Mooring assembly for a floating vessel

The invention relates to a mooring arrangement (2, 2′) for a floating device (1, 2) comprising a band (5) and a drum (3) adapted to pay out and pull in the band (5). The invention being distinctive in that the mooring arrangement (2, 2 further comprising a band guide (14, 15,22), said band (5) is extending from the drum (3) via the band guide (14, 15, 22) and is adapted to be coupled to an anchoring arrangement (13), said band said band guide (4, 15, 22) being configured to tilt about an articulation axis (A, B) being parallel with a longitudinal axis of the part of the band (5a) situated between the drum (3) and the band guide (14, 15, 22) in order to position the band (5) to compensate for movement in the floating device (1,12, 12′) and thus reduce the wear in the band (5).

TECHNICAL FIELD OF THE INVENTION

This invention relates to a mooring arrangement for a floating vessel.

BACKGROUND OF THE INVENTION

WO2010/067341 shows a wave power plant with a floating body which is set up to move under influence of waves, the floating body hosting an energy absorbing device. The energy absorbing device comprising a drum adapted to receive a wire. The wire is adapted to rotate the drum as a result of movement of the power plant. This movement could because of wave motion or other movement on the sea. The motion causes this movement causing only a small part of the wire to rotate on the drum. The wire being repeatedly bent over the drum under tension will lead to wear and eventually failure of this part of the wire.

Replacement of the wire with a flat band will reduce this wear mechanism and increase the lifetime of the system.

The introduction of a flat band in the mooring arrangement bring about other challenges. The relative wide band will require good alignment with drum as it is being winched on to avoid any strain gradient and kinks on the band.

An additional guide pulley mechanism that makes sure that the band is rotated correctly with a suitable angle on the drum is therefore preferably arranged to make sure that the band is rolled straight over the drum. An illustration of the mooring arrangement with and without a band guide is shown inFIGS. 9aand 9band discussed in relation to these figures.

BRIEF SUMMARY OF THE INVENTION

Forces imposed on the floating device by current, wind and waves cause horizontal drift. This gives rise to a horizontal distance between floating device and mooring point (clump weight). This gives again rise to an angle between band and drum.

The horizontal distance causes an angle between the band and the floating device. Since the drum having an axial plane that is substantially parallel with the floating surface of the floating device, this could cause an askew winding of the band on the drum.

The band guide would prevent this and make sure the guide pulley follows the band and articulates relative to the drum to turn the angle between the band and drum. There will be a twist in the band in the area between the guide pulley and the drum but this is considered less harmful and causing less wear on the band than without the band pulley.

The floating device could also be exposed to roll and pitch motion due wave motion. In this situation the plane through the surface of the floating device will have a different angle than the seabed.

A band guide is also preferably under these conditions to compensate for the angle difference between the floating device and the band.

In order for the band to roll straight over the guide pulley when the winch is pulling the band in, it is crucial that the guide pulley is aligned with the lower part of the band.

The guide is free to rotate around its axis and the band is therefore the only force that pose any moment on the guide and decide its rotational angle of the guide and guide pulley.

The second guide pulley and the first guide pulley are connected in the same housing. The second pulley is arranged below the first guide pulley. The second guide pulley has an increased arm to the rotational axis that greatly increases the bands moment on the guide and hence the bands ability to align guide and guide pulley with itself to avoid sideways tracking.

The two pulley setup also reduces risk of misalignment between band and guide pulleys.

The invention relates to a mooring arrangement for a floating device comprising a drum. The mooring arrangement further comprising a band and a band guide, said band is extending from the drum via the band guide and is adapted to be coupled to the anchoring arrangement, said band guide being configured to rotate and position the band to compensate for movement of the floating device in order to reduce the strain on the band.

This will reduce wear on the band, avoiding strain/kink because of an unsuitable angle of the band when winched on the drum.

Preferably the mooring arrangement further comprising base part adapted to be connected to the floating device, said band guide is pivotably coupled to the base part.

Preferably the base part is a frame having two legs adapted to support the band guide two on opposite sides.

Preferably the band guide comprising a single pulley.

Preferably, the band guide comprises a first and second pulley said first and second pulley are arranged in series in the longitudinal direction of the band guide.

Preferably the first pulley and second pulley are coupled to the same housing.

This provides better force control on the band.

Preferably the mooring arrangement having a sensor/load cell arrangement for measuring lateral load between the band and guide pulley flange.

It is therefore able to measure and reduce the tension if the lateral force on the band is too large.

Preferably the mooring arrangement further comprising a band end fitting coupling the mooring arrangement to the anchoring arrangement.

Preferably the band end fitting having a bend constrainer arranged on both sides of the band.

This ensures a certain minimum bending radius of the band.

Preferably the band end fitting comprising a float.

This ensures that the assembly is in an upright position even without the tension in the band.

Preferably the load cell is arranged between the band end fitting and the anchoring arrangement.

The tension could be measured in the mooring arrangement in order to compensate for the movement.

A floating device such as a lifesaver wave energy converter comprising at least one mooring arrangement according to any one of the embodiments disclosed.

The floating device is preferably a Fred. Olsen BOLT lifesaver wave energy converter.

The device preferably comprising three mooring arrangement disposed on the floating device, said at least one of the mooring arrangements is a double pulley arrangement.

Preferably said guide pulley comprising a winch portion adapted to receive the band and flanges arranged outside of the winch portion.

Preferably the height of the flanges above the winch portion are at least the thickness of the band5.

This will prevent the bands tendency to track laterally on the guide pulley and to keep the band in the winch portion of the guide pulley.

FIG. 1shows a floating device1with one mooring arrangement2. The mooring arrangement is arranged in the center of the floating device1. The mooring arrangement2comprises a drum3and a band guide4,15. The band guide4,15could be a single band guide4as shown in theFIG. 1or a double band guide15as disclosed inFIG. 5a. A band5is extending from the drum3via the band guide4, through an opening11in the floating device1towards an anchoring arrangement13. The anchoring arrangement13comprising a subsea buoy6, an anchor7and a rope8arranged below the sea surface10(FIG. 2). The band5is connected to the subsea buoy6through a band end fitting or a termination clamp9. This will be further described inFIGS. 7 and 8.

The subsea buoy6are normally arranged between 8-12 m below the sea surface10but other distances from the sea surface10are also possible. The subsea buoy6is coupled to an anchor7or clump weight arranged at the seabed. The anchor7could have different shapes, like for instance chain basket as shown in the figures. The subsea buoy6is coupled to the anchor7through a rope8, for instance a dyneema rope or nylon rope.

FIG. 2shows a floating device shaped as a ring shaped floating foundation12. The floating device12according to this embodiment having three mooring arrangements2disposed around the floating device12. The mooring arrangements2are preferably equally disposed around the ring12.

The composition of each of the mooring arrangements2are equal to the composition disclosed inFIG. 1with a drum3and band guide4with a band5extending between the drum3and band guide4. The same reference numbers are therefore refers to equal parts in the embodiments. The anchoring arrangements13are also similar as described inFIG. 1. Each mooring arrangement2is attached to one anchoring arrangement13as shown in the figure.

In this embodiment of the floating device1, each of the mooring arrangements2comprising a single pulley arrangement4. The single pulley arrangement4having only one guide pulley14for guiding the band5from the drum3towards the anchoring arrangement13and the seabed. A detailed view of the single band guide4can also be seen inFIGS. 3aand3b.

The invention is not limited to one or three mooring arrangements2. The floating device1could have two mooring arrangements or more than three mooring arrangements2as embodiments of the invention.

FIG. 3ashows a detailed view of the mooring arrangement2of the floating device1,12according to the embodiment shown inFIGS. 1 and 2viewed from the side.

FIG. 3bshows the single pulley arrangement4front viewed. The single guide pulley14is arranged inclined in relation to the drum3. This will be described more in detail below.

InFIG. 4another embodiment of a floating device12′ according to the invention is shown. The floating device12′ having a mooring arrangement2′. The single pulley arrangement4as disclosed inFIGS. 3aand 3bis in this embodiment replaced by a double band guide15. This double band guide15having a first, top pulley17and a second, lower pulley16. The first, top pulley17and the second, lower pulley16are connected to the same housing20,30. (shown inFIG. 6c-6f.) A detailed view of the double band guide15can also be seen inFIGS. 5aand5b.

InFIG. 5a-5bboth the first top pulley17and the second, lower pulley16are arranged inclined in relation to the drum3. This will be described in more detail below.

The embodiment of the floating device of theFIG. 4having one double band guide15and two single pulley arrangement4. Other arrangement of the single4and double pulley arrangement15on the floating device12′ are possible embodiments of the invention, for instance could there be two double band guides15and one single pulley arrangement4.

The single band guide4and the double band guide15are only shown schematically in theFIGS. 1-5. In addition the guide pulley14,16,17must be supported by a housing18,20,30or similar as shown in theFIGS. 6a-6k.

FIG. 6ashows the single guide pulley14arranged in a housing18. This housing18comprising a first part18awhere the single guide pulley14is arranged, and a second part18bconnected to the deck of floating device1,12. The first part and second part are connected through bearings that allow relative articulation between the parts. The second part18bhaving a cylindrical shape as shown inFIG. 6b. The second part18bis rigidly connected to a base part19. The base part19is fixedly attached to the deck of the floating device1,12. The base part19is extending upwardly on both sides the second part18b. The housing18is adapted to rotate in relation to the base part19and the second part18b.

The housing18is adapted to rotate around a center axis A of the cylindrical second part18b, this center axis A is in the following called articulation axis A. The housing18and the base part19are pivotably connected to each other.

The guide pulley14is arranged in the first part18aso that the articulation axis A is a tangential line of the single guide pulley14. The guide pulley14will therefore not rotate in relation to its center, but will instead rotate around a point C on the periphery of the guide pulley14. The point C is also a point on the articulation axis A.

The articulation axis A is congruent with the longitudinal axis of the band part5asituated between the drum3and the guide pulley14. This results in that the band rotates around its own longitudinal axis to compensate for the movement of the floating device.

In order for the band5to roll straight over the guide pulley14when the band5is winched in, it is crucial that the guide pulley14is aligned with a lower part5bof the band5arranged below the guide pulley14. The housing18rotates to compensate for the roll/pitch or the horizontal movement that the floating device are exposed to. This principle is shown inFIGS. 9a-11d.

The guide pulley arrangement4is free to articulate around its rotation point C, the band5itself is the only force that pose any moment on the guide arrangement4and decide the articulation angle of band guide4and guide pulley14(gravity contribution is neglectable).

FIGS. 6cand 6dshows a similar arrangement with double band guide15. The arrangement having a similar housing20with a first part20aand a second part20b. The second part20bis equal to the second part18bof the single pulley arrangement13. The second part20bis resting in a base part21as described in relation to the single pulley arrangement14. The housing20is adapted to rotate around a center axis B of the second part20bof the housing20. In the first part20athere are arranged a first pulley17and a second pulley16. The pulleys16,17are connected to the first part of housing20a. The second, lower pulley16and the first, top pulley17is arranged in the same housing and rotates simultaneously about the center axis B.

The articulation of the first part20ais defined as an axis through the center axis B of the second part20band which also is tangential line to the first, top guide pulley17. The articulation axis is the same as the center axis B. The double guide pulley arrangement1will therefore rotate around a point D situated on this articulation axis B. The second, lower pulley16will therefore have an increase arm up to the articulation axis B that greatly increases the bands5moment on the guide pulleys16,17and hence the bands5ability to align the guide arrangement15and guide pulleys17,16with itself to avoid sideway tracking. The second, lower pulley16also principally denies any misalignment angle to form between band5and first, upper guide pulley17, which would cause sideway tracking of band5on the first, upper guide pulley17.

In the embodiments described inFIG. 6a-fthe housing18,20are supported only on one side by the base part19,21.

The followingFIG. 6e-6kshows another embodiment of the invention of the mooring arrangement2. The figure shows a housing30with a double guide pulley16,17in an arrangement22. The housing30in this embodiment is supported on two sides by a frame31. The housing30is rotatable coupled to the frame31on two sides instead of one as the previous embodiments.

FIG. 6eshows this arrangement in detail. The frame31could be attached to the floating device1,12,12′ through bolts and nuts, but it could also be attached to the floating device1,12,12′ in other ways.

As shown in theFIGS. 6eand 6f, the housing having a first cylinder shaped end32aand a second cylinder shaped end32b. These ends32a,32bare supported by bearings33arranged in the frame31. The cylinder is adapted to rotate in relation to the frame through the bearings33.

The cylinder shaped end32ahas an opening adapted to receive the band from the drum3. The band5is further extending via the first guide pulley17and second guide pulley16and further through the opening to the anchoring arrangement13as described in the embodiment inFIG. 6a-6d. The opening11in the floating device1,12,12′ is arranged within the frame31.

The frame31provides a better support to the band guide22and is therefore a preferred embodiment of the invention over the embodiments shown inFIG. 6a-6d.

The housing is adapted to rotate about a center axis B extending through the center of the cylinder shaped ends32a,32b. This is called the articulation axis B and is also a tangential line to the first, top pulley17in a point D. The center axis is also tangential over the drum3as shown inFIG. 6f. The part of the band5asituated between the drum3and the first, top guide pulley is congruent with this line.

This ensures that the part of the band5abetween the drum3and the first top, pulley is not displaced laterally during articulation of the band guide22, but rather twisting about its center.

The double band guide22will rotate about the articulation axis B which is not the center of the two guide pulleys16,17. The first, top guide pulley17will rotate bout the tangential point D. The second, lower guide pulley16is arranged beneath the first, top guide pulley17and there is a distance between the periphery of the guide pulley16and the articulation axis B. This results in an increased arm to the to the articulation axis B that greatly increases the bands5moment on the guide pulleys16,17and hence the bands5ability to align the guide arrangement15and the guide pulleys17,16with itself to avoid sideway tracking.

The principle is equal to the embodiments described inFIG. 6a-6d.

It is also another possible embodiment to replace the double pulley arrangement15as described inFIGS. 6eand 6fwith a single pulley arrangement4as described inFIG. 3aso that the single pulley arrangement4is supported on two sides by the frame31.

FIG. 6gshows the band guide in the housing30. The band guide15is in this figure in a resting position where both guide pulleys are aligned in the vertical direction.

InFIG. 6hthe band guide is in an active position where the guide pulleys and the housing are rotated in relation to the frame31. The guide pulleys are also rotated in relation to the drum in this position.

A pair of constrainer plates34and a set of bars35encapsulate the guide pulley16,17to ensure that the band5do not end up outside a winch portion16′,17′ of the pulley16,17even in case of zero or negative tension. The winch portion16′,17′ is the center part of the pulley16,17where the band is in contact with the guide pulley17,16as shown also in particular inFIG. 6j.

The bars35are adapted to hold the constrainer plates34in a suitable distance from each other and the winch portion16′,17′ between the constrainer plates3434, and to ensure band cannot be displaced upwards during zero or negative band tension.

This arrangement is also equally relevant for the single pulley arrangement4as well. The difference is that there is arranged only one guide pulley in the arrangement of constrainer plates34and bars35.

FIG. 6l-6pshows a detail view of the guide pulley14,16,17viewed from different angles.

FIG. 6lshows the guide pulley14,16,17viewed from the same direction as the guide pulleys16,17inFIG. 6k, but it is shown without the band5. The guide pulley14,16,17comprising two side flanges40arranged on opposite sides of the guide pulley14,16,17and a smooth winch portion14′,16′,17′ where the guide pulley14,16,17is adapted to be in contact with the band5. This winch portion14′,16,17is equal to the winch portion as described inFIG. 6i.

FIG. 6m-nshows the guide pulley viewed from the sides. InFIG. 6monly a back wall to hold the parts of the guide pulley together is shown. InFIG. 6nthe different parts of the guide pulley14,16,17are viewed.

FIG. 6oshows a sectional view of the inside of the guide pulley14,16,17andFIG. 6pshows a detailed view of a load cell45arranged at the inside of the guide pulley shown in detail C.

The load cell45is arranged so that it is fixed rigidly to the back wall36.

Spacers46are rigidly fixed to back wall36. The flange40is also bolted to the back wall36, though spacers46, but load cell sits in between spacers46and flange40. This way flange40is pretensioned against load cell45. It important that there is a gap between flange40and spacers46to allow deformation of flange40without flange40interfering with spacers46to ensure all load of flange40goes through load cell arrangement45.

Load cell signal is transferred from rotating part14,16,17to a stationary shaft38by slip rings43. From slip rings43signal wires exits pulley through center of shaft44.

The flanges40and the winch portion are arranged to rotate around a center shaft38situated in the center of the guide pulley14,16,17. Bearings39are arranged between the flanges36, winch portion14′,16,17′ and the center shaft38as shown in theFIG. 6n.

An important property of the guide pulley14,16,17is the geometry and positioning of the guide pulley flanges40. The bands5ability to ensure that the guide4,15,22and band5is aligned relies on the center plane of band and center plane of guide pulleys to intersect as much as possible, ie the band must be centered on the guide pulleys in the winch portion of the guide pulley14′,16,17′. In practice, due to imperfections in fabrications, band5will have a tendency to track laterally on the guide pulley14,16,17. To ensure the above mentioned plan intersection, the flanges40on the guide pulleys14,16,17will prevent this tracking. The flanges40must have a vertical part41at least the height of the band5, plus a tapered part42to ensure a smooth entry of the band5. To minimize wear on the band5from interference with the flanges40, there must be a certain clearance between the flange40and the band5, hence the flange spacing ie the width of the winch portion14′,16′,17′ must be marginally larger than width of the band5by typically 1-2% of the band width.

FIG. 7a-7fshows a band fitting arrangement that could be used in relation to one of the embodiments of the invention.

FIG. 7ashows a detailed view of the anchoring arrangement described inFIG. 1, the anchoring arrangement13is situated below the floating device1,12in the sea. The band5is in the lower end5battached to a band end fitting9as shown inFIGS. 7b-7d.

A thin bend constrainer23are arranged on both sides of the band5to ensure a minimum bend radius about the orthogonal axis/the axis parallel to the band plane E. The bend constrainer23could be made of polyetylen or other flexible material. The bend constrainer is best shown inFIGS. 7cand7d.

The band end fitting9could also have a buoyancy float24to ensure that the end fitting is always straight even without the band tension.

The band end fitting9is connected to the subsea buoy6through a bolted connection25. The band end fitting9is thus allowed to pivot freely about the bolted connection25. The connection allows articulation about one axis normal to the band plane.

The subsea buoy6will be influenced by forces from both the band tension and the buoyancy.

Depending on the magnitude of the tension of the band5, the subsea buoy6will find a static equilibrium orientation. This orientation may be angled in relation to an axis E through the longitudinal direction of the band5. The orientation may also be in line with the axis E.

FIG. 7ashows the band end fitting9used in a floating device1with only one mooring arrangement2. This embodiment of the band end fitting9could easily also be used in a floating device with more than one mooring arrangement2, for example three as shown inFIG. 8b.

FIG. 7cshows a band end fitting drum28which is arranged between the band5and the subsea buoy6. The band end fitting drum28is adapted to wind the band5on the drum28. Normally the band is wrapped 2.5 times around the band end fitting drum28, but more or less of the band wrapped around the band end fitting28is possible embodiments.

FIGS. 7eand 7fshows the fastening device29of the band5to the band fitting drum28. The fastening device29has a cylinder shaped end portion29athat is adapted to match with a pin or similar in the band fitting drum28.

The pin/cylinder connection allows a quick connection or disconnection of the band5from the band end fitting drum28.

The fastening device also comprises a clamp29badapted to be connected to the band. The clamp29bhas a curved surface to minimize the interference to band wrapping on top of the clamp29b.

The pin/cylinder connection also allows the clamp29bto swing out in case all band5on the drum3is pulled out and the end stop is reached.

FIG. 8a-8cshows another embodiment of a band end fitting26. In this embodiment, there are arranged floats27on both sides of the belt end fitting26. There are also shown a load cell28arranged between the band end fitting26and the subsea buoy6.

The load cell28are configured to monitor the tension between the band5and the mooring arrangement and adjust the tension accordingly.

The load cell is also a possible embodiment in the band end fitting arrangement9inFIG. 7a-7f.

FIGS. 8band 8cshows the band end fitting and subsea buoy arranged in a floating device12with three mooring arrangements2. The load cell27and the band end fitting27could also easily be used in a floating device with only one mooring arrangement2as shown inFIG. 7a-7f.

Both the embodiments of the band end fittings9,26are embodiments to both the single pulley arrangement2and double pulley arrangement2′.

The floating device is anchored to the seabed through chain basket7as shown inFIGS. 7aand 8b. The number of chain baskets7are equal to the number of mooring arrangements2on the floating device1,12,12′.

The functioning of the invention will now be described with help from theFIGS. 9a-11d.

FIGS. 9a-bare illustrating the mooring arrangement without any band guides. When the floating device1,12,12′ is exposed to horizontal motion, roll or pitch motion, the band5will be pulled away from the vertical resting position. The drum3and anchor arrangement13will be positioned relative each other so that there will be a bend in the band5. This will cause a strain or kink in the band5when the band is rolled up on the drum3, which after a while may lead to tear and break of the band5.

When the floating device1,12,12′ are moored to the seabed, the horizontal movement, roll and pitch movement will cause the drum3to winch the band5to adjust the movement and keep the mooring arrangement straight at all times. There will be only a small part of the band5that are winched on and off the drum3because of the movement of the floating device1,12,12′ It is therefore only a small part of the band5that repeatedly will be exposed to wear due to movement of the floating device1,12,12′.

The band guide4,15is therefore introduced. This arrangement is adapted to tilt and follow the band5so that the band5as a result enters a pulley that is aligned due to the movement of the floating device1,12,12′. The band guide4,15is in this position in the active position as shown inFIG. 6h.

The part of the band between the drum and the band guide will experience a twist between the guide pulley and the drum, but this is considered to be less harmful than the previous arrangement without the band guide shown inFIG. 9a.

The ability for the guide pulley to rotate and follow the angle of the band5as shown inFIG. 9bwill result in a winching of the band5that is more gentle to the band5and reduce the wear of the band5. In addition it will be easier to winch the band5and reduce any kink since the band guide4,15improves the position of the part5aof the band5that are winched onto the drum3.

The band guide4,15is adapted to rotate so that the guide pulley14,16,17is aligned with the lower part of the band5b. This will cause an even distribution the tension forces in the band5over the whole length of the guide pulley14,16,17.

FIGS. 10aand 10bshows the relation between the drum and the band guide4,15. The embodiment with the single guide pulley14and the housing supported on one side (FIG. 6a-6d) is used as an illustrative example but there will no difference with the double band guide15and the housing with two support (FIG. 6e-6h).

The band guide4,15is adapted to rotate to adjust for the movement of the floating device1,12. The band guide4,15is adapted to rotate or pivot about a central axis A of the cylindrical part18b,20bof the housing as described earlier.

In other words, the guide pulley14,16,17is adapted to articulate about the articulation axis A that passes in the longitudinal direction of the band5.

A plane G through the drum3and a plane H through the guide pulley14,16,17remain parallel at all positions of the band guide4,15.

FIG. 11aandFIG. 11bshows the principle where the floating device1,12is displaced in the vertical direction. The axis through the longitudinal direction of the band5is inclined in relation to a vertical line. The angle difference is shown as a in theFIGS. 11aand11b.

FIG. 11cillustrating possible movements of the guide pulley14,16,17due to roll movement. The guide pulley14,16,17could for instance rotate in the direction of the arrow up to +/−35° but also larger angle is possible.

FIG. 11dshows movements of the band5due to pitch movement. The band5will be forced a distance from the guide pulley or towards the guide pulley14,16,17depending on the direction of movement. This movement will not cause any rotation of the band guide because drum3and the guide pulley14,16,17are substantially aligned in a straight line during the movement.

In all the embodiments of the invention there could be arranged a sensor (not shown) that measures the lateral forces between the band5and the guide pulley flanges. The tension could then be reduces if the lateral force is too large.

FIGS. 12-15fshows different position or movement of the floating device1illustrated by a floating arrangement with one mooring arrangement inFIG. 12-14and by the floating arrangement with three mooring arrangements inFIGS. 15a-f.

FIG. 12shows the floating device1where there is no roll, pitch or drift motion acting on the floating device.

The band5, rope9and the anchor7are arranged in a vertical line. In this position, there is no articulation angle or increased wrap sector imposed on the guide pulley14.

FIG. 13a-13bshows the floating device exposed to roll and pitch motion. This roll and pitch motion are imposed to the rigid floating device from the waves. Usually the floating device will tilt about +/−5 degrees from the horizontal plane. Tilting angles up to +/−45 degrees and higher are however possible.FIG. 13ashows a floating device exposed to roll motion, whileFIG. 13bshows the floating device exposed to pitch motion.

FIG. 14shows the floating device exposed to horizontal drift. Horizontal drift is caused by current, wind and waves that leads to a horizontal distance between the floating device1,12and mooring point (anchor)7. This gives rise to an angle between the band5and drum3.

FIG. 15a-fshows the floating device12and movement of this in the sea when a wave is passing from left. The mooring2and anchoring arrangement13are configured to maintain constant tension by controlling torque on the drum, allowing band to be pulled out when floating structure is displaced relative to anchoring point, and wound back onto drum3when floating structure moves back.