GB2549488A

GB2549488A - Active heave compensation apparatus

Info

Publication number: GB2549488A
Application number: GB1606741.5A
Authority: GB
Inventors: David Screaton Lee
Original assignee: Screaton And Ass
Current assignee: Screaton And Ass
Priority date: 2016-04-18
Filing date: 2016-04-18
Publication date: 2017-10-25

Abstract

An active heave compensation device has a framework 1 supporting a rotatable armature 3. This may be driven by a plurality of electrical motors 2 which may engage with the circumference of the armature via spur gears and cause a slewing action. Rotatable sheaves 5 may be located diametrically opposite each other on the armature. A wire rope or cable 6 may be passed over a first guide pulley, around the sheaves 5 and then exits the device via a second guide pulley 7. In use the armature rotates causing the sheaves to pull the cable into a tortuous path (Fig 1). The device damps out shock loading on the cable and may be used in a marine environment with the device located between a main lifting winch (Fig 2, 9) and a crane or derrick. A motion reference instrument (Fig 2, 14) measures movement of the vessel and acts to control the electric motors. The device also reduces cyclic bending stresses of the rope or cable. The device may rotate in the vertical or horizontal planes.

Description

FIELD AND BACKGROUND OF INVENTION

[0001] The invention is generally related to the lifting of marine suspended loads, more particularly, to an arrangement for the active heave compensation of the load.

[0002] Marine loads are suspended from shipboard cranes or winches when being deployed or 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 that frequently leads to damage to the load, the lifting arrangement or the location the load is to be left in.

[0003] There are two primary classifications of heave compensation: Passive Heave Compensation and Active Heave Compensation. Passive heave compensation achieves heave compensation without additional power or control/ instrumentation. Examples of passive heave compensation would include dampers, shock absorbers, springs, etc. Active heave compensation utilizes power and instrumentation such as a Motion Reference Unit to achieve heave compensation.

[0004] Heave compensation can be applied by lengthening and shortening the lifting wire using such arrangements as a rotating winch drum or a sheave arrangement that expands or contracts via cylinders in response to heave motion. These can be considered the typical methods for heave compensation 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. The invention has similarities to the sheave/ cylinder arrangement in that it is located on the vessel between the lifting winch and the point where the lift rope exits the vessel however it differs in that the lift rope is routed through sheaves within the device that are mounted on a rotating mechanism to accumulate rope rather than accumulation through extending cylinders and therefore the distance between the sheaves. The advantages of using a rotating mechanism rather than cylinders are that the space used by the device is significantly less, the rope is subjected to less bending fatigue and also the methods for kinetic energy recovery are more effective when used with motors than cylinders.

[0005] By using sheaves and the routing of the lift rope around them as the means to accumulate the lift rope the space advantages, when compared to a traditional cylinder arrangement, become clear as increasing the ability of the system to store rope becomes a function of the sheave diameter rather than the cylinder stroke. For larger storage the sheave diameter is increased which increases the circumference relative to PI whereas for larger storage using cylinder systems the cylinder must become longer leading to a proportionally larger mechanism. The size of a mechanism on a marine vessel is of paramount importance as deck space is always at a premium. The invention offers a more compact package for the same storage performance of traditional systems.

[0006] Lifting rope has a finite life that is reduced when continually loaded and offloaded from a drum, routed through sheaves or subjected to cyclic loading. Active heave compensation is known to significantly increase fatigue on lifting ropes using traditional mechanisms as a winch based solution damages the lift rope on the drum and a cylinder based system passes the lift rope through a number of sheaves. The invention improves the situation by only applying the sheaves to the rope when necessary and when it does, the rope is generally only required to pass across a part of the circumference as opposed to ¾ of the circumference which is the case for most cylinder based arrangements.

[0007] As implied, there are in existence a variety of both active and passive heave compensation systems. The key difference however is that this invention uses a sheave route that rotates to accumulate lift rope as the prime mover. When combined with electric motors, the invention significantly improves deck space utilization and power manipulation for offshore lifting operations.

SUMMARY OF INVENTION

[0008] The present invention is directed to an active heave compensation device installed aboard a marine vessel within the lift rope route arrangement of a typical marine crane or winch. The device consists primarily of a main chassis that supports the drive system and a rotating structure that includes at least two sheaves. The drives interface with the rotating structure by means of a slew ring and spur gears or a similar geared, chain or high friction arrangement. As the rotating structure does not complete 360 degrees of movement a cylinder could be used for limited rotation however the primary approach is expected to be the use of motors. The main chassis would include the drives and drive support systems as well as any stored energy units and power distribution. Additional equipment such as motion reference units, power generation, kinetic energy recovery systems, telemetry systems, etc. could also form part of the main chassis in order to provide more lifting functions.

[0009] The primary arrangement of the invention is expected to be in the vertical orientation however it will also function in a horizontal arrangement that may have advantages when vertical space is limited.

[0010] 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

[0011] 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: [0012] GENERAL ARRANGEMENT is an elevation of the basic arrangement illustrating the full, stand-by and empty states.

[0013] FIG. 1 illustrates the basic ‘accumulation’ process [0014] FIG. 2 is an indication of the installation aboard a marine vessel.

[0015] FIG. 3 illustrates the use of the invention with a typical marine vessel winch.

[0016] FIG. 4 illustrates the use of the invention with a typical marine crane.

[0017] FIG. 5 illustrates the use of the invention in a horizontal orientation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As seen in GENERAL ARRANGEMENT the marine lifting apparatus is generally comprised of a main chassis (1) that supports the motors and gearboxes (2) and the rotating mechanism (3). The motors (2) are arranged logically around a slew ring (4).The rotating mechanism includes the accumulation sheaves (5). Lift rope (6) is shown to route through the invention. Routing sheaves (7) are shown in order to illustrate their potential location however their inclusion is not necessary for the claims of this invention. For ease of illustration and clearly illustrating the inventive concept, it should be noted that drive control systems, power distribution, power transmission and power storage are not shown in the drawings.

[0019] As seen in FIG. 1, the rotation of the rotating mechanism (3) can be shown to pull lift rope (6) into the marine lifting apparatus [0020] Typical marine lifting arrangements are illustrated in FIG. 3 and FIG.4.

[0021] An alternative orientation is illustrated in FIG. 5. This horizontal arrangement illustrates that the drive arrangement could be a circumferential arrangement rather than a slew ring.

[0022] As seen in FIG. 2 and with reference to the GENERAL ARRANGEMENT, the device (8) is located between the winch (9) and the over-boarding arrangement (10). As the vessel (11) is supported by the sea (12), when the sea (12) raises and lowers due to wave action, the vessel (11) will also raise and lower. If the device (8) was inactive, the load (13) would raise and lower in time with the movements of the vessel (11). When the device (8) is active, the motion reference instrumentation (14) detects the motion and actuates the motors (2) which in turn rotates the rotating mechanism (3) in such a manner that the lift rope (6), and therefore the load (13), is raised or lowered in an opposite direction to the heave motion of the vessel (11). The net effect is that the load (13) will be able to be positioned without having to consider the heave effect of the vessel (11).

[0023] The invention provides several advantages.

[0024] One advantage provided by the invention is that motors can be used as the prime mover without typical problems associated with winches such as inertia of the drum, tension control between a traction winch and a storage winch, etc. This allows for smaller motors for the same lifted load.

[0025] Another advantage is that when motors are used, kinetic energy recovery systems such as a spinning flywheel are easily implemented. Utilizing kinetic energy recovery systems can lead to less power consumption.

[0026] Another advantage is that motors can be electrical which offers the advantage of mitigating any pollution effects due to loose hoses, etc. that are applicable to a hydraulic based system.

[0027] Another advantage is that the lift rope is routed around sheaves that can be sized to store more rope within the system through increasing the circumference without linearly increasing the size of the system which is the case with cylinder based systems. This leads to a comparatively smaller overall system which is a major advantage to space restricted environments such as a marine vessel.

[0028] A further advantage is that the lift rope encounters less cyclic bending over sheaves (CBoS) when compared to a cylinder based system as the lift rope is only routed around sheaves when required whereas the rope must always traverse multiple sheaves when routed through a cylinder system. This feature reduces the fatigue damage to the lift rope and therefore extends the lift ropes operational life.

[0029] While specific embodiments and/or details of the invention have been shown and described above to illustrate the application of the principles of the invention, it is understood that this invention may be embodied as more fully described in the claims, or as otherwise known by those skilled in the art (including any and all equivalents), without departing from such principles.

Claims

1. An active heave compensation device comprising of a drive system that actuates a rotating mechanism consisting of an armature that supports two sheaves that accumulate lift rope when the armature is rotated.

2. An active heave compensation device according to claim 1 in which the drive system is by motors, gearboxes, spur gears and slew rings.

3. An active heave compensation device according to claim 1 in which the drive system is by motors driving the rotating mechanism at the circumference of the mechanism.

4. An active heave compensation device according to claim 1 in which the drive system is by cylinders, bearings and linkages.

5. An active heave compensation device according to claim 1 in which the rotating mechanism contains multiple sheaves in order to accumulate more lift rope that a dual sheave arrangement.

6. An active heave compensation device according to claim 1 in which the lift rope is diverted through or around incoming and/ or outgoing sheaves or diverting devices such as a chute or low friction profiled surfaces to improve the lift rope routing.

7. An active heave compensation device according to the preceding claims that can be vertically or horizontally mounted depending on the requirements of the environment.