GB2554902A

GB2554902A - Active heave compensation apparatus

Info

Publication number: GB2554902A
Application number: GB1617358.5A
Authority: GB
Inventors: David Screaton Lee
Original assignee: Screaton And Ass
Current assignee: Screaton And Ass
Priority date: 2016-10-13
Filing date: 2016-10-13
Publication date: 2018-04-18
Anticipated expiration: 2036-10-13
Also published as: GB2554902A9; GB201617358D0; GB2554902B

Abstract

An active heave control system (Fig 9, 100) used in marine, subsea lifts may be located between a crane or winch (Fig 9, 720) and the load to be lifted (Fig 9, 600). The device comprises a chassis (Fig1, 105) having a motor 200 and gears 210 that may drive a pair of leadscrews 160.Travelling beams 150 having ballscrews or ball nuts 165 may move towards each other or apart as the lead screws rotate. Movement of the beams in one plane is converted to movement of a scissor means 130 comprising a plurality of pivoting linkages 140 forming a parallelogram or pantograph arrangement in a plane perpendicular to the beams. The device moves in response to a signal from accelerometers in an MRU or motion response unit that, in conjunction with a control means (Fig 6) may be located in a container 300. The device may be connected to a lifting cable via a connector 120. Umbilical leads may also be connected to the device.

Description

(71) Applicant(s):

Lee David Screaton

Office 24, Durham Workspace, Abbey Road, Pity Me, DURHAM, County Durham, DH1 5JZ, United Kingdom

Screaton and Associates

Office 24, Durham Workspace, Abbey Road, Pity Me, DURHAM, County Durham, DH1 5JZ, United Kingdom (56) Documents Cited:

JP 2003201091 A US 20140377004 A (58) Field of Search:

INT CL B63B, B66C, B66F, E21B Other: WPI, EPODOC, INTERNET (72) Inventor(s):

Lee David Screaton (74) Agent and/or Address for Service:

Lee David Screaton

Office 24, Durham Workspace, Abbey Road, Pity Me, DURHAM, County Durham, DH1 5JZ, United Kingdom (54) Title of the Invention: Active heave compensation apparatus

Abstract Title: Active heave control system with scissor, parallelogram linkage (57) An active heave control system (Fig 9, 100) used in marine, subsea lifts may be located between a crane or winch (Fig 9, 720) and the load to be lifted (Fig 9, 600). The device comprises a chassis (Figi, 105) having a motor 200 and gears 210 that may drive a pair of leadscrews 160.Travelling beams 150 having ballscrews or ball nuts 165 may move towards each other or apart as the lead screws rotate. Movement of the beams in one plane is converted to movement of a scissor means 130 comprising a plurality of pivoting linkages 140 forming a parallelogram or pantograph arrangement in a plane perpendicular to the beams. The device moves in response to a signal from accelerometers in an MRU or motion response unit that, in conjunction with a control means (Fig 6) may be located in a container 300. The device may be connected to a lifting cable via a connector 120. Umbilical leads may also be connected to the device.

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Active Heave Compensation Apparatus

Description

FIELD AND BACKGROUND OF INVENTION [0001] The invention is generally related to the lifting of marine suspended loads, more particularly, to apparatus and methods for the active heave compensation of the load.

[0002] Marine loads are suspended from shipboard cranes or winches when being moved from one location to another. These suspended loads are subjected to additional movement due to the action of the surrounding waves on the ship or vessel. Of the six degrees of motion (roll, pitch, yaw, heave, sway and surge), it is the heave component that adds unwanted vertical movement to the load. Unwanted vertical movement frequently leads to damage to the load or the lifting arrangement, or improper placement of the load.

[0003] There are two primary classifications of heave compensation: Passive Heave Compensation (PHC) and Active Heave Compensation (AHC). PHC achieves heave compensation without additional power or control/ instrumentation. Examples of PHC would include dampers, shock absorbers, springs, etc. AHC utilizes power and instrumentation such as a Motion Reference Unit (MRU) to achieve heave compensation. It is important to note that, through the use of the MRU, AHC reacts to the movement of the ship and not to tension in the lift rigging.

[0004] Conventional AHC can be applied by lengthening and shortening the lifting wire, umbilical or rope using such arrangements as a rotating a shipboard winch drum or a sheave arrangement that expands or contracts in response to heave motion. These can be considered the typical methods for AHC and are well proven as the means to accomplish the task. Another method is to add a mechanism between the end of the lift rigging and the load which extends or retracts to reduce the effects of heave. This method has to date only been cylinder based and also passive in its application of heave compensation i.e. PHC. The invention is dissimilar to this method as, while it is located at the end of the lift rigging, it differs in that the vertical motion is achieved through the use of a ‘scissor’ frame arrangement rather than purely as a cylinder or cylinders. In this context, the term ‘scissor’ implies an assembly consisting of multiple pivoted structural members arranged to pass through one or more fulcrums which when activated can extend and contract the assembly by pushing apart or drawing together opposing structural elements. The advantages of using a scissor assembly arrangement is that when contracted the vertical height of the package is substantially less than an equivalent cylinder based arrangement.

[0005] The physical dimensions of subsea systems and their associated sub systems are very important when lifting the subsea system across the vessel as they frequently make use of a davit or ‘A’ frame lifting arrangement that has height limitations during the lifting process. The invention is intended to provide a tightly compacted arrangement that is mounted on the subsea device which provides the heave compensation performance of other systems without the penalty of excessive additional height or any additional items of equipment required to be mounted on the deck of the vessel. The invention also negates the requirement to modify the deck equipment such as the lift winch in any way and as such is both a space and cost efficient solution to adding AHC to existing vessel equipment layouts.

[0006] With the invention mounted at the load rather than aboard the vessel, a number of problems associated with deep water active heave compensated lifting operations are also significantly reduced. When a typical vessel based AHC system is used as part of deep water operations the lifting arrangement can experience instability and synchronization issues as the lifting rigging is likely not to be perfectly straight in which case the shortening and extending of the lifting rigging may only serve to remove the curve in the wire, umbilical or rope. The invention avoids these problems by being placed at the load and so suffers no impact due to the wire, umbilical or rope being straight or otherwise. There are PHC systems that offer this function however the invention provides AHC which is a different category of heave compensation.

[0007] As implied, there are in existence a variety of both AHC and PHC systems. The key difference however is that this AHC invention uses a scissor frame arrangement to allow for a highly compacted package when so required. When combined with being suspended with the load the invention eliminates or heavily mitigates dimensional, modification/ cost and accuracy issues associated with deep water lowering operations.

SUMMARY OF INVENHON [0008] Embodiments of the invention address the above identified needs by providing apparatus for AHC that may be placed between a lift wire, umbilical or rope and the load being lifted. Advantageously, such embodiments require no significant length of wire, umbilical or rope deployed from the vessel.

[0009] Aspects of the invention are directed to an apparatus for use in combination with a sensor operative to detect heave motion. The apparatus consists primarily of a main chassis that supports the drive and control systems and an assembly of structural members arranged in a mutually pivoting ‘scissor’ pattern that support a lifting point for the attachment of lift rigging. The lifting point, via the pivoting scissor assembly, is translatably disposed within the main chassis. The means of actuating the scissor assembly can be through the use of a lead or ball screw rotationaliy coupled to the rotational motion of the drives although a cylinder based actuation of the scissor assembly could be used without impact to the claims relating to the invention. The pivoting of the scissor assembly is translated into linear motion though interfacing with the main chassis perpendicular to the longitudinal axis. The device is suspended from the lifting rigging by the lifting point which is connected to the scissor assembly and the load is suspended from the mam chassis although reversing this orientation would not impact the claims relating to the invention. The main chassis would include the control, drives and drive support systems as well as any stored energy units and power distribution although these components may be distributed elsewhere without impact to the claims relating to the invention. The control system is operative to command the drive system to cause the scissor assembly to translate relative to the main chassis based on the heave motion detected by the sensor or MRU. Additional equipment such as power generation, kinetic energy recovery systems, telemetry systems, buoyancy arrangements, etc. could also form part of the main chassis in order to provide more lifting functions.

[0010] The invention differs from a ship based winch or sheave based AHC system in that AHC function is independent of the length of wire, umbilical or rope deployed from the vessel crane or winch.

[0011] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the present invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter, forming a part of this disclosure, in which a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] In the accompanying drawings, forming a part of this specification, and in which reference numerals shown in the drawings designate like or corresponding parts throughout the same:

[0013] FIG. 1 shows a perspective view of an AHC apparatus in accordance with an illustrative embodiment of the invention [0014] FIGS. 2 and 3 show perspective views of the FIG 1 AHC apparatus in the extended and retracted orientations [0015] FIG. 4 shows a partially broken or exploded perspective view of the FIG. 1 AHC apparatus.

[0016] FIG. 4 A shows an enlarged perspective view of the region indicated in FIG. 4 [0017] FIG. 5 shows another exploded perspective view of the FIG. 1 AHC apparatus [0018] FIG. 6 shows a block diagram of various electronic and electrically actuated components in the FIG. 1 AHC apparatus [0019] FIGS. 7 and 8 show the FIG 1 AHC apparatus reacting to different heave conditions [0020] FIG. 9 shows an elevational view of the FIG. 1 AHC apparatus suspended from a docking device and supporting a subsea system

DESCRIPTION OF THE PREFERRED EMBODIMENTS [0021] The present invention will be described with reference to illustrative embodiments. For this reason, numerous modifications can be made to these embodiments and the results will still come within the scope of the invention. No limitations with respect to the specific embodiments described herein are intended or should be inferred.

[0022] FIGS. 1-5 show aspects of an AHC apparatus (100) in accordance with an illustrative embodiment of the invention. FIG. 1 shows a perspective view of the illustrative AHC apparatus (100), while FIGS. 3 and 4 show the AHC apparatus in the extended and retracting arrangements. FIG. 4 shows a partially-broken, exploded perspective view, and FIG. 5 shows another exploded perspective view. FIG. 4A shows an enlarged perspective view of the region indicated in FIG. 4.

[0023] In the AHC apparatus (100), a main chassis (105) includes structural members (110) that defines a rectangular volume ((115)) therein. An upper lifting point (120) is attached to the top of the scissor assembly (130) proximate to a pair of interface ring semi circles (125). The lifting point has a lifting umbilical (400) terminated into it through the use of mechanical entrapment and epoxy compound. Below the main chassis (105) is a connection point (500) for connection to the subsea system.

[0024] Structural members (140) are combined at pin based pivot points (135) and anchored to travelling beams (150) to form the scissor assembly (130). The pins (190) are preferred to be used in conjunction with a self-lubricating bush within the pivot (135) assembly.

[0025] The travelling beams (150) are supported by both screws (160) and guide rails (170). The travelling beams (150) are fitted with nut (165) that interface with the screws (160) and bushes (175) that allow the travelling beams (150) to slide the guide rails (170). The screws (160) are supported on the main chassis (105) by bearings (180) whereas the guide rails (170) are supported on the main chassis (105) by clamps (185).

[0026] In FIG 4 and FIG 4A, each of the screws (160) are driven by a motor assembly (200) consisting of a motor (240), drive gear (220), sprockets (225) and drive chain (230). Through the use of left hand and right hand screws, the screws (160) rotate counter to one another. A respective drive assembly cover (210) covers the drive assembly (200) and protects its drive assembly (200) from surrounding seawater.

[0027] Through the rotation of the drive assembly (200) each screw (160) rotates thereby forcing the nut (165) of each travelling beam (150) longitudinally along the length of the screw (160). As the nut (165) moves, the associated travelling beam (150) is carried either towards the opposing travelling beam (150) or away from the travelling beam (150) depending on the direction of the screws (160) rotation. As the scissor assembly (130) is connected to the travelling assemblies (150) by pivot points (135) the scissor structural members (140) translate the travelling beam (150) horizontal motion to vertical motion of the lifting point (120).

[0028] In addition to the several elements set forth above, the AHC apparatus (100) further comprises a number of electronic components, which are isolated from seawater a water-proof enclosure (300). A position encoder (245) occupies a location within the motor assembly (240) enclosure. At the same time, the AHC apparatus (100) also includes control circuitry (310), a heave sensor (320) which occupies a subsea enclosure (300). The motor (240) and subsea enclosure (300) are disposed on the main chassis (105). Power and control signals for the system are transmitted to the system through the lifting umbilical (400) that is terminated into the lifting point (120). Wiring among these various components is also present in the AHC apparatus (100), but it is not explicitly shown in the figures. Wire (250), umbilicals, for example, may span between the motor assembly (240) and the subsea enclosure (300), and between the lifting point (120) and the subsea enclosure (300). Wire (340), umbilicals may further span between the power distribution (330) and the subsea system (500) suspended from the AHC apparatus (100). The wire, umbilicals may be enclosed in waterproof conduits where they would be exposed to seawater if left unprotected.

[0029] FIG. 6 shows a block diagram of the various electronic and electrically-actuated components in the AHC apparatus (100) and the manner in which they cooperate. As the name would suggest, the heave sensor (320) is operative to detect heave motion at the sensor. The heave sensor (320) may, for example, comprise an MRU. The heave sensor (320) is located in or around the lifting point (120). The position encoder (245) preferably comprises a rotary encoder. The rotary encoder may be coupled to the rotation of the motor (240) via a rigid or flexible shaft. The position encoder (245) is thereby operative to report rotation of the motor (240), which may be converted into the position of the lifting point (120) in the main chassis (105).

[0030] The control circuitry (310) receives signal inputs from the heave sensor (320) and the position encoder (245), and utilizes this information to instruct the motor drive circuitry (350) which in turn drive the motors (240) so as to cause the scissor assembly (130) to translate in the main chassis (105). The control circuitry (320) may comprise one or more data processing portions, one or more memory portions, and one or more input/output portions. The control circuitry (320) may, for example, be configured in the form of one or more microprocessorcontrolled programmable logic controllers (PLCs). Instructions for the PLCs may be in the form of firmware and/or software stored in nonvolatile memory.

[0031] Power is supplied to the control circuitry (320) and ultimately to the motors controller (350) and motor (240) via the lifting umbilical (400).

[0032] Once understood from the teachings herein, the various elements forming the abovedescribed AHC apparatus (100) may be formed from conventional materials utilizing conventional manufacturing techniques, or alternatively, obtained commercially. The main chassis (105), the scissor assembly (130), and their associated static appendages, for example, are preferably formed from a metal such as, but not limited to steel, with a protective paint or coating suitable for marine use. When not available commercially, these components may be custom manufactured utilizing conventional metal forming techniques, which will be familiar to one skilled in the relevant metal forming arts. Gaskets may be utilized to create watertight seals as required.

[0033] The sets of gears (220)(225), the motors (240), the drive chain (230) may be obtained commercially. Suitable gears (220)(225) and the drive chains (230) may, for example, be obtained from HMK Automation & Drives (Cheshire, UK). Suitable subsea motors (240) are available from, for example, IKM Elektro AS (Stavanger, Norway). Drive circuitry (350) are available from, for example, ABB (Warrington, UK).

[0034] The electronic components may also be sourced commercially. A suitable MRU for the heave sensor (320) may be sourced from, for instance, Kongsberg Maritime, (Kongsberg, Norway). Suitable components for the control circuitry (310) may be sourced from, for example, MEC Ltd (Thornaby, UK) and Scantrol (Bergen, Norway). Advantageously, once the unique functionality of the AHC apparatus (100) is understood from the teachings herein, the programming of the control circuitry (310) to support the desired functions will be well within the skill of one having ordinary skill in the relevant arts. Configuring and programming PLCs is described in a number of readily available references, including, for example, W. Bolton, Programmable Logic Controllers, Fifth Edition, Newnes, (200)9; and F. Petruzella, Programmable Logic Controllers, Fourth Edition, McGraw-Hill Science/Engineering/Math 2010, which are both hereby incorporated by reference herein.

[0035] So configured, the AHC apparatus (100) may be made to reduce the heave motion of a load suspended from a vessel. FIGS. 7 and 8 show elevational views of the AHC apparatus (100) configured to perform this function for a load (600) suspended from a lifting umbilical (400). The upper lift point (120) of the scissor assembly (130) is suspended from lifting umbilical (400). The load (600) in this example consisting of a Remotely Operated Vehicle (ROV) (620), Tether Management System (TMS) (610) and Tether (630) is suspended from the lower attachment point (500) of the main chassis (105).

[0036] While active, the heave sensor (320) detects the heave motion at the lift point (120) and reports this motion to the control circuitry (310). The control circuitry (310), in turn, commands the motor (240) to cause the scissor assembly (130) to move proportionally in a direction opposite to the detected heave motion. When the scissor assembly (130) needs to be translated upward in the main chassis (105), for example, the control circuitry (310) commands the motor (240) to rotate the drive gears (220)(225) such that the scissor assembly (130) retracts at the desired rate. When the scissor assembly (130) needs to be translated downward in the main chassis (105), for example, the control circuitry (310) commands the motor (240) to rotate the drive gears (220)(225) such that the scissor assembly (130) extends at the desired rate. If the heave motion stops and the scissor assembly (130) doesn’t need to move, the motor (240) applies maximum torque while at zero speed to prevent rotation of the screws (160) to hold the scissor assembly (130) in place.

[0037] This functioning of the AHC apparatus (100) is illustrated in the elevational views in FIGS. 7, 8 and 9. In FIG. 7, the vessel launch and recovery system (700) connected to the AHC apparatus (100) by the lifting umbilical (400) and the main chassis (105) are descending downward due to heave motion acting from the sea (900) on the vessel (800). The control circuitry (310) therefore causes the scissor assembly (130) to proportionally retract in the main chassis (105). In FIG. 8, the opposite motion is occurring. That is, the vessel (800) and the main chassis (105) are rising upward due to heave motion and the control circuitry (310) is causing the scissor assembly (130) to be proportionally extending in the main chassis (105). The net effect is that the main chassis (105) and the load (600) remain relatively stationary in space while the remainder of the AHC apparatus (100) and the vessel (800) rise and drop due to sea motion. Note the common datum indicated on FIGS. 7 and 8.

[0038] The operational example shown in FIGS. 7 and 8 specifically relate to TMS (610) based ROV (620) operations whereby it is advantageous to have the TMS (610) stationary while the ROV (620) docks and undocks. The arrangement shown in FIG. 9 illustrates the load (600) when all elements are together, which is the case when loading and launching the load (600) from the vessel (800) via a launch and recovery system (700). This is not the only operation that will benefit from the invention as a subsea load could be a subsea template, manifold or similar system. The launch and recovery system (700) consists of a docking system or ‘snubber’ (710), lifting winch (720) and crane (730) although alternative arrangements will perform the same function without impacting on the invention.

[0039] The AHC apparatus (100) provides several advantages. Fundamentally, canceling any heave motion at a load allows that load to be held steady while subsea so significantly improving docking, undocking, inspection and manipulation operations on subsea systems.

[0040] Positioning an AHC system near the load rather than aboard the vessel also provides several benefits. For example, when a typical vessel-based AHC system is used as part of deep water operations, the lifting arrangement can experience instability and synchronization issues as the lifting wire, umbilical or rope is likely not to be perfectly straight. Shortening and extending the wire, umbilical or rope may therefore only serve to remove the curve in the wire, umbilical. Embodiments of the invention avoid these problems by being placed at the load, and so suffer no impact due to the wire, umbilical or rope being straight or otherwise. There are passive heave compensation systems that offer this function. However embodiments of the invention provide active heave compensation in a significantly space efficient form.

[0041] The use of motors in the AHC apparatus (100), as opposed to crane-mounted or deckmounted rotating winches or a deck-mounted in-line cylinders for AHC, also provides several advantages. The use of motors, for example, avoids typical problems associated with winches such as inertia of the drum, tension control between a traction winch and a storage winch, etc. Moreover, the motors can be electrical, in which case the arrangement lends itself to subsea operations where the motors can be driven locally by batteries or similar energy storage systems. Electrical systems offer the advantage of mitigating any pollution effects due to loose hoses, etc. that are applicable to a hydraulic based system. At the same time, having the AHC apparatus be self-powered aids portability and reduces the need for significant installation on a vessel before use. Lastly, motors are typically lighter than the equivalent load bearing cylinders. Embodiments in accordance with aspects of the invention may therefore allow loads to be handled more efficiently than equivalent cylinder-based systems.

[0042] It should again be emphasized that the above-described embodiments of the invention are intended to be illustrative only. Other embodiments can use different types and arrangements of elements for implementing the described functionality. These numerous alternative embodiments within the scope of the appended claims will be apparent to one skilled in the art.

[0043] While a single drive assembly (200) is shown in the AHC apparatus (100), additional embodiments of the invention may utilize a greater number. Alternative embodiments may, as just a few examples, utilize 2 or even 4 drive assemblies without a fundamental redesign of the system or components. AHC apparatus in accordance with aspects of the invention are therefore scalable. As would be predicted, a greater number of drive assemblies increases the load capacity of an AHC apparatus at the cost of greater power consumption, greater weight, and greater cost. A single motor version with one 15 kilowatt (kW) motor may, as just an illustration, be capable of handling two metric tons (Te), while a two motor version with 30 kW motors may be able to accommodate 4 Te. These numbers, however, are merely illustrative and not intended to limit the scope of the invention.

[0044] Alternative embodiments of the invention may, as another example, not utilize a screw but instead may be supplied with another form of linear drive assembly such as a linear actuator or cylinder. In even other embodiments, a cylinder or linear actuator could be used in a different orientation within the scissor assembly to impart the necessary forces required to extend or retract the scissor assembly as is common in non-subsea scissor lift applications.

[0045] In addition, alternative embodiments of the invention may, as another example, not utilize power via a lifting umbilical (400), but instead may be supplied with battery power. Such power may be supplied by a battery pack included in the main chassis (105), for example. In even other embodiments, power may be supplied at the AHC apparatus by an alternative power solution such as a fuel cell.

[0046] It should also be recognized that, while the sets of gears (220)(225) in the illustrative, nonlimiting AHC apparatus (100) utilize multiple gears coupled to the screws (160) via a drive chain (230), alternative embodiments may utilize very different arrangements of gears for performing that function. Instead of utilizing one of each type of gear, alternative embodiments may, for example, comprise a respective set of gears for a given drive assembly that comprises two or more drive gears, two or more transfer gears, two or more pinions, or some combination thereof. Thus, it is reinforced that the arrangement of gears in the illustrative AHC apparatus (100) is exemplary only and is non-limiting with respect to the scope of the present invention.

[0047] In even other embodiments, the scissor assembly may consist of multiple or differently arranged ‘stages’. In one or more embodiments, for example, a scissor assembly may have two or more stages to increase the extension. At the same time, while the various electronic components in the illustrative AHC apparatus (100) (e.g., the heave sensor (320), the control circuitry (310), drive circuitry (350) and power distribution (330)) occupy a single subsea enclosure (300), alternative embodiments in accordance with aspects of the invention may locate their electronics elsewhere, such as within multiple subsea enclosures. In even other embodiments, some or all of the electronic components for an AHC apparatus may be located remote from the remainder of the AHC apparatus, such as on a vessel. Power, data and instructions may then be communicated between the remote electronic components and the remainder of the AHC apparatus via an umbilical cable or other communication medium (e.g., data and instructions by radio). Thus, an “apparatus” falling within the scope of the invention need not be unified in structure, but may be distributed in space.

[0048] All the features disclosed herein may be replaced by alternative features serving the same, equivalent, or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

Claims

Claims

What is claimed is:

1. An apparatus for use in combination with a sensor operative to detect heave motion, the apparatus comprising:

• a main chassis;

• a drive assembly, the drive assembly mounted to the main chassis and comprising a drive gear or cylinder;

• a scissor assembly, the scissor assembly translatably disposed within the main chassis and comprising of multiple mutually pivoting structural members that extend and retract along a vertical axis;

• control circuitry, the control circuitry operative to command the drive assembly to cause the scissor assembly to translate perpendicular to the main chassis based on the heave motion detected by the sensor.
2. The apparatus of claim 1, wherein the drive assembly comprises an electric motor, hydraulic motor, electric cylinder/ linear actuator or hydraulic cylinder.
3. The apparatus of claim 1, wherein the drive assembly comprises an electromagnetic brake, hydraulically actuated brake, mechanical brake or pneumatic brake.
4. The apparatus of claim 1, wherein the drive assembly comprises gears, sprockets and chain.
5. The apparatus of claim 1, wherein the main chassis defines a mounting platform defining a space therebetween.
6. The apparatus of claim 5, wherein the drive assembly is mounted to the mounting platform such that the drive or actuating gear occupies a portion of the space.
7. The apparatus of claim 1, wherein the scissor assembly terminates in a lifting point, hook or a ring.
9. The apparatus of claim 1, wherein the control circuitry is operative to command the drive assembly to cause the scissor assembly to translate perpendicular to the main chassis in a direction opposite to the heave motion detected by the sensor.
11. The apparatus of claim 1, wherein the sensor is mounted to the apparatus or in a location necessary to determine the appropriate heavy motion of the vessel.
12. The apparatus of claim 1, further comprising a battery.
13. The apparatus of claim 1, further comprising:

• a second drive assembly, the second drive assembly mounted to the main chassis and comprising a second drive gear or cylinder • wherein the control circuitry is operative to command the second drive assembly to cause the scissor assembly to translate perpendicular to the main chassis based on the heave motion detected by the sensor.
15. The apparatus of claim 1, further comprising a plurality of additional drive assemblies.
16. The apparatus of claim 1, further comprising a shear stop, the shear stop protruding into the main chassis or scissor assembly and mechanically limiting an extent of translation of the scissor assembly in the main chassis.
17. The apparatus of claim 1, further comprising:

• a vessel;

• lifting rigging, the lifting rigging attached to the vessel; and • a load;

• wherein the apparatus is suspended from the lifting rigging, and the load is suspended from the apparatus.
18. The apparatus of claim 17, wherein the apparatus is operative to reduce heave motion of the load relative to the heave motion detected by the sensor.
19. A method for reducing heave motion in a load suspended from a vessel, the method comprising the steps of:

(a) providing a sensor, the sensor operative to detect heave motion;

(b) suspending an apparatus from the vessel, the apparatus comprising:

(i) a main chassis;

(ii) a drive assembly, the drive assembly mounted to the main chassis and comprising a drive gear or cylinder;

extend and retract along a vertical axis;

(iv) control circuitry, the control circuitry operative to command the drive assembly to cause the scissor assembly to translate perpendicular to the main chassis based on the heave motion detected by the sensor; and (c) suspending the load from the apparatus

Intellectual

Property

Office

Application No: GB1617358.5