GB2157628A - Buoyancy lifting apparatus - Google Patents

Abstract

Buoyancy lifting apparatus for lifting sunken vessels or other objects has at least one horizontal array of upright cylindrical buoyancy cells 12 each made of flexible material reinforced by synthetic plastics material. The cells 12 are individually secured at their lower end by ropes 42 to a frame 10, the ropes 42 being attached to stiffening rings 40 attached to the cells 12. If multiple arrays are used they are arranged one above the other. The frame 10 is either wholly beneath the cells 12 or includes an upright sub-section which can be secured to the side of a vessel to be lifted. The frame can be of box shape at least partly accommodating the cells 12 within its boundary, one upright side of the frame being securable to a vessel's side so that it can be lifted above the sea surface. <IMAGE>

Description

SPECIFICATION Buoyancy lifting apparatus The invention relates to buoyancy lifting apparatus.

Various forms of apparatus have been proposed for lifting sunken or grounded vessels or other sunken objects by means of the buoyancy of chambers or bags into which air is introduced underwater.

For example, multiple hollow steel submersible pontoons to receive air are attached to lifting frameworks described in specifications Nos.

378166 and 687825. A single submersible fabric balloon-like container open at the bottom is proposed in specification No. 446648. A plurality of semi-submersible upright hollow steel columns to receive air form part of a lifting platform described in specification No. 568612. In specification No.

1190621 a large vessel such as a tanker has a horizontal array of open bottomed air compartments in the base of its hull to create buoyancy for refloating the vessel if it runs aground.

However, such proposals suffer from the following drawbacks: Rigid steel air containers are bulky and relatively heavy. Accordingly they are difficult to handle and relatively few can be taken on deck on a salvage vessel.lt is difficult to remove air from inside lifting bags in order to collapse them for stowage on board the salvage vessel. Furthermore, the bags expand as the lift progresses which limits the lifting capacity. A single balloon of the kind proposed also has very limited lifting capacity. Accordingly, the methods actually used currently for lifting objects from the seabed are restricted to direct lifting from the salvage vessel at the surface using relatively heavy equipment or by attaching one or more air bags each independently secured to the object to be lifted.

The object of the invention is to provide buoyancy apparatus in which those drawbacks are reduced or eliminated.

Buoyancy lifting apparatus according to the invention comprises a frame which is securable to the object to be lifted and at least one horizontal array of buoyancy calls each having means in the region of its lower end by which the cell is individually secured to the frame, each cell being made of flexible material so as to be collapsible from a working shape in which the cell is an upright hollow cylinder open at the lower end and closed at the upper end by an upwardly convex end wall and the apparatus also comprising means for admitting air into each cell.

Preferably each cell has in the region of its lower and a circumferential stiffening ring at which the cell is secured to the frame.

Preferably each cell is secured to the frame by ropes.

Preferably the cells are releasably retainable each in collapsed shape.

Apparatus will now be described by way of example to ilustrate the invention with reference to the accompanying drawings in which: Figure 1 is a schematic three dimensional view of part of a vessel having two sets of apparatus secured to its sides for lifting: and Figures 2 and 3 are respectively a schematic side elevation and a plan of cells forming part of the apparatus of Figure 1, the elevation being partly in vertical section.

The apparatus shown in the drawings includes a frame 10 (Figure 1) and cells 12 (Figures 2 and 3) secured to the frame 10. As shown in Figure 1 the frame 10 is of rectangular box shape made up of elongate vertical steel members 14, elongate horizontal steel members 16, horizontal steel cross-ties 18 and steel bracing struts 20.

Each frame 10 is shown secured to a respective side of a sunken vessel 22 by means of steel hawsers or chains 24.

Each frame 10 contains at least one and preferably several horizontal arrays of buoyancy cells 12 (Figures 2 and 3) arranged above the base members of the frame.The number of arrays depends on the size of the vessel to be lifted but where several arrays are used they are arranged one above the other with each cell individually secured directly to the base of the frame 10. The topmost cells 12 may protrude partly above the top of the frame 10.

Figures 2 and 3 show parts of two arrays 30, 32 one above the other each array containing several cells 12 each of which is shown in its working shape in which it contains air under pressure in a volume 34 above a surface 36 of the seawater. In that shape each cell 12 is an upright, hollow cylinder open at its lower end and closed at its upper end by an upwardly convex end wall 38. Each cell 12 has in the region of its lower end a steel stiffening ring 40 having means (not shown) by which ropes 42, for example of polypropylene, can be secured to the rings 40. The ropes 42 secure the cells 12 individually, directly to the frame 10.

Each cell 12 preferably has four ropes 42 spaced about the cell at 90 and the ropes 42 descend to four equiangularly spaced points (Figures 2 and 3) on the frame members 16. Two securing points are on a common member 16 and the two other points are on the neighbouring members 16.

Each cell 12 is made of a flexible airtight material such as a rubberised material reinforced with synthetic plastics filaments of material such as that sold under the trade mark "Nylon". Each cell 12 has an internal body 50 of buoyancy synthetic plastics foam material which ensures that the cell 12 will readily rise from a collapsed shape (not shown) to its working shape as shown. It is preferred that each cell 12 is retained when inoperative in its collapsed shape (not shown) in which the end wall 38 is close to the ring 40 and all the arrays are close to the base of the frame 10.Releasable means (not shown) are preferably provided for each cell 12 to retain it in its collapsed shape.

The tops of the cells 12 in array are interconnected by horizontal ropes 60 of synthetic plastics material secured to rings of metal or synthetic plastics material attached to the end walls 38.The ropes 60 ensure no strain is imposed on flexible air tubes 62 of rubber or synthetic plastics material, which interconnect the air volumes 34 of the cells 12 and which are secured at their ends to the end walls 38 at ports therethrough.

The cells 12 are arranged so as to exert lifting force on the frame 10 as uniformly as possible and each cell preferably has a valve or other means (not shown) by which air can be released from the cell to control buoyancy. The frame 10 may have provision (not shown) for attachment to one end of a cable which passes through a pulley block for anchoring to the seabed. The other end of the cable is secured to a winch on board the salvage vessel so that, by paying out cable from the winch, the rate of lift can be controlled.

Operation The frames 10 are lowered by derrick or crane from the salvage vessel to their positions alongside the sunken vessel 22 and secured by the hawsers 24. At this time the cells 12 are all releasably retained in collapsed shape so that the cells contain little air and have minimal buoyancy.When the frames 10 are secure the releasable means retaining the cells 12 collapsed are freed. Air is pumped from the salvage vessel to the pipes 62 and thence into the cells 12 to increase their buoyancy and lift the vessel 22. Each cell 12 exerts its own lift force through its four ropes 42 directly onto a member of the frame 10.Thus the cylindrical wall of each cell 12 is subjected to the vertical stress due to the lift force and the hoop stress due to the air pressure. The end wall 38 is subjected to corresponding curvilinear and hoop stresses.The symmetry of lift and the pressures in the cells 12 are controlled by control of the supply of air to individual cells, or groups of cells, and by control of the release of air from cells 12, whether under the control of divers or remotely from the salvage vessel.

The apparatus is very convenient to use and al lows relatively rapid operations underwater because the cells 12 do not each have to be secured to the vessel 22. The frame 10 is secured to the vessel 22 relatively quickly.

The frame 10 can readily be extended by module assembly and the number of cells in each array, their distribution and the number of arrays is read ily variable to suit different salvage operations.

The construction of each cell 12 is quite simple and a standard- cell is useful in a very wide range of magnitudes of lift. For example a typical size of standard cell 12 would be 1.83 Metre (6 feet) high and 0.76 m. (2.50 ft.) in diameter its volume being 0,83 Cubic Metres (29.40 Cubic ft.).This gives a maximum buoyancy of 853 Kilogrammes (0.84 Tons).

For example, for a vessel of deadweight508,000 kg. (500 Tons) and allowing an additional 508,000 kg. (500 Tons) for seabed suction and contingen cies, a total lift of 1,016,000 kg. (1000 Tons), some 1-200 cells 12 can be used. Conveniently they would be arranged on both sides of the hull in two 10 x 30 arrays of cells. It would be convenientto use frames 10 whose plan proportions are 9.14 m.

x 27.45 m. (30 ft. x 90 ft.) allowing a space in plan of 0.92 m. x 0.92 m. (3 ft. x 3 ft.) for each cell 12.

This gives a lift force of 2044 kgisq.m. (0.187 Tons per sq. ft.).

Typically the maximum air pressure in the air volume 34 at the top of each cell 12 is some 18,410 N/sq.m. (2.67 Ibs. per sq. inch). The resultant working stress in the fabric of the cell is some 804 kgf m. (45 Ibs. per inch) which is easily within the strength of the reinforced material envisaged.

In modifications (not shown), the frame may consist only of horizontal members including longitudinal and transverse members, all the cells 12 being above the frame. Such a frame would be secured to the vessel by means extending downwardly beneath the frame: or the frame may consist of a section similar to that modification just mentioned connected to an upstanding sub-section made up of upright members and horizontal members. The sub-section is securable against the side of a vessel or other sunken object to be lifted; if required that sub-section is hingedly connected to the remainder of the frame so that it can be folded down onto the remainder when not in use. Struts would be provided to brace the sub-section in its upright position.

The form of apparatus shown in Figure 1 and the modification just mentioned in which there is an upstanding sub-section can be used to lift a vessel above the sea surface to allow the hull to be pumped out.

In a further modification (not shown) each cell is secured by six ropes instead of four to the frame.

The ropes are equiangularly spaced, two being secured to a member 16 which is aligned with the centre of the cell. Two of the remaining ropes are secured to one neighbouring member 16 and the last two ropes are secured to the other neighbouring member 16.

Claims (12)

1. Buoyancy lifting apparatus comprising a frame which is securable to the object to be lifted and at least one horizontal array of buoyancy cells each having means in the region of its lower end by which the cell is individually secured to the frame, each cell being made af flexible materiaL so as to be collapsible from a working shape in which the cell is an upright hollow cylinder open at the lower end and closed at the upper end by an upwardly convex end wall, the apparatus also comprising means for admitting air into each cell.

2. Apparatus according to Claim 1, in which each cell has in the region of its lower end a circumferential stiffening ring at which the cell is secured to the frame.

3. Apparatus according to Claim 1 or Claim 2, in which each cell is secured to the frame by ropes.

4. Apparatus according to any preceding Claim, in which the cells are releasably retainable each in collapsed shape.

5. Apparatus according to any preceding Claim, in which the frame comprises only horizontal elon gate members including longitudinal and transverse members and the cells are all above the frame.

6. Apparatus according to Claim 5, in which the frame also comprises upright members interconnected by further horizontal members forming an upstanding sub-section securabie against the side of an object to be lifted.

7. Apparatus according to Claim 6, in which the sub-section is hingedly connected to the remainder of the frame to allow the sub-section to be folded down onto the remainder when not in use, struts being provided to brace the sub-section in its upright position.

8. Apparatus according to Claim 6, in which the frame is of rectangular box shape, those members beneath the cells forming the base thereof.

9. Apparatus according to any preceding Claim, in which each cell is made of flexible impervious material including synthetic plastics reinforcement.

10 Apparatus according to any preceding Claim comprising two or more arrays of cells, the arrays being arranged above one another.

11. Apparatus according to Claim 1, in which the cells are substantially as herein described with reference to Figure 2 and 3 of the accompanying drawings.

12. Apparatus according to Claim 1, substantially as described with reference to Figures 1 to 3 of the accompanying drawings.