U.S. patent application number 11/458818 was filed with the patent office on 2007-01-25 for reverse tensioned mooring system.
Invention is credited to John Mathew Riggs.
Application Number | 20070017429 11/458818 |
Document ID | / |
Family ID | 39107469 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070017429 |
Kind Code |
A1 |
Riggs; John Mathew |
January 25, 2007 |
REVERSE TENSIONED MOORING SYSTEM
Abstract
In a method of mooring floating structures a chain receiving
device is secured to an anchor and a forerunner chain is extended
through the chain receiving device, after which the anchor is
secured in engagement with the sea floor. A mooring line is
extended between a floating structure and the forerunner chain. A
tensioning device on an anchor handling vessel is employed to apply
mooring tension to the forerunner chain thereby applying mooring
tension to the mooring line secured between the forerunner chain
and the floating structure. Mooring tension is maintained by the
chain receiving device on the anchor.
Inventors: |
Riggs; John Mathew;
(Woodlands, TX) |
Correspondence
Address: |
Michael A. O'Neil;Michael A. O'Neil, P.C.
Suite 820
5949 Sherry Lane
Dallas
TX
75225
US
|
Family ID: |
39107469 |
Appl. No.: |
11/458818 |
Filed: |
July 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60701369 |
Jul 21, 2005 |
|
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|
Current U.S.
Class: |
114/293 |
Current CPC
Class: |
B63B 21/50 20130101 |
Class at
Publication: |
114/293 |
International
Class: |
B63B 21/50 20060101
B63B021/50 |
Claims
1. A method of mooring floating structures comprising the steps of:
providing a subsea anchor; providing a chain receiving device;
securing the chain receiving device to the anchor; providing a
forerunner chain; extending the forerunner chain through the chain
receiving device on the anchor; securing the anchor having the
chain receiving device secured thereto and having the forerunner
chain extending through the chain receiving device in operative
engagement with the sea floor; providing a floating structure;
providing a mooring line; securing the mooring line in engagement
with the floating structure; securing the mooring line in
engagement with the forerunner chain; providing an anchor handling
vessel; providing a tensioning device on the anchor handling
vessel; securing the forerunner chain in operative engagement with
the tensioning device on the anchor handling vessel; utilizing the
tensioning device on the anchor handling vessel to apply mooring
tension to the forerunner chain and thereby applying mooring
tension to the mooring line secured to the floating structure; and
utilizing the chain receiving device on the anchor to maintain
mooring tension.
Description
CLAIM OF PRIORITY
[0001] This application claims priority of provisional application
Ser. No. 60/701,369 filed Jul. 21, 2005, currently pending, the
entire contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates generally to systems for mooring
floating structures, and more particularly to a mooring system
which eliminates the requirement for providing tensioning
mechanisms on floating structures to be moored, and in lieu thereof
utilizes tensioning mechanisms mounted on one or more anchor
handling vessels to apply mooring tension.
BACKGROUND AND SUMMARY OF THE INVENTION
[0003] Traditionally, floating structures such as drilling rigs,
production rigs, CALM buoys, SPARs, FPSOs, FSOs, etc. have been
moored to an anchor system that is put under operating tension by
tensioning equipment on the floating structure. For large surface
structures the mooring tensioning equipment usually contains
winches, fairleads, chain lockers, presets, and excess wire reels.
When the floating structure is brought onto location, the anchors
are run out, or alternatively, the preset mooring lines are
connected to the anchors (the so called preset anchor system).
[0004] Once the floating structure is connected to the anchors, by
either method, the mooring legs are tensioned to the design
specifications and the structure is secured at the desired
location. Thus, tensioning is done at the structure for large
floating structures. For smaller structures, such as CALM buoys,
the tensioning is done by temporary winches or cranes. The concept
is the same; the tensioning is done at the floating structure.
[0005] For example, in the case of suction anchors, the mooring
padeye is commonly located two-thirds of the way down the side of
the anchor. The suction anchor is preinstalled and the anchor
forerunner chain is attached to the mooring padeye. The end of the
forerunner chain is run out and extends to a subsea connector which
is typically positioned on the sea floor. When the floating
structure is brought on location, the mooring line is connected to
the subsea connector and the mooring leg is tensioned by tensioning
equipment on the floating structure. Plate anchors, driven piles,
and other vertically loaded anchors have the same arrangement and
means of tensioning.
[0006] The mooring system of the present invention differs in that
tensioning is done at the anchors with the aid of tensioning
equipment on an anchor handling vessel. There is no need for any
tensioning equipment on the floating structure. The mooring line is
connected to the floating structure by means of a simple, fixed
padeye or similar appurtenance. No winches, fairleads, etc. are
needed on the floating structure.
[0007] For each anchor type the modifications necessary in order to
implement the present invention are the same. The padeye is
replaced with a turning shoe or chain whelp. In addition to the
shoe or whelp, a stopper mechanism such that the chain can pass in
one direction only (away from the floating structure) is
incorporated. If the anchor has a portion of its structure above
the mudline the stopper may be located at the top of the anchor.
For completely embedded anchors the stopper may be incorporated
into the turning shoe or whelp. The stopper mechanism has a release
line or mechanism such that the mooring line tension can be
released, if necessary. The forerunner chain is run through the
turning shoe or whelp and back to the surface, either on top of the
pile or suction anchor, or on the sea floor for plate anchors or
vertically loaded anchors. The subsea connector arrangement is the
same as with conventionally tensioned mooring systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A more complete understanding of the invention may be had by
reference to the following Detailed Description when taken in
conjunction with the accompanying Drawings, wherein:
[0009] FIG. 1 is an illustration of a prior art mooring system;
[0010] FIG. 2 is an illustration of an initial step in a method of
mooring floating structures comprising a first embodiment of the
invention;
[0011] FIG. 3A is an illustration of a somewhat later step in the
method of mooring floating structures comprising the first
embodiment of the invention;
[0012] FIG. 3B is an illustration of a still later step in the
method of mooring floating structures comprising the first
embodiment of the invention;
[0013] FIG. 3C is an illustration of a still later step in the
method of mooring floating structures comprising the first
embodiment of the invention wherein a tensioning device on an
anchor handling vessel is connected to a mooring line extending to
a floating structure;
[0014] FIG. 3D is an illustration of a still later step in the
method of mooring floating structures comprising the first
embodiment of the invention wherein the tensioning device of the
anchor handling vessel is utilized to apply mooring tension to the
mooring line extending to the floating structure;
[0015] FIG. 4A is an illustration of an initial step in a method of
mooring floating structures comprising a second embodiment of the
invention; and
[0016] FIG. 4B is an illustration of a later step in the method of
mooring floating structures comprising the second embodiment of the
invention.
DETAILED DESCRIPTION
[0017] Referring to the drawings, and particularly to FIG. 1 there
is shown a conventional floating structure 10. Although a
particular type of floating structure is illustrated in FIG. 1,
those skilled in the art will understand that the floating
structure 10 may comprise a drilling rig, a production rig, a CALM
buoy, a SPAR, an FPSO, an FSO, etc. As is also well known, larger
floating structure are typically provided with a plurality of
permanently installed tensioning devices 12 such as winches or the
like. In the case of smaller floating structures, such as CALM
buoys, one or more tensioning mechanisms may be temporarily
installed thereon for use during the mooring process.
[0018] Regardless of the type of tensioning devices that are
installed on the floating platform 10 and regardless of whether the
tensioning devices are temporarily or permanently installed, the
tensioning devices are utilized to apply mooring tension to a
plurality of mooring lines 14 which extend from the floating
structure 10 to a plurality of anchors 16 each individual to one of
the mooring lines 14. Those skilled in the art will appreciate the
fact that the anchor 16 illustrated in FIG. 1 is a suction pile of
the type shown and described in U.S. Pat. No. 6,009,825 the
disclosure of which is incorporated herein by reference. However,
the mooring system of FIG. 1 can also be utilized in conjunction
with other anchor types such as plate anchors, driven piles,
vertically loaded anchors, etc., all of which are well known in the
art.
[0019] The method of mooring floating structures of FIG. 1 begins
with the installation of a plurality of anchors at spaced apart
locations around a mooring location. When the anchor is installed,
a forerunner chain connected thereto is extended along the sea
floor in the general direction of the mooring location. After all
of the necessary anchors are installed, the floating structure 10
is moved to the mooring location and the mooring lines 16 thereof
are connected to the forerunner chains extending from the
previously installed anchors 16. At this point the tensioning
mechanisms 12 mounted on the floating structure 10 are employed to
apply mooring tension to the mooring lines 14. After the necessary
mooring line tension has been achieved, the tensioning mechanisms
12 mounted on the floating structure 10 serve no further purpose
unless and until the floating structure 10 is repositioned or
relocated.
[0020] FIGS. 2, 3A, 3B, 3C, and 3D illustrate a method of mooring
floating structures comprising a first embodiment of the present
invention. Referring particularly to FIG. 2, an otherwise
conventional suction anchor 20 is lowered into engagement with the
sea floor by a line 22 extending from an anchor handling vessel.
The suction anchor 20 is provided with a chain receiving device 24
which may comprise a turning shoe, a chain whelp, etc. A chain 26
extends around the device 24. One end of the chain is secured to
the suction anchor 20 by a chain stopper 28. The opposite end of
the chain includes a subsea connector 30 which is initially
connected to the anchor handling vessel by a line 32.
[0021] As the line 22 is payed out from the anchor handling vessel,
the suction anchor 22 initially penetrates the uppermost layers of
the sea floor under its own weight. Thereafter a pumpskid 40 is
engaged with the suction anchor 20. The pumpskid 40 is preferably
of the type illustrated and described in U.S. Pat. No. 5,927,904
the disclosure of which is incorporated herein by reference. The
function of the pumpskid 40 is to pump water out of the interior of
the suction anchor 20 whereby the suction anchor 20 is driven
downwardly into the sea floor under the action of the pressure that
is imposed upon the suction anchor 20 by the sea. Operation of the
pumpskid 40 and downward movement of the suction anchor 20 into the
sea floor continue until only the uppermost portion of the suction
anchor 20 remains exposed above the upper surface of the sea
floor.
[0022] Referring to FIG. 3A, the suction anchor 20 is shown fully
installed in the sea floor. The forerunner chain 26 extends
upwardly from the device 24, and then along the surface of the sea
floor to the subsea connector 30. An anchor handling vessel 42
connects a mooring line 44 to a floating structure 46 in the
conventional manner. The floating structure 46 may comprise many of
a wide variety of floating structures such as a drilling rig, a
production rig, a CALM buoy, a SPAR, an FPSO, an FSO, etc. The
floating structure 46 is identical to the floating structure 10 of
FIG. 1 except that the floating structure 46 is not equipped with
conventional mooring tensioning equipment.
[0023] Referring to FIGS. 3A and 3B, the mooring line 44 is
initially secured to the anchor handling vessel 42 by a line 48.
The mooring line 44 extends to a subsea connector 50 adapted for
mating engagement with the subsea connector 30. A remotely operated
vehicle (ROV) 52 operatively secured to the anchor handling vessel
42 is employed to connect the subsea connector 50 to the subsea
connector 30, and to confirm that the connection has been properly
made. After the subsea connectors 30 and 50 are joined one to
another, the ROV 52 disengages the line 48 from the mooring line
44. After disengaging the line 48 from the mooring line 44, the ROV
52 connects the line 48 to the end of the chain 26 remote from the
subsea connector 30 in the manner illustrated in FIG. 3C.
[0024] After the line 48 is connected to the chain 26, the anchor
handling vessel 42 applies an upwardly directed force to the line
48 in the manner indicated by the arrow 54 in FIG. 3D. This causes
the chain 26 to be pulled through the device 24 thereby applying
mooring tension to the mooring line 44 and the floating structure
46. As will be appreciated by those skilled in the art, the chain
stopper 28 (FIG. 2) prevents the chain 26 from moving in the
reverse direction through the device 24. However, the chain stopper
28 is preferably constructed such that the chain 26 can be
disengaged therefrom by the ROV 52 should it become necessary to
release mooring tension from the line 44 and the floating structure
46 for any reason. The final step in the method of mooring floating
structures according to the first embodiment of the invention
comprises utilization of the ROV 52 to disengage the line 48 from
the chain 26 whereupon the line 48 and the ROV 52 are withdrawn
onboard the anchor handling vessel 42.
[0025] FIGS. 4A and 4B illustrate a method of mooring floating
structures comprising a second embodiment of the invention. Many of
the component parts utilized in the practice of the second
embodiment of the invention are substantially identical in
construction and function to component parts utilized in the
practice of the first embodiment of the invention and described
hereinabove in conjunction therewith. Such identical component
parts are designated in FIGS. 4A and 4B with the same reference
numerals utilized in the foregoing description of the first
embodiment of the invention but are differentiated therefrom by a
prime (') designation.
[0026] Referring particularly to FIG. 4A, in the practice of the
method of the second embodiment of the invention the suction pile
20' does not, in and of itself, serve as an anchor. Rather, the
suction pile 20' serves as an installation device for a plate
anchor 60. The construction of the plate anchor 60 and the
utilization of the suction pile 20' to effect installation thereof
in the sea floor are fully described in U.S. Pat. No. 6,122,847
issued Sep. 26, 2000 the disclosure of which is incorporated herein
by reference.
[0027] In accordance with the present invention the plate anchor 60
is provided with a chain 26'. During installation of the plate
anchor 60, one end of the chain 26' is secured to the suction pile
20 by a chain keeper 28A. The opposite end of the chain 26' extends
to a subsea connector 30' which is in turn connected to an anchor
handling vessel by a line 32'. The chain 26' extends through a
device 62 which serves both as a turning shoe or chain whelp and as
a chain stopper.
[0028] FIG. 4B illustrates the plate anchor 60 installed in the sea
floor. The plate anchor 60 may be provided with a recovery device
64. If used, the recovery the device 64 is deployed on the sea
floor and is connected to the plate anchor 60 by lines 66. The
purpose of the recovery device 64 is to allow the plate anchor 60
to be withdrawn from the sea floor and recovered to the surface for
installation at a different location.
[0029] The chain 26' includes a first end 26'A which extends to a
floating platform and a second end 26'B which extends to a buoy 61.
A chain is connected between the anchor handling vessel and the end
26'B of the chain 26' that is secured to the buoy 61. A tensioning
mechanism on the anchor handling vessel draws the chain 26' through
the device 62. The chain stopper feature of the device 62 prevents
the chain from passing through the device 62 in the opposite
direction. A line 68 extends to a release mechanism comprising the
device 62 whereby the chain may be permitted to pass from the
anchor handling vessel toward the floating platform if
necessary.
[0030] Although preferred embodiments of the invention have been
illustrated in the accompanying Drawings and described in the
foregoing Detailed Description, it will be understood that the
invention is not limited to the embodiments disclosed, but is
capable of numerous rearrangements, modifications, and
substitutions of parts and elements without departing from the
spirit of the invention.
* * * * *