GB2487919A

GB2487919A - Lifting Rig for use in Lifting a Buoyant Load out of Water

Info

Publication number: GB2487919A
Application number: GB201102130A
Authority: GB
Inventors: Paul Frederick Jauncey
Original assignee: Gobbler Oil Recovery Boats Ltd
Current assignee: Gobbler Oil Recovery Boats Ltd
Priority date: 2011-02-08
Filing date: 2011-02-08
Publication date: 2012-08-15
Anticipated expiration: 2031-02-08
Also published as: GB2487919B; GB201102130D0

Abstract

A lifting rig is provided for lifting out of the water a buoyant load such as a bladder 19 containing oil recovered from an oil spill. The lifting rig comprises a sling assembly 301 having two opposed rigid side elements 310, 311 and a material sling 315 attached along two opposite sides to respective ones of the rigid side elements. The sling assembly is attached to a rigid lifting frame 303 by lifting lines 302 which are of a length such that the sling provides a cradle for supporting a load along its length when lifted clear of the water. The lifting frame serves to space out the lifting lines. The sling assembly has a buoyancy distribution such that, when lowered into water, the sling stays afloat along one side and sinks on the other side to permit a buoyant load to be manoeuvred over the sling. Preferably the sling is made from a non-buoyant material and one of the rigid side elements is made buoyant by means of floats 340. Detachable end panels (330, figure 1) may close off the ends of the cradle formed by the sling in lifting a load.

Description

Lifting Rig for use in Lifting a Buoyant Load Out of Water

BACKGROUND

[0001] Oil spills at sea, in lakes, rivers, harbours, marinas or coastal areas are a serious environmental hazard. Wild life, marine life and coastal welfare, including commercial businesses, are at risk with each and every incident. In responding to an oil spill, critical factors are speed of response and operational efficiency. These factors tend to favour the use of small skimmer-equipped vessels that can be rapidly transported to the area of an oil spill, can work multiple environments, and with the use of the latest drum skimmer technology, are reasonably efficient in recovering oil. However, small oil spill recovery vessels inherently have limited onboard oil storage capacity and this has led to the use of floating bladders for the storage of recovered oil.

[0002] Generally, a bladder filled with recovered oil is emptied by being pumped out to a tank on a mother ship or dock with the bladder still in the water. However, this is not always possible, for example due to adverse sea conditions or due to extreme cold causing the oil to become waxy and difficult to pump. Also, where pumping facilities are distant from an oil spill, towing filled bladders all the way back to the pumping facility increases the risk of damage to the bladders and possible oil leakage. The risk of bladder damage and oil leakage is also increased by having a bladder alongside a mother ship or marine structure during pumping out as ships and marine structures harbour marine life such as barnacles that can easily damage the bladder. There are therefore advantages to lifting a bladder out of the water for pumping out or storage aboard a mothership or on a dock; however, this is not usually done due to the fragility of the fabrics used to construct bladders.

SUMMARY OF THE INVENTION

[0003] According to one aspect of the present invention, there is provided a lifting rig for lifting a buoyant load out of water, the lifting rig comprising: a sling assembly comprising two opposed elongate rigid side elements, and a material sling attached along two opposite sides to respective ones of the rigid side elements; a rigid lifting frame; and lifting lines attaching the sling assembly to the lifting frame, the lifting lines connecting to the rigid side elements of the sling assembly such that the sling provides a cradle for supporting a load along its length when lifted clear of the water; the lifting frame serving to space out the lifting lines and to provide for connection of the lifting rig to a crane or other lifting mechanism; and the sling assembly having a buoyancy distribution such that when lowered into water the sling stays substantially afloat along one side whereas the remainder of the sling can sink thereby to permit a buoyant load to be manoeuvred over the sling between the lifting lines connected to the two rigid side elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Embodiments of the invention will now be described, by way of non-limiting example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagram illustrating operation of an oil spill recovery vessel which is arranged to store recovered oil to a towed bladder; Figure 2 is a perspective view of a lifting rig for use in lifting a bladder containing recovered oil out of the water; Figure 3A is an end view of the Figure 2 lifting rig at a stage during its use when it has been lowered into the water and a bladder is being manoeuvred into position for lifting; and Figure 3B is an end view of the Figure 2 lifting rig at a stage during its use when the rig is just taking the weight of a bladder immediately prior to lifting.

DETAILED DESCRIPTION

[0005] Figure 1 depicts an oil spill recovery vessel 10 provided with a skimmer unit 11 carried between twin hulls of a catamaran bow section 12 of the vessel 10. The skimmer unit recovers oil from an oil spill 6 on a body of waterS as the vessel 10 moves through the oil spill; the recovered oil is then transferred to a towed bladder 19 through a flexible oil transfer hose 17 that is suspended from a towing cable 14 by slip rings.

[0006] The Figure 1 arrangement is simply illustrative of one way in which floatable storage bladders can be used for storing oil recovered from an oil spill; more conventionally, recovered oil is temporarily stored in small onboard tanks before being transferred to a bladder moored alongside during breaks in the skimming operation.

[0007] Suitable floatable bladders for storing recovered oil are available from Elastec / American Marine, IL, USA in standard sizes ranging from 1.89 cubic metres (500 US gallons) to 13.3 cubic metres (3500 US gallons), the latter being 16.5 m in length. Bladders intended to be used as towed bladders will generally be equipped with a towing bridle and be hydro-dynamic when towed. Apart from possible bow and stem features, such bladders are generally of a uniform depth and cross section over their length.

[0008] Upon a bladder 19 being filled, it is generally towed to a mothership or to a shore facility for further handling. According to the present invention, a lifting rig is provided for use in lifting an oil-containing bladder out of the water either to enable the bladder to be temporarily stored or to be pumped out for immediate return to service.

[0009] One embodiment of the lifting rig will now be described, by way of example, with reference to Figures 2 and 3. The lifting rig 300 is shown in Figure 2 in a position clear of the water but without a bladder held in the rig. The lifting rig 300 comprises a sling assembly 301 arranged to provide a cradle for supporting a bladder substantially horizontal along its length during lifting, and a rigid lifting frame 303, here of rectangular form, that is connected to the sling assembly30l by lifting lines 302. The lifting frame 303 serves to space out the lifting lines 302 and to provide for connection of the lifting rig 300 to a ship or dockside crane or other lifting mechanism (not shown); in the present embodiment, this connection to a lifting mechanism is provided by lines 304 extending between the lifting frame 303 and a lifting head 305 (such as a crane ring) to which a cable 306 of the lifting mechanism attaches.

100101 The sling assembly comprises two opposed elongate rigid side elements 310 and 311, and a material sling 315 of rectangular form that is attached along two opposite sides to respective ones of the rigid side elements 310, 311. In the present embodiment the side elements 310, 311 are made of hollow tubes for lightness (for example, marine grade aluminium but other suitable materials can be used). Furthermore, to facilitate stowage, each of the side tubes 310, 311 is formed from three identical lengths assembled together by tube joiners(not shown) that insert into adjacent ends of tube lengths to be joined, the joiners being secured in place by screws or pins (in Figure 2, reference 312 indicates the joins between tube lengths). It will be appreciated that the side elements 310, 311 can be differently formed, for example, each could be made up of different number of sections or simply constituted by a single length of solid material.

[00111 Whatever its form, each side element 310, 311 is provided along its top surface with a plurality of apertured metal lifting gussets 318 (for example, welded in position) to which the lifting lines 302 attach (for example, using shackles, the shackle pins passing through the apertures in the lifting gussets 318). In the illustrated embodiment, each of the three tube lengths making up the side elements 310, 311 is provided with two lifting gussets 318.

100121 The lifting lines 302 which connect the sling assembly 301 to the lifting frame303 are of equal length and are, for example, 7x19 flexible stainless steel wire rope or similar, swaged or spliced with thimbles inserted to provide loop eye rope ends.

[0013J As for the sling 3 15, this is made of a material resistant to salt water and an oily environment. For reasons explained below, the sling material is preferably (but not necessarily) one that does not float. A suitable material for the sling is the marine range of the fabric marketed under the trademark Sunbrella' by Glen Raven Inc. North Carolina, USA; other suitable materials are most sailcloth and canvas materials. The main body of the sling 315 is formed by a rectangular sheet of material of a suitable length and width to accommodate any of a range of sizes of towable bladder, the width of the sheet being such that when passed around the underside of a floating bladder, the sheet will extend up on both sides higher than the mid-point of the sides of the bladder. By way of example, the main body of the sling is dimensioned 9m by 2. 8m (in which case suitable dimensions for the lifting frame 303 would be 9m by 1.8m).

[0014] The main body of the sling 315 is, in the present embodiment, reinforced with lengths of webbing 318 spaced at 300mm centres and passing under the main material body and ending in loops 317 through which the two side elements3 10, 311 extend thereby attaching the sling 315 to these side elements 310, 311. It is the webbing that takes the weight of a bladder cradled in the sling assembly 301. The webbing loops 317 are made large enough to permit the side elements 310, 311, with attached gussets 318, to be passed through the loops during assembly and disassembly of the sling assembly 301. The main body of the sling can be further strengthened by stitching.

[0015] The two ends of the elongate cradle formed by the sling 315 can be closed off by respective detachable end panels 330 only one of which is illustrated in Figure 2; the illustrated end panel 330 is shown prior to attachment to the main body of the sling.

Attachment of each end panel 330 to the sling main body is effected by using plastic ties (or similar coupling means) to join loops 331 sewn onto the end panels 330 with loops 332 sewn along the end edges of the main body of the sling 315.

10016] Further series of attachment loops 333, 334 may also be provided at intermediate positions along the length of the sling body in order to enable the end panels 330 to be attached at positions appropriate to the length of a bladder to be lifted where the bladder is shorter than the full length of the sling.

[0017] In order to permit water to drain away as a bladder is lifted out of the water, the method of attachment of the end panels 330 to the main body of the sling 15 should preferably be such as to permit water to drain out therebetween.

[0018] The sling assembly 301 is arranged to have a buoyancy distribution such that when lowered into water, the sling 315 stays afloat along one side whereas the remainder of the sling can sink; as will be explained below, this facilitates the manoeuvring of a filled bladder over the sling and between the two rows of lifting lines302. In the present embodiment, the desired buoyancy distribution is achieved by the use of a non-floating material for the sling and the provision of an appropriately sized set of floats 340 securely attached to the side element 311. Other arrangements are possible, for example, a buoyant sling material could be used and suitable weights the distributed over the sling to give it overall negative buoyancy; furthermore, rather than attaching floats to the side element 311, the latter could be made from a sealed tube of sufficient displacement to ensure that it floats and can buoy up the side of the sling attached to the side element 311.

[00191 Regarding the rectangular lifting frame 303, this comprises two elongate side members 320, 321 interconnected, for example, by four spreader bars 322. The side members 320, 321 and spreader bars 322 are, for example, made from aluminium tube. The side members 320, 321 can, like the side elements 310, 311 of the sling assembly 301, be made up of multiple shorter lengths (in the present case, three per side member) joined together to enable the side members 320, 321 to be dissembled for stowage. The spreader bars 322 are preferably also detachable from the side members to facilitate stowage.

[0020] Along its bottom surface each side member 320, 321 is provide with a series of apertured gussets 325 corresponding in number and positions to the gussets 318 on the side elements 310, 311 of the sling assembly 301. The upper ends of the lifting lines 302 are shackled to the gussets 325.

[0021] A further series of apertured gussets 326 is provided along the top surface of each side member 320, 321 to provide attachment points to which the lines 304 are shackled.

Like the lifting lines 302, the lines 304 are, for example, 7x19 flexible stainless steel wire rope or similar, swaged or spliced with thimbles inserted to provide loop eye rope ends.

[0022] The upper gussets 326 are located along the side members 320, 321 at positions corresponding to the lower gussets 325. The gussets 325, 326 are, for example, welded to the side members 320, 321. Each upper gusset 326 is angled such as to line up with the attached line 304 during lifting (see Figure 3A) so as to reduce stress on the weld joining the gusset to the side member.

100231 In an alternative embodiment, each pair of gussets 325, 326 is manufactured as a single piece suitably cranked' to give the desired angling of the upper gusset 326. This single piece is then fitted through a close-fitting slot cut top and bottom of the relevant side member 320, 321, and welded in place top and bottom.

[0024] The lengths of the lines 302 and 304 are such that the sling assembly 301 provides a cradle for supporting a bladder substantially horizontally along its length when lifted clear of the water.

100251 All components including the various lines 302, 304, the side elements 310, 311 and sling 315 of the sling assembly 301, and the elements of the lifting frame 303 are sized to suit the maximum weight of bladder to be lifted plus a safety margin.

[0026] In operation of the lifting rig 300, after assembly of the sling assembly 30 land lifting frame 303 from the kit' of their component parts (including the shackling of all lines 302, 304 in place and attachment of the buoys 340), the lifting rig 300 is attached to the lifting cable 306 of a crane or other lifting mechanism. The lifting rig is then raised clear of the deck or dockside to assume its configuration as illustrated in Figure 2. The lifting rig 300 is then swung out over the water and lowered.

[0027] As the sling assembly 301 enters the water, it will sink under its own weight except along the side corresponding to the side element 311 to which the floats 340 are attached (see Figure 3A). The lifting lines 302 attached to the side element 311 will slacken off but those attached to the side element 310 remain taut. Lowering of the lifting rig 300 is stopped when the side element 310 has reached a sufficient depth to ensure that the sling 315 is well under water except for a near vertical portion attaching to the side element 311 (in Figure 3, the water level is indicated by wavy line 335). A clear channel is now defined between the lifting lines302 attached to the side element 310, and the side element 311 kept afloat by the buoys 340. A full bladder 19 can now be manoeuvred into this channel from one end until the full length of the bladder 19 lies over the sling 315; this manoeuvring will generally be done by the crew of an attending craft, for example, the oil spill recovery vessel responsible for filling the bladder.

[0028] With the bladder in position the crane is operated to start raising the lifting rig 300.

As the lifting frame 303 rises, the side element 310 is raised out of the water pulling with it the corresponding side of the sling 315 which thereby wraps around the lower half of the bladder. In due course, the lifting lines 304 on both sides of the bladder 19 become taut (see Figure 3B) and the bladder sits in an elongate cradle formed around it by the sling assembly 301. The end panels 330 can now be attached to close off the cradle and support the ends of the bladder (in fact, the end panels can be attached by their middle loops 331 at the time of the assembly of the lifting rig, leaving final closure until the bladder is nestling in the cradle formed by the sling 315).

[0029] Continued operation of the crane lifts the bladder 19 out of the water supported along its length by the sling assembly 301 in a substantially horizontal position. Water within the cradle formed by the sling assembly 301 drains out through the gaps between the end panels 330 and the main body of the sling 315. The lifting frame 303 automatically prevents the lifting lines 302 from closing and cutting into the filled bladder, or exerting side pressure to the filled bladder during the lifting process.

10030] The bladder 19 is in due course deposited on the deck of a mother-ship deck or on the dockside and is then pumped out in situ before being lifted back into the water using the lifting rig 300.

[0031] As illustrated in Figure 3B, there will be some slight lateral bowing of the bladder as it is lifted. Some forms of floatable bladders are given hydrodynamic shape with shallow V-bottoms which are readily accommodated by the sling during lifting. Furthermore, although the bladder 19 is shown as floating only partially submersed, the bladder may, in practice, be fully submersed, floating just under the surface of the water.

10032] It will be appreciated that many variations are possible to the illustrated forms of the lifting frame and sling assembly. For example, the end panels 330 can be omitted entirely if the bladder ends are sufficiently self supporting with the bladder full. Where provided, the end panels can be permanently attached to the main body of the sling (for example, cut from the same sheet) over a small arc.

[0033] Rather than the main body of the sling 315 being one continuous sheet ofmaterial, the sling material can be non-continuous ( for example, apertured or net-like in form) provided the gaps between the sling material elements are sufficiently small to avoid undue load concentrations on the bladder; the sling can even be made up solely of closely spaced webbing strips.

[0034] The lifting frame need not be designed for disassembly. The shape of the lifting frame can be varied provided it produces the appropriate spreading function in relation to the lifting lines 302; the manner in which the lifting frame is connected to the lifting cable of a crane or other lifting mechanism can also be varied from that shown as will be appreciated by persons skilled in the art.

[0035] To facilitate connection of the lines 304 to the lifting frame 303 during assembly of the lifting rig, the ends of the lines 304 and the gussets 326 are color coded to match the appropriate length of line 304 to the corresponding gusset 326. The floats 340 are preferably brightly colored or otherwise made highly visible to help the crew of the attending craft identify the position of the sling assembly, particularly during night-time operations.

[0036] It will be appreciated that reference above to a filled' bladder covers bladders that may be only partly full of recovered oil as well as completely full bladders. Furthermore, although the lifting rig 300 has been described in relation to lifting oil-filled bladders, the lifting rig can equally be used to lift other buoyant loads out of water, a buoyant load' in this context meaning a load that floats on or near the surface of salt or fresh water.

[0037] The provision of a practical lifting rig 300 permitting filled bladders to be lifted out of the water gives a number of advantages, including: * the reduced possibility of damage to the bladder, and consequential oil leakage, resulting either from a need to tow filled bladders through the water over extended distances for emptying, or from collision or contact between the bladder and a mother-ship or dock when pumping out the bladder (marine growths such as bamacles present a particular hazard to bladder fabric in this context).

* elimination ofthe need to pump out the contents of a bladder in adverse conditions such as rough seas or in cold or Arctic conditions when collected oil waxes solid and cannot be pumped; instead, the storage bladders can be lifted aboard a mother ship / ashore for emptying.

The above-described form of lifting rig 300 is of particular practicality due to the following features: * the lifting rig facilitates the easy, safe positioning of the bladder into the sling; * the sling assembly is supportive along the length and breadth of a filled bladder to prevent unnecessary pressure build up within the bladder, and subsequent leakage from the bladder relief valve (the end panels providing support to the bladder end where needed); * the lifting rig can be disassembled for ease of storage and is lightweight for ease of handling.

However, as already indicated, at least the last of these features need not be present in all embodiments of the lifting rig.

Claims

CLAIMS1. A lifting rig for lifting a buoyant load out of water, the lifting rig comprising: a sling assembly comprising two opposed elongate rigid side elements, and a material sling attached along two opposite sides to respective ones of the rigid side elements; a rigid lifting frame; and lifting lines attaching the sling assembly to the lifting frame, the lifting lines connecting to the rigid side elements of the sling assembly such that the sling provides a cradle for supporting a load along its length when lifted clear of the water; the lifting frame serving to space out the lifting lines and to provide for connection of the lifting rig to a crane or other lifting mechanism; and the sling assembly having a buoyancy distribution such that when lowered into water the sling stays substantially afloat along one side whereas the remainder of the sling can sink thereby to permit a buoyant load to be manoeuvred over the sling between the lifting lines connected to the two rigid side elements.
2. A lifting rig according to claim 1, wherein the sling is made from a non-buoyant material and one of the rigid side elements is made buoyant by means of floats whereby to keep the corresponding side of the sling afloat when the sling assembly is lowered into the water.
3. A lifting rig according to claim br 2, wherein the material sling comprises a main body of material reinforced by webbing strips that loop around the rigid side elements.
4. A lifting rig according to claim 1 or claim 2, wherein the material sling comprises a main body made from an apertured or net-like material, or from closely spaced webbing strips extending between the side elements.
5. A lifting rig according to claim 1 or claim 2, wherein the material sling comprises closely spaced webbing strips extending between the side elements.
6. A lifting rig according to any one of the preceding claims, wherein the sling assembly further comprises detachable end panels for closing off the ends of the cradle formed by the sling in lifting a load.
7. A lifting rig according to claim 6, wherein the sling assembly is adapted to enable the end panels to be attached at intermediate positions along the cradle according to the size of the buoyant load to be lifted.
8. A lifting rig according to any one of the preceding claims, wherein at least the lifting frame can be dissembled for stowage.
9. A lifting rig according to any one of the preceding claims, adapted to lift a buoyant load in the form of a towable bladder at least partially filled with oil.19. A kit of parts that can be assembled to provide a lifting rig according to any one of the preceding claims.