GB2519997A - Multi-cable subsea lifting system - Google Patents

Abstract

A subsea anti-cabling device 20 for a multi-cable subsea lifting system comprises two or more sets of two or more spaced apart and slidable cable connections 22a, 22b, 24a and 24b for neighbouring load cables 4a, 4b and a rigid framework 26 between each set of cable connections 22a, 22b, 24a and 24b. The multi-cable subsea lifting system may comprise two or more load-cable lifting apparatus 2a, 2b, a load cable 4a, 4b extending from each load-lifting apparatus 2a, 2b to a subsea co-terminal loading point which may be a triplate 14, one or more subsea anti-cabling devices 20, an anti-cabling device lifting apparatus 30 and an anti-cabling line 28 extending from the anti-cabling device lifting apparatus 30 to one anti-cabling device 20. A load cell 18 may monitor the tension and/or torsion of the load cable 4a, 4b. The cable connections 22a, 22b, 24a and 24b may be open sleeves and attachment clips and the connections of each set may be separate 22a, 22b and 24a, 24b or a continuous body 52a, 52b. The rigid framework 26 may include bracing members 42, 58 and cross-struts 40a, 40b, 56a, 56b. The lifting system may be carried on a ship such as a pipe laying service vessel or PLSV 6. The anti-cabling device 20 is able to maintain a defined distance or space between the cables 4a, 4b due to its rigid framework 26 and thereby prevent twisting or entanglement of the load cables 4a, 4b. The anti-cabling device 20 is also slidable with respect to the load cables 4a, 4b, allowing it to be best positioned or deployed where the concern of cabling is more expected.

Description

Multi-cable subsea lifting system The present invention relates to a multi-cable subsea lifting system for raising and lowering loads in water, particularly deep water, as well as a subsea anti-cabling device and a method of raising or lowering a subsea load using the lifting system.

The use multi-cables to lift loads, either due to the increasing weight of the load, or increasing operating depth, or both, is known. Loads of hundreds of tonnes are no longer exceptional, typically often now over 400 tonnes.

Sometimes, multi-cable lifting systems are formed using a single looped cable as shown in EP0312336A. Sometimes, the equipment involves a number of separate cables, ropes, wires, etc., as shown for example in W003/062042A1, US5951227 and W02010/046649A1. Generally, the cables are provided from a reel, and optionally run through one or more drive mechanisms or winches to control their movement and loading.

"Cabling" is a phenomenon whereby imbalanced torsional characteristics of two cables, being used in 2-fall or parallel operation to lower or raise a load, can result in the cables axially rotating, causing the effective cable separation to decrease, and possibly resulting in rotational entanglement of the two cables employed. This can occur both in single cable hoist systems used in 2-fall configuration, as well as in parallel winch operations using cables of opposite hand lay.

Naturally, cabling is undesirable. It can even lead to situations where the integrity of the hoist cables is compromised, with damage resulting, or even overloading of a single wire. The required recovery of the cables can then be difficult, involving extensive OPEX including delay.

Meanwhile, there is an ever increasing drive to work at greater water depths, certainly beyond 1000 metres, and now commonly in excess of 2000 metres or even 3000 metres. The greater the required depth, the greater the extension of cables from their lifting platform or base, and the greater potential for cabling. Cabling at greater depths requires even greater OPEX.

W02012/060715A1 shows a lifting tool for opposing twisting of generally submerged ropes, the lifting tool comprising a body with a centre axis and having a operable lock adapted to catch a rope connector, and a structure that is designed to be connected to a hoist or cranes wherein the lifting tool is equipped with at least one water flow inducing means positioned at a radial distance from the centre axis.

Preferably, this includes rudders. W02012/060715A1 is particularly concerned with hoisting operations at sea with heavy items, and where the hoisting operations are heave-compensated, such that the lifting rope will be continuously reeled in and out from a winch due to the heave motion of the lifting vessel. As it states, "an inherent problem when utilising parallel ropes is the tendency to twist and to get entangled in each other. As the ropes have to move independently of each other in the sea, an entanglement may in a worst case lead to cutting of the ropes and the loss of a valuable item." An object of the present invention is to provide an improved multi-cable subsea lifting system which reduces or avoids cabling or twisting.

Thus, according to one aspect of the present invention, there is provided a multi-cable subsea lifting system comprising: -two or more load-cable lifting apparatus; -a load cable extending from each load-lifting apparatus to a subsea co-terminal loading point; -one or more subsea anti-cabling devices comprising two or more sets of two or more spaced apart and slidable cable connections around neighbouring load cables, and a rigid framework between each set of cable connections; -an anti-cabling device lifting apparatus; and -an anti-cabling line extending from the anti-cabling device lifting apparatus to one anti-cabling device.

The anti-cabling device is able to maintain a defined distance or space between the cables due to its rigid framework. The anti-cabling device is also slidable with respect to the load cables, allowing it to be best positioned or deployed where the concern of cabling is more expected.

The load-cable lifting apparatus may be one or more units, mechanisms, apparatus etc. known in the art, including winches, winch assemblies, drive assemblies, traction control units, etc. and all of which are known in the art to be operable either singly or in parallel or serial combination. It or they are intended to provide control for the movement of the load cable, generally to and from a reel, and generally in and out of the water, optionally via one or more cranes or pulleys or other apparatus, units or mechanisms for deployment of load cables from an above sea position on a base or platform, such as on a vessel or unit on the sea surface.

Each load-cable is also not limited in the present invention, and includes any form of wire, rope, cable, line etc., optionally being multi-stranded or otherwise formed, and generally for subsea lifting operations. Load-cables are often steel wires, optionally stranded steel wires, but are increasingly being replaced by ropes, particularly fibre ropes, to reduce their weight for greater depth work.

The present invention is not limited by the number or nature of the load-cables, or the number and nature of the load-cable lifting apparatus, which maybe particularly adapted to suit the relevant load-cable.

The load-cables extend to a subsea co-terminal loading point. The co-terminal loading point may be any device, unit or apparatus, or combination of same, intended to provide the interaction between the load-cables and the load. Many tools, plates, pulleys or blocks, or combinations of same, are known in the art, and the present invention is not limited in this regard. A typical co-terminal load point is a triplate having two or more connection points along a top edge or surface, and a single, usually symmetrical or otherwise balanced, loading point at its lower edge or point. Other useful units such as tension or torsion load cells could also be introduced at or near the co-terminal loading point as is known in the art.

In one embodiment of the present invention, the lifting system comprises a two or three load-cable lifting apparatus, and two or three load cables respectively extending to a co-terminal triplate with a single load end.

The anti-cabling device comprises two or more sets of two or more spaced apart cable connections, which cable connections are slidable around neighbouring load cables. The neighbouring load cables maybe two parallel cables, such cables being separately provided, or formed from a single cable looped at one end, generally at the loading end. Alternatively, the neighbouring load cables may be three, four or more parallel cables, generally being parallel in the sense of from the water surface down to the loading point The cable connections of the anti-cabling device may also be terminations that are locked axially, or integrated axial swivels that allow torsional release.

Optionally, the cable connections comprise open sleeves and one or more attachment clips. The open sleeves generally have an inner circumference or inner perimeter greater than the general outer circumference of the load-cable, so as to be slidable therealong and allow independent movement of the anti-cabling device with respect to the load-cable. The open sleeve generally includes a longitudinal slot or gap between the ends of the sleeve, to allow the fitment of the cable connection around a load-cable. The attachment clip(s) may have any form, shape or design, and are generally intended to extend across the open part or nature of the open sleeve, so as to maintain the cable connection around the load-cable and prevent its dislocation therefrom in use. Attachments clips can include any form of strap, line or band, generally rotatable or extendable from one side of the open sleeve across the slot or gap in the sleeve, to a fixing point on the other side of the sleeve, so as to fix the rnachment clip across the slot or gap of the open sleeve.

In one embodiment of the present invention, the cable connections of each set are separate from each other.

In another embodiment of the present invention, the cable connections of each set comprise a continuous body. For example, the sets of cable connections could comprise a continuous open sleeve having two or more attachment clips at different locations therealong, the attachment clips creating the locations where the cable connections are fitted around the load cables in use so as to form at least two different locations for the fitment of the cable connections around the load-cable.

In another embodiment of the present invention, the cable connections are (wholly or substantially] closed sleeves able to be opened for fitting around the load cables in use. They could be opened by the use of hinges or by being formed of separable parts, which can then be closed' around the load cables, preferably securely closed or even locked around the load-cables.

The axial length of the cable connections is not limiting on the invention, such that a short sleeve may also be a collar' or even a ring.' Preferably, the cable connections are slidable with respect to the load cables by having a low friction therewith or thereinbetween, in particular by having low friction contact surfaces with a radiused entry/exit to protect the wires from damage from sharp edges, etc. The anti-cabling device may comprise two, three, four or more sets of cable connections along each load-cable, each cable connection being the same or different or a combination of different connections.

Preferably, at least one cable connection around one load-cable, and at least one cable connections around another, generally parallel, load-cable, are laterally displaced2 or otherwise arranged orthogonally to the direction of the load-cables.

The anti-cabling device includes a rigid framework between a set of cable connections around one load-cable, and a set of cable connections around another, generally parallel, load-cable. The rigid framework may comprise any arrangement, form, design or shape, adapted to maintain a distance between each set of said cable connections, and therefore between each load-cable, in use.

Optionally, the rigid framework is a relatively open' structure to allow water to flow therearound or therethrough without such water affecting its position and its use.

In one embodiment of the present invention, the frame comprises a cross-strut between lateral displaced cable connections, and at least one bracing member between the cross-struts. That is, the cross-struts fit between each set of cable connections to form a generally square or rectangular shape, in combination with the load-cables between the cable connections. The at least one bracing member provides the rigidity needed for the framework.

Optionally, the at least one bracing member comprises two vertical bracing members between the cross-struts.

Alternatively or additionally, at least one bracing member comprises an angled bracing member between opposite ends of different cross-struts.

The skilled man is aware of various patterns, arrangements and designs using struts, members, etc., that are able to form a rigid framework, and the present invention is not limited by the nature and design of the rigid framework able to ensure a defined distance between each set of cable connections.

The anti-cabling device lifting apparatus may comprise one or more units, mechanisms, apparatus etc. known in the art, including winches, winch assemblies, drive assemblies, traction control units, etc. and all of which are known in the art to be operable either singly or in parallel or serial combination. It or they are intended to provide control for the movement of the anti-cabling line, generally to and from a reel, and generally in and out of the water, optionally via one or more cranes or pulleys or other apparatus, units or mechanisms for deployment of lines from an above sea position on a base or platform, such as on a vessel or unit on the sea surface.

Generally, the anti-cabling device lifting apparatus will not have the same load bearing capacity as the load-cable lifting apparatus, but may still be required to operate at the same level or depth.

An anti-cabling line extends from the anti-cabling device lifting apparatus to one anti-cabling device. The anti-cabling line may be any form of wire, rope, cable, line etc., optionally being multi-stranded or otherwise formed, and generally for subsea lifting operations.

In an embodiment of the present invention, the lifting system comprises two or more anti-cabling devices spaced along the same neighbouring load cables.

According to another aspect of the present, there is provided a subsea anti-cabling device for a multi-cable subsea lifting system comprising two or more spaced apart and slidable connections for each cable, and a rigid framework thereinbetween.

The anti-cabling device may comprise or include one or more of the embodiments or features discussed hereinbefore, particularly with respect to the nature of the cable connections and the rigid framework. The anti-cabling device, by being located around the load-cables, creates a physical or defined distance between them, which prevents cabling. The anti-cabling device can be raised or lowered to a point at which cabling is expected or otherwise determined to occur.

Multiple anti-cabling devices may be used along the extent of load cables in use, optionally at different points or depths at which cabling is expected or otherwise determined to occur.

According to another aspect of the present invention, there is provided a method of raising or lowering a subsea load using the multi-cable subsea lifting system as defined herein, comprising at least the steps of; (i) providing the load to the loading point; (ii) locating an subsea anti-cabling device around neighbouring load cables, (iii) raising or lowering the load by extending or distending the load cables from the load-cable lifting apparatus; (iv) raising or lowering the anti-cabling device by extending or distending the anti-cabling line from the anti-cabling device lifting apparatus.

Preferably, there is independent raising or lowering of the anti-cabling device compared with raising or lowering of the load, and/or raising or lowering of the load-cables. In this way, the anti-cabling device can be maintained at a particular depth, position or location at which cabling is considered to possibly occur, independently of the location of the load.

The present invention provides the ability to maintain parallel spacing between subsea load cables, which allows the subsea lifting system to have increased cabling stability, either at existing depths, or at greater depths. The present invention preferably creates a system of parallelogram arranged linkages, and being driven by an independent lifting system.

In particular, the present invention allows a user or operator to more frequently consider the use of multiple ropes or cables for lowering and recovering operations, where the use of multi-cables may have previously been thought of as at a disadvantage due to their expected cabling problems, compared with the use of a single wire or cable.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a schematic side view of a multi-cable subsea lifting system according to one embodiment of the present invention; Figure 2 is a side view of the first subsea anti-cabling device in Figure 1, and according to another embodiment of the present invention; and Figure 3 is a side view of a second subsea anti-cabling device according to another embodiment of the present invention.

Referring to the drawings, Figure 1 shows a multi-cable subsea lifting system. The system comprises two load-cable lifting apparatus 2a, 2b, and two load cables 4a, 4b respectively extending from each load-lifting apparatus 2a, 2b to a subsea co-terminal loading point. The load-cable lifting apparatus 2a, 2b are located on a vessel 6, such as pipe laying service vessel or PLSV, on a sea 8. Each load-cable lifting apparatus 2a, 2b could be a winch or sheave, generally able to provide control for the movement of the respective load-cable 4a, 4b through the sea 8 to raise and lift a load 10.

Figure 1 also shows a seabed 12, which could be any distance below the surface of the sea 8, and towards which and optionally onto which it is desired to guide the load 10. However, the greater the subsea depth for location of the load 10, such as increasingly beyond 2000 or even 3000 metres, and the greater the actual load 10, such as being hundreds of tonnes, [increasingly up to or greater than 400 tonnes), then the greater is the desire to use multi-cable subsea lifting systems for obvious engineering reasons, compared with conventional single lifting cables or single cable lifting systems.

The load-cables 4a, 4b in Figure 1 can be provided from one or more reels (not shown] to the load-cable lifting apparatus 2a, 2b in a manner known in the art The nature, design and operation of the load-cable lifting apparatus 2a, 2b, and the nature, design, etc. of the load-cables 4a, 4b, are not limiting in the present invention, and can be those conventionally used and operated.

It will also be appreciated that Figure 1 is a schematic drawing intended to show the present invention, and is not dimensionally accurate in relation to the relative sizes of the features shown. In particular, the distance between the load-cables 4a, 4b could be any suitable distance, optionally based on or according to the load operation, the nature and number of the load cables etc., and possibly the load-lifting apparatus. For example, the distance between the load-cables could be less than lm, lm, or greater than lm, such as 2m, 3m, 4m, Sm, or even more. The use of multiple anti-cabling devices may use different anti-cabling devices at different depths or points of the loading operation.

With a distance between the load cables of less than im, or possibly only a few metres, it can be appreciated that, as the extent of the parallel winch operation is greater with increasing depth operation, the potential for cabling increases, where the load-cables could move relative to one another, in particular, come closer to one another and even result in rotational entanglement Whilst this may seen more expectant for a two-cable subsea lifting system, the problem can occur also with multi-cable subsea lifting systems using more than two cables, especially where the lifting system may be divided into subsets or pairs of cables, each subset comprising closely spaced cables.

Thus, the present invention extends to aiming to maintain a defined divide or distance or space between any two load-cables in a multi-cable subsea lifting system.

Indeed, the present invention also extends to aiming to simultaneously maintain the defined divide, distance or space between more than two cables, generally running in parallel operation, by extension of the subsea anti-cabling device to having two or more sets of two or more spaced apart and slidable cable connections to go around the relevant number of neighbouring load-cables, and having a rigid framework between each set of cable connections.

Figure 1 shows the load-cables 4a, 4b extending to a subsea co-terminal loading point being a triplate 14 having an upper edge or surface with apertures therein for connection with each load-cable 4a, 4b, and a converging lower load end for connection to the load 10. Figure 1 also shows a tension/torsion load cell 18 able to provide tension and torsion information to a monitor or control (not shown) to identil' the on-going tension and torsion of each load-cable 4a, 4b to an operator.

Figure 1 also shows a subsea anti-cabling device 20 comprising two sets of two spaced apart and slidable cable connections; a first set being 22a and 22b, and a second set 24a and 24b, located around the neighbouring load-cables 4a, 4b respectively; and having a rigid framework 26 between each set of cable connections 22a, 22b, 24a, 24b. The anti-cabling device 20 is supported by an anti-cabling line 28, whose movement is controlled by an anti-cabling device lifting apparatus 30, generally being a winch or winch assembly, etc. as hereinbefore described, and operating the anti-cabling line 28 via a pulley 32 supported on a crane or tower (not shown) to operate the anti-cabling line 28 between the load-cables 4a, 4b in use.

Optionally, information about the subsea lifting system can be provided to a control or monitor via one or more video links, such as from one or more ROVs (not shown), to assist with the positioning of the anti-cabling device 20 with respect to the extension of the load-cables 4a, 4b. That is, with increasing extension or depth of the load-cables 4a, 4b, and possibly based on sea conditions both above the surface of the sea 8, (such as the heave of the vessel 6) and in the sea 8, the possible or expected locations or areas of the risk of cabling may be known or identifiable or otherwise predicable. Additionally or alternatively. monitoring of the status of the tension and/or torsion of the load-cables 4a, 4b, through the load cell 18 or one or more other monitors, including visual monitors from for example ROVs, can indicate locations or areas of risk of cabling during the operation of the lifting system.

As the cable connections 22a, 22b and 24a, 24b are slidable with respect to the load-cables 4a, 4b, the anti-cabling device can be positioned at the location or area known or expected to be at greater risk of cabling.

Optionally, there is provided more than one anti-cabling device along the lengths of the load-cables 4a, 4b, to maintain a defined distance or space between the load-cables 4a, 4b in multiple locations therealong, especially where the load-cables are extending to greater depths, and/or the sea conditions are expected to provide greater risk of cabling.

Thus, it is possible for the user or operator of the subsea lifting system to position the anti-cabling device 20 independently of the extension of the load-cables 4a, 4b from the load-cable lifting apparatus 2a, 2b, and the present invention extends to positioning the anti-cabling device 20, by extending or retracting the anti-cabling line 28, or a multiple thereof, to a position or positions known, expected or shown in use to be at greatest risk of cabling Figure 2 shows the anti-cabling device 20 in Figure 1 in more detail! In particular, it shows each cable connection 22a, 22b, 24a, 24b as an open sleeve 36 and an attachment clip 38. The attachments clips may be slotted like Christmas tree guide wires, or extend fully circumferentially around the sleeves 36. The open sleeves 36 are able to be fitted around the cables 4a, 4b due to a slot or gap along their length, which gap is then closed by movement of the attachment clips 38 from an open position (not shown] to a closed position as shown in Figure 2. This secures the location of the cable connections 22a, 22b and 24a, 24b around the cables 4a, 4b, whilst allowing the same cable connections to slide along the load-cables 4a, 4b and not be permanently attached thereto.

The rigid frame 26 of the anti-cabling device 20 comprises a cross-strut 40a between the two upper' cable connections 22a, 24a that are lateral or orthogonal to each other, and a second cross-strut 4Gb between the two lower' cable connections 22b, 24b that are also lateral or orthogonal to each other. Between the first and second cross-struts 40a, 4Db there are two vertical bracing members 42 to complete the rigid framework.

From Figure 2 it can be seen that the anti-cabling device 20 creates a defined regular physical shape and thus divide between the load-cables 4a, 4b. Whilst Figure 2 shows the arrangement of the anti-cabling device 20 with the load-cables 4a, 4b as a rectangle, the skilled man can see that other regular shapes can be created between the two cables 4a, 4b so long as there is a rigid framework thereinbetween.

Figure 2 shows the anti-cabling device 20 having a sort of "H" frame, which does not impede or in any way influence the direction and loading on the load-cables; nor indeed, due its open nature, the flow of water around the load-cables 4a, 4b. In this way, the anti-cabling device 20 provides a spacer between the parallel load-cables 4a, 4b whilst its cable connections 22a, 22b, 24a, 24b, which preferably feature low friction contact surfaces, allow the anti-cabling device to be positioned independently without damaging the load-cables 4a, 4b.

Figure 3 shows a second anti-cabling device 50, wherein the each set of spaced apart and slidable cable connections 52a, 52b comprises a continuous body, generally being a continuous open sleeve having a gap or slot therealong, and so locatable around a continuous length of each load-cable 4a, 4b. The cable connections 52a, 52b comprise a plurality of attachment clips 54 [being two for each cable connection shown in Figure 3], able to provide locations for securement of the cable connections 52a, 52b around each load-cable 4a, 4b at different locations along their length.

Figure 3 also shows the second anti-cabling device 50 having a rigid framework comprising a first cross-strut 56a generally locatable at or near an upper end of each cable connections 52a, 52b, and a second cross-strut 56b generally locatable at or near a lower end of each cable connections 52a, 52b, with an angled bracing member 58 between opposite ends of the two cross-struts 56a, 56b. The combinations of the cross-struts 56a, 56b and the angled brace member 58 provides a rigid framework which is intended to maintain a defined distance for space between the load-cables 4a, 4b as described above.

The present invention provides a subsea anti-cabling device able to be deployed in a multi-cable subsea lifting system to reduce the risk of cabling. In particular, the anti-cabling device can be positioned at a point at which cabling is determined to occur. This increases the competitive advantage of the use of multi-cable lifting systems compared with single cable lifting systems, and thus their commercial applicability to use at increasing depth capacity for parallel winch operations. In particular, it can provide the user or operator with greater confidence of the use of multi-cable subsea lifting systems at greater depths, by aiming to reduce or even avoid completely one of a disadvantage associated with multi-cable subsea lifting systems.

Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope of the invention as defined herein. Although the invention has been described in connection with specific preferred embodiments it should be understood that the invention as defined herein should not be unduly limited to such specific embodiments.

Claims (15)

1. Claims 1. A multi-cable subsea lifting system comprising: -two or more load-cable lifting apparatus; -a load cable extending from each load-lifting apparatus to a subsea co-terminal loading point; -one or more subsea anti-cabling devices comprising two or more sets of two or more spaced apart and slidable cable connections around neighbouring load cables, and a rigid framework between each set of cable connections; -an anti-cabling device lifting apparatus; and -an anti-cabling line extending from the anti-cabling device lifting apparatus to one anti-cabling device.
2. 2. A lifting system as claimed in claim 1 comprising two or three load-cable lifting apparatus, and two or three load cables respectively extending to a co-terminal triplate with a single load end.
3. 3. A lifting system as claimed in any one of the preceding claims comprising two or more anti-cabling devices spaced along the same neighbouring load cables.
4. 4. A lifting system as claimed in any one of the preceding claims wherein the cable connections comprise open sleeves and attachment clips.
5. 5. A lifting system as claimed in any one of the preceding claims wherein the cable connections of each set are separate.
6. 6. A lifting system as claimed in any one of claims 1 to 4 wherein the cable connections of each set comprise a continuous body.
7. 7. A lifting system as claimed in any one of the preceding claims wherein the frame comprises a cross-strut between each lateral cable connection, and at least one bracing member between the cross-struts.
8. 8. A lifting system as claimed in claim 7 comprising two vertical bracing members between the cross-struts.
9. 9. A lifting system as claimed in claim 7 comprising an angled bracing member between opposite ends of different cross-struts.
10. 10. A subsea anti-cabling device for a multi-cable subsea lifting system comprising two or more spaced apart and slidable connections for each cable, and a rigid framework thereinbetween.
11. 11. A subsea anti-cabling device as claimed in claim 10, and as further defined in one or more of claims 4 to 8
12. 12. A method of raising or lowering a subsea load using the multi-cable subsea lifting system as defined in any one of claims 1 to 9 comprising at least the steps of: (i) providing the load to the loading point; (ii) locating an subsea anti-cabling device around neighbouring load cables, (iii) raising or lowering the load by extending or distending the load cables from the load-cable lifting apparatus; (iv) raising or lowering the anti-cabling device by extending or distending the anti-cabling line from the anti-cabling device lifting apparatus.
13. 13. A method as claimed in claim 12 comprising independently raising or lowering the anti-cabling device compared with raising or lowering the load.
14. 14. A multi-cable subsea lifting system substantially as described herein and with reference to Figure 1 of the accompanying drawings.
15. 15. A subsea anti-cabling device for a multi-cable subsea lifting system substantially as described herein and with reference to either Figure 2 or Figure 3 of the accompanying drawings.