizontal direction.

It is an object of the present invention to provide a mooring line which consists of a wire rope permanently coupled to a long chain for use in an integrated chain-wire rope mooring system and employing an interior sheave which is adapted to sequentially move over its periphery in either direction a chain, a wireline, and a connector therebetween. Accordingly the integrated mooring system of this invention requires no making and breaking of the connection between the wireline and the chain each time that the mooring line is paid out or hauled in.

SUMMARY OF THE INVENTION

An integrated mooring system is provided having a mooring line consisting of a chain and a wireline, permanently coupled to each other by a connector device. The wireline is wound on a drum, preferably, though not necessarily, positioned adjacent to and at the same time elevation as a wildcat, so that both the drum and the wildcat can be powered and controlled together. An interior sheave is positioned in the path of the mooring line between the drum and the wildcat. The sheave is preferably in or in the vicinity of the chain locker and sufficiently below the drum so as to continuously maintain contact with the wireline and maintain an acceptable fleet angle. To pay out the mooring line, the drum remains stationary and the wildcat is rotated until the chain has been completely run out from its locker. The chain or wire rope then forms a loop around the interior sheave, applying tension to the wireline which causes the drum to start to rotate with the wildcat to unwind the wireline. After all the chain is paid out, the wildcat acts only as an unpowered fairlead sheave for the wire line, which is being paid out from the wireline drum, passing around the lower or chain locker sheave, over the wildcat, and thence overboard. The wireline can then follow the chain's path over the components of the mooring system.

The mooring line is retrieved by rotating the drum in an opposite direction thereby winding the wireline on the drum until the connector device is pulled just past the lower sheave. The drum is then stopped and only the wildcat is rotated to retrieve the chain which is allowed to pile up in the chain locker. For a brief period of time, during which the connector between chain and wire has passed over the wildcat but has not yet reached the position in which it will remain while the wire has been retrieved to the maximum extent and is stored on the drum, both the wireline winch and the windlass wildcat are hauling in under power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the integrated chain-wire rope mooring system of this invention with the chain piled up in the chain locker and the leading end of the wireline and connector just past the outer periphery of the sheave;

FIG. 2 is similar to FIG. 1, showing the chain after it has been completely taken out from its locker, and the wireline drum has begun paying out so that the connector has passed over the lower sheave and over the windlass wildcat; and

FIG. 3 is similar to FIG. 2, but with the mooring line further advanced, the connector now being outboard of the outer fairlead.

Referring now to the drawings wherein the same numerals are used to designate the same parts, the integrated mooring system 12 of this invention is conveniently mounted on a suitable support, such as a column or mooring tower 10. System 12 uses a mooring line 14 which consists of a wireline 16, a chain 18, and a connector 20 for permanently connecting the wireline to the chain. The connector can be of the type as manufactured by Pusnes or Skagit Corporations or others skilled in the design and manufacture of mooring equipment.

Wireline 16 is wound on the cylindrical periphery of a spool or drum 22 which is rotatably mounted about a shaft 24. Drum 22 is mounted at an elevated position relative to a chain locker 26 in which chain 18 is piled. An anchor windlass wildcat 28, preferably positioned adjacent to drum 22, is rotatably mounted about a shaft 30. Wildcat 28 is followed by a fairleader 32 rotatably mounted about a shaft 34 supported on an exterior bracket 35 extending from tower 10 below wildcat 28.

In accordance with the gist of this invention, an interior fairleading device such as a sheave 36 is located in, on top of, or underneath locker 26 and is rotatably mounted about a shaft 38. Sheave 36 has a circumferential periphery adapted to accept sequentially chain 18, connector 20, and rope 16 in either direction. It is essential to position sheave 36 sufficiently below drum 22 to allow proper fleet angles between the sheave and drum and at a distance from a vertical plane passing through shaft 24. Any other arrangement will be acceptable as long as the wireline continuously maintains contact with sheave 36 when all the chain is out of the locker.

Thus the term "interior sheave" as used herein and in the claims indicates an appropriately located sheave relative to the other components of the mooring system 12, including chain locker 26, drum 22, and wildcat 28. The appropriate location for sheave 36 may include any position that enables the sheave to serve its intended function between wildcat 28 and drum 22.

It is also desired to locate wireline drum 22 and wildcat 28 adjacent to one another so that they can be driven by a single drive unit 40 and controlled by a control-transmission unit 42, whereby shafts 24 and 30 can be driven simultaneously or independently.

The operation of the novel integrated mooring system 12 of this invention will now be described. When the mooring system is not in use, chain 18 is piled up in chain locker 26 with its leading end extending over wildcat 28 and under fairleader 32. The wireline is wound on drum 22. In use, the leading end of the chain is attached to an anchor or to any other object desired to be used in mooring. Wildcat 28 is rotated clockwise (FIG. 2) until the entire chain is taken out from chain locker 26. The chain then forms a bottom loop around interior sheave 36. When that happens, both drum 22 and wildcat 28 are made to rotate in a clockwise direction and in synchronism, thereby causing wireline 16, chain 18 and connector 20 to move sequentially over the components of the mooring system 12.

In the position of the mooring line 14 shown in FIG. 3, the chain is completely submerged in the body of water and the wireline extends from tower 10 down to a desired depth. The wireline forms a desired mooring angle 41 which is considerably smaller than a comparable angle that would have been formed if only chain were used in the mooring line. The smaller this mooring angle, the greater will be the horizontal component of the required restoring force imposed on the mooring system.

To retrieve the mooring line, the above described process is repeated in reverse, that is, drum 22 and wildcat 28 are rotated counterclockwise until connector 20 returns to the chain locker 26 and preferably past and above interior sheave 36 (FIG. 1). At that point, drum 22 is stopped and only wildcat 28 is allowed to continue to rotate until the chain piles up in chain locker 26 with only the leading end of the chain remaining past fairleader 32.

The integrated mooring system of the present invention is characterized by several advantages, chief among which are: there is no need to make and break the connection between wireline 16 and chain 18 each time that the mooring line 14 is paid out or hauled in. The location of the interior sheave in the vicinity of the chain locker allows for an orderly transition from chain to wireline and vice versa. The entire mooring line can be controlled by a single controltransmission unit.

Changes will readily suggest themselves to those skilled in the art without departing from the scope of the attached claims:

Claims

What is claimed is:

1. An integrated mooring system for a floating structure, said system comprising:

a mooring line including a wireline, a chain and a connector coupling the wireline to the chain;

a drum for winding and unwinding the wireline, said drum being mounted on a mooring tower which defines a chain locker;

a wildcat mounted on said structure for paying-out and paying-in said mooring line from and into said chain locker;

an interior sheave mounted inside said tower and disposed at a sufficient distance below said drum and in a position so as to allow the wireline to continuously remain in engagement with the sheave; and

power means adapted to rotate said drum and said wildcat simultaneously or sequentially; and

said means being operable to stop the drum and continue rotation of said wildcat to effect storage of said chain in said locker during a pay-in of said mooring line.

2. An integrated mooring system mounted on a floating structure having a chain locker, said system comprising:

a mooring line including a wireline, a chain and a connector coupling the wireline to the chain;

a drum for winding and unwinding the wireline;

a wildcat mounted on said structure for paying-out and paying-in said mooring line from and into said chain locker;

an interior sheave mounted at a sufficient distance below said drum and in a position so as to allow the wireline to continuously remain in engagement with the sheave; and

power means adapted to rotate said drum and said wildcat simultaneously or sequentially, said means being operable to stop the drum and continue rotation of said wildcat to effect storage of said chain in said locker during a pay-in of said mooring line.

3. An integrated mooring system for mooring a structure floating on a body of water, said system comprising:

a mooring line consisting of: a wireline, a chain, and a connector coupling the wireline to the chain;

a drum rotatably mounted on said structure, a chain locker in said structure for housing said chain;

a wildcat mounted on said structure for paying-in and paying-out said mooring line;

a suitably disposed interior sheave adapted to remain in continuous engagement with said wireline; and

power means adapted to rotate said drum and said wildcat simultaneously or sequentially,

said power means being operable to stop said drum after winding said wireline thereon and continue rotation of said wildcat to effect storage of said chain in said chain locker during a pay-in of said mooring line.

4. An integrated mooring system for mooring a structure floating on a body of water, said system comprising:

a mooring line consisting of: a wireline, a chain, and a connector coupling the wireline to the chain;

a drum rotatably mounted on said structure, a chain locker in said structure for housing said chain;

a wildcat mounted on said structure for paying-in and paying-out said mooring line; and

power means adapted for selectively powering said drum and said wildcat simultaneously or sequentially,

said power means being operable to stop said drum after winding said wireline thereon and continue rotation of said wildcat to effect storage of said chain in said chain locker during a pay-in of said mooring line.