Upending elongate structures offshore

Abstract

A hoisting tool (18 fig.1a) for upending a load (12 fig.1a), such as a monopile has a pull-in system 72 and a pay-out system 72 acting respectively on variable-length upper link 24 and lower 26 link c

Description

This invention relates to the challenges of upending a bulky elongate structure such as a monopile foundation or a jacket structure that is being lifted into a body of water by 5 an installation vessel. A monopile is a hollow cylindrical column, installed in a vertical orientation, that is commonly used as a foundation for an offshore wind turbine. Typically, installation of a monopile involves transporting it horizontally to an installation site and then upending it 10 by lifting one end using a floating crane. Once vertical, the monopile is driven down vertically into the seabed. Sometimes a monopile is transported aboard the vessel that supports the crane; alternatively, the monopile can be transported aboard a separate vessel or barge. 15 A pivot axis for upending a monopile may be defined on a crane vessel as shown in EP 3517479, where the crane lifts the top end of the monopile while an upend frame on the main deck of the vessel controls the pivoting motion. However, if a monopile is longer than the height that is available between the crane hook and the water surface, transporting and installing the monopile by this conventional method may not be 20 possible. Also, upending over the side of the vessel is restricted by the load capacity of its deck and hull. Consequently, this technique is not suitable for future extra-extra-large (XXL) monopiles that could, for example, weigh about 3000 metric tons. It is also possible to launch an elongate structure from a vessel, as shown for suction 25 piles in WO 99 / 64684, but such a method does not allow for fine control of the position and verticality of the pile. A third installation method involves floating a monopile closed with plugs at its top and bottom ends, hence making the hollow monopile positively buoyant. Upending is done 30 by suspending the top end of monopile from a crane hook and then ballasting the monopile through the bottom plug. This is an example of ballasting an elongate structure to upend it in water by creating differential buoyancy along its length, as also described for a jacket in US RE30823. However, controlling flooding of a structure with ballasting water can be complex and risks uncontrolled sinking. Also, for a monopile, it 35 adds considerable time and expense to manufacture, install and remove the plugs. 11 06 25 More generally, upending of a structure can be performed in air or in water, with the structure suspended between two cranes and / or winches or between two hooks of the 5 same crane. In EP 2372143, for example, a cable arrangement for upending a pile employs two winches mounted on a self-elevating platform, also known as a ‘jack-up’. The pile swings below the deck of the jack-up, between the legs that support the deck. This renders the teaching of EP 2372143 unsuitable for use with a floating crane vessel, as the pile would clash with the hull of the vessel. 10 CN 109879182 discloses a crane that supports a pair of winches. A cable of one of the winches is connected to a top end of a pile and a cable of the other winch is connected to a bottom end of the pile. With the crane suspending the pile from the winch cables, opposed movement of the winch cables is then synchronised to raise the top end of the 15 pile while simultaneously lowering the bottom end of the pile. Similarly in CN 202745060, a crane handles the top of a pile while a separate winch handles the bottom of the pile. Employing a combination of winches and / or cranes in these ways adds risk to the 20 operation because even a slight discrepancy in the control of the two winches and / or cranes could generate excessive tension in either of their cables. Various other upending solutions are known in the art, for example as taught in DE 88005030969, JP 2011079634, KR 20140004422, CN 107840254, CN 110803609, CN 25 11021 8098, CN 108726359, EP 2364949, WO 2015 / 014491 and WO 2018 / 052291. WO 2021 / 175871 discloses a crane that supports elongate rigging elements connected to a monopile at respective longitudinally-spaced connection axes. A pair of those elements, of fixed length, extend to a first connection axis and another of those 30 elements, of variable length, extends to a second connection axis. A frame suspended from the crane supports a winch that pays out the variable-length element to lower the second connection axis relative to the first connection axis, which serves as a pivot axis about which the structure is upended. The monopile requires trunnions to which the fixed-length elements must be attached to define the first connection axis and from 35 which the fixed-length elements must therefore eventually be detached. 11 06 25 EP 3559442 discloses an apparatus for lifting and mounting a wind turbine blade on a wind turbine. US 2015 / 0228366 describes a tool for lifting and rotating a shipping container. The tool 5 includes a rigging line that connects to the container at a lifting point and winch cabling that connects to the top of the container. The winch draws in the winch cabling to rotate the container about the lifting point from a horizontal orientation to a vertical orientation. US 5205544 describes a system for lifting a building panel. The system includes a 10 frame that houses a winch acting on a winch cable to re-orient the panel, A fixed-length cable suspended from a sheave is secured to two locations at an end of the panel. EP 2423146 discloses an arrangement for rotating a load in which a trolley that can be moved along a carrier supports a lifting mechanism from which the load can be 15 suspended. The arrangement further includes a hoist, also suspended by the carrier, and a suspension element also attached to the load. The suspension element is used exclusively to hold the load, with all lifting undertaken by the lifting mechanism. Against this background, the invention resides in a hoisting tool for upending an 20 elongate load. The tool comprises a suspension point by which a frame of the tool can be suspended from a crane and about which the tool can pivot about a horizontal axis. The tool further comprises a pull-in system acting on a variable-length upper link for connecting the tool to an upper side of a centre of gravity of the load and a pay-out system acting on a variable-length lower link for connecting the tool to a lower side of 25 the centre of gravity of the load. The terms ‘upper’ and ‘lower’ for the links do not necessarily, or always, relate to their positions relative to each other but instead to where the links connect to the load. For example, the upper link may connect to the upper end or upper portion of a monopile 30 on an upper side of the centre of gravity and the lower link may connect to the lower end or lower portion of a monopile on a lower side of the centre of gravity. In some embodiments, not described herein, the links could exchange their respective roles. The pull-in system and the pay-out system comprise respective drum portions on which 35 parts of the upper link and the lower link can be wound, for example in mutually- opposed circumferential directions. The drum portions are arranged to rotate relative to 11 06 25 the frame to pull in the upper link and to pay out the lower link simultaneously. The drum portions are also coupled together to offset torque applied to one of the drum portions by tension in the upper link against torque applied to another of the drum portions by tension in the lower link. This allows a small-capacity winch to be used to 5 control rotation of the drum portions, in which case a drive belt driven by the winch may conveniently be disposed between the drum portions. The drum portions can be coupled to rotate together about a common axis. For example, the drum portions may be portions of a common drum distributed along a 10 common axis. Nevertheless, a drum portion on which the upper link is wound can have a different diameter, or average diameter, than a drum portion on which the lower link is wound. The upper link and / or the lower link may comprise two or more limbs that are each 15 wound on a respective one of the drum portions. Such limbs are apt to be wound on respective drum portions that are in mirrored relation about a central plane. At least one of the drum portions can taper along its axis of rotation, for example by having a substantially frusto-conical shape, and the drum portions may share a 20 common direction of taper. A tapered drum portion is apt to support successive coils of the upper link or the lower link, those coils decreasing in diameter in the direction of taper or increasing in diameter against the direction of taper. The tool can therefore be arranged such that while successive coils of the upper link of increasing diameter are being wound onto one of the drum portions, successive coils of the lower link of 25 decreasing diameter are paid out simultaneously from another of the drum portions. The frame of the tool may comprise an upper frame member and a lower frame member that is movable relative to the upper frame member, the upper frame member extending from the frame suspension point to an upper link suspension point and the 30 lower frame member supporting a lower link suspension point that is movable with the lower frame member relative to the upper frame member. The drum portions may, for example, be mounted on the lower frame member. The frame may further comprise a variable-length mechanism that connects the upper 35 and lower frame members and that is operable to effect said movement of the lower frame member. The variable-length mechanism may comprise a frame adjustment 11 06 25 winch, suitably mounted on the upper frame member, acting on a wire of a reeving system that extends between the upper and lower frame members. The upper frame member may be relatively upright whereas the lower frame member 5 may be relatively horizontal. A longitudinal axis of the lower member can be moved from an acute angle to an obtuse angle relative to a longitudinal axis of the upper member. In consequence, the longitudinal axis of the upper member may be pivotable about the frame suspension point to adopt a substantially vertical orientation. 10 Correspondingly, the inventive concept also embraces a method of upending an elongate load. The method comprises suspending a hoisting tool and suspending the load from the tool via upper and lower links, the upper link extending from the tool to an upper side of a centre of gravity of the load and the lower link extending from the tool to a lower side of the centre of gravity of the load. At least one pull-in drum portion of the 15 tool is rotated to pull in the upper link, hence shortening the upper link to lift an upper end of the load toward the tool. Simultaneously, at least one pay-out drum portion of the tool is rotated to pay out the lower link, hence lengthening the lower link to lower a lower end of the load away from the tool. Conveniently, the lower link can be unwound and the upper link can be wound about a common axis. Torque applied to the or each 20 pull-in drum portion by tension in the upper link is offset against torque applied to the or each pay-out drum portion by tension in the lower link so as to reduce aggregate torque required to control rotation of the drum portions. During upending of the load, the upper link may be pulled in at a greater linear speed 25 than the lower link is paid out. Also, the upper link can be pulled in with increasing linear speed during upending whereas the lower link can be paid out with decreasing linear speed during upending. Nevertheless, the pull-in drum portion and the pay-out drum portion can rotate at the same angular velocity throughout. Thus, a gear ratio applied by a pull-in or pay-out drum portion to the upper link and / or the lower link may 30 be varied during upending of the load. This may, for example, be achieved by progressively spooling the upper link or unspooling the lower link along a tapered pull-in or pay-out drum portion. A pull-in drum portion and a pay-out drum portion can rotate in a common 35 circumferential direction while the lower link and the upper link are wound about the associated portions in mutually-opposed circumferential directions. 11 06 25 The method of the invention may further comprise: suspending the tool via a frame suspension point at which an upper frame member of the tool can pivot about a horizontal upper pivot axis; reconfiguring the tool by moving the lower frame member 5 relative to the upper frame member to lower a suspension point of the lower link; and pivoting the upper frame member about the upper pivot axis to move a suspension point of the upper link toward an upright axis that extends from the upper pivot axis to the centre of gravity of the load. 10 The tool may be reconfigured by moving an axis of the lower frame member from an acute angle to an obtuse angle relative to an axis of the upper frame member, for example by lengthening a variable-length mechanism that connects the upper and lower frame members. 15 A spreader of the upper link may be lifted and docked to the tool using an auxiliary coupling. Subsequently, with the weight of the load supported substantially or exclusively through the coupling, the lower link can be released from the load. In embodiments of the invention, a hoisting arrangement for upending an elongate load 20 comprises a hoisting tool having a reconfigurable frame comprising an upper frame member that is pivotably suspended about an upper pivot axis and a lower frame member that is movable relative to the upper frame member. For example, the upper and lower frame members may be pivotably connected to each other about a hinge axis. A variable-length upper link extends from an upper side of the centre of gravity of 25 the load to a pull-in system supported by the frame. Conversely, a lower link extends from the load on a lower side of the centre of gravity to a lower link suspension point that is movable with the lower frame member. The arrangement may further comprise a crane from which the load is supported via the hoisting tool and the upper and lower links. 30 A variable-length mechanism that connects the upper and lower frame members may be operable to effect said movement of the lower frame member. The variable-length mechanism may comprise a frame adjustment winch mounted on the frame, for example on the upper frame member, acting on a wire of a reeving system that 35 extends between the upper and lower frame members. 11 06 25 The upper frame member may be relatively upright and the lower frame member may be relatively horizontal. A longitudinal axis of the lower frame member can be moved from an acute angle to an obtuse angle relative to a longitudinal axis of the upper frame member. The longitudinal axis of the upper member can be pivoted about the upper 5 pivot axis to adopt a substantially vertical orientation. The upper link may extend to the pull-in system via an upper link suspension point that is spaced along the upper frame member from the upper pivot axis. The pull-in system may conveniently be mounted on the lower frame member. 10 The upper link may comprise an upper sling that extends from the load to a spreader and an upper wire that extends from the spreader to the pull-in system. The upper link may further comprise an auxiliary fixed-length coupling that acts between the spreader and the frame. The lower link may comprise a lower sling that is connected to the load, 15 a lower wire that extends to a pay-out system supported by the hoisting tool and a spreader that is disposed between the lower wire and the lower sling. The upper link is suitably attached to the load at a position in alignment with a central longitudinal axis of the load. Conversely, the lower link is suitably attached to the load 20 at a position offset laterally from the central longitudinal axis of the load. The upper and lower links may conveniently be attached to the load at respective ends of the load. Embodiments of the invention implement a corresponding method of upending an elongate load, the method comprising suspending a hoisting tool via a frame 25 suspension point at which an upper frame member of the hoisting tool can pivot about a horizontal upper pivot axis, and suspending the load from the hoisting tool via upper and lower links. The upper link extends to an upper side of the centre of gravity of the load from an upper link suspension point of the upper frame member of the hoisting tool. Conversely, the lower link extends to the load on a lower side of the centre of 30 gravity from a lower link suspension point of a lower frame member of the hoisting tool. The upper link is shortened to lift an upper end of the load toward the hoisting tool, for example by pulling in an upper wire of the upper link using a pull-in system mounted on the hoisting tool. A spreader of the upper link connected to the upper wire can then be 35 docked to the hoisting tool with an auxiliary coupling. This enables all or part of the 11 06 25 weight of the load to be directed through the upper frame member via the coupling before eventually releasing the lower link from the load. The hoisting tool is then reconfigured by moving the lower frame member relative to the 5 upper frame member to lower the lower link suspension point, for example by moving an axis of the lower frame member from an acute angle to an obtuse angle relative to an axis of the upper frame member. This can be achieved by lengthening a variablelength mechanism such as a reeving system that connects the upper and lower frame members. The upper frame member also pivots about the upper pivot axis to move the 10 upper link suspension point toward an upright axis that extends from the upper pivot axis to the centre of gravity. Embodiments of the invention also disclose a hoisting tool for upending an elongate load, the tool comprising: a reconfigurable frame comprising an upper frame member 15 arranged to support a variable-length upper link for connecting the tool to an upper side of a centre of gravity of the load and a lower frame member that is movable relative to the upper frame member and is arranged to support a lower link for connecting the tool to a lower side of the centre of gravity of the load; and a pull-in system arranged to act on the upper link. The upper frame member extends from a frame suspension point at 20 which the frame can be pivotably suspended from a crane to an upper link suspension point that is spaced from the frame suspension point. The lower frame member supports a lower link suspension point that is movable with the lower frame member relative to the upper frame member. 25 Embodiments of the invention implement a method to transport and upend an elongate object such as a monopile for an offshore wind turbine. In that method, a hoisting tool suspended from a crane hook comprises a hoisting winch that carries a lifting cable. The elongate object is suspended between a first sling connected to a spreader bar or frame, itself suspended on the lifting cable, and a second sling connected to the 30 hoisting tool. The first sling is attached to the elongate object at a point close to a first end of the object, and the second sling is attached to the object at a point close to the centre of gravity of the object but opposed to the first end. A third sling, functionally connected to 35 the second sling, is arranged along the elongate object between a point at or close to a second end of the object and the attachment point of the second sling. 11 06 25 After transporting the elongate object in a substantially horizontal orientation in this first configuration, the lifting cable is paid in until the initially remote spreader bar or frame is close to the hoisting tool, whereupon the spreader bar or frame may optionally be 5 docked to the hoisting tool. Load is progressively transferred from the second sling to the third and first slings as the spreader bar or frame approaches the hoisting tool and the elongate object approaches an upright orientation. The geometry of the hoisting tool is then modified to disconnect the second and third slings from the object. 10 Embodiments of the invention also disclose a hoisting tool for upending an elongate object, the tool comprising: an upper frame assembly interfaced with a crane lifting system such as a hook or a wire; a lower frame assembly hinged to the upper frame; and a frame control system acting on and between the frame assemblies. The frame control system may, for example, comprise a winch and a cable, the cable being 15 reeved in a pulley arrangement between the upper frame and the lower frame to define a triangle with the frame assemblies. The upper and / or the lower frame assemblies can each comprise two or more frame sections. A storage drum can carry two distinct lifting cable sections, an end of each lifting cable 20 section being connected to a respective spreader bar or frame. Each spreader bar or frame may be connected to or adjacent to a respective end of the elongate object. Each spreader bar or frame can be coupled to a frame assembly. The storage drum may have a shape that tapers along its axis of rotation, for example 25 from the centre to ends of the drum. A storage drum control system that may, for example, comprise a winch and a cable acts on the storage drum. The storage drum may comprise sections or portions that can be partitioned from each other. For example, there could be at least two or at least three such portions. At least 30 one portion can store a first lifting cable section and at least one other portion can store a second lifting cable section. Another portion, which can be disposed between the other portions and could be in the centre of the drum, may provide for the storage drum control system to control motion of the drum. 35 Embodiments of the invention also implement another method to transport and upend an elongate object. In that method, a hoisting tool suspended from a crane hook 11 06 25 comprises a storage drum for storing at least two distinct lifting cable sections, each lifting cable section carrying a respective spreader bar or frame. The elongate object is suspended from slings connected to the spreader bars or frames. 5 When the elongate object is in a first, substantially horizontal orientation, one spreader bar or frame is relatively close to the hoisting tool and the other spreader bar or frame is relatively close to the elongate object, hence being relatively remote from the hoisting tool. The distances between the hoisting tool and the connections of the slings to the elongate object may then be substantially equivalent. 10 After transporting the object in the first orientation, the first lifting cable section can be paid in onto the storage drum while the second lifting cable section is simultaneously paid out from the storage drum to tilt the elongate object towards an upright or vertical orientation, as the initially remote spreader bar or frame is brought closer to the 15 hoisting tool. That spreader bar or frame may then be docked to the hoisting tool. Conversely, the sling of the other spreader bar can be disconnected from the elongate object, optionally after modifying the geometry of the hoisting tool. The geometry of the hoisting tool may, for example, be modified be widening or 20 lengthening a variable-length side of a triangular structure of the tool. The triangular structure may be defined by two frame members of the tool that are hinged together at a hinge end and a cable extending between the ends of the frame assemblies opposed to the hinge end. The cable may, for example, be arranged around pulleys at the ends of the frame assemblies opposed to the hinge end. 25 When the elongate object is in a horizontal lift configuration, forces in first and second lifting cables or ropes are approximately equal and forces in first and second slings are also approximately equal. The first and second lifting ropes may be regarded as upper and lower ropes respectively, reflecting their relative positions when upending begins. 30 Thus, the mutually-opposed moment arms applied by the upper and lower ropes to the storage drum of the storage winch are close to equal, which results in a substantially zero or at least minimal resulting moment on the storage drum. This means that the storage drum control system requires only a relatively small-capacity winch to upend the object by turning the storage drum. 11 06 25 During upending, the storage winch can pay in the upper ropes to an increasing diameter of the storage drum, which may be tapered or frusto-conical, while the storage winch can pay out the lower ropes from a decreasing drum diameter. As the upper sling force decreases and the lower sling force increases during upending, the 5 resulting aggregate moment on the storage drum remains minimal. For example, when the object has been upended to an inclination of about 68° to 80° to the horizontal, the upper sling force can be about one third of the lower sling force while the moment arm of the upper cables or ropes on the storage drum can be about three times the moment arm of the lower cables or ropes. The resulting moment on the storage drum remains 10 low, potentially close to zero. When upending is complete, load transfer through the storage winch can cease if the spreader bar of the upper winch is then suspended from or coupled to the frame of the upending tool. The frame of the storage tool can unfold to release the bottom 15 connection, for example by paying out cable from a second winch to allow members of the frame to hinge apart from each other. Thus, the invention provides solutions to lift and upend a monopile in one lifting operation using a single crane, enjoying a significant competitive advantage over 20 conventional monopile upending techniques. To achieve this, the invention contemplates a hoisting tool to be suspended from a crane, the tool comprising a frame with two winches. A monopile is suspended from the crane, via the frame, to be upended from a horizontal to an upright orientation. The mechanics of the system are such that the winches can be relatively small. 25 The invention also contemplates a hoisting arrangement in which a monopile is lifted at its top and bottom parts or ends. Wires or ropes connected to the upper part or end of the monopile and to the lower part or end of the monopile are connected to a storage drum that is supported by the frame of the hoisting tool. Rotation of the drum may be 30 driven by a winch or by another system for applying torque to the drum. By virtue of the tapered shape of the drum and variation of the ratio between upper and lower sling forces during upending, the resulting torque on the storage drum remains minimal. This minimises the capacity required of the winch or other system for driving the drum. 35 In summary, an elongate load such as a monopile may be upended in accordance with the invention by suspending the load from a hoisting tool with a reconfigurable frame. 11 06 25 The frame comprises an upper frame member through which the tool is pivotably suspended from an upper pivot axis and a lower frame member that is movable relative to the upper frame member. A variable-length upper link extends from an upper side of the centre of gravity of the load to a pull-in system supported by the frame. A lower link 5 of fixed or variable length extends from the load on a lower side of the centre of gravity to a lower pivot axis that is movable with the lower frame member. During reconfiguration, the upper frame member pivots about the upper pivot axis to move a suspension point of the upper link toward an upright axis that extends from the upper pivot axis to the centre of gravity. 10 A hoisting tool of the invention for upending a monopile comprises a pull-in system and a pay-out system acting respectively on variable-length upper and lower links for connecting the tool to upper and lower sides of the centre of gravity of the monopile. The pull-in system and the pay-out system comprise respective drum portions on which 15 the upper link and the lower link are wound respectively in mutually-opposed circumferential directions. The drum portions rotate together to pull in the upper link and to pay out the lower link simultaneously, counterbalancing torque applied to the drum portions by tension in the upper and lower links to reduce aggregate torque required to control rotation of the drum portions. 20 In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: Figures 1a to 1d are a sequence of schematic side views showing a monopile 25 being upended in accordance with a first method of the invention; Figures 2a and 2b are schematic side views of a hoisting tool in accordance with a first embodiment of the invention, used in the upending method shown in Figures 1a to 1d; and 30 Figures 3a to 3c are schematic side views of a drum of the hoisting tool shown in Figures 2a and 2b in conjunction with diagrams showing forces acting on upper and lower links wound on the drum and moments experienced by the drum in consequence. 11 06 25 Referring firstly to Figures 1a to 1d of the drawings, a hook 10 of a floating crane supports an elongate load that is exemplified here by a monopile 12. The monopile 12 is a hollow tubular structure that is rotationally symmetrical about a central longitudinal axis 14. As is conventional, the monopile 12 comprises a relatively narrow top portion 5 12A and a relatively wide base portion 12B that are joined by a frusto-conical intermediate portion 12C. In this example, the centre of gravity 16 of the monopile 12 lies on the central longitudinal axis 14 within the enlarged base portion 12B. As a non-limiting example, the monopile 12 may have a length of about one hundred 10 metres, a width of about ten metres at its wider bottom end and an overall weight of about two thousand tons. Even larger monopiles are envisaged by the offshore wind industry, hence adding to the challenges that are addressed by the invention. The monopile 12 is shown here supported by a hoisting tool 18 of the invention, which 15 is suspended from the hook 10 via a lifting sling 20. During upending as shown sequentially in Figures 1a to 1 d, the centre of gravity 16 of the monopile 12 remains in alignment with the hook 10 and the lifting sling 20 along a common vertical axis 22. The monopile 12 is coupled to the hoisting tool 18 by an upper link 24 that is connected 20 to the top end of the monopile 12 and by a lower link 26 that is connected to the bottom end of the monopile 12. Both the upper link 24 and the lower link 26 are under tension by virtue of bearing the weight load of the monopile 12 between them. As will be explained, the shares of the weight load and hence the tensile forces borne by the upper link 24 and the lower link 26 will vary as the monopile 12 is upended. In this 25 embodiment, the upper link 24 and the lower link 26 are each of variable length. The upper link 24 comprises an upper sling 28 attached to a monopile lifting tool 30 that is mounted to the top end of the monopile 12 on the central longitudinal axis 14. The upper link 24 further comprises an upper wire 32 that extends from the hoisting 30 tool 18 to an upper link spreader bar 34 at the top end of the upper sling 28. The upper wire 32 may, for example, have a nominal static load capacity of about two hundred to three hundred tons. The upper sling 28 and the upper wire 32 are in mutual axial alignment. 35 In this example, the lower link 26 comprises a lower sling 36 attached to a pile hook 38 that engages the tubular wall of the monopile 12 at the bottom end of the monopile 12. 11 06 25 Consequently, there is no need for the monopile 12 to have trunnions protruding from its sides to provide attachment points for the lower sling 36. The lower sling 36 extends from the pile hook 38 to a lower link spreader bar 40 at the top end of the lower sling 36. The lower link 26 further comprises a lower wire 42 that extends from the hoisting 5 tool 18 to the lower link spreader bar 40. The lower sling 36 and the lower wire 42 are in mutual axial alignment. As best appreciated in Figures 2a and 2b, the hoisting tool 18 comprises a reconfigurable triangular frame 44. Two sides of the triangular frame 44 are defined by 10 rigid, fixed-length beams or frame members 46, 48 that are hinged to each other about a horizontal hinge axis 50 at their mutual intersection, in the manner of lever arms. The frame members 46, 48 are also connected to each other by a variable-length mechanism 52 that acts in tension between their free ends to define the third side of the triangular frame 44. 15 More specifically, the frame members 46, 48 are an upper frame member 46 that is relatively upright and a lower frame member 48 that is relatively horizontal. The upper frame member 46 extends between the hinge axis 50 and a horizontal upper pivot axis 54 about which the lower end of the lifting sling 20 is connected to the frame 44. 20 The interface between the lifting sling 20 and the frame 44 defines a frame suspension point by which the hoisting tool 18 is pivotably suspended by virtue of the upper frame member 46 being pivotable with respect to the lifting sling 20 about the upper pivot axis 54. The upper pivot axis 54 is in alignment with the hook 10 along the common vertical 25 axis 22. The upper link 24 is pivotably suspended from the frame 44 at an upper link suspension point supported by the upper frame member 46 whereas the lower link 26 is pivotably suspended from the frame 44 at a lower link suspension point supported by 30 the lower frame member 48. In this example, the upper link suspension point corresponds to where the upper link 24 curves around the hinge axis 50 that is spaced from the upper pivot axis 54 along the upper frame member 46. Conversely, the lower link suspension point corresponds to where the lower link 26 curves around a horizontal lower pivot axis 56 that is spaced from the hinge axis 50 along the lower 35 frame member 48. In this example, the upper and lower links 24, 26 curve around 11 06 25 pulleys centred on the respective axes 50, 56 as will be explained although, in principle, guide formations other than pulleys are also possible. In this example, the variable-length mechanism 52 acting between the upper and lower 5 frame members 46, 48 is driven by a frame adjustment winch 58 that is mounted on the upper frame member 46 between the hinge axis 50 and the upper pivot axis 54. The frame adjustment winch 58 acts on a reeving wire 60 that is wound around an upper reeving pulley 62 on the upper frame member 46 and a lower reeving pulley 64 on the lower frame member 48. This defines a reeving system 66 that comprises, for example, 10 twenty-four falls of the reeving wire 60 extending between the upper and lower reeving pulleys 62, 64 to define the third side of the triangular frame 44. Conveniently, as in this example, the upper reeving pulley 62 turns about the upper pivot axis 54 and the lower reeving pulley 64 turns about the lower pivot axis 56, although other horizontal axes are possible. 15 When the frame adjustment winch 58 retracts or pays in the reeving wire 60, the lower frame member 48 is lifted toward the upper frame member 46 to adopt an acute angle relative to the upper frame member 46 as shown in Figure 2a. When the lower frame member 48 is in the approximately horizontal orientation shown here, a stop formation 20 68 protruding upwardly from the lower frame member 48 bears against the upper frame member 46. This limits further convergence between the frame members 46, 48 and holds them rigidly in fixed relation by virtue of tension in the reeving system 66 that defines the third side of the triangular frame 44. 25 Initially, when the monopile 12 is oriented horizontally for transportation as shown in Figure 1a, the upper link 24 comprising the upper wire 32 lies on an axis that is substantially aligned with the longitudinal axis of the upper frame member 46. Conversely, the lower link 26 comprising the lower sling 36 lies on an axis that is substantially aligned with the longitudinal axis of the reeving system 66. These 30 orientations of the upper wire 32 and the lower sling 36 when the monopile 12 is oriented horizontally are also apparent in Figure 2a. Figures 2a and 2b show that the upper wire 32 of the upper link 24 and the lower wire 42 of the lower link 26 extend around respective pulleys 70 on the frame 44 to a 35 common upending drum 72 that is mounted on the lower frame member 48. The drum 72 turns relative to the frame 44 of the hoisting tool 18 about a horizontal drum axis 74, 11 06 25 driven by a drum control winch 76 in this example. The drum control winch 76 is coupled to the drum 72 by a drum control wire 78 that is wrapped around both the drum control winch 76 and the drum 72. 5 Conveniently, as in this example, the pulley 70 guiding the upper wire 32 to the drum 72 can turn about a horizontal axis that coincides with the hinge axis 50 between the upper and lower frame members 46, 48. Similarly, the pulley 70 guiding the lower wire 42 from the drum 72 can turn about a horizontal axis that coincides with the lower pivot axis 56 at the free end of the lower frame member 48. 10 When the upper wire 32 is retracted by, or paid in to, the drum 72, the upper link 24 shortens as the upper link spreader bar 34 and the upper sling 28 lift the top end of the monopile 12 as shown in Figure 3b. Simultaneously, the lower wire 42 is deployed by, or paid out from, the drum 72, causing the lower link 26 to lengthen as the lower link 15 spreader bar 40 and the lower sling 36 lower the bottom end of the monopile 12. In response, the monopile 12 pivots away from the horizontal about a transverse horizontal axis and as the monopile 12 becomes more upright, its weight load is transferred progressively to the lower link 26. 20 As it shortens, the upper link 24 initially pivots to a shallower inclination as shown in Figure 1b before steepening as the monopile 12 approaches the more upright orientation shown in Figure 1c. Conversely, the lower link 26 steepens as it lengthens throughout the upending process. In response to these reconfigurations of the upper and lower links 24, 26, the hoisting tool 18 can pivot about the upper pivot axis 54 at 25 which the lifting sling 20 is connected to the frame 44. Eventually, as the top end of the monopile 12 is lifted further, pivoting the monopile 12 closer to the vertical as shown in Figure 1c, further retraction of the upper wire 32 lifts the spreader bar 34 up to the level of the hoisting tool 18. Optionally but 30 advantageously, the spreader bar 34 can then be docked to the hoisting tool 18, for example with a coupling 80 extending between the frame 44 and the spreader bar 34 as shown in Figure 2b. In that case, the upper wire 32 no longer needs to support any of the weight of the monopile 12, which is then instead supported directly by the frame 44. This allows the upper wire 32 to have a lesser load capacity than the weight of the 35 monopile 12, as exemplified previously. 11 06 25 The frame 44 of the hoisting tool 18 can then, or previously, be reconfigured or unfolded to complete upending as shown in Figures 1d and 2b. Specifically, the frame adjustment winch 58 deploys or pays out the reeving wire 60 to allow the lower frame member 48 to pivot down away from the upper frame member 46 about the hinge axis 5 50. The lower frame member 48 thereby adopts an obtuse angle relative to the upper frame member 46 as shown in Figure 2b, hence lowering the top of the lower link 26 where the lower wire 42 is supported by the pulley 70 at the free end of the lower frame member 48. 10 Simultaneously, the upper frame member 46 pivots about the upper pivot axis 54 into a more upright orientation. This causes the hinge axis 50 at the bottom of the upper frame member 46, and hence the top of the upper sling 28, to swing toward the vertical axis 22 that extends between the hook 10 and the centre of gravity 16 of the monopile 12. 15 As a result of these movements of the upper and lower frame members 46, 48, the weight load is transferred progressively back from the lower link 26 to the upper sling 28 during reconfiguration of the frame 44. Eventually, as shown in Figures 1d and 2b, the upper frame member 46 adopts a substantially vertical orientation in which the 20 upper pivot axis 54, the hinge axis 50, the upper sling 28 and the monopile lifting tool 30 all lie on or close to the vertical axis 22. The upper sling 28 that is connected to the frame 44 via the spreader bar 34 and the coupling 80 can then bear the full weight of the monopile 12. This allows the lower link 25 26 to be disengaged from the monopile 12 as shown in Figure 1 d, facilitated by the aforementioned downward movement of the lower frame member 48 that lowers the lower sling 36 defining the bottom part of the lower link 26. The lower sling 36 can be disengaged from the pile hook 38 at the bottom end of the monopile 12, or the pile hook 38 can be disengaged from the monopile 12. 30 It will be apparent from the above description and from Figures 2a and 2b that the same drum 72 both pays in the upper wire 32 and pays out the lower wire 42 during upending of the monopile 12, as rotation of the drum 72 is driven by the drum control winch 80. For this purpose, the upper and lower wires 32, 42 are wound onto the drum 35 72 in mutually-opposed circumferential directions. Thus, the drum 72 serves both as a 11 06 25 pay-out system for the lower wire 42 and as a pull-in system for the upper wire 32, which are both wound around the common drum axis 74. The drum 72 is shown in end view in Figures 2a and 2b, from which it can be seen that 5 the horizontal drum axis 74 about which the drum 72 turns is substantially parallel to the hinge axis 50 and to the upper and lower pivot axes of the frame of the hoisting tool 18. The drum 72 is also shown in side view in Figures 3a, 3b and 3c, which show the drum 10 72 supported by bearings 82 mounted on a horizontal axle or spindle 84. It will also be apparent from Figures 3a, 3b and 3c that, in this example, the upper and lower wires 32, 42 each comprise two parallel limbs that are wound onto respective frusto-conical portions 72A, 72B of the drum 72. 15 The frusto-conical drum portions 72A, 72B are spaced longitudinally along the drum axis 74 and are paired in mirrored relation about a central vertical plane 86 that bisects the drum 72 and that extends orthogonally with respect to the drum axis 74. The limbs of the lower wire 42 are wound around an outer pair of the drum portions 72A and the limbs of the upper wire 32 are wound around an inner pair of the drum portions 72B. 20 The central vertical plane 86 may coincide with the common vertical axis 22 of the hook 10 and the lifting sling 20. Figures 3a, 3b and 3c show that the drum 72 further comprises a central portion 88 of uniform cross-section that lies between the inner pair of drum portions 72B and that is 25 bisected by the central vertical plane 86. The drum control wire 78 extending from the drum control winch 80 is wrapped around the central portion 88 to act on the drum 72 in the manner of a drive belt. Figures 3a, 3b and 3c also show that the drum portions 72A, 72B taper away from the 30 central vertical plane 86 in mutually-opposed directions along the drum axis 74. The average diameter of the outer pair of drum portions 72A, supporting the limbs of the lower wire 42, is less than the average diameter of the inner pair of drum portions 72B that support the limbs of the upper wire 32. Specifically, in this example, the inner pair of drum portions 72B tapers down from a maximum corresponding to the diameter of 35 the central portion 88 to a minimum that corresponds to the maximum diameter of the 11 06 25 outer pair of drum portions 72A. The outer pair of drum portions 72A then tapers down further to a minimum diameter at the opposed outward ends of the drum 72. The various portions 72A, 72B, 104 of the drum 72 are bounded at their ends by 5 circumferential flanges 90 that lie in parallel planes orthogonal to the drum axis 74. The flanges 90 serve as partitions between adjacent drum portions 72A, 72B that guide and confine the limbs of the upper and lower wires 32, 42 to their appropriate drum portions 72A, 72B. 10 Figure 3a shows the drum 72 in a starting state corresponding to Figure 1a of the drawings. Comparison of the number of coils shows that a greater length of the lower wire 42 is spooled on the outer drum portions 72A than the length of the upper wire 32 spooled on the inner drum portions 72B. 15 Figure 3b shows the drum 72 in an intermediate state corresponding to Figure 1b of the drawings. Comparison of the number of coils shows that similar lengths of the lower wire 42 and the upper wire 32 are now spooled, respectively, on the outer drum portions 72A and on the inner drum portions 72B. 20 Figure 3c shows the drum 72 in a finishing state corresponding to Figures 1c or 1d of the drawings. Comparison of the number of coils shows that a lesser length of the lower wire 42 is now spooled on the outer drum portions 72A than the length of the upper wire 32 spooled on the inner drum portions 72B. 25 During upending, the coils of the lower wire 42 are paid out in the direction of taper of the outer drum portions 72A. Thus, the coils of the lower wire 42 remaining on the outer drum portions 72A reduce in diameter successively as the limbs of the lower wire 42 are unwound or paid out from the outer drum portions 72A. In other words, the lower wire 42 is unspooled from the drum 72 down the taper of the outer drum portions 72A. 30 Conversely, the coils of the upper wire 32 are wound in against the direction of taper of the inner drum portions 72B. Thus, the coils of the upper wire 32 wound onto the inner drum portions 72B increase in diameter successively as the limbs of the upper wire 32 are paid in to the innerdrum portions 72B. In other words, the upper wire 32 is spooled 35 onto the drum 72 up the taper of the inner drum portions 72B. 11 06 25 The relative diameters and taper angles of the drum portions 72A, 72B define a gear ratio that varies progressively during upending, effecting a corresponding continuous variation in mechanical advantage between the drum 72 and the upper and lower wires 32, 42. Advantageously, the relative diameters and taper angles of the drum portions 5 72A, 72B can be configured to minimise the aggregate moment applied to the drum 72 during upending. This allows the capacity, and hence the size, weight and cost, of the drum control winch 76 and the drum control wire 78 to be reduced. In this respect, the upper graphs of Figures 3a, 3b and 3c plot sling forces Fil and FL, 10 being tensile forces in the upper and lower links 24, 26 respectively, against angle_MP being the angle of the monopile 12 relative to the horizontal. On the left of those graphs, where the monopile 12 is oriented horizontally as shown in Figure 1a and as represented by the vertical dashed line in Figure 3a atangle_MP = zero, Fil and FL are substantially equal and are in balance. As upending of the monopile 12 proceeds as 15 shown in Figures 1b and 1c and as represented by the vertical dashed lines in Figures 3b and 3c, its weight load initially transfers from the upper link 24 to the lower link 26. FU and FL therefore diverge as FU increases and FL decreases, before eventually beginning to converge as the monopile 12 approaches the more upright orientation as shown in Figures 1c and 3c, where its weight load begins to transfer back to the upper 20 link 24 from the lower link 26. As can be seen in the lower graphs of Figures 3a, 3b and 3c, the opposed moments MU and ML applied to the drum 72 by the upper and lower links 24, 26 respectively remain close to each other throughout and therefore largely cancel each other out. 25 Indeed, it will be apparent that the aggregate moment Mtot applied to the drum 72 never exceeds 200 tons in this example. Thus, by offsetting or counterbalancing torque applied to the inner drum portions 72B by tension in the upper link 24 against torque applied to the outer drum portions 72A by tension in the lower link 26, the aggregate torque required to control rotation of the drum 72 is greatly reduced. 30 In view of the relative diameters of the drum portions 72A, 72B, it will be apparent that the upper wire 32 will be pulled in at a greater linear speed than the lower wire 42 is paid out. This applies even though the drum portions 72A, 72B all turn at the same angular velocity because they are portions of the same drum 72. 11 06 25 It will also be apparent that during upending of the monopile 12, the tapers of the drum portions 72A, 72B have the effect of pulling in the upper wire 32 with increasing linear speed and conversely of paying out the lower wire 42 with decreasing linear speed. Yet, by virtue of the effect of the tapers on the gear ratio, these changes of linear speed 5 occur without changing the angular velocity of the drum 72. Many other variations are possible within the inventive concept. For example, at least one of the frame members could be of variable length. 10 The variable-length mechanism of the hoisting tool could comprise an actuator system other than a reeving system, such as a mechanism incorporating hydraulic actuators. Similarly, the drum could be turned by a system other than a winch, such as a hydraulic drive. 15 The various winches, or equivalent drives, and the drum shown in the exemplary embodiments could be repositioned on the frame. For example, the pull-in winch could be on the upper frame member, the frame adjustment winch could be on the lower frame member, or the pull-in winch and the frame adjustment winch could both be on the same frame member. 20 The drum portions could taper inwardly toward the longitudinal centre of the drum, and need not taper in the same directions. The drum portions could taper non-uniformly along their length. 25 The drum portions need not necessarily be coupled together rigidly on a common drum. For example, the drum portions could be coupled by a coupling system such as a geartrain for transmitting and offsetting or counterbalancing torque. Such a geartrain could allow the drum portions to contra-rotate, not necessarily about a common axis. 30 Torque applied to the respective drum portions by the upper and lower wires could be counterbalanced other than by contra-winding the wires around a common drum. For example, the drum portions could be coupled by a reversing geartrain or other intermediate drive system. 11 06 25

Claims

1. A hoisting tool for upending an elongate load, the tool comprising:5 a frame suspension point for suspending a frame of the tool from a crane;a pull-in system acting on a variable-length upper link for connecting the tool to an upper side of a centre of gravity of the load; and10 a pay-out system acting on a variable-length lower link for connecting the tool toa lower side of the centre of gravity of the load;wherein the pull-in system and the pay-out system comprise respective drum portions on which the upper link and the lower link are wound, the drum15 portions being arranged to rotate relative to the frame to pull in the upper linkand to pay out the lower link simultaneously and being coupled together to offset torque applied to one of the drum portions by tension in the upper link against torque applied to another of the drum portions by tension in the lower link.

202. The tool of Claim 1, wherein the upper link and the lower link are wound about the respective drum portions in mutually-opposed circumferential directions.

3. The tool of Claim 1 or Claim 2, wherein the drum portions are coupled to rotate25 together about a common axis.

4. The tool of Claim 3, wherein the drum portions are portions of a common drum, those drum portions being distributed along the common axis.30 5. The tool of any preceding claim, wherein the upper link and / or the lower linkcomprise two or more limbs that are each wound on a respective one of the drum portions.

6. The tool of Claim 5, wherein the limbs are wound on respective drum portions that35 are in mirrored relation about a central plane.11 06 257. The tool of any preceding claim, wherein at least one of the drum portions tapers along its axis of rotation.

8. The tool of Claim 7, wherein the at least one tapered drum portions is substantially 5 frusto-conical.

9. The tool of Claim 7 or Claim 8, wherein the at least one tapered drum portion supports successive coils of the upper link or the lower link, those coils decreasing in diameter in a direction of taper or increasing in diameter against the direction of taper.1010. The tool of Claim 9, arranged such that while successive coils of the upper link of increasing diameter are being wound onto one of said drum portions, successive coils of the lower link of decreasing diameter are paid out simultaneously from another of said drum portions.1511. The tool of any of Claims 7 to 10, wherein two or more of the tapered drum portions share a common direction of taper.

12. The tool of any preceding claim, wherein the or each drum portion on which the20 upper link is wound has a greater average diameter than the or each drum portion on which the lower link is wound.

13. The tool of any preceding claim, further comprising a winch that is arranged to drive rotation of the drum portions.2514. The tool of Claim 13, wherein a drive belt driven by the winch is disposed between the drum portions.

15. The tool of any preceding claim, being arranged to pivot about the frame 30 suspension point.

16. The tool of any preceding claim, wherein the frame comprises an upper frame member and a lower frame member that is movable relative to the upper frame member, the upper frame member extending from the frame suspension point to an 35 upper link suspension point and the lower frame member supporting a lower link11 06 25suspension point that is movable with the lower frame member relative to the upper frame member.

17. The tool of Claim 16, wherein the drum portions are mounted on the lower frame5 member.

18. The tool of Claim 16 or Claim 17, further comprising a variable-length mechanism that connects the upper and lower frame members and is operable to effect said movement of the lower frame member.1019. The tool of Claim 18, wherein the variable-length mechanism comprises a frame adjustment winch mounted on the frame and acting on a wire of a reeving system that extends between the upper and lower frame members.15 20. The tool of Claim 19, wherein the frame adjustment winch is mounted on the upperframe member.

21. The tool of any of Claims 16 to 20, wherein the upper frame member is relatively upright and the lower frame member is relatively horizontal.2022. The tool of any of Claims 16 to 21, wherein a longitudinal axis of the lower member is movable from an acute angle to an obtuse angle relative to a longitudinal axis of the upper member.25 23. The tool of Claim 22, wherein the longitudinal axis of the upper member is pivotableabout the frame suspension point to adopt a substantially vertical orientation.

24. A method of upending an elongate load, the method comprising:30 suspending a hoisting tool;suspending the load from the tool via upper and lower links, the upper link extending from the tool to an upper side of a centre of gravity of the load and the lower link extending from the tool to a lower side of the centre of gravity of 35 the load;11 06 25rotating at least one pull-in drum portion of the tool to pull in the upper link, hence shortening the upper link to lift an upper end of the load toward the tool;simultaneously rotating at least one pay-out drum portion of the tool to pay out5 the lower link, hence lengthening the lower link to lower a lower end of the loadaway from the tool; andoffsetting torque applied to the or each pull-in drum portion by tension in the upper link against torque applied to the or each pay-out drum portion by tension 10 in the lower link to reduce aggregate torque required to control rotation of thedrum portions.

25. The method of Claim 24, comprising pulling in the upper link at a greater linear speed than paying out the lower link.1526. The method of Claim 25, comprising turning the or each pull-in drum portion at the same angular velocity as the or each pay-out drum portion.

27. The method of any of Claims 24 to 26, comprising pulling in the upper link with20 increasing linear speed during upending of the load.

28. The method of any of Claims 24 to 27, comprising paying out the lower link with decreasing linear speed during upending of the load.25 29. The method of Claim 27 or Claim 28, comprising changing the linear speed of theupper link and / or the lower link without changing angular velocity of an associated pull-in or pay-out drum portion.

30. The method of any of Claims 27 to 29, comprising changing a gear ratio applied by 30 a pull-in or pay-out drum portion to the upper link and / or the lower link during upending of the load.

31. The method of Claim 30, comprising changing the gear ratio by progressive spooling of the upper link or unspooling of the lower link along a tapered pull-in or pay-35 out drum portion.11 06 2532. The method of any of Claims 24 to 31, comprising unwinding the lower link and winding in the upper link about a common axis.

33. The method of any of Claims 24 to 32, comprising rotating the or each pull-in drum5 portion and the or each pay-out drum portion in a common circumferential direction while the lower link and the upper link are wound about their associated portions in mutually-opposed circumferential directions.

34. The method of any of Claims 24 to 33, comprising:10suspending the tool via a frame suspension point at which an upper frame member of the tool can pivot about a horizontal upper pivot axis;reconfiguring the tool by moving the lower frame member relative to the upper15 frame member to lower a suspension point of the lower link; andpivoting the upper frame member about the upper pivot axis to move a suspension point of the upper link toward an upright axis that extends from the upper pivot axis to the centre of gravity of the load.2035. The method of Claim 34, comprising reconfiguring the tool by moving an axis of the lower frame member from an acute angle to an obtuse angle relative to an axis of the upper frame member.25 36. The method of Claim 34 or Claim 35, comprising reconfiguring the tool bylengthening a variable-length mechanism that connects the upper and lower frame members.

37. The method of any of Claims 34 to 36, comprising lifting a spreader of the upper30 link and docking the spreader to the tool with an auxiliary coupling.

38. The method of Claim 37, comprising subsequently supporting a full weight of the load through the coupling and releasing the lower link from the load.

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