FIELD OF INVENTION

This invention relates to a device and system for mooring and/or controlling a position of a floating structure, and to a method relating to the device and system. The floating structure may be, for example, an offshore structure such as a drilling rig or the like.

BACKGROUND TO INVENTION

Offshore structures, such as floating structures or platforms, can be moored by mooring lines, such as mooring chains. This may include attaching at least one mooring line to the structure to be moored and directly or indirectly coupling each mooring line to another structure, such as an anchor or pile located on the seabed.

A tension may be applied to each of the mooring lines. A necessary tension can be applied to each mooring line, for example, by the use of a tensioning apparatus. The application of tension may serve to moor the floating structure or platform at a desired location.

US 20030159638 A1 (LAY THOMAS et al) entitled“Method and system for mooring” describes a conventional mooring system as shown in Figure 1 , which shows a semi-submersible drilling platform. Mooring lines carried on the semi-submersible drilling platform are shown deployed. These mooring lines typically consist of a length of chain, which is attached at one end to the anchor and at the opposite end to a steel cable (also referred to as wire rope). The cable is attached to a traction winch, which provides necessary tension, and is stored on a remotely located storage reel.

Figure 2 shows a close-up of onboard hardware for the mooring system of Figure 1. The chain for the anchor is carried in chain lockers, while cable is carried on a spool. A combination traction winch/windlass is positioned on the upper deck to enable handling of the cable and chain. The traction winch/windlass has three major components: a traction winch which handles and tensions the wire rope, a windlass which handles and tensions the chain, and a shaft which, combined with an electric motor (not shown), provides the drive power to run the other two components.

After mooring a floating structure at the desired location, the floating structure may be subject to changes in environmental conditions. For example, the floating structure may be subject to changes in direction or force of the wind, waves and/or currents. Such environmental conditions may affect the tension on the mooring lines and, thus, may alter the location of the floating structure.

Further, after mooring a floating structure in the vicinity of a desired location, i.e. with an acceptable margin of error in the location of the structure, it may be necessary to further alter a position of the structure such that the structure is located more precisely at the desired location, i.e. within a tighter margin of error.

Conventional position control systems may employ thruster assist systems to position, i.e. Dynamically Position (DP), a floating structure at or within an allowable distance from a desired location. However, the capability of such systems is generally determined by a depth of water in which they operate. In particular, when the floating structure is a drilling rig, it may be necessary to maintain a near vertical orientation of a riser that extends from the rig to the seabed. As the rig moves away from the vertical centreline of the riser due, for example, to changes in environmental conditions, an angle of the riser may increase relative to vertical, resulting in an increase in bending forces at a base of the riser. Thus, such systems are typically only suited to water depths in excess of 500m.

Fixed mooring lines in combination with thruster systems may be used in shallower water depths. While such mooring lines may be generally employed to control a position of a floating structure, it may be necessary to adjust the fixed mooring lines, in particular to effect a fine tuning of the position of the floating vessel.

It is an object of at least one embodiment of at least one aspect of the present invention to obviate or mitigate one or more problems or disadvantages of the prior art.

It is an object of at least one embodiment of at least one aspect of the present invention to provide a technically simple and/or commercially more cost-effective device, system apparatus and/or method for mooring a floating structure than in the prior art.

SUMMARY OF INVENTION

FIRST INVENTION

According to a first aspect of the present invention there is provided a mooring system for a floating structure, the mooring system comprising:

a first tensioning means adapted for connecting the floating structure to a line, such as a mooring line; and

a second tensioning means adapted for disposal on or along the line. Preferably, the second tensioning means may be distal the floating structure. Preferably, second tensioning means may be submerged, i.e. underwater, in use.

The mooring system may comprise a positioning and/or tensioning system.

Preferably, the second tensioning means may be adapted to apply a tension, e.g. an initial tension, to the line.

Preferably, the first tensioning means may be adapted to adjust (e.g.“tension up” or tighten) the tension applied to the line.

Preferably, the first tensioning means may be adapted to adjust the tension applied to the line by the second tensioning means.

Preferably, the second tensioning means may be adapted to apply a tension to the line to imprecisely, coarsely or initially position the floating structure.

Preferably, the first tensioning means may be adapted to adjust the applied tension on the line to precisely, finely or finally position the floating structure.

Preferably, the first tensioning means may be adapted to adjust a position of the floating structure by a maximum of +/- 3 metres. More preferably, the first tensioning means may be adapted to adjust a position of the floating structure by a maximum of +/- 5 metres.

Preferably, the first tensioning means may be adapted to adjust a position of the floating structure over a continuous range. Preferably, the first tensioning means may be adapted to adjust a position of the floating structure over a continuous range of +/- 3 metres, or more preferably over a continuous range of +/- 5metres.

Preferably, the second tensioning means may be adapted to adjust a position of the floating structure in discrete increments or steps. For example, where the line is a chain, the second tensioning means may be adapted to adjust a position of the floating structure with a resolution related to, for example, an integer quantity or number of links of the chains.

Preferably, the first tensioning means may be located above a surface of the water. The first tensioning means may be disposed on, or otherwise affixed to, the floating structure such that, in use, the first tensioning means is and/or remains above a surface of a body of water.

Preferably, the second tensioning means may be located below a surface of the water. The second tensioning means may be disposed on the line such that, in use, the second tensioning means is and/or remains below a surface of a body of water.

Advantageously, the provision of the first tensioning means allows a position of the floating structure to be fine-tuned or adjusted without the need to adjust the second tensioning means. In particular, the position of the floating structure may be adjusted to compensate for changes in environmental conditions, such as changes in a direction or force of wind, waves or current.

Preferably, the first tensioning means may comprise a hydraulic apparatus, e.g. the first tensioning means may be a hydraulic tensioning means.

The hydraulic apparatus may comprise at least one hydraulic cylinder, piston, or the like.

Preferably, the first tensioning means may comprise a first locking means.

Preferably, the first locking means may comprise a ball and taper arrangement.

Preferably, the first tensioning means may comprise an element for connecting to the line.

The element for connecting to the line may be adapted to be movable, such as movable relative to the floating structure.

Preferably, the first tensioning means may be configured to move the element longitudinally or linearly, such as vertically or horizontally.

Preferably, the first locking means may act upon the element.

The first locking means may act upon the line.

Preferably, the first locking means may be adapted to maintain tension on the line.

Preferably, the first locking means may be adapted to selectively inhibit or allow movement of the element and/or line relative to the floating structure.

Preferably, the first locking means may be adapted to selectively inhibit or allow movement of the element in a first direction and/or in a second direction relative to the floating structure.

Preferably, the first locking means may be adapted to automatically inhibit or allow movement of the element in the first and/or second direction relative to the floating structure when a tension is applied to the line.

Preferably, the movable element may comprise at least one groove arranged along an axial direction of travel of the movable element. Preferably, the at least one groove may be adapted to interface with, fit or cooperate, with the ball and taper arrangement.

Preferably, the second tensioning means may be an in-line tensioner or mid-line tensioner.

Preferably, the second tensioning means may comprise a first portion for receiving a portion of a line, such as the line extending from the floating structure.

Preferably, the second tensioning means may comprise a guide portion for guiding a portion of the line received by the first portion. The guide portion may be movably, e.g. rotationally, connected to the first portion. The guide portion may be a chain wheel or the like.

Preferably, the second tensioning means may comprise an arrangement or a second portion for connecting or coupling the second tensioning means to a seabed or a further structure located thereon, e.g. coupling the second tensioning means to a seabed or a further structure by means of a second mooring line.

Preferably, the second portion may be movably connected to the first portion and/or the guide portion. For example, the first portion and the second portion may be arranged relative to each other such that a longitudinal axis of the first portion may be substantially in line, collinear or coaxial with a longitudinal axis of the second portion.

Preferably, the second tensioning means may comprise an arrangement for connecting or coupling the second tensioning means to the second mooring line..

Preferably, the guide portion may be movably, e.g. pivotably, connected to the arrangement.

Preferably, the lock or locking means may be connected to, attached to or provided on the arrangement.

Preferably, the guide portion may be movably connected to the arrangement.

Preferably, the second tensioning means may comprise a second locking means.

Preferably, the second locking means may be a chain stopper, or the like.

The system may comprise the line.

The system may comprise the floating structure.

Preferably, the floating structure may be a semi-submersible or a substantially cylindrical rig, such as a rig adhering to a‘Sevan Design’.

Preferably the first tensioning means may be disposed on a hull of the floating structure.

Preferably, the system may comprise a mooring system controller. The mooring system controller may be computer controlled and/or manually controlled.

The mooring system controller may activate and/or control at least one tensioning means and/or at least one locking means.

The mooring system controller may be adapted to monitor and/or maintain and/or vary a tension on one or more lines.

The mooring system controller may be adapted to adjust, e.g. move, at least one movable element based on a measured tension on the line.

The mooring system controller may be adapted to operate the at least one locking means based on at least one measurement of tension on the line. The mooring system controller may be adapted to operate at least one tensioning means and/or locking means in cooperation with at least one other tensioning means and/or locking means.

The mooring system controller may be adapted to maintain a tension on at least one line when moving the floating structure. The mooring system controller may be adapted to adjust a tension on at least one line in response to a change in a tension on at least one other line.

The mooring system controller may be adapted to adjust a tension on at least one line in response to a change an environment in which the floating structure reside, i.e. a change in direction or force of wind, waves or current.

The mooring system controller may be adapted to activate and/or control each at least one tensioning means based on received and/or determined information.

The received and/or determined information may relate to a desired position of the floating structure and/or a tension to be applied to, or maintained on, at least one line, e.g. mooring line.

The received and/or determined information may comprise or be based on at least one of: at least one value relating to a measured tension in at least one line; at least one value relating to a wind speed; at least one value relating to a wind direction; at least one value relating to a heading or orientation of the floating structure; at least one value relating to direction and/or size of waves or a swell; at least one value relating to direction and/or speed of a current; an angle between the line and at least a part of the floating structure; at least one value relating to one or more properties of the line, i.e. an elasticity of the line; at least one value relating to a depth of a body of water upon which the floating structure is located; at least one value relating to a pressure in a well, wherein the floating structure is communicably connected to the well; at least one value relating to a tension measured at a location on a riser, such as the top of the riser, wherein the riser communicably connects the floating structure to a well; at least one value relating to a speed, velocity or acceleration/deceleration of the floating structure; at least one value relating to a time required to disconnect the floating structure from a well and/or a time required to shut-in the well; and/or at least one value relating to the Response Amplitude Operator (RAO) characteristics of the floating structure.

According to a second aspect of the present invention there is provided a method of mooring a floating structure, the method comprising the steps of:

connecting a line, such as a mooring line, to a floating structure by a first tensioning means; disposing a second tensioning means on or along the line.

Preferably, the method may further comprise the step of adapting or using the second tensioning means to apply a tension to the line.

Preferably, the method may further comprise the step of adapting or using the first tensioning means to adjust a/the tension applied to the line.

Preferably, the step of using the second tensioning means to apply a tension to the line may occur or be carried out before the step of using the first tensioning means to adjust a/the tension applied to the line.

Preferably, the step of adapting or using the second tensioning means to apply a tension to the line may imprecisely or coarsely position the floating structure.

Preferably, the step of adapting or using the first tensioning means to adjust the tension on the line may precisely or finely position the floating structure.

Preferably, precisely positioning the floating structure may comprise maintaining the position of the floating structure to within an allowable distance from a desired position.

Preferably, precisely positioning the floating structure may comprise returning the floating structure to within an allowable distance from a desired position and/or an initial position.

Preferably, precisely positioning the floating structure may comprise more precisely locating the floating structure with respect to a desired position than is possible by means of the second tensioning means.

Preferably, the allowable distance may be approximately +/- 3 metres. More Preferably, the allowable distance is approximately +/- 1 metre. More preferably, the allowable distance is approximately +/- 0.5 metres.

Imprecisely positioning the floating structure may comprise maintaining the position of the floating structure to within a second allowable distance from a desired position.

Imprecisely positioning the floating structure may comprise returning the floating structure to within the second allowable distance from a desired position an initial position.

Preferably, imprecisely positioning the floating structure may comprise less precisely locating the floating structure than is possible by the first tensioning means.

According to a third aspect of the present invention there is provided a first tensioning means adapted for use in the mooring system of the first aspect of the present invention. Preferably, the second tensioning may comprise a first locking arrangement and a first line tensioning arrangement.

SECOND INVENTION

According to a fourth aspect of the present invention there is provided a device for connecting a line, such as a mooring line, to a floating structure, the device comprising:

a hydraulic tensioning means configured to control a tension on the line by moving an element for connecting to the line; and

a locking means.

Preferably, the hydraulic tensioning means may be configured to move the movable element in a longitudinal direction and/or vertical direction and/or linear direction.

Preferably, the hydraulic tensioning means may be configured to move the movable element longitudinally relative to the floating structure.

Preferably, the hydraulic tensioning means may be configured to move the movable element longitudinally or linearly, such as vertically or horizontally.

The hydraulic tensioning means may comprise a first collar. The first collar may be arranged around the element.

The hydraulic tensioning means may comprise a second collar. The second collar may be arranged around the element.

The first collar may be adapted to selectively grip or release the element.

The second collar may be adapted to selectively grip or release the element.

The first collar may comprise the locking means and/or the second collar may comprise the locking means.

The locking means may comprise a first locking means and a second locking means.

The first collar may comprise the first locking means.

The second collar may comprise the second locking means.

The first and/or second locking means may comprise a ball and taper arrangement. The first locking means may comprise a first ball and taper arrangement and the second locking means may comprise a second ball and taper arrangement.

The first and/or second ball and taper arrangements may be arranged to selectively grip or release the element.

The first and second collars may be adapted to move together and apart relative to one another, for example, along a first axis. The hydraulic tensioning means may comprise at least one primary hydraulic device. The at least one primary hydraulic device may be a cylinder, a piston or the like.

The first and second collars may be adapted to move relative to one another by means of at least one primary hydraulic device.

The at least one primary hydraulic device may be adapted to push or pull the first and second collars together or apart.

The first collar may comprise at least one upper hydraulic device.

The second collar may comprise at least one lower hydraulic device.

The first locking means may comprise a first ball and taper arrangement.

The second locking means may comprise a second ball and taper arrangement.

The at least one upper hydraulic device may be adapted to selectively engage or disengage the first ball and taper arrangement. As such, the at least one upper hydraulic device may be adapted to selectively grip or release the element by the first collar.

The at least one lower hydraulic device may be adapted to selectively engage or disengage the second ball and taper arrangement. As such, the at least one lower hydraulic device may be adapted to selectively grip or release the element by the second collar.

As such, by operating in a defined sequence (as will be described in further detail below) the hydraulic tensioning means may increase or decrease a tension on the line by moving an element for connecting to the line

Preferably, the locking means may be adapted to selectively inhibit or allow movement of the element.

The locking means may be adapted to selectively grip or release the element.

The locking means may be adapted to act upon the line.

The locking means may be adapted to act upon the guide portion.

The locking means may be adapted to act upon the movable element.

The locking means may be adapted to prevent the line being hauled in or paid out or pushed or pulled in or out relative to the floating structure.

The locking means may be a mechanical lock. The locking means may be a chain stopper.

The locking means may be operated manually and/or may be powered.

The locking means may be electrically and/or hydraulically and/or pneumatically powered.

The locking mean may be remotely operated. The locking means may be operated and/or controlled by a mooring system controller.

The movable element may be movable relative to the floating structure.

The device may comprise a guide portion.

The guide portion may be a chain wheel or a sheave.

The guide portion may be movably connected to the floating structure and/or to the device.

The device may comprise at least one lever arm and/or fairlead.

The leaver arm and/or fairlead may comprise at least one guide portion.

The tensioning means may comprise an arrangement for moving the movable element relative to the floating structure.

The tensioning means may comprise a jack, such as a hydraulic jack.

The tensioning means may comprise a machine screw jack, a ball screw jack, a roller screw jack, a strand jack, a farm jack, a bottle jack and/or a barrel jack.

The tensioning means may comprise a winch and/or pulley.

The tensioning means may comprise a ratchet mechanism, a rack and pinion arrangement, or any other suitable mechanical mechanism or arrangement.

The tensioning means may be manually and/or electrically and/or hydraulically and/or pneumatically powered.

The tensioning means may comprise tension monitoring means, such as a load cell, strain gauge, or the like.

The tensioning means may comprise monitoring means to detect or measure an amount of line hauled in or payed out by the device.

The tensioning means may comprise monitoring means to detect or measure an amount of movement of the movable element.

The floating structure may be or may comprise a drilling rig.

The floating structure may be or may comprise a semi-submersible or a substantially cylindrical rig, such as a rig adhering to a‘Sevan Design’.

The floating structure may be or may comprise an offshore structure, a vessel, a floating platform, a subsea structure, an underwater structure or buoy, or the like.

The device may be disposed on a hull of the floating structure, such as when the floating structure is of the Sevan-design type, i.e. a substantially cylindrical hull.

In an exemplary embodiment a floating structure, such as a floating structure conforming to the Sevan-design, may comprise a plurality of devices.

The plurality of devices may be circumferentially disposed about the hull. The plurality of devices may be located in groups, wherein optionally the groups are circumferentially disposed about the hull.

The or each device may be disposed on a column of the floating structure, such as when the floating structure is a semi-submersible comprising one or more columns.

Advantageously, the provision of the device for connecting a line to a floating structure allows adjustment of the position of the floating structure without requiring large quantities of equipment on the floating structure, such as chain lockers and the like.

Advantageously, because the device does not necessarily require large quantities of equipment on the floating structure, such as a winch/windlass system or chain lockers, the device can be easily retro-fitted to existing floating structures.

THIRD INVENTION

According to a fifth aspect of the present invention there is provided a device for connecting a line, such as a mooring line, to a floating structure, the device comprising: a tensioning means configured to control a tension on the line by moving an element for connecting to the line; and

a locking means adapted to inhibit movement of the element, wherein the locking means comprises a ball and taper arrangement

Preferably, the locking means may be adapted to selectively inhibit or allow movement of the element.

Preferably, the ball and taper arrangement may comprise a plurality of balls.

Preferably, the ball and taper arrangement may comprise at least one tapered surface(s).

Preferably, the locking means may comprise at least one collar. The collar may be arranged around the element.

Preferably, the plurality of balls may be arranged in a chassis or carriage. The chassis or carriage may be arranged around the element.

The chassis or carriage may be arranged concentrically with the collar and the element. The chassis or carriage may be arranged between the collar and the element.

Preferably, the at least one tapered surface may be arranged on an inner surface of a collar.

Preferably, the at least one tapered surface and/or the element may be arranged to engage with the plurality of balls.

Preferably, the chassis or carriage may be adapted to be movable relative to the device and/or the element. Preferably, the balls may be engaged with or disengaged from the tapered surfaces and/or the element by moving the chassis or carriage.

Preferably, the chassis or carriage may be adapted to be moved by at least one hydraulic element.

Preferably, the locking means may comprise at least one hydraulic element.

Preferably, the at least one hydraulic element may be a cylinder or piston.

Preferably, the at least one hydraulic element may be adapted to move the chassis or carriage between an engaged position and a disengaged position.

FOURTH INVENTION

According to a sixth aspect of the present invention there is provided a device for connecting an end or end portion of a line, such as a mooring line, to a floating structure, the device comprising:

a tensioning means configured to control a tension on the line by moving a/the end or end portion of the line; and

a locking means.

The line may be or may comprise a mooring line, offshore mooring line, underwater mooring line or subsea mooring line.

The line may be or may comprise a chain, wire or rope or the like.

The end or end portion of the line may be configured to be connected to or coupled to the device.

The line may be adapted for connecting to a mooring. The mooring may be an anchor, a drag embedment anchor, a vertically loaded anchor, a driven pile, a suction pile, a suction anchor, a suction embedded plate anchor or another type of anchor or structure, such as a natural formation or the like.

An/the end or end portion of the line may be configured to be connected to or coupled to a further tensioning means. The further tensioning means may be a winch, or the like. The further tensioning means may be mounted on a further floating structure.

The end or end portion of the line may be attached to the floating structure by means of a clevis.

Preferably, the locking means may be adapted to selectively inhibit or allow movement of the end or end portion of the line.

Advantageously, because the device connects to the end or end portion of the line, there is no requirement or necessity for large quantities or amounts of equipment on the floating structure, such as chain lockers or the like. FIFTH INVENTION

According to a seventh aspect of the present invention there is provided a device for connecting a line to a floating structure, the device comprising:

a movable element for connecting to the line;

a tensioning means configured to control a tension on the line by moving the movable element; and

a locking means.

Preferably, the tensioning means may be a hydraulic tensioning means.

Preferably, the movable element may be movable relative to the floating structure.

Preferably, the locking means may be adapted to selectively inhibit or allow movement of the movable element.

The movable element may comprise an attachment means, such as a clevis, or fastener, or the like, for connecting the movable element to a line.

The movable element may comprise a pillar, a column or the like. The movable element may comprise a substantially cylindrical portion.

The movable element may be adapted to move along a first axis.

The movable element may comprise at least one groove. The at least one groove may be arranged along an axial direction of travel of the movable element.

The at least one groove may be adapted to interface with, fit or cooperate, with at least one ball or ball bearing.

The locking means may comprise at least one ball or ball bearing.

The locking means may comprise a ball and taper arrangement.

The at least one groove may be adapted to fit, or cooperate, with at least one ball or ball bearing of the locking means. As such, the movable element may be adapted to be gripped by the locking means.

The movable element may comprise a plurality of circumferentially arranged grooves.

The plurality of circumferentially arranged grooves may be adapted to interface with, fit or cooperate, with a plurality of balls or ball bearings of the locking means.

The device may comprise a body.

The body may comprise at least one guide.

The movable element may comprise at least one protrusion.

The at least one protrusion may be a trunnion.

The movable element may comprise a pair of trunnions. The at least one protrusion may be adapted to fit in the at least one guide.

The at least one protrusion may be adapted to move within the at least one guide.

The at least one protrusion and the at least one guide may be arranged to limit movement of the movable element to movement along the first axis.

According to an eighth aspect of the present invention there is provided a mooring system comprising the mooring system according to the first aspect, wherein the first tensioning means may comprise a device according to any of the fourth, fifth, sixth or seventh aspects of the present invention.

According to an ninth aspect of the present invention there is provided a method of mooring a floating structure comprising the method according to the second aspect, wherein the first tensioning means may be a device according to any of the fourth, fifth, sixth or seventh aspects of the present invention.

It should be understood that the features defined above in accordance with any aspect of the present invention or below relating to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, which are:

Figure 1 an example of a prior art mooring system;

Figure 2 a magnified view of the prior art mooring system of Figure 1 ;

Figure 3 an exemplary embodiment of an arrangement of mooring lines;

Figure 4 a further exemplary embodiment of an arrangement of mooring lines; Figure 5 a mooring system according to a first embodiment of a first aspect of the present invention;

Figure 6 a graphical representation of operating areas of a floating structure; Figure 7 a perspective view of a device according to an embodiment of a third, fourth, fifth or sixth aspect of the present invention;

Figure 8 a side view of the device of Figure 7;

Figure 9 a front view of the device of Figure 7;

Figure 10 a cross-sectional side view of the device of Figure 7;

Figure 11 a magnified perspective view of a portion of the device of Figure 7; Figure 12 a magnified perspective view of a further portion of the device of Figure

7;

Figure 13a a cross-sectional view of a hydraulic tensioning means of the device of

Figure 7 in a first state;

Figure 13b a cross-sectional view of the hydraulic tensioning means of Figure 13a in a second state;

Figure 14 a cross-sectional view of the hydraulic tensioning means of Figure 13a with an element in situ ; and

Figure 15a-d a sequence of cross-sectional views of the hydraulic tensioning means of Figure 14.

DETAILED DESCRIPTION OF DRAWINGS

Referring initially to Figure 1 , there is shown an example of a prior art mooring system, as described in US 20030159638 A1 (LAY THOMAS et a!), entitled“Method and System for Mooring”. Figure 1 shows an example of a semi-submersible drilling platform 10. Mooring lines 15 carried on the semi-submersible drilling platform 10 are shown deployed. These mooring lines 15 typically consist of a length of chain, which is attached at one end to the anchor 20 and at an opposite end to a steel cable (also referred to as wire rope). The cable is attached to a traction winch 25, which provides necessary tension, and is stored on a remotely located storage reel.

Figure 2 is a close-up of the onboard hardware for the mooring system of Figure 1. Chain for the anchor is carried in chain lockers 30, while cable is carried on a spool 35. A combination traction winch/windlass 40 is positioned to enable handling of the cable and chain.

Figure 3 shows an exemplary embodiment of an arrangement of mooring lines generally denoted 50. Semi-submersible drilling platform 55 comprises four stability columns 60. Each stability column 60 has four mooring lines 65a-d attached. Each stability column may comprise more than or fewer than four mooring lines.

Figure 4 shows an exemplary embodiment of an arrangement of mooring lines generally denoted 70. The floating structure 75 is of the‘Sevan-design type’ i.e. has a substantially circular hull. The hull has a plurality of circumferentially disposed mooring lines 80a-h (in this case eight lines 80a-h. It will be appreciated that more or fewer than eight lines may be provided. Further, the lines 80a-h may be arranged in groups, as shown with respect to the semi-submersible drilling platform 55 of Figure 3. In the exemplary embodiment of Figure 4, the floating structure also comprises a mooring system controller 85. It will be appreciated that the embodiment of Figure 3 may also comprise a mooring system controller 85.

Referring now to Figure 5 there is shown a mooring system, generally denoted 100, according to a first embodiment of the present invention.

The mooring system 100 is for a floating structure 105. The mooring system 100 comprises a first tensioning means 110. The first tensioning means 110 is adapted for connecting the floating structure 105 to a line 115.

The first tensioning means 110 is arranged on a side of the floating vessel 105. It will be appreciated that the first tensioning means 110 may be arranged on a hull, on a stability column, or the like, as exemplified in Figures 3 and 4.

A second tensioning means 120 is disposed on the line 115. The second tensioning means 120 is a mid-line tensioner, e.g. as described in WO 2018/025018 A1 (FLINTSTONE TECHNOLOGY LIMITED) or in WO 2018/197883 A1 (FLINTSTONE TECHNOLOGY LIMITED).

Examples of second tensioning means 120 are shown in figure 5, generally denoted as second tensioning means 120a, 120b, 120c.

In a first example embodiment of the second tensioning means 120a, the second tensioning means 120a comprises a first portion 160a for receiving a portion of a line, such as the line 115, extending from the floating structure 105.

In the first example embodiment, the second tensioning means 120a comprises a guide portion 140a for guiding a portion of a line 115 received by the first portion 160a. The guide portion 140a is movably connected to the first portion 160a.

In the first example embodiment, the second tensioning means 120a also comprises a second portion 160b for connecting or coupling the second tensioning means 120a to a seabed or a further structure located thereon, e.g. coupling the second tensioning means 120a to a seabed or a further structure by means of a second mooring line 145.

In the first example embodiment of the second tensioning means 120a, the second portion 160b is movably connected to the first portion 160a and/or the guide portion 140a. For example, the first portion 160a and the second portion 160b may be arranged relative to each other such that a longitudinal axis of the first portion 160a is substantially in line, collinear or coaxial with a longitudinal axis of the second portion The first example of the second tensioning means 120a comprises a lock or locking means 135. In this example embodiment, the locking means 135 is a chain stopper.

In a modified or further embodiment of the second tensioning means 120b, the second tensioning means 120b comprises a guide portion 140b for guiding a portion of the line 115, an arrangement 170b for connecting or coupling the second tensioning means 120b to the second mooring line 145, and a lock or lock means 135b, wherein the guide portion 140b is movably connected to the arrangement, and the lock 135b is connected to, attached to or provided on the arrangement.

The lock or locking means 135b of the further embodiment of the second tensioning means 120b is a chain stopper.

In another modified or further embodiment of the second tensioning means 120c, the second tensioning means 120c comprises a guide portion 140c for guiding a portion of the line 115, an arrangement 170c for connecting or coupling the second tensioning means 120c to the second mooring line 145, and a lock or lock means 135c, wherein the guide portion 140c is movably connected to the arrangement, and the lock 135c is connected to, attached to or provided on the arrangement.

The lock or locking means 135c of the further embodiment of the second tensioning means 120c is a chain stopper.

A further floating structure 130 is shown. The further floating structure 130 comprises means to apply a tension to the line 115, e.g. by means of a winch or the like.

In the exemplary embodiment of Figure 5, the floating structure 105 comprises a guide portion 125. The line 115 is guided by the guide portion 125.

Figure 6 shows a graphical representation of an area of operation of a floating structure, e.g. drilling rig. The centre of a circle represents a desired (“green”) position of the floating structure. In particular, when the floating structure is a drilling rig, the centre of the circle may be representative of a vertical centreline of a riser. A first circle 150 represents an acceptable operating area of the floating structure. That is, the floating structure may drift or move within the acceptable operating area represented by the first circle 150 without causing undue tension or stress on the riser (not shown). The area represented by the difference between first circle 150 and a second circle 155 is an (“amber”) area where the well (not shown) would be in a“shut-in” state, i.e. not producing. This would be due to risks associated with tension or stress on the riser. Finally, a (“red”) area represented by the difference between second circle 155 and a third circle 160 represents an area within which the riser may be at or exceed an allowable stress limit, thus requiring either correction to the position of the floating structure or disconnection from the riser.

Figure 7 shows a perspective view of a device for connecting a line to a floating structure, generally denoted 200, according to a third, fourth, fifth or sixth aspect of the present invention. The device 200 comprises a first tensioning means 210. The first tensioning means 210 comprises a plurality of primary hydraulic devices 215. The primary hydraulic devices 215 are cylinders. The first tensioning means 210 comprises a first locking means, which will be described in more detail with reference to Figures 13a to 15d.

The first tensioning means 210 comprises an element 220 for connecting to a line (not shown). The element 220 for connecting to the line is adapted to be movable. In the exemplary embodiment of Figure 7, the first tensioning means 210 comprises a body 225. However, it will be appreciated that the first tensioning means 210 may be directly connected, e.g. welded, to a floating structure and thus a hull or body of the floating structure may form the body 225 of the first tensioning means 210.

The element 220 is adapted to be movable relative to the body 225, and thus to the floating structure. The body 225 comprises a guide 230. The element 220 is adapted to be movable along a first axis X. The element 220 is adapted to be moved within the guide 230, as will be described with reference to Figure 11.

Figure 8 shows a side view of the device 200 of Figure 7. It will be appreciated that shoulder 235 of the body 225 may be a portion of the floating structure, such as a deck or the like.

Figure 9 shows a front view of the device 200 of Figure 7. The element 220 comprises a clevis 240 for connecting the element 220 to a line (not shown).

Figure 10 shows a cross-sectional side view of the device 200 of Figure 7. In the exemplary embodiment shown the element 220 is a hollow element. However, it will be appreciated that element 220 could be a solid, or at least partially solid, element.

Figure 11 shows a magnified perspective view of a portion of the device 200 of Figure 7. The guide 230 is shown as transparent for illustrative purposes. The element 200 comprises clevis 240. The element 200 comprises a pair of trunnions 245a-b. The trunnions 245a-b are adapted to fit within the guide 230. That is, the trunnions 245a-b are adapted to fit within corresponding grooves in the guide 230. As such, the element 220 is restricted to movement along a (substantially vertical) axis X. Further, rotational movement of the element 220 about or around axis X is prevented by the interaction of the trunnions 245a-b and the guide 230. Figure 12 shows a magnified perspective view of a further portion of the device 200 of Figure 7. It can be seen that the movable element 220 is of the form of a column. The movable element 220 comprises a plurality of grooves 250. The grooves 250 are arranged along an axial direction of travel of the movable element. The grooves 250 are arranged circumferentially around the element 220. The groves 250 do not extend the full length of the element 220. As such, a length of the grooves 250 may define an extent of movement of element 220, as will be described below.

Figure 13a shows a cross-sectional view of a portion of the first tensioning means, generally denoted 300, in a first state. The first tensioning means 300 is a hydraulic tensioning means, and is hereinafter referred to as hydraulic tensioning means 300. The hydraulic tensioning means 300 comprises a first collar 310. In use, the first collar 310 is arranged around the movable element 220 (not shown). The hydraulic tensioning means 300 comprises a second collar 315. In use, the second collar 315 is arranged around the movable element 220. The first collar 310 is adapted to selectively grip or release the movable element 220. The second collar 315 is adapted to selectively grip or release the movable element 220.

The first collar 310 comprises a first locking means 320. The second collar 315 comprises the second locking means 325. The first locking means 320 comprises a first ball and taper arrangement 330. The second locking means 325 comprises a second ball and taper arrangement 335. The first and second ball and taper arrangements 330, 335 are arranged to selectively grip or release the movable element 220.

The first locking means 320 comprises a first carriage 340. The second locking means 325 comprises a second carriage 345. Each carriage 340, 345 is arranged concentrically with the associated collar 30, 315 and the movable element 220. The first carriage 340 is arranged between the first collar 310 and the movable element 220. The second carriage 345 is arranged between the second collar 315 and the movable element 220.

The first carriage 340 comprises a plurality of first balls 350. The first balls 350 are arranged circumferentially around the first carriage 340. Similarly, the second carriage 345 comprises a plurality of second balls 355. The second balls 355 are arranged circumferentially around the second carriage 345.

The first collar 310 comprises a plurality of first tapered surfaces 360. The first tapered surfaces 360 are arranged on an inner surface of the first collar 310. The second collar 315 comprises a plurality of second tapered surfaces 365. The second tapered surfaces 365 are arranged on an inner surface of the second collar 310.

The first tapered surfaces 360 of the first collar 310 and the movable element 220 are arranged to engage with the plurality of first balls 350. Similarly, the second tapered surfaces 365 of the second collar 315 and the movable element 220 are arranged to engage with the plurality of second balls 355.

Figure 13b shows a cross-sectional view of the hydraulic tensioning means 300 in a second state.

The hydraulic tensioning means 300 comprises a plurality of primary hydraulic devices 215. Primary hydraulic devices 215 is/are a cylinder. In one exemplary embodiment, primary hydraulic device 215 may be an “Enerpac”® cylinder. The primary hydraulic devices 215 are adapted to push or pull the first collar 310 and second collar 315 together or apart, in the direction indicated by arrow 375, as is clear by comparing Figure 13a and Figure 13b.

First collar 310 also comprises upper hydraulic devices 380. Second collar 315 also comprises lower hydraulic devices 385. The upper hydraulic devices 380 are adapted to selectively engage or disengage the first ball and taper arrangement 330.

The upper hydraulic devices 380 selectively engage or disengage the first ball and taper arrangement 330 by moving the first carriage 340 in a direction along axis X. For example, the upper hydraulic devices 380 engages the first ball and taper arrangement 330 by moving the first carriage 340 in a downwards direction along axis X, forcing the balls 350 to wedge between the movable element 220 and the tapered surfaces 360 of the first collar 310. The upper hydraulic devices 380 disengages the first ball and taper arrangement 330 by moving the first carriage 340 in an upwards direction along axis X, forcing the balls 350 not to wedge between the movable element 220 and the tapered surfaces 360 of the first collar 310.

As such, the upper hydraulic device 380 is adapted to selectively grip or release the movable element 220 by the first collar 310. The lower hydraulic device 385 is adapted to selectively engage or disengage the second ball and taper arrangement 335.

The lower hydraulic device 385 selectively engage or disengage the second ball and taper arrangement 335 by moving the second carriage 345 in a direction along axis X. For example, the lower hydraulic device 385 engage the second ball and taper arrangement 335 by moving the second carriage 345 in a downwards direction along axis X, forcing the second balls 355 to wedge between the movable element 220 and the tapered surfaces 365 of the second collar 315. The lower hydraulic devices 385 disengages the second ball and taper arrangement 335 by moving the second carriage 345 in an upwards direction along axis X, forcing the second balls 355 to not wedge between the movable element 220 and the tapered surfaces 365 of the second collar 315. As such, the lower hydraulic device 385 is adapted to selectively grip or release the movable element by the second collar 315.

By operating in a defined sequence, as will be described in further detail below with reference to Figures 15a-d, the hydraulic tensioning means 300 may increase or decrease a tension on the line 115 by moving an movable element 220 for connecting to the line 115.

Figure 14 shows a cross-sectional view of the hydraulic tensioning means 300 of Figure 13a with the movable element 220 in situ. The first ball and taper arrangement 330 is shown in an engaged state. That is, the first balls 350 of the first ball and taper arrangement 330 are wedged between the movable element 220 and the tapered surfaces 360 of the first collar 310. Similarly, the second ball and taper arrangement 335 is shown in an engaged state. That is, the second balls 355 of the second ball and taper arrangement 335 are wedged between the movable element 220 and the tapered surfaces 365 of the second collar 315.

Figures 15a-d show a sequence of cross-sectional views of the hydraulic tensioning means 300 of Figure 14, which describe the operation of the hydraulic tensioning means 300 according to an embodiment of the present invention. Figure 15a shows Step 1 in a process of lifting the movable element 220. In use, for example in the system 100 according to the first aspect (shown in Figure 5), the lifting of movable element 220 would increase the tension on the line 115.

At Step 1 , the upper hydraulic devices 380 engages the first ball and taper arrangement 330 by moving the first carriage 340 in a downwards direction along axis X, forcing the first balls 350 to wedge between the movable element 220 and the tapered surfaces 360 of the first collar 310. This causes the first collar 310 to grip the movable element 220 by means of the first ball and taper arrangement 330.

Figure 15b shows Step 2 in the process of lifting the movable element 220. The primary hydraulic devices 215 push the first collar 310 and second collar 315 apart. Simultaneously, or substantially simultaneously, the lower hydraulic devices 385 disengage the second ball and taper arrangement 335 by moving the second carriage 345 in an upwards direction along axis X, forcing the second balls 355 to not wedge between the movable element 220 and the tapered surfaces 365 of the second collar 315. The second collar 315 is directly or indirectly connected to the body 225 or to the floating structure and, therefore, does not move relative to the body 225 or to the floating structure. The first collar 310 moves upwards relative to the floating structure. Due to the gripping of the movable element 220 by the first collar 310, the movable element 220 moves upwards with the first collar 310.

Figure 15c shows Step 3 in the process of lifting the movable element 220. Once the first collar 310 has lifted the movable element 220 by a desired amount, which is limited by the stroke of the primary hydraulic device 215, the lower hydraulic devices 385 engage the second ball and taper arrangement 335 by moving the second carriage 345 in a downwards direction along axis X, forcing the second balls 355 to wedge between the movable element 220 and the tapered surfaces 365 of the second collar 315. At this stage, both the first collar 310 ad the second collar 315 are gripping the movable element 220. Next, the first collar 310 disengages the movable element 220. That is, the upper hydraulic devices 380 disengage the first ball and taper arrangement 330 by moving the first carriage 340 in an upwards direction along axis X, forcing the first balls 350 not to wedge between the movable element 220 and the tapered surfaces 360 of the first collar 310.

Finally, the primary hydraulic devices 215 push or pull the first collar 310 and second collar 315 together, resulting in the hydraulic tensioning means 300 returning to the state shown in Figure 15d.

This sequence of steps may be repeated to lift movable element 220 further. Alternatively, this sequence of steps may be carried out in reverse order to lower the movable element 220. That is, by lifting first collar 310 away from the second collar 315, then engaging the first ball and taper arrangement 330, then disengaging the second ball and taper arrangement 335, then lowering the first collar 310 towards the second collar 315, then engaging the second ball and taper arrangement, the movable element 220 may be lowered.

It should be understood that the features herein disclosed in accordance with any aspect of the present invention or in relation to any embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in or from any other aspect or embodiment of the invention.

It would also be appreciated that the embodiment of the invention hereinbefore described are given by way of example only, and are not meant to be limiting of the scope of the invention in any way.