GB2034649A

GB2034649A - Improvements in or relating to a gangway transfer system

Info

Publication number: GB2034649A
Application number: GB7935182A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-10-11
Filing date: 1979-10-10
Publication date: 1980-06-11
Also published as: SE7908460L; NO145132C; NO783437L; GB2034649B; FI793158A; DE2941275A1; NL7907526A; DK429979A; NO145132B

Abstract

A system for offshore transfer of persons and goods, between a supply vessel 14 and a fixed platform 4, comprises a rigid gangway 1 of which one end is pivotable about a vertical. The second end of the rigid gangway 1 is connected to one end of a collapsible bellowshaped gangway 10 where changes of the total length is approximately equalized between the various elements, and the second end of the gangway can be located on the vessel 14. When the bellowshaped gangway is in use it is supported by ropes, elastic rod(s) or similar supporting lines 7. Each supporting line 7 is fixed at one end and is connected to a winch 8 at the other end. The winch 8 can compensate the line tension when the fixing points are moving relative to each other. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a transfer system This invention relates to a transfer system, and more particularly to a system for offshore transfer of persons and goods, for example between a supply vessel and a fixed or moored structure.

Different methods are known and use for the transfer of personnel and goods between a structure offshore such as an oil drilling platform and the shore with the use of vessels the methods being designed for high speed and safety during the entire transportation phase from a shore base to the platforms offshore.

Even in good weather swells occur in the sea making it difficult to establish a safe connection for personnel transfer from a transfer vessel to the platform. The difficulties increase in increasing windforce and waves.

One of the most known and used transfer systems comprise a line fixed between the vessel and the offshore structure. On the line a pulley is arranged, carrying a seat, sometimes termed a bosun's chair, or a personnel carrying basket, a cabin which is pulled between the vessel and the structure by a pulling rope connected to a winch at one end of the iine, although winches can be provided at both ends of the line.

Another transfer method is to use a crane provided with a basket or a cabin which can be lowered down to the transfer vessel from the offshore structure so that the personnel can enter or leave the basket on the deck of the vessel.

The problem with this method is that it is difficult for the crane operatorto lower the cabin safely onto the transfer vessel, since the basket or cabin is exposed to the effect of the wind, and as a result of the swell there is often a considerable relative motion between the cabin and transfer vessel.

Obviously there are methods for determining the various motions of the vessel caused by the waves and for controlling the crane to ensure that the cabin is safely lowered onto the deck, the crane being compesated automatically to take account of the wave in direct motions of the vessel. However, such equipment is relatively complicated and expensive.

The object of this invention is to provide a system for the transfer of personnel and goods based on relatively simple mechanical components avoiding use of sophisticated equipment, as described above.

According to the broadest aspect of this invention there is provided a system for the offshore transfer of persons and goods, between a vessel and a fixed platform or another vessel, comprising a rigid gangway of which one end is mounted on the platform on one of said vessels about the second end of the rigid gangway being connected to one end of a collapsible bellows shaped gangway, any change of the total length of which is approximately equalized between the various bellow elements, which can connect the second end of the gangway to the vessel or the other vessel respectively supporting lines or the like being provided to support the bellows shaped gangway when in use.

Preferably the supporting lines are each fixed at one end and connected at the other end to a device which device can compensate the line tension.

Conveniently the bellows section is of square section and the supporting line (s) are arranged in at least one of the corners of the square section bellows section.

Advantageously the compensating device for the line tension is fixed to the rigid gangway or the support for the rigid gangway.

Preferably the compensating device for each line is a winch and signals from a sensor for the supporting line tension controlling the winch to keep the line tension within certain limits.

Conveniently the compensation of the supporting line tension is accommodated fully or partly by elastic ropes.

In one embodiment the fixed gangway has a cross section which fully or substantially encircles the bellows shaped gangway in the collapsed position but In an alternative embodiment the collapsible gangway has a cross-section which in collapsed position fully or substantially encircles the fixed gangway.

Preferably tension balancing means are provided between the supporting lines at their attachment to the vessel or other vessel respectively.

In one embodiment the lines are inter connected diagonally over pulleys which are arranged in a frame to constitute said tension balancing means.

In another embodiment the lines are fixed to a frame which is suspended in a cardan joint to constitute said tension balancing means.

In order that the invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings, in which; Figure 1 is a diagrammatic side view of one embodiment of the invention; Figures 2a-2d correspond to Figure 1 but illustrate the action of the waves; Figure 3 is an enlarged view of part of the apparatus of Figure 1; and Figure 4 is a view corresponding to Figure 3 of an alternative embodiment of the invention.

Referring initially to Figure 1 a transfer system in accordance with the invention comprises a rigid gangway 1 hinged at 2 to a base 3. The base 3 is rotatably mounted on a platform 4 by a support bearing 5, for rotation about a vertical axis.

The rigid gangway, is preferably of square sectioned tubular configuration, thus resembling a tunnel, and comprises guide devices 6 which accom modatethe supporting lines 7. The ends 16, 16' of the lines 7 are connected to winches 8 arranged on the base 3 or on the rigid structure 8. Preferably a sensor senses the tension in each line 7 and controls the respective winch 8 to maintain a substantially constant tension in the line 7. At the other ends 15, 15' of the supporting lines 7, a frame 9 is connected.

One end 13 of a collapsibletubular bellows 10 is connected to the end 12 of the rigid gangway. The collapsible bellows 10 is supported by the lines 7 in the operational position illustrated and is fixed to the frame 9 at points 15, 15'. In the stowed position the bellows 10, the supporting lines and the frame 9 are retracted in the rigid gangway 1 and the gangway itself is stowed in a horizontal position on the platform deck. The frame 9 thus supporting lines is connected to a pulling line 11, intended to be transferred to the transfer vessel 14 by a pick-up line connected to a buoy.

In use of the system the transfer vessel 14 is positioned in a reasonable distance from the platform, for example 30-50 m and the seamen on the vessel pull in the line 11, the frame 9 and the supporting lines 7. When connection is established the collapsible bellows 10 containing a walkway can be brought, on the supporting lines 7, over the transfer vessel 14. The collapsible bellows 10 and supporting lines can also be brought into position in one operation. The transfer vessel 14 keeps a reasonable tension in the supporting lines 7 to establish more or less a catenary curve in the lines 7 and the bellows 10. The personnel may now walk or crawl from the transfer vessel 14 to the platform 4 and vice versa on a walkway formed in the bottom of the bellows 10 which is equipped with an antisliding coating or steps.

Due to the flexibility of the transfer system, the transfer vessel 14 is allowed to move relative the platform 4 in a way that avoids extreme loads in the lines 7 or the bellows 10. A change in the total length of the bellows 10 is approximately equalized between the various bellows elements.

The winches 8 may be the so called mooring winches, maintaining a constant tension in the lines 7 and the lines 7 may also be connected to a motion compensating cylinders, springs or elastic line, which can give and take depending on the tension in the lines 7 caused by the motions of the transfer vessel 14.

The mode of operation for the transfer system according to the invention is shown in Figures 2a-d.

The figure shows the interaction between the bellow shaped, long extended body, with supporting lines and the transfer vessel, moving in the waves, and the fixed structure. Obviously the fixed structure may be a moored semisubmersible rig or any type resting in the seabottom with one or more legs.

When transfer operation is completed the bellows 10 and the lines 7 with frame 9 are retracted to the rigid gangway and stowed away until the next operation.

The complete transfer system may be placed on a movable arrangement which may move along the platform deck to cover two or more edges of the platform or which may be moved by crane to cover a greater operating area around the platform.

The fixed gangway may be telescopic and will be outstretched in the operating phase.

In the embodiment shown in Figure 1 the bellows 10 is connected by its end 13 to the rigid gangway at 12. The bellow 20 may alternatively be connected to the opposite end of the rigid gangway, to increase the effective length of the collapsible gangway.

The supporting lines 7 may be connected to a tension balancing means between the lines 7, comprising diagonal interconnections between the lines which are connected over pulleys arranged in frame 9, or the supporting lines 7 may be connected to a frame which is suspended in a cardan joint 9', 9" shown in Figures 3 and 4 respectively.

The described transfer system may also be used to effect transfers between two vessels.

Claims

1. A system for the offshore transfer of persons and goods, between a vessel and a fixed platform or another vessel comprising a rigid gangway of which one end is mounted on the platform on one of said vessels about the second end of the rigid gangway being connected to one end of a collapsible bellows shaped gangway, any change of the total length of which is approximately equalized between the various bellow elements, which can connect the second end of the gangway to the vessel or the other vessel respectively, supporting lines or the like being provided to support the bellows shaped gangway when in use.

2. A system according to claim 1, wherein the supporting lines are each fixed at one end and connected at the other end to a device which device can compensate the line tension.

3. A system according to claim 1 or 2, wherein the bellows section is of square section.

4. A system according to claim 3, wherein the supporting line(s) are arranged in at least one of the corners of the square section bellows section.

5. A system according to claim 2 or any claim dependent thereon, wherein the compensating device for the line tension is fixed to the rigid gangway or the support for the rigid gangway.

6. A system according to claim 2 or any claim dependent there wherein the compensating device for each line is a winch.

7. A system according to claim 6 wherein signals from a sensor for the supporting line tension controlling the winch to keep the line tension within certain limits.

8. A system according to any one of the previous claims wherein the compensation of the supporting line tension is accommodated fully or partly by elastic ropes.

9. A system according to any one of the previous claims wherein the fixed gangway has a crosssection which fully or substantially encircles the bellows shaped gangway in the collapsed position.

10. A system according to any one of czai ^ns 1 to 8 wherein the collapsible gangway has a cross- section which in collapsed position fully or substantially encircles the fixed gangway.

11. A system according to any one of the previous claims wherein tension balancing means are provided between the supporting lines at their attachment to the vessel or other vessel respectively.

12. A system according to claim 11 wherein the lines are interconnected diagonally over pulleys which are arranged in a frame to constitute said tension balancing means.

13. A system according to claim 11 wherein the lines are fixed to a frame which is suspended in a cardan joint to constitute said tension balancing means.

14. A system for the transfer of persons and goods substantially as herein described with referpence to and as shown in Figures 1 to 3 of the accompanying drawings.

15. A system for the transfer of persons and goods substantially as herein described with reference to and as shown in Figures 1 to 3 as modified by Figure 4 of the accompanying drawings.

16. Any novel feature or combination of features as disclosed herein.