The present invention relates to a mooring system, and particularly, but not exclusively to a mooring system for use in anchoring a floating offshore wind turbine installation.

BACKGROUND

It is known to anchor floaters such as a semi-submersible floating wind turbine installation using a plurality of mooring lines each of which extends from a connection point on the floater to an anchor. Where there are a plurality of floaters, the floaters in the array may share anchors, so that a plurality of mooring lines are attached to each anchor, each mooring line attached to any one anchor extending to a different floater in the array.

Publications which may be useful to understand the background are W02022/031175, US2013/0276687, and WO22098288.

SUMMARY

According to a one embodiment we provide a mooring system comprising a floater, a first anchor and first and second mooring lines, the first and second mooring lines being secured to the first anchor and extending to the floater, the first mooring line being secured to the floater at a first connection point and the second mooring line being secured to the floater at a second connection point, the first connection point being spaced from the second connection point.

The system may comprise a second anchor and a third mooring line which is connected to the second anchor and extends from the second anchor to the floater, the third mooring line being connected to the floater at a third connection point which is spaced from the first and second connection points.

The system may comprise a third anchor and a fourth mooring line which is connected to the third anchor and extends from the third anchor to the floater, the fourth mooring line being connected to the floater at a fourth connection point which is at or adjacent the third connection point.

Alternatively, the fourth mooring line may be connected to the floater at a fourth connection point which is spaced from the first, second and third connection points. Alternatively, the system may comprise a fourth mooring line which is connected to the second anchor and extends from the second anchor to the floater, the fourth mooring line being connected to the floater at a fourth connection point which is at or adjacent to either the first or second connection point.

The floater may be a first floater and the mooring system further comprise one or more additional floaters, and an additional anchor for each additional floater, each additional floater having two mooring lines which are secured to one of the additional anchors and to the respective floater at a first connection point and a second connection point, the first connection point being spaced from the second connection point, the system further comprising at least one additional mooring line by means of which each floater is connected to the other or one of the other floaters.

The floater may be a first floater and the mooring system further comprise two or more additional floaters, and an additional anchor for each additional floater, each additional floater having two mooring lines which are secured to one of the additional anchors and to the respective floater at a first connection point and a second connection point, the first connection point being spaced from the second connection point, the system further comprising one additional mooring line for each floater by means of which each floater is connected to two of the other floaters. For example, the system may further comprise a second and third floater, and a second and third anchor, the second and third floater each having two mooring lines which are secured to the second and third anchor respectively and to the respective floater at a first connection point and a second connection point, the first connection point being spaced from the second connection point, the system further comprising three additional mooring lines by means of which each floater is connected to each of the other floaters.

The floater may comprise a foundation structure. The foundation structure may have a plurality of corners, the first mooring point being provided at a first one of the corners, and the second mooring point being provided at a second one of the corners. Where the foundation structure is provided with more than three corners, the first and second mooring points may be provided at adjacent corners.

The foundation structure may comprise a platform formed from a plurality of buoyant elements joined by a plurality of generally rigid connectors, a buoyant element being provided at each corner of the foundation structure. The foundation structure may comprise, for example, three buoyant elements arranged in a triangular array.

Alternatively, the base may comprise four buoyant elements arranged in a square or rectangular array. Further alternatively, the base may comprise more than four buoyant elements arranged in a polygon array, with a buoyant element being provided at each corner of the polygon.

The floater may further comprise a wind turbine supported on the foundation structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which

FIGURE 1a is a schematic illustration of a plan view of an embodiment of the innovative mooring system comprising a triangular floater,

FIGURE 1b is a schematic illustration of a plan view of the embodiment of the innovative mooring system illustrated in Figure 1a but comprising a square floater,

FIGURE 1c is a schematic illustration of a plan view of the embodiment of the innovative mooring system illustrated in Figure 1a but comprising a heptagonal floater,

FIGURE 1d is a schematic illustration of a plan view of the embodiment of the innovative mooring system illustrated in Figure 1a but comprising a circular floater,

FIGURE 2 is a schematic illustration of a plan view of an alternative embodiment of mooring system,

FIGURE 3 is a schematic illustration of a plan view of the mooring system shown in Figure 2 as part of an array of mooring systems,

FIGURE 4 is a schematic illustration of a plan view of an alternative embodiment of mooring system,

FIGURE 5 is a schematic illustration of a plan view of the mooring system shown in Figure 4 as part of an array of mooring systems, FIGURE 6 is a plan view of an alternative embodiment of mooring system according to the invention,

FIGURE 7 is a plan view of a further alternative embodiment of mooring system according to the invention,

FIGURE 8 is a plan view of a further alternative embodiment of mooring system according to the invention,

FIGURE 9 is a plan view of a further alternative embodiment of mooring system according to the invention,

FIGURE 10 is a plan view of a further alternative embodiment of mooring system according to the invention,

FIGURE 11 is a plan view of a further alternative embodiment of mooring system according to the invention,

FIGURE 12 is a plan view of an array of a plurality of mooring systems as illustrated in Figure 6,

FIGURE 13 is a plan view of an alternative array of a plurality of mooring systems as illustrated in Figure 6

FIGURE 14 is a schematic illustration of a plan view of an alternative embodiment of mooring system not in accordance with the claimed invention,

FIGURE 15a, 15b, 15c are examples of floaters suitable for use in the innovative mooring systems each floater comprising a plurality of buoyant elements connected by rigid connecting elements,

FIGURE 16 is a plan view of part of one embodiment of mooring system showing the connectors by means of which the mooring lines are connected to the floater,

FIGURE 17 is a side view of part of an alternative embodiment of mooring system showing the connectors by means of which the mooring lines are connected to the floater,

FIGURE 18 is a perspective view of an embodiment of floating off-shore wind turbine installation which may comprise the floater of the mooring systems according to the present disclosure. DETAILED DESCRIPTION

The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, “upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

In all the figures, the mooring system 10 is illustrated schematically as if viewed from directly above when the floater is floating on a body of water.

Figures 1a - 1d show a mooring system 10 comprising a floater 12, a first anchor 14 and first and second mooring lines 16, 18, the first and second mooring lines 16, 18 being secured to the first anchor 14 and extending to the floater 12, the first mooring line 16 being secured to the floater 12 at a first connection point 20 and the second mooring line 18 being secured to the floater 12 at a second connection point 22, the first connection point 20 being spaced from the second connection point 22. The first mooring line 16 is separate from the second mooring line 18 along the entire length from the floater 12 to the anchor 14 in the sense that from their point of connection to the anchor 14 to their point of connection to the floater 12, the first mooring line 16 and second mooring line 18 extend along entirely separate paths.

Advantageously, the first and second connection points 20, 22 are arranged such that when the floater 12 is floating on a calm body of water a line connecting the first and second connection points 20, 22 is generally horizontal. This line need not be exactly horizontal, but there should be a significant horizontal separation between the first and second connection points 20, 22, however.

In the embodiment illustrated in Figure 1a, the floater is generally triangular in plan view cross-section (ie. parallel to the water surface), and the first and second connection points 20, 22 are located at or adjacent to two of the three corners of the triangle.

In an alternative embodiment illustrated in Figure 1b, the floater 12 is square in plan view cross-section (ie. parallel to the water surface), and the first and second connection points 20, 22 are located at or adjacent to two adjacent corners of the square. The floater may equally be annular or circular, or a polygon in plan view, with more than 4 sides. In the embodiment illustrated in Figure 1c, the floater 12 is heptagonal, and the first and second connection points 20, 22 are located at or adjacent to two adjacent corners of the heptagon. In the embodiment illustrated in Figure 1 d, the floater 12 is circular, and the first and second connection points 20, 22 are spaced along the circumference of the floater 12.

It will be appreciated that in the arrangements illustrated in Figures 1a- 1 d, the anchor 14 and mooring lines 16, 18 will prevent the floater 12 from moving when subjected to forces acting parallel to a line between the anchor 14 and the floater 12 pushing the floater 12 away from the anchor 14. In order to restrain the floater 12 when subjected to forces acting in other directions, the mooring system advantageously comprises a second anchor 24 and a third mooring line 26 which is connected to the second anchor 24 and which extends from the second anchor 24 to the floater 12, the third mooring line 26 being connected to the floater 12 at a third connection point 28 which is spaced from the first and second connection points 20, 22, as is illustrated in Figure 2.

Whilst Figure 2 shows this in relation to a triangular floater, it will be appreciated that this could also be applied to any of the floaters illustrated in and described in relation to Figures 1b - 1d.

In the embodiment illustrated in Figure 2, the mooring system 10 further comprises a third anchor 30 and a fourth mooring line 32 which is connected to the third anchor 30 and which extends from the third anchor 30 to the floater 12, the fourth mooring line being connected to the floater 12 at a fourth connection point which is at or adjacent the third connection point 28.

The first, second and third anchors 14, 24, 30 are generally evenly spaced around the floater 12, so if the mooring lines 16, 18, 26, 32 are all taut, generally horizontal movement of the floater 12 in any direction is significantly restricted. It will be appreciated by a person of skill in the art that, in practice, the mooring lines 16, 18, 26, 32 will never be completely taut. In order to extend from the floater 12 at the water surface to the anchor 14, 24, 30 at the sea bed, the mooring lines 16, 18, 26, 32 can be very long and heavy, and therefore, tend to follow an arcuate path from the floater 12 to the anchor 14, 24, 30, as illustrated in Figure 13 of

LIS2013/0276687 for example. This is generally known to persons of skill in the art as a “catenary” mooring system. The weight of the mooring lines 16, 18, 26, 32 will, however, provide a force which resists the mooring lines 16, 18, 26, 32 straightening any further, and thus horizontal movement of the floater 12 will, nonetheless, be substantially prevented or at least significantly restricted.

It should also be appreciated that, whilst the first, second and third anchors 14, 24, 30 may be generally evenly spaced around the floater 12, this need not be the case. Depending on the prevailing environmental loads (prevailing wind direction, tide, currents etc), two of the anchor 14, 24, 30 may be closer to each other than they are to the other anchor.

The floater 12 may be provided in an array of floaters as illustrated in Figure 3.

In this embodiment, the different floaters 12 in the array share anchors. The first anchor 14 of one mooring system 10 is the second anchor 26a of another mooring system 10a and the third anchor 30b of yet another mooring system 10b. Similarly, the second anchor 24 of the mooring system 10 is the third anchor 30c of another mooring system 10c and the first anchor 14d of yet another mooring system 10d, and the third anchor 30 is the first anchor 14e of yet another mooring system 10e and the second anchor 24f of yet another mooring system 10f. As such, it will be appreciated that for all the mooring systems which are not at the edge of the array, four mooring lines are connected to each anchor 14, 24, 30.

Typically the array is arranged so that the mooring systems 10, 10, 10”, 10”’, 10”” are arranged such that the prevailing direction of the environmental loads (e.g. winds, waves, and/or current loads - indicated by arrow A) is parallel to a line between the first anchor 14 and the floater 12 and directed to drive the floater 12 away from the first anchor 14.

As mentioned above, the same principle may be applied to the other types of floater illustrated in Figures 1b - 1d. In these cases, however, the fourth mooring line may be connected to the floater at a fourth connection point which is spaced from the first, second and third connection points. For example, where the floater 12 is generally square or rectangular each of the first, second, third or fourth mooring lines 16, 18, 26, 32 may be connected to connection point at or adjacent a different corner of the floater 12. A further alternative embodiment is illustrated in Figure 4. In this embodiment, the fourth mooring line 32 is connected to the second anchor 24 and extends from the second anchor 24 to the floater 12, and is connected to the floater 12 at a fourth connection point which is at or adjacent to the second connection point 22.

In this embodiment, the system 10 also has a third anchor 30, and fifth and sixth mooring lines 34, 36 extend from the third anchor 30 to the floater 12. The fifth mooring line 34 is connected to the floater 12 at a fifth connection point 33 which is at or adjacent to the third connection point 28, whilst the sixth mooring line 36 is connected to the floater at a sixth connection point which is at or adjacent the first connection point 20.

The mooring system 10 may be provided in an array of mooring systems as illustrated in Figure 5.

As specified in relation to Figure 3 above, the different floaters 12 in the array share anchors. The first anchor 14 of one mooring system 10 is the second anchor 26a of another mooring system 10a and the third anchor 30b of yet another mooring system 10b. Similarly, the second anchor 24 of the mooring system 10 is the third anchor 30c of another mooring system 10c and the first anchor 14d of yet another mooring system 10d, and the third anchor 30 is the first anchor 14e of yet another mooring system 10e and the second anchor 24f of yet another mooring system 10f. As such, it will be appreciated that for all the anchors which are not at the edge of the array, four mooring lines are connected to each anchor 14, 24, 30.

Also as specified in relation to Figures 2 & 3 above, the first, second and third anchors 14, 24, 30 are generally evenly spaced around the floater 12, so if the mooring lines 16, 18, 26, 32 are all taut (or in a catenary arrangement as discussed above), generally horizontal movement of the floater 12 in any direction is substantially prevented or at least significantly restricted.

A further alternative embodiment of mooring system 10’ is illustrated in Figure 6. This embodiment is similar to the mooring system 10 illustrated in Figure 2, except that, instead of being secured to anchors 24, 30, the third and fourth mooring lines 26, 32 are each secured to another floater 12’, 12”.

This embodiment of mooring system 10’ can include three of the mooring systems illustrated in Figures 1a - 1d, This embodiment of mooring system 10’ therefore includes three floaters 12, 12’, 12”, each of which is connected to an anchor 14, 14’, 14” via two mooring lines 16, 18, 16’, 18’, 16”, 18” which extend from two separate (first and second) connection points 20, 22, 20’, 22’, 20”, 22” on the floater 12, 12’, 12”.

In the embodiment illustrated in Figure 6, the mooring system illustrated in Figure 1a is used, i.e. the floaters 12, 12’, 12” are triangular. This need not be the case, however.

The mooring system 10’ further comprises one additional mooring line 37, 37’, 37” for each floater 12, 12’, 12” - so three additional mooring lines 37, 37’, 37” in total. Each additional mooring line 37, 37”, 37” is used to connect one of the floaters 12, 12’, 12” to each one of the others. The additional mooring lines 37, 37’, 37” are connected to a third connection point 28, 28’, 28” on each of the floaters 12, 12’, 12”, the third connection point 28, 28’, 28” being spaced from the first and second connection points 20, 22, 20’, 22’, 20”, 22” on each floater 12, 12’, 12”.

In this embodiment, the additional mooring lines 37, 37’, 37” are all substantially equal in length, and therefore the three floaters 12, 12’, 12” are arranged at the points of an equilateral triangle. The additional mooring lines 37, 37’, 37” could, however, be different lengths, depending on the desired relative positions of the anchors 12, 12’, 12”.

This mooring system 10’ could comprise auxiliary anchors and mooring lines, as illustrated in Figure 7. In this embodiment, the mooring system 10” includes three auxiliary anchors 15a, 15b, 15c, the first of which 15a is secured to the first and third floaters 12, 12” by a first pair of auxiliary mooring lines 35a, a second one of which 15b is secured to the first and second floaters 12’, 12” by a second pair of auxiliary mooring lines 35b, and a third one of which 15a is secured to the second and third floaters 12’, 12” a third pair of auxiliary mooring lines 35c. In this embodiment, each auxiliary mooring line 35a, 35b, 35c is connected to its respective floater at a connection point at or adjacent one of the first or second connection points 20, 22, 20’, 22’, 20”, 22” of the respective floater 12, 12’, 12”. The first auxiliary anchor 15a is generally equidistant between the first and third anchors 14, 14”, the second auxiliary anchor 15b is generally equidistant between the first and second anchors 14, 14’, and the third auxiliary anchor 15c is generally equidistant between the second and third anchors 14’, 14”. Such auxiliary anchors 15a, 15b, 15c and auxiliary mooring lines 35a, 35b, 35c assist in maintaining the position of the floaters 12, 12’, 12” in particularly harsh environments.

The auxiliary mooring lines 35a, 35b, 35c could equally be secured to a connection point at or adjacent the third connection points 28, 28’, 28” to which the additional mooring lines 37, 37’, 37” are connected, as illustrated in Figure 8.

A further alternative embodiment of mooring system 10’” is illustrated in Figure 9. This embodiment of mooring system 10” is the same as that illustrated in Figure 6 except that it includes three more additional mooring lines 39, 39’, 39”, so that two additional mooring lines 37, 39, 37’, 39’, 37”, 39” are provided for each floater 12, 12’, 12”, and each floater 12, 12’, 12” is connected to one adjacent floater 12, 12’, 12” by one pair of additional mooring lines 37, 39, 37’, 39’, 37”, 39”, and to another adjacent floater 12, 12’, 12” by another pair of additional mooring lines 37, 39, 37’, 39’, 37”, 39”, one additional mooring line 37, 37’, 37” of each pair being secured to a connection point at or adjacent one of the first or second connection points 20, 22, 20’, 22’, 20”, 22”, and the other of the pair 39. 39’, 39”, 39’” being secured to a connection point at a third corner of the floater 12, 12’, 12”.

It will be appreciated that such mooring systems 10’, 10”, 10’” could include more than three of the systems illustrated in Figures 1a - 1d. It could, for example, include four such systems, and four additional mooring lines, and be arranged such that the each floater is connected to two of the other floaters, the additional mooring lines forming a square, as illustrated in Figures 10 and 11. It could equally comprise two such systems, with a single additional mooring line extending between the two floaters.

In the embodidment illustrated in Figure 10, the mooring system 10”” comprises four of the systems illustrated in Figure 1a (the floaters 12, 12’, 12”, 12” being triangular). Each floater 12, 12’, 12”, 12’” has an anchor 14, 14’, 14’, 14”, 14’”, the anchors 14, 14’, 14”, 14’” being connected to the floater 12, 12’, 12”, 12’” by two mooring lines 16, 18, 16’, 18’, 16”, 18”, 16’”, 18’”, a first one of which 16, 16’, 16”, 16’” is secured to a first connection point 20, 20’, 20”, 20’” at a first corner of the floater 12, 12’, 12”, 12’”, and a second one of which 18, 18’, 18”, 18’” is secured to a second connection point 22, 22’, 22”, 22’” at a second, adjacent corner of the floater 12, 12’, 12”, 12’”. There are four additional mooring lines 37, 37’, 37”, 37’” which are used to connect one of the floaters 12, 12’, 12”, 12”’ to two of the others so that the additional mooring lines 37, 37’, 37”, 37’” form a square. The additional mooring lines 37, 37’, 37”, 37’” are connected to a third connection point 28, 28’, 28”, 28’” on each of the floaters 12, 12’, 12”, the third connection point 28, 28’, 28”, 28’” being spaced from the first and second connection points 20, 22, 20’, 22’, 20”, 22”, 20’”, 22’” on each floater 12, 12’, 12”, 12””.

In the embodiment illustrated in Figure 11, the mooring system 10’”” comprises four of the systems illustrated in Figure 1b (each floater 12, 12’, 12”, 12’” being square). Each floater 12, 12’, 12”, 12” has two anchors 14a, 14b, 14a’, 14b’, 14a”, 14b”, 14a’”, 14b’”, the first anchors 14a, 14a’, 14a”, 14a’” being connected to the floater 12, 12’, 12”, 12’” by two mooring lines 16, 18, 16’, 18’, 16”, 18”, 16’”, 18’”, a first one of which 16, 16’, 16”, 16’” is secured to a first connection point at a first corner of the floater 12, 12’, 12”, 12’”, and a second one of which 18, 18’, 18”, 18’” is secured to a second connection point at a second, adjacent corner of the floater 12, 12’, 12”, 12’”. The second anchors 14b, 14b’, 14b”, 14b’” are also connected to their respective floater 12, 12’, 12”, 12’” by two mooring lines 26, 32, 26’, 32’, 26”, 32”, 26’”, 32’”, a first one of which 26, 26’, 26”, 26’” is secured to a first connection point at the first corner of the floater 12, 12’, 12”, 12’”, and a second one of which 32, 32’, 32”, 32’” is secured to a third connection point at a third, adjacent corner of the floater 12, 12’, 12”, 12’”.

In this embodiment, two additional mooring lines are provided for each floater 12, 12’, 12”, 12’”, so that each floater 12, 12’, 12”, 12’” is connected to one adjacent floater 12, 12’, 12”, 12’” by one pair of additional mooring lines, and to another adjacent floater 12, 12’, 12”, 12’” by another pair of additional mooring lines, one additional mooring line 37, 37’, 37”, 37’” of each pair being secured to a connection point at a corner of the floater 12, 12’, 12”, 12’” to which one of the anchor connected mooring lines 16, 18, 16’, 18’, 16”, 18”, 16’”, 18’” is secured, and the other of the pair 39, 39’, 39”, 39’” being secured to a connection point at a fourth corner of the floater 12, 12’, 12”, 12’”.

A plurality of the mooring systems 10’, 10”, 10’”, 10”” illustrated in any of Figures 6 - 11 may be connected in an array as illustrated in Figures 12 and 13, with one or more anchor 14 of each mooring system 10’ being shared with one or two other such mooring systems 10’. The embodiments include a plurality of the mooring systems 10’ illustrated in Figure 6, but it will be appreciated that the same principal could equally be applied to the systems illustrated in Figures 7, 8, 9, 10 or 11.

In the embodiment illustrated in Figure 12, each anchor 14, 14’, 14” is connected to one floater 12, 12’, 12” from one, two or three different mooring systems 10’. In the embodiment illustrated in Figure 13, each anchor 14, 14’, 14” is connected to one floater 12, 12’, 12” from up to six different mooring systems 10’.

By virtue of these arrangements, the number of anchors per floater, and therefore damage to the seabed, may be reduced. Moreover, the use of suspended mooring lines between floaters may facilitate a reduction in the total footprint of (i.e. area occupied by) the system.

In any of the embodiments described above, the floater 12 may comprise a foundation structure which has a plurality of corners, each of the connection points being provided at one of the corners.

The foundation structure may comprise a platform formed from a plurality of buoyant elements 12a joined by a plurality of generally rigid connecting elements 12b. The connecting elements 12b may, for example, comprise trusses, pontoons or other means for bracing. A buoyant element 12a is advantageously provided at each corner of the array, the first and second connection points being provided on different buoyant elements 12a.

Various possible arrangements of such foundation structures are illustrated in Figures 15a - 15c , with the buoyancy elements 12a drawn as circles, and joined by connecting elements 12b. The foundation structure may comprise three buoyant elements 12a arranged in a triangular array as illustrated in Figures 15a and 15b. Alternatively, the foundation structure may comprise four buoyant elements 12a arranged in a square or rectangular array as illustrated in Figure 15c. Further alternatively, the foundation structure may comprise more than four buoyant elements 12a arranged in a polygonal or generally circular array. Typically the first and second connection points are provided on adjacent buoyant elements 12a, but this is not necessarily the case.

The floater 12 may be a semi-submersible platform of the sort described in LIS2013/0276687, which comprises a plurality of generally vertical buoyancy columns coupled together with a tubular truss system that includes horizontal and vertical bracing beams with a horizontal water-entrapment plate attached to the lowermost portion of some or all of the columns. Whilst all of the columns may be substantially hollow buoyancy columns, this need not be the case. For example, some of the columns may be substantially hollow buoyancy columns, whilst the others are stabilising columns. Where the foundation structure is provided with a mixure of buoyancy columns and stabilising columns, the mooring points 20, 22, 28 could be provided on buoyancy columns only, stabilising columns only, or on mixture of buoyancy columns and stabilised columns. It should be appreciated that the floater 12 could equally comprise a single, continuous buoyant element,

The floater 12 may further comprise a wind turbine 50 supported on the foundation structure 48, as illustrated in Figure 18. Where the foundation structure is formed from a plurality of columns, the wind turbine may be mounted directly above one buoyancy column which provides some or all of the buoyant force required to support the weight of the wind turbine, the other columns including a ballast system, and therefore acting as stabilizing columns to stabilse the foundation structure. Alternatively, the wind turbine could be supported symmetrically by all of the columns. Examples of such a floating wind turbine installation is illustrated and described in at least LIS2013/0276687.

More than one wind turbine could be mounted on the foundation structure. Moreover, another energy generating apparatus, such as a solar panel, could be mounted on the foundation structure in addition to a wind turbine.

The floater 12 could equally be a fish farm, or an array of floating solar panels.

The or each anchor 14, 24, 30 may be a dead weight anchor, a driven pile, a drag anchor, a suction pile, a torpedo pile, a vertical load anchor or any other suitable form of anchor device.

The mooring lines 16, 18, 26, 32, 34, 36 may be chains, ropes or cables, and may be made from metal or polymers such as polyester, nylon, or high modulus polyethylene. The mooring lines 16, 18, 26, 32, 34, 36 need not be all be made from the same material or be of the same construction - some may be chains, others ropes etc.

In the embodiments of mooring system 10’ illustrated in Figures 6 - 11, the mooring lines that extend from one floater 12, 12’, 12” to another are suspended lines which may be suberged in the water or suspended above the water level, without connecting to any anchors. These lines may be made of chains, ropes, or cables, and may be made from metal or polymers such as polyester, nylon, or high modulus polyethylene. Where fiber ropes are used and are submerged in the water, however, it may be advantageous to provide one or more clump weights in the middle of each line to maintain tension in the line and keep it submerged.

Each mooring line may be connected to the floater 12 using a connector such as a fairlead or bi-axial joint, as illustrated in Figures 16 and 17. Figure 16 shows one corner of the floater 12 in plan view, specifically the corner to which the third and fifth mooring lines 26, 32 are secured. In this embodiment, the mooring lines 26, 32 are chains, are each connected to the floater 12 via a bi-axial joint connector 38, 40 at the third and fifth connection points 28, 33 respectively. Figure 17 shows the same corner of the floater 12, but this time as a side view. In this embodiment, the floater 12 comprises a column at each corner, and the mooring lines 26, 32 are again chains, but in this embodiment each is secured to the floater by means of a fair-lead 42, 44

Where a mooring line is connected to the floater 12 at a connection point which is at or adjacent to the connection point associated with a different mooring line, whilst both mooring lines could be connected to the same connector, typically this will not be the case, and each mooring line will be provided with its own connector. In this case, the connectors may be mounted side-by-side on the floater 12 as illustrated in Figures 16 and 17, or they may simply be secured to the same buoyant element.

By virtue of connecting two separate mooring lines (each of which extend from two different and horizontally spaced connection points on the floater all the way to the anchor) to the same anchor, the number of anchors used to restrain the floater 12 may be reduced, thus reducing the cost (both in terms of equipment and installation), and environmental impact on the sea floor of the mooring system 10.

In fact, computer simulations carried out by the applicant reveal that when compared with the mooring system 10’ illustrated in Figure 14, in which each mooring line is connected to a separate anchor, with the new mooring system illustrated in Figure 4, the restoring forces acting to resist translational movement of the floater 12 in two perpendicular directions are likely to be substantially the same for both systems, whilst the yaw stiffness (ie. resistance to rotation of the floater 12 about a generally horizontal axis) of the new mooring system 10 illustrated in Figure 4 may be increased compared to the system 10’ illustrated in Figure 14.

The invention is not limited by the embodiments described above; reference should be had to the appended claims.