Patent Description:
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 by lifting one end using a floating crane. Once vertical, the monopile is driven 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.

A pivot axis for upending a monopile may be defined on a crane vessel as shown in <CIT>, 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 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 <NUM> metric tons.

It is also possible to launch an elongate structure from a vessel, as shown for suction piles in <CIT>, 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 monopile positively buoyant. Upending is done 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 <CIT>. However, controlling flooding of a structure with ballasting water can be complex and risks uncontrolled sinking. Also, for a monopile, it adds considerable time and expense to manufacture, install and remove the plugs.

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 same crane.

In <CIT>, 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 <CIT> unsuitable for use with a floating crane vessel, as the pile would clash with the hull of the vessel.

<CIT> 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 pile while simultaneously lowering the bottom end of the pile. Similarly in <CIT>, 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 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.

<CIT> describes a tool for lifting and rotating a shipping container. The tool 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. Upending devices in general are known in the art, for example in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, which shows the preamble of claim <NUM>, and <CIT>. <CIT> relates to an apparatus for lifting and mounting a wind turbine blade on a wind turbine.

Against this background, the invention resides in a combination of an elongate structure and a lifting arrangement for upending the structure. The arrangement comprises: rigging of elongate elements that are connected to the structure at respective connection axes spaced longitudinally along the structure, at least one of those elements extending to a first connection axis and at least one other of those elements extending to a second connection axis and being of variable length; and a frame suspended from a crane, the frame supporting at least one winch that acts on the at least one variable-length element of the rigging.

The frame is suspended via a hoisting system of the crane, for example via a hook of the crane.

Conveniently, the first connection axis may define a pivot axis about which the structure is upended. The at least one element extending to the first connection axis is preferably of substantially fixed length.

In examples to be described, the structure has a pair of connection points on the first connection axis on mutually-opposed sides of the structure, to which respective rigging elements extend. For example, the connection points may be trunnions that protrude from the structure in opposite directions on the first connection axis.

The at least one element extending to the first connection axis may be attached at an opposite end to the frame or directly to the crane.

The centre of gravity of the structure lies in a vertical plane that is disposed between the first and second connection axes. The longitudinal distance along the structure between the second connection axis and that plane is preferably substantially greater than a longitudinal distance along the structure between the first connection axis and that plane. For example, the longitudinal distance between the second connection axis and that plane may be at least five times greater than the longitudinal distance between the first connection axis and that plane.

The or each variable-length element of the rigging extends from a suspension point of the frame that is offset laterally from the vertical plane containing the centre of gravity of the structure. For example, the suspension point may be offset laterally from that plane by a distance of at least half of a diameter of the structure extending through the second connection axis. That plane, nevertheless, intersects the winch. The or each variable-length element of the rigging extends laterally from the winch and over a sheave that defines the laterally-offset suspension point of the frame.

The inventive concept also embraces a corresponding method of upending an elongate structure to an upright orientation. The method comprises: suspending the structure from a crane, for example over water, via elongate rigging elements that are attached to the structure respectively at first and second connection axes spaced longitudinally along the structure, at least one of the rigging elements extending from a winch over a sheave that defines a suspension point offset laterally relative to a vertical plane containing the centre of gravity of the structure; and by paying out at least one of the rigging elements from the winch that is also suspended from the crane and that is intersected by said vertical plane, lowering the second connection axis relative to the first connection axis, hence pivoting the structure around the first connection axis to the upright orientation.

The first connection axis may be held at a substantially fixed height relative to the crane, conveniently by maintaining a rigging element attached to the first connection axis at a substantially fixed length.

Where the winch is suspended from a hook of the crane, the centre of gravity of the structure is preferably kept on a vertical axis that intersects the hook.

A majority of the weight of the structure is preferably borne through the first connection axis, such that less than <NUM>% of the weight of the structure may be borne through the second connection axis.

While upending the structure, the weight of the structure may be transferred from one or more rigging elements attached at the second connection axis to one or more rigging elements attached at the first connection axis. Then, after completing the transfer of weight, the or each rigging element may be detached from the structure at the second connection axis while suspending the weight of the structure from the or each rigging element attached at the first connection axis.

A rigging element extends to the second connection axis from a suspension point that is offset laterally relative to a plane containing the centre of gravity of the structure. Such a suspension point may remain in fixed relation to the winch while upending the structure. Similarly, the second connection axis may be offset radially relative to a longitudinal axis of the structure. In that case, the lateral offset of the suspension point is preferably greater than or equal to the radial offset of the second connection axis. When the structure is upright, one or more rigging elements preferably extend to the first connection axis substantially in alignment with the centre of gravity of the structure.

Thus, the invention provides an integrated modular spreader bar/winch unit that is defined by and within a truss frame suspended from a crane hook. The purposes of this frame are twofold: firstly to act as a spreader bar to enable upending of a monopile over monopile trunnion lift points that lie beneath the frame and the crane hook; and secondly to act as a modular additional hoist comprising a winch/sheave/hook configuration connected to monopile bottom rigging, for example using a pile hook arrangement.

In this respect, the invention may be implemented in an installation method comprising the following steps:.

The monopile may then be transferred by the crane into a conventional outrigger/gripper attached to the hull of the vessel, whereupon the rigging can be released from the trunnions and the monopile can be driven into the seabed to a final penetration depth.

The invention allows for upending of elongate structures such as monopiles while realising cost reduction through faster offshore operations and improved workability. The invention is suitable for use with XXL monopiles that could weigh as much as <NUM> metric tons as noted above.

Specifically, the system of the invention allows lift-off of a monopile or other elongate structure from a deck or barge and upending in a single lift operation. The monopile can be upended perpendicularly to the boom of the vessel crane. Hence, there is no need first to rotate the monopile in line with the crane boom before upending. Upending is easily and reliably controlled by lowering the bottom rigging with a winch while the centre of gravity of the monopile remains directly under the crane hook during both lift-off and upending.

The capacity or power of the winch can be limited as its duty is mainly to lower rather than to raise the load. Another factor that limits the required winch capacity is the location of the trunnions close to the centre of gravity of the monopile. Thus, at least <NUM>% of the weight of the monopile is supported through the trunnions during lift-off and upending, whereas only the remaining weight load of less than <NUM>% of the total is carried through the winch, bottom rigging and pile hook.

The spreader truss frame with the integrated winch is a module that can be suspended from any crane with sufficient capacity, thus providing a modular system that can be transferred between and used on multiple vessels.

Compared to the alternative of floating a monopile before upending it in water, no expensive plugs are required to close the ends of the monopile.

Embodiments of the invention provide a device for upending an elongate, horizontal item, the device comprising: a structure such as a spreader frame to be suspended from the hook of a crane; a rigging arrangement between the structure and a pivot axis of the elongate item; and at least one winch mounted on the structure, the cable of the winch being connected to a point of the elongate item distant from the pivot axis. The cable of the winch may, for example, be connected at the end of the elongate item that will be the bottom end after upending.

The rigging arrangement may comprise at least one sling connected to each side of the elongate item. Conveniently, the rigging arrangement may have constant length.

The winch may be cantilevered so that the cable exits the winch at a distance from the rigging connection substantially equivalent to the radius of the elongate element.

Embodiments of the invention also implement a method for upending an elongate item, the method comprising: suspending a spreader structure from a crane, the spreader structure comprising a winch; arranging rigging between the spreader structure and a pivot axis of the elongate element; connecting the winch cable to an end of the elongate item that will be the lower end after upending; adjusting the paid-out length of the winch cable so that it is tensioned when the elongate element is horizontal; horizontally lifting the elongate element to a pre-determined height; and paying out the winch cable until the elongate element is vertical.

In summary, therefore, the invention adapts a crane to upend an elongate structure such as a monopile. The crane supports, directly or indirectly, elongate rigging elements that are connected to the structure at respective connection axes spaced longitudinally along the structure. At least one of those elements, which may be of fixed length, extends to a first connection axis and at least one other of those elements, which is of variable length, extends to a second connection axis. The centre of gravity of the structure lies on a vertical plane disposed between the connection axes, that plane preferably being much closer to the first connection axis than to the second connection axis.

A frame suspended from the crane supports a winch that pays out the variable-length element of the rigging to lengthen that element. This lowers the second connection axis relative to the first connection axis, the latter therefore serving as a pivot axis about which the structure is upended. Gradually the pivot axis approaches the vertical plane that contains the centre of gravity and eventually lies in that plane, directly over the centre of gravity, when the structure is fully upright.

<FIG>, <FIG> and <FIG> show an installation vessel <NUM> floating on the surface <NUM> of the sea at an installation site. The vessel <NUM> has a main deck <NUM> surmounted by a crane <NUM> whose jib or boom <NUM> can slew around a vertical slew axis <NUM>. The slew axis <NUM> and the centreline of the boom <NUM> both lie on a common vertical plane.

As is conventional, the hoisting system of the crane <NUM> comprises a main hook <NUM> that is suspended from an array of sheaves <NUM> on the boom <NUM>. The main hook <NUM> also lies on the common vertical plane that contains the slew axis <NUM> and the centreline of the boom <NUM>.

In accordance with the invention, a horizontally-extending spreader frame <NUM> is suspended from the crane <NUM>, in particular from the main hook <NUM> via downwardly-diverging spreader rigging <NUM> in this example. The spreader frame <NUM> is shown in detail in <FIG>.

Via the spreader frame <NUM>, the crane <NUM> supports an elongate load that is exemplified here by a monopile <NUM>. In this example, the monopile <NUM> is a hollow tubular structure that is rotationally symmetrical about a central longitudinal axis <NUM>.

The monopile <NUM> shown in the drawings comprises a relatively narrow top portion 28A and a relatively wide base portion 28B joined by a frusto-conical intermediate portion 28C. Thus, the centre of gravity <NUM> of the monopile <NUM> is offset longitudinally along the central longitudinal axis <NUM> toward the base end of the monopile <NUM>; indeed, in this example, the centre of gravity <NUM> lies within the enlarged base portion 28B of the monopile <NUM>.

The centre of gravity <NUM> of the monopile <NUM> lies directly beneath the main hook <NUM> of the crane <NUM>, hence lying on the common vertical plane that contains the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>.

The monopile <NUM> is suspended by load rigging that extends from the spreader frame <NUM> to longitudinally-spaced, horizontally-extending connection axes on the monopile <NUM>. The load rigging comprises three rigging elements, one element <NUM> being of variable length and the other two elements <NUM> being of fixed length in this example. One of fixed-length elements <NUM> is hidden behind the other fixed-length element <NUM> in the side views of the drawings.

To define one of the connection axes, the variable-length element <NUM> of the load rigging is fixed by a hook at its lower end to a radially-protruding lifting shoe <NUM> at one end of the monopile <NUM>, which is the lower or bottom end when the monopile <NUM> is upended as shown in <FIG>. The lifting shoe <NUM> is on an upper side of the monopile <NUM> when the monopile <NUM> is in a horizontal orientation. Thus, the lifting shoe <NUM> lies on a vertical plane that contains the central longitudinal axis <NUM> of the monopile <NUM>.

The two fixed-length elements <NUM> of the load rigging comprise slings that are fixed at their lower ends to respective trunnions <NUM> of the monopile <NUM>. The trunnions <NUM> are diametrically opposed to each other about the monopile <NUM> on the other horizontal connection axis, which intersects the central longitudinal axis <NUM> of the monopile <NUM>. Thus, the connection axis that joins the trunnions <NUM> is orthogonal to the vertical plane that contains both the central longitudinal axis <NUM> and the lifting shoe <NUM> of the monopile <NUM>.

The variable-length element <NUM> of the load rigging emerges from the spreader frame <NUM> at a suspension point <NUM> that is offset laterally from the vertical plane containing the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>. The lateral offset of the suspension point <NUM> from that vertical plane corresponds approximately to the radial offset of the lifting shoe <NUM> relative to the central longitudinal axis <NUM> of the monopile <NUM>. Thus, that lateral offset is slightly greater than the outer radius of the base portion 28B of the monopile <NUM>.

As <FIG> shows, the spreader frame <NUM> comprises a truss structure <NUM> defining a winch platform that supports a winch <NUM>. The variable-length element <NUM> of the load rigging comprises a wire <NUM> extending from the winch <NUM> and a sling <NUM> that is joined end-to-end to the wire <NUM> by a sling coupling <NUM>. The sling <NUM> extends from the sling coupling <NUM> to the lifting shoe <NUM> at the bottom end of the monopile <NUM>.

In this example, the laterally-offset suspension point <NUM> of the spreader frame <NUM> is defined by a sheave <NUM> that is offset laterally from the centrally-located winch <NUM>. The wire <NUM> extending between the winch <NUM> and the sling coupling <NUM> passes over the sheave <NUM>. However, in principle, it would be possible instead to offset the winch <NUM> laterally and to dispense with the sheave <NUM>.

The spreader rigging <NUM> is fixed to the truss structure <NUM>, arranged symmetrically with respect to the vertical plane <NUM> that bisects the spreader frame <NUM> and that also contains the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>. The fixed-length elements <NUM> of the load rigging are also fixed centrally to the truss structure <NUM>.

The monopile <NUM> is shown in <FIG> in a horizontal orientation, suspended over the side of the vessel <NUM> above the surface <NUM>, having been lifted in that orientation from a barge (not shown) on which the monopile <NUM> was transported to the installation site. The clearance between the monopile <NUM> and the surface <NUM> ensures that the monopile <NUM> is not directly subject to wave action at this initial stage.

As the centre of gravity <NUM> lies between the trunnions <NUM> and the lifting shoe <NUM> at the bottom end of the monopile <NUM>, the weight of the monopile <NUM> is shared between the elements <NUM>, <NUM> of the load rigging, which are therefore all in tension. However, as the centre of gravity <NUM> is much closer to the trunnions <NUM> than to the lifting shoe <NUM>, the vast majority (about <NUM>%) of the weight of the monopile <NUM> is borne by the fixed-length elements <NUM> of the load rigging and the remainder (hence only about <NUM>%) is borne by the variable-length element <NUM> of the load rigging. The winch <NUM> of the spreader frame <NUM> that acts against the tension in the variable-length element <NUM> therefore needs only to have a correspondingly small capacity.

<FIG> shows the upending operation in progress. It will be apparent that by paying out the wire <NUM> from the winch <NUM> and hence lengthening the variable-length element <NUM> of the load rigging, the bottom end of the monopile <NUM> is lowered relative to the trunnions <NUM>. Thus, the monopile <NUM> tilts toward being upright.

The trunnions <NUM> remain at a substantially unchanged height above the surface <NUM> by virtue of the fixed-length elements <NUM> of the load rigging and so define a nearly-fixed pivot axis as the monopile <NUM> tilts away from the horizontal. The trunnions <NUM>, suspended on the fixed-length elements <NUM>, merely swing slightly toward the vertical plane that contains the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>. This minor movement of the trunnions <NUM> allows the centre of gravity <NUM> of the tilting monopile <NUM> to remain on that vertical plane.

<FIG> shows the upending operation now completed after paying out more of the wire <NUM> from the winch <NUM>, further to lengthen the variable-length element <NUM> of the load rigging and hence further to pivot the monopile <NUM> about the trunnions <NUM>. The monopile <NUM> is now upright, with its central longitudinal axis <NUM> substantially vertical and in the vertical plane that contains the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>. The trunnions <NUM> and the fixed-length elements <NUM> of the load rigging also now lie on that vertical plane, directly above and aligned with the centre of gravity <NUM> of the monopile <NUM>.

When the monopile <NUM> is vertical as shown in <FIG>, the variable-length element <NUM> of the load rigging is also close to vertical but is offset laterally from the vertical plane that contains the main hook <NUM>, the slew axis <NUM> and the centreline of the boom <NUM>. The lateral offset of the variable-length element <NUM> is determined by the lateral offset of the suspension point <NUM> defined by the sheave <NUM> of the spreader frame <NUM>, and also by the radial offset of the lifting shoe <NUM> relative to the central longitudinal axis <NUM> of the monopile <NUM>. In practice, the variable-length element <NUM> need not be perfectly vertical at this stage and may, conveniently, converge downwardly toward the plane of the fixed-length elements <NUM> as shown in <FIG>.

As the monopile <NUM> reaches verticality, all of its weight is supported by the fixed-length elements <NUM> of the load rigging via the trunnions <NUM>. Thus, the minor portion of the weight load supported by the variable-length element <NUM> is transferred progressively to the fixed-length elements <NUM>. When the variable-length element <NUM> is no longer under tension, it can be detached from the lifting shoe <NUM>. This allows the crane <NUM> to transfer the upright monopile <NUM> into a conventional outrigger/gripper of the vessel <NUM> to be driven into the seabed as noted previously.

<FIG> shows that the spreader frame <NUM> can tilt relative to the boom <NUM> of the crane <NUM> as may be required to balance the system.

In the orientations shown in <FIG> and <FIG>, the bottom end of the monopile <NUM> is submerged beneath the surface <NUM>. However, partial submergence of the monopile <NUM> in this manner is not essential: in principle, with a shorter monopile <NUM> and/or a higher crane hook <NUM> or shorter rigging, uprighting could be performed entirely in air.

Other variations are possible within the inventive concept. For example, the fixed-length elements of the load rigging could be attached directly to the main hook of the crane and not via the spreader frame.

The load rigging could comprise more than one variable-length element or any number of fixed-length elements.

It is not essential that a variable-length rigging element is attached to an end of the structure being upended. The variable-length rigging element could instead be attached to the structure at a connection point inboard from its end.

The structure could be lowered into or onto the water in a horizontal orientation and then upended by paying out a variable-length rigging element. In that case, a lower end of the structure may be flooded with ballasting water either through an open end or a bottom plug.

Claim 1:
A combination of an elongate structure (<NUM>) and a lifting arrangement for upending the structure (<NUM>), the arrangement comprising:
rigging of elongate elements that are connected to the structure (<NUM>) at respective connection axes spaced longitudinally along the structure (<NUM>), at least one of those elements (<NUM>) extending to a first connection axis and at least one other of those elements (<NUM>) extending to a second connection axis and being of variable length, wherein the structure (<NUM>) has a centre of gravity (<NUM>) that lies in a vertical plane disposed between the first and second connection axes; and
a frame (<NUM>) suspended from a crane (<NUM>), via a hoisting system of the crane (<NUM>), the frame (<NUM>) supporting at least one winch (<NUM>) that acts on the at least one variable-length element (<NUM>) of the rigging;
wherein the at least one variable-length element (<NUM>) of the rigging extends laterally from the winch (<NUM>) and over a sheave (<NUM>) that defines a suspension point of the frame (<NUM>) that is offset laterally from said vertical plane, and the combination being characterised in that said vertical plane intersects the winch (<NUM>).