GB2224262A - Gondola assembly eg for offshore platform - Google Patents

Abstract

Maintaining the underside of offshore structures such as drilling platforms has hitherto required erection of temporary scaffolding. This can be hazardous, expensive and may provide only limited access. This invention consists of a gondola assembly comprising a first elongate arm 14; means to mount the arm on the platform with the arm extending in a generally vertical plane; a second elongate arm 30; means 24 to connect said second arm to the first arm for adjustment about an axis 31 extending through the connection; and means to mount a gondola 50 on the second arm, wherein the second arm is rotatable about a longitudinal axis of the first arm to enable the gondola to be manoeuvred into a required position about the platform. <IMAGE>

Description

GONDOLA ASSEMBLY The invention relates to a gondola assembly for the transport of objects, in particular for use in the field of offshore engineering.

The maintenance of offshore structures such as oil drilling platforms and the like comprises essential tasks requiring considerable use of personnel and resources. Tasks which are typically carried out to effect the repair and maintenance of offshore structures include spraying of members with paints and specialised coatings to reduce corrosion damage; welding of members either to repair or modify the structure; and fire-fighting operations.

Additionally, there are occasions when it is necessary to rescue stranded workmen or objects from some point on an offshore structure, or even from the sea.

In particular, the underside and sides of the deck of an offshore structure, along with the support legs, are difficult to work upon since access to such regions is limited and involves considerable danger to personnel involved.

Hitherto, access to and maintenance of the underside of the deck of an offshore structure has been accomplished with the use of a scaffolding construction, which is a network of mechanically interlinked scaffold pipe members temporarily fixed below the deck of an offshore structure. To gain access to the underside of an offshore structure, workmen must use ladders to reach the scaffolding construction and then negotiate the construction to gain access to a region of the offshore structure.

Due to the hazardous nature of erecting the scaffolding construction, workmen are generally roped to reduce the danger of any of them falling off the structure. Further, the resulting scaffolding construction is fixeS at one leva below the deck of the offshore structure, which means that access to the support legs of the structure at levels other than that of the scaffolding construction is limited. It is possible to build a height-adjustable scaffolding construction about the legs of the platform, but this is both?time consuming and hazardous to accomplish. In addition, transport of objects to and abqut the scaffolding construction is often difficult and dangerous.

One embodiment of the invention therefore provides a gondola assembly for use on a platform structure comprising: a first elongate arm, means to mount the arm on the platform with the arm extending in a generally vertical plane; a second elongate arm; means to connect said second arm to the first arm for adjustment about an axis extending through the connection; and means to mount a gondola on the second arm, wherein the second arm is rotatable about a longitudinal axis of the first arm to enable the gondola to be manoeuvred into a required position about the platform.

The use of an actuator to luff the second member with respect to the first member is advantageous since such an arrangement allows a greater turning moment to be accommodated about the hinge than if an internal mechanism is used to control operation of the hinge. By "luffing" is meant the raising of a second arm by rotating it about an axis perpendicular to the longitudinal axis of a first member, as in a derrick. Thus, the second member of the gondola assembly can be made long and can carry significant loads. In addition, the mechanism of the connection is simpler and hence more reliable than one having a self-contained means of operation such as a motor and drive linkage.

An advantage of such an arrangement is that, if the mounting is disposed on the topside of the deck adjacent an edge thereof, it is possible to transport objects, workmen and maintenance or fire-fighting services to any region of the topside or underside of the deck of an offshore structure quickly and in safety.

Preferably the first arm is longitudinally extendable. This arrangement confers greater versatility on the present invention since it permits movement of the gondola, and hence anything supported thereon, to horizontal planes considerably removed from that of the deck itself. Thus, it is possible to gain access to any region of the support legs of an offshore structure disposed above sea level, the surface of the sea itself and regions of constructions extending vertically of the deck of an offshore structure.

Further, it is preferable that the second arm is longitudinally extendable. This feature has the advantage that the full range of access of the articulated arm in a horizontal plane is maintained even if the second member is inclined at an angle to the first member in order to negotiate an obstacle.

It is further preferable that the means to mount the first arm on the platform comprises bearing means permitting rotation of said arm about a horizontal axis; and a toothed ring fixedly mounted in a vertical plane to said first arm to engage a toothed drive disposed to cause rotation of said ring, and hence said arm, about said horizontal axis on selective operation of said drive means, thereby permitting positioning of the gondola under, alongside or above the platform.

Alternatively, it is preferable that the means to mount the first arm on the platform comprises bearing means permitting rotation of said arm about a horizontal axis, and a toothed drive fixedly mounted to said first arm to engage the teeth of a vertically mounted fixed ring disposed to cause rotation of said arm about said horizontal axis on operation of said drive means,thereby permitting positioning of the gondola under, alongside or above the platform.

Preferably, the means to mount the first arm comprises a plurality of bracket and clamp combinations distributed about the platform, each combination comprising a bracket from which the gondola assembly may be hung; and a clamp which may encircle an upper part of the first arm, to retain it against the edge of the platform, whereby the gondola may be mounted to gain access to any predetermined part of the underside of the platform.

Conveniently, the means to connect the second arm to the first arm may comprise: a hinged joint interconnecting the two arms and orientated to provide rotation of said second arm about an axis perpendicular to the longitudinal axis of said first arm; and at least one hydraulic actuator hingedly connected to said first arm at one end and hingedly connected to said second arm at the other end thereof, said hydraulic actuator selectively operating to rotate said second arm about an axis perpendicular to said longitudinal axis of said first arm.

In accordance with a second embodiment of the invention, there is provided a gondola assembly for use on a platform structure comprising: a first elongate arm; means to mount the arm on the platform with the arm extending in a generally vertical plane; a second elongate arm: means to connect said second arm to the first arm for adjustment about an axis extending through the connection; and means to mount a gondola on the second arm, wherein the second arm is rotatable about a longitudinal axis of the first arm to enable the gondola to be manoeuvred into a required position about the platform, and wherein said mounting comprises a wheeled carriage to move on rails disposed on the underside of said generally horizontal overhang.

According to a third embodiment of the invention, there is provided a gondola assembly for use on a platform structure comprising: a first elongate arm; means to mount the arm on the platform with the arm extending in a generally vertical plane; a second elongate arm; means to connect the second arm to first arm for adjustment about an axis extending through the connection; and means to mount a gondola on the second arm, wherein the second arm is rotatable about a horizontal axis of the first arm to enable the gondola to be manoeuvred into a required position about the platform, and wherein said mounting is disposed at one end of a movable member, the other end of said member being hingidly connected to said generally horizontal overhang.

There now follows a description of four specific embodiments of the invention, reference being made to the accompanying drawings, in which Figure 1 is a perspective view of a gondola assembly according to a first embodiment of the invention; Figure 2 is a perspective view of a gondola assembly according to a second embodiment of the invention and showing an alternative method of supporting the assembly; Figure 3A is a plan view of an upper bracket of the embodiment of Figure 2; Figure 3B is a plan view of a lower clamp of the embodiment of Figure 2; . .Figure.4 is a perspective view of a gondola assembly according to a third embodiment of the invention; Figure 5 is a side elevational view of the embodiment of Figure 4 showing it in two working positions; Figure 6 is a plan view of the arrangement of Figures 4 and 5 in a parked position; Figure 7 is a perspective view of a gondola assembly according to a fourth embodiment of the invention; Figure 8 shows an arrangement for conducting power and services through articulated portions of the arms of Figures 1 to 3.

Figure 9 is a perspective view of a multiple swivel joint used to interconnect the second and third arms of the embodiments of Figures 1 to 7; and Referring firstly to Figure 1, there is shown a gondola assembly 10 according to the invention mounted via a mounting 11 on the outer periphery of the topside 12 of the deck 13 of an oil drilling platform.

Gondola assembly 10 comprises a first arm 14 extending generally of mounting 11 via an arrangement to be described below. Arm 14 is telescopically extendable along the longitudinal axis thereof, as indicated by arrows A. The extension of arm 14 is accomplished under the action of hydraulic cylinder 15 (shown by dotted lines in Figure 1) disposed within an upper portion 16 of arm14. Cylinder 15 selectively operates to extend or retract a lower extension 17 of arm 14 as required.

Alternatively, lower extension 17 may selectively be raised and lowered by a cable and motor arrangement either inside or outside arm 14.

A slewing ring 18 is disposed between upper portion 16 and extension 17 of arm 14. Slewing ring 18 is arranged to permit rotation through 3600 of extension 17 relative to portion 16 about the longitudinal axis 20 of arm 14, portion 16 and extension 17.

Longitudinal axis 20 of first arm 10 is shown as vertical in Figure 1, but can be rotated through an angle of 1800 to occupy any orientation between the limits indicated by axes 20' and 20". The rotation of longitudinal axis 20, and hence first arm 14, is effected by a swivel ring 19, to which upper portion 16 of arm 14 is rigidly attached. Swivel ring 19 is secured to mounting 11 and is rotatable about axis 21 which lies perpendicular to axes 20, 20' and 20".

Motor 22, which may be an electric or hydraulic motor is mounted either on mounting 11 or on swivel ring 19. In the case where motor 22 is secured to mounting 11, the output drive shaft (not shown) of motor 22 comprises a toothed gear to engage a toothed ring (not shown) formed in the outer periphery of swivel. ring 19 and rotate it on operation of motor 22. Alternatively, when motor 22 is secured to swivel ring 19, a toothed gear on the output drive shaft (not shown) of motor 22 engages teeth in a track or ring disposed on mounting 11 to rotate swivel ring 19 on operation of motor 22.

Disposed adjacent one end 23 of lower extension 17 of first arm 14 is a hinge arrangement 24. The end 23 of lower extension 17 is the opposite end of extension 17 to that which engages hydraulic cylinder 15.

Hinge 24 interconnects lower extension 17 and a second arm 30 such that arm 30 may pivot about an axis 31 perpendicular to the longitudinal axis 20 of arm 14.

A pair of hydraulic linear actuators 32, 33 are each pivotally secured at each end respectively to lower extension 17 and second arm 30. The purpose of linear actuators 32, 33 is to luff second arm 30 with respect to first arm 14. By "luffing" is meant the action of raising second arm 30 by pivoting it-about the axis 31. The sense of raising the arm 30 is similar to that of raising the jib boom of a derrick.

Second arm 30 comprises two longitudinal extensions 34, 35 arranged to extend telescopically under the action of one or more hydraulic cylinders 36 shown by dotted lines in Figure 1 and disposed inside second arm 30.

Alternatively, an internal or extended cable arrangement may be used to extend or retract the extensions.

Second arm 30 is hinged about a hinge arrangement 37 disposed in longitudinal extension 35. The operation of hinge arrangement 37 is described below with reference to Figure 9, but it should be realised that pivoting of hinge 37 mutually perpendicular axes 38, 39.

A third arm 40 extends of hinge 37 and is rigidly secured at one end to gondola 50.

It will therefore be clear that operation of hinge 37 permits positioning of gondola 50 in a wide variety of locations.

The gondola 50 comprises a cradle 51 having a safety cage 52 rigidly secured thereto. Cradle 51 can readily accommodate the equipment and workmen required for maintenance and service tasks on offshore structures. Fire-fighting equipment can also be carried.

Trunking for electrical power, hydraulic fluid, control wiring, welding gas and water for fire extinguishing runs the length of the gondola assembly 10 to supply the gondola 50. Such trunking is not shown in Figure 1, but Figure 8 shows an arrangement whereby trunking 60 is run inside the arms of the gondola assembly to negotiate the articulated regions thereof. Where it is required to pass trunking through an articulated joint or an extension, the trunking 60 is enclosed in a segmented sheath 61 which is folded over on itself twice as shown in Figure 8. The sheath 61 protects the trunking from wear due to movement at the joint or extension, and the fact that there is considerable slack in the trunking where it is folded over on itself allows for the extension of the trunking required due to operation of the joint or extension.

Services for the cradle are therefore carried either within or along the exterior of the gondola assembly and can be supplied from main sources located elsewhere on the offshore structure.

Referring again to Figure 1, there is shown a control panel 53 remotely to control the operation of the arm, the supply of services and the orientation of the gondola 50. A similar control panel 54 is located on the topside 12 of platform 13 for safety override control and remote operation of gondola 50.

Control panel 54 may be portable about topside 12..

In use, the gondola assembly of the invention is initially parked with the cradle 51 adjacent the topside 12 of the deck 13. Equipment may be loaded into the cradle 51 and any workmen required for the task to be completed may enter at this time. The cradle is then manoeuvred either from control panel 53 or control panel 54 as appropriate to occupy a predetermined position about the offshore structure.

Such manoeuvring may comprise rotation of arm 14 about pivot 21, extension of arms 13, 34 and 35, operation of hinges 23 and 37, pivoting of cradle 51, luffing of arm 30 and rotation of extension 17.

Referring now to Figure 2, there is shown a side elevational view of a second embodiment of the invention. The arrangement of the gondola assembly 110 of Figure 2 is generally the same as that of assembly 10 in Figure 1, but differs in that the mounting 111 of Figure 2 does not permit rotation of the entire gondola assembly 110 in a vertical plane about a horizontal axis extending of the platform 113. The arrangment of Figure 2 does not therefore permit access of the gondola 150 to the topside 112 of platform 113, unlike the arrangment of Figure 1.

The gondola 150 is shown in various operational positions, including packing and loading positions, in Figure 2.

Figures 3A and 3B show the mounting arrangement of the embodiment of Figure 2 in greater detail.

At the top of first arm 114 of gondola assembly 110, there is (as shown in plan view in Figure 3A) a pair of hooks 160, 161 extending parallel to one another and laterally of arm 114.

Hooks 160, 161 are engageable with corresponding lugs 162, 163 formed in the horizontal upper surface of a mounting bracket 164 which is rigidly secured to the topside 112 of platform 113, or in the absence of mounting bracket 164, directly onto the strong frame work of topside 112.

In use therefore, gondola assembly 110 hangs by the hooks 160, 161 from lugs 162, 163, and this arrangement constrains arm 114 against vertical movement relative to platform 113.

Referring now to Figure 3B, there is shown a clamping device which is disposed about a lower region of arm 114 to restrain it against horizontal movement relative to platform 113.

Figure 3B, which is a plan view of the clamping device, including a horizontal section through arm 114, shows a collar 165 which clamps across arm 114 and retains it within pillow block 166 which is secured onthe periphery of platform 113.

Collar 165 can be released (as shown by dotted lines in Figure 3B) to permit removal of the gondola assembly 110 from the bracket and clamp arrangment.

Clearly, if there is a sufficient number of such bracket and clamp arrangments distributed about the periphery of platform 113, a gondola assembly 110 can be hung from the most appropriate point to complete a particular job. When not in use, the gondola assembly can be steered on the platform 113.

Figures 4 and 5 shows a third embodiment of the invention which is similar in function to the embodiments of Figures 1 and 2, but differs in that the mounting shown generally at 311 in Figures 4 and 5 comprises a wheeled carriage 312 to move on rails 313 fixed underneath the deck 350 of an offshore structure.

The wheels 320, 321 of the carriage 312 are contained in bogies comprising three wheels each, the upper two wheels 320 of a bogie being used primarily to support the carriage 312 on the rail 313 while the lower wheel 321 runs underneath the rail 313 and stabilises the carriage 312. Carriage 312 is therefore constrained to move in directions indicated by arrows B in Figure 4.

Extending downwardly of carriage 312 is a first arm 314 in the form of a column. A slewing ring 351 (not visible in Figure 4) permits rotation through 3600 of column 314 about the longitudinal axis 315 thereof. A motor means may be employed to provide controlled rotation of column 314.

An access platform 316 is suspended from the underside of carriage 312 and comprises an access and loading deck 317, and remote power generation equipment 318 such as a diesel generator set. A remote control console 319 for controlling the gondola assembly may be placed on the deck 317.

Guard railing 330 and a cut-away portion 340 of the deck which allows downward movement of arm 334 therethrough are also provided.

Disposed at the lower end of column 314 is hinged joint 333 which pivotally interconnects column 314 and arm 334. The axis about which arm 334 hinges with respect to column 314 is indicated at 332 in Figure 4 and is generally perpendicular to axis 315.

Hydraulic actuators 335, 336 are pivotally secured at each end respectively to column 314 and arm 334. Hydraulic actuators 335, 336 operate selectively to luff arm 334 with respect to column 314 in a similar manner to that in which hydraulic actuators 32, 33 operate in the embodiment of the invention shown in Figure 1.

Arm 334 is selectively telescopically extendable along the longitudinal axis thereof and therefore comprises extensions 337, 338 which are selectively extendable or retractable in the directions indicated by the arrows C under the action of hydraulic actuators (not shown in Figure 4) disposed within arm 334, or under the action of a cable extension and retraction mechanism.

Two-directional swivel 360 interconnects arm 334 and further, rigid arm 361. Arm 361 carries gondola 362 which is secured thereto in a rigid joint 363.

Gondola 362, as in the embodiment shown in Figure 1, comprises a cradle 364, safety cage 365, and a control console 366.

Arm 361 pivots about two mutually perpendicular axes 367, 368 which arrangement permits arm 361 to maintain a desired orientation, if required, regardless of the angle to which the main telescopically extending portion of arm 334 has been luffed.

In use, the embodiment of Figures 4 and 5 operates to provide access of workmen, equipment and services to all parts of the underside of the deck of a structure. The gondola assembly is initially maintained in a parking position in which the carriage 312 is held at a preselected position on the rails below a trapdoor or similar access way (not shown) in the deck 350. In the parking position, as shown in plan view in Figure 6, the gondola assembly is folded back upon itself to position the gondola 362 adjacent access deck 317.

As in the embodiment of Figure 1, the second embodiment of the invention comprises power, control and services trunking running either inside or outside the arms as required. Motors and actuators (not shown) to control the use of hinges and pivots are also included where required. A sheath as shown in Figure 8 and referred to above may be used to protect trunking at points where excessive movement of joints or extensions would lead to wear of the trunking.

Referring now to Figure 7 there is shown a perspective view of a fourth embodiment of the invention. The embodiment of Figure 7 is very similar to that shown in Figure 1, but differs in that the mounting 400 of the first arm 414 of the gondola assembly is securely attached to one end of a parallelogram mechanism 401, the opposite end of which is rigidly attached to the topside 412 of the deck 413 of an offshore structure.

Parallelogram mechanism 401 comprises upper arm 402 which is pivotally connected at the upper end 403 thereof between an upper pair of flanges 404 secured to mounting 400 and is further pivotally connected at the lower end 405 thereof between the rearmost portions of a pair of deck-mounted flanges 406.

Parallelogram mechanism 401 further comprises a lower arm 407 which is pivotally connected at one end 408 thereof between the lowermost part of a pair of flanges 409 secured to mounting 400 and is further pivotally connected at the end 410 thereof about the forwardmost portions of deck-mounted flanges 411.

A pair of parallel hydraulic actuators, 430, 431, is disposed to provide controlled operation of parallelogram mechanism 401 by selectively applying a force between the two pairs of flanges.

In use, parallelogram mechanism 401 serves selectively to raise and lower mounting 400 and hence raise and lower the entire gondola assembly. This provides greater versatility of movement for the gondola assembly. The action of parallelogram mechanism 401 also has the effect of selectively moving mounting 400, and hence the entire gondola assembly, either closer to or further from deck 413 in the plane of the deck. Thus it will be clear that the embodiment of the invention shown in Figure 7 is particularly suited for tasks which require the gondola 451 to face onto the deck 413 and be either level with the deck or raised above it.Such tasks include fire fighting, fpr which fire.monitors.(not shown) can be mounted on the gondola The remainder of the component parts of the embodiment of Figure 7 differ little from those shown in Figure 1.

Disposed in a horizontal plane below mounting 400 is a toothed slewing ring 440 which may be driven by motor 441 to cause rotation of arm 414 about vertical axis 442. At least 3600 rotation are possible.

The embodiment of Figure 7 also includes a two-directional swivel 450 interconnecting a second arm 420 and a third arm 421, which is itself rigidly connected to the gondola 451.

Swivel 450 of Figure 7, swivel 360 of Figures 4 and 5, swivel 176 of Figure 2 and hinge 37 of Figure 1 all operate in the same manner and have essentially the same components. Their operation will now be described with reference to Figure 9 of the drawings, which is a perspective view of the hinge/swivel joint, indicated generally by the reference sign 500.

In Figure 9, a pair of arms 501 and 502 are interconnected in such a way as to permit relative rotation therebetween about two mutually perpendicular axes, 503 and 504.

Arm 501 is rigidly secured to flange block 505, which has a pair of forwardly extending flanges 506, 507 and a pair of downwardly extending flanges of which only one, 508, is visible in Figure 9.

Pivotably disposed between flanges 506 and 507 is the head 510 of a T-bar 511. T-bar 511 is pivotable about axis 503 by virtue of journal pin 512 passing therethrough and beating at each end respectively in the appropriate flange 506 or 507.

T-bar 511 extends forwardly of flange block 505 and has a downwardly extending plate 513 disposed along the underside thereof. Plate 513 has a through-going bore which, by means of a pivot pin 514, pivotably secures the end of the actuating rod of a hydraulic cyclinder 515. This is achieved by pivot pin interconnecting an eye 516 formed in the rod end and the plate 513, in a direction parallel to axis 503.

The hydraulic actuator 515 is arranged to pivot about pivot bar 517 which pivotably locates between downwardly extending flanges 508, 509. Thus, operation of cylinder 515 causes T-bar 511 to rotate in a vertical plane about axis 503, as indicated by the arrows X of Figure 9.

T-bar 511 terminates in a gear sprocket 518 disposed within a housing 519 secured to arm 502.

Gear sprocket 518 is rotatable in housing 519 and the centre of gear sprocket by virtue of journal pin 520 passing through housing 519 and the centre of gear sprocket 518 along axis 504. Therefore, arms 501 and 502 are rotatable relative to one another both about axis 503 and about axis 504.

A hydraulic motor 520 is rigidly mounted on a periphery of housing 519 and has its output drive engaged with the teeth in gear sprocket 518.

Operation of motor 520 therefore causes controlled relative rotation between arms 501 and 502 about axis 504.

It will be clear from the foregoing descriptions that the invention is very versatile and is not limited to applications involving the repair and maintenance of offshore structures. The invention can be used in many situations where it is required to negotiate a horizontal overhang or move objects above or below a mounting. Such applications occur, for instance, in shipyards, fabrication yards, bridge building and maintenance, and oil refinery and power station construction.

Bellows seals are used extensively throughout the embodiments of the invention described above to prevent ingress of dirt, water and other contaminants at articulated joints. The telescopic arms and swivels are sealed with rubber seals.

The embodiments of the invention can be manufactured as a kit of parts for assembly on site, this feature enabling easy transport of the gondola assembly in offshore supply boats if required.

Alternatively, the entire gondola assembly can be folded up to permit transport in a containerised frame. Figure 10 shows one arrangement wherein the gondola assembly 522 is folded within a container frame 525 and, in the example of Figure 10, is being transported slung from a crane hook 523.

Claims (11)

CLAIMS:

1. A gondola assembly for use on a platform structure comprising: a first elongate arm; means to mount the arm on the platform with the arm extending in a generally vertical plane; a second elongate arm; means to connect said second arm to the first arm for adjustment about an axis extending through the connection; and means to mount a gondola on the second arm, wherein the second arm is rotatable about a longitudinal axis of the first arm to enable the gondola to be manoeuvred into a required position about the platform.

2. A gondola assembly according to claim 1 wherein the first arm is longitudinally extendible.

3. A gondola assembly according to claim 1 or claim 2 wherein the second arm is longitudinally extendable.

4. A gondola assembly according to any preceding claim wherein the means to mount the first arm on the platform comprises bearing means permitting rotation of said arm about a horizontal axis; and a toothed ring fixedly mounted in a vertical plane to said first arm to engage a toothed drive disposed to cause rotation of said ring, and hence said arm, about said horizontal axis on selective operation of said drive means, thereby permitting positioning of the gondola under, alongside or above the platform.

5. A gondola assembly according to any of claims 1 to 3 wherein the means to mount the first arm on the platform comprises bearing means permitting rotation of said arm about a horizontal axis, and a toothed drive fixedly mounted to said first arm to engage the teeth of a vertically mounted fixed ring disposed to cause rotation of said arm about said horizontal axis on operation of said drive means, thereby permitting positioning of the gondola under, alongside or above the platform.

6. A gondola assembly according to any of Claims 1 to 3 wherein the means to mount the first arm comprises a plurality of bracket and clamp combinations distributed about the platform, each combination comprising a bracket from which the gondola assembly may be hung; and a clamp which may encircle an upper part of the first arm, to retain it against the edge of the platform, whereby the gondola may be mounted to gain access to any predetermined part of the underside of the platform.

7. A gondola assembly according to any preceding claim wherein the means to connect the second arm to the first arm comprises: a hinged joint interconnecting the two arms and orientated to provide rotation of said second arm about an axis perpendicular to the longitudinal axis of said first arm; and at least one hydraulic actuator hingedly connected to said first arm at one end and hingedly connected to said second arm at the other end thereof, said hydraulic actuator selectively operating to rotate said second arm about an axis perpendicular to said longitudinal axis of said first arm.

8. A gondola assembly according to any preceeding claim wherein a third arm interconnects the gondola and the second arm, said third arm being rotatable with respect to said second arm, thereby to assist in adjusting the position of the gondola, means being provided to control the relative rotation between said second arm and said third arm

9. A gondola assembly according to any of claims 1 to 8 wherein said mounting comprises a wheeled carriage to move on rails disposed on the underside of said generally horizontal overhang.

10. A gondola assembly according to any of claims 1 to 8 wherein said mounting is disposed at one end of a movable member, the other end of said member being hingedly connected to said generally horizontal overhang.

11. A gondola assembly generally as herein described and with reference to and as illustrated in the accompanying drawings.