WO2013174886A1

WO2013174886A1 - Vessel gangway system

Info

Publication number: WO2013174886A1
Application number: PCT/EP2013/060546
Authority: WO
Inventors: John KECSMAR; Mark Nigel WARREN; Nigel Warren
Original assignee: Otso Limited
Priority date: 2012-05-22
Filing date: 2013-05-22
Publication date: 2013-11-28
Also published as: EP2847069A1; GB201209028D0

Abstract

A gangway system for providing passage between a structure (102) and an independent vessel (101), comprising: a pedestal (104) for mounting to said vessel (101); an elongatedly gangway (103) comprising: an inboard root hingedly mounted to said pedestal (104), and an outboard end (106) for interfacing with said structure (102); a processor; one or more sensors configured to report to said processor; a control system responsive to signals from the processor; a ram responsive to signals from the control system and mounted on the pedestal for adjusting the vertical position of said gangway outboard end; and a ram responsive to signals from the control system and mounted on the gangway for adjusting the horizontal position of said gangway outboard end; wherein the system is arranged to allow for roll of the vessel without active roll compensation.

Description

VESSEL GANGWAY SYSTEM

The present invention relates to a gangway system, more particularly a system for aiding passage from a floating vessel to a structure, where such structure is typically stationary.

With increasing concern over climate change, peak oil and environmental issues there are increasing amounts of attention paid to renewable and sustainable sources of energy provision. Wind farms and tidal energy capture have been of particular interest in countries with seaboards or expanses of fresh water, being both typically of minimal environmental impact and capable of producing reliable returns of energy.

In addition, such installations are often capable of being left unattended for some time, with little maintenance required or work needed to ensure smooth running and reliable production of electrical energy. However, when maintenance work to such installations is required it can be very difficult to make passage for users from a floating vessel to a marine structure such as a wind turbine, especially during adverse conditions. Furthermore, there is a well-recognised need for reliable and safe passage from afloat vessels to docks, oil rigs and other marine structures.

Accordingly a number of patent applications have been filed for systems which attempt to resolve the problem or similar, including the following.

International patent application publication number WO 201 1 154 730 (Dudson et. al) discloses a vessel comprising a roller assembly, the assembly comprising at least one roller arranged to bear against a structure to be accessed, the assembly further comprising a damper to inhibit rotation of the roller such that the roller is arranged to inhibit relative movement of the vessel to the structure. The design also has a base that compensates for roll of the vessel.

European patent application publication number EP 2 316 721 (Prins et. al) discloses a method for stabilising a floating vessel against a stationary object, wherein the vessel is provided with: a hull; a motor for the propulsion of the vessel; a buffer body which protrudes with respect to the hull; and at least a first engagement arm, which at one end is provided with an engagement member for engaging on the stationary object; and wherein the method comprises: the pushing of the buffer body of the vessel against the stationary object by means of the motor, whereby the buffer body is substantially stabilised against the stationary object; the engagement of the engagement member on the stationary object while the buffer body and the stationary object are mutually stabilised by the pushing; and the subjection of the engagement arm to tensile load while the engagement member engages on the stationary object. Granted Norwegian patent number NO 145 131 (Ryan) discloses a marine ramp transfer system, wherein personnel and/or material are to be transferred between two relatively moving objects, such as for example a marine vessel and a fixed structure or another vessel at sea, capable of use in both calm and rough weather conditions, comprising the following mechanical elements: elongated ramp means of significant width being at least connectable between said relatively moving objects for supporting the personnel or material during the transfer between the objects and for producing a gradual transition for the personnel or material in the amount of relative motion between the objects being accommodated, said ramp means including: at least two opposed, at least relatively stiff, longitudinal stringer members separated from each other in a lateral direction by a significant distance and extending the length of said ramp means, said stringer members being rigid when in use; at least two lateral means connected across said stringer members for supporting a deck surface; and deck surface means connected between said stringer members and supported by said lateral means for providing a support surface on which the personnel or material are transferred; said stringer members being substantially fixed in separation distance between each other but movable with respect to each other in a longitudinal, "vertical" plane, and the ends of each said lateral means with each said deck surface area being independently rotatable or otherwise moveable about a longitudinal axis in their respective connections to said stringer members, whereby said ramp means is flexible along its length in a lateral plane; and two, separate ramp connection means each for connecting a respective end of said ramp means through said stringer members to one of the relatively moving objects for causing its respective end of the ramp means to assume a lateral direction the same alignment as that of the major "horizontal" plane of the object, the lateral alignment of at least one of which objects is changing with respect to the other in their relative movement; whereby said ramp means through its flexible structure and its end connections gradualise the relative motion between the objects in a directly proportional manner.

The thesis entitles "Ampelmann, Development of the Access System for Offshore Wind Turbines" by D. J. Cerda Salzmann; ISBN: 978-90-8891-194-1 describes a system which compensates for motion of a vessel in all six degrees of freedom and has a telescopic access bridge.

According to a first aspect of the present invention there is provided a gangway system for providing passage between a structure and an independent vessel, comprising: a pedestal for mounting to said vessel; an elongatedly extendable gangway comprising: an inboard root hingedly mounted to said pedestal, and an outboard end for interfacing with said structure; a processor; one or more sensors configured to report to said processor; a control system responsive to signals from the processor; a ram responsive to signals from the control system and mounted on the pedestal for adjusting the vertical position of said gangway outboard end; and a ram responsive to signals from the control system and mounted on the gangway for adjusting the horizontal position of said gangway outboard end; wherein the system is arranged to allow for roll of the vessel without active roll compensation.

In one example said gangway system further comprises hinging in at least two orthogonal directions of the gangway inboard root with respect to the pedestal, enabling heave, pitch and roll of the vessel to be accommodated. In one example said gangway system further comprises hinging of the pedestal with respect to the vessel.

In one example said gangway system further comprises: hinging and/or one or more resiliently deformable parts and/or one or more springs within the gangway, arranged to allow twisting of the gangway or parts thereof under roll of the vessel.

In one example the ram for adjusting the horizontal position of the gangway outboard end is arranged to ensure firm interface contact through substantially constant force on the structure in order to compensate for pitch motion of the vessel. In one example the gangway comprises two plates, an uppermost plate of the two plates being at the outboard end of the gangway, wherein said plates allow free extension and retraction at least of the uppermost plate to accommodate changes in distance from the gangway inboard root to an interface contact point with the structure.

In one example said gangway system has a modular design with interchangeable heads for the gangway outboard end to create variance in interface with differing structures.

In one example the gangway outboard end comprises a flexible, deformable or adaptable face for interfacing with the structure closely and flexibly.

In one example said face comprises sprung biased rollers or balls.

According to a second aspect of the present invention there is provided a method for providing passage between a structure and an independent vessel via an elongatedly extendable gangway, said gangway comprising an inboard root hingedly mounted to a pedestal mounted on said vessel, and an outboard end for interfacing with said structure, the method comprising: sensing data indicating the position of the outboard end with respect to the structure; and processing said data to determine appropriate control signals to control the vertical position of the gangway outboard end by adjusting a ram mounted on the pedestal and the horizontal position of the gangway outboard end by adjusting a ram mounted on the gangway such that the gangway outboard end maintains an interface with the structure while allowing for roll of the vessel without active roll compensation.

According to a third aspect of the present invention there is provided a computer program comprising code means adapted to perform the method steps above when the program is run on processor apparatus.

According to a fourth aspect of the present invention there is provided a computer program embodied on a computer-readable medium, configured to control the method above. Aspects of the present invention will now be described by way of example with reference to the accompanying figures, in the figures:

Figure 1 illustrates an example gangway system in use;

Figure 2 illustrates various operational modes of an example gangway system;

Figure 3 is a flowchart illustrating operation of an example gangway system;

Figure 4 shows an example control panel;

Figure 5 shows an example vessel fitted with an example gangway system; and Figure 6 illustrates components of an example gangway system.

The following description is presented to enable any person skilled in the art to make and use the system, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

A gangway system for providing passage to a structure from an independent vessel will now be described. The system may comprise: an elongatedly extendable gangway with an outboard end defining an interface with the structure, and a proximal inboard root hingedly attached to a pedestal, wherein in use said pedestal is mounted on the vessel; and wherein the pedestal includes at least one automatically adjusting ram to compensate for vertical vessel movement in respect of the structure and at least one ram capable of impelling the outboard end away from the pedestal to maintain the interface.

The system enables a user to step from the gangway to a turbine pile or other marine structure from a floating vessel, even where the vessel is experiencing significant movement relative to the structure. In use, the gangway is pressed against the structure, creating and maintaining the interface without requiring attachment, mooring or connection. The system provides a means of providing passage from floating vessels to structures such as wind turbines or rig piles, without needing to seek to fasten or attach to any part of the structure. The user does not need to secure a portion or part of the gangway to the structure or attempt to make passage to the pile at an appropriate moment.

The mounting of the gangway on the pedestal accommodates, absorbs, cancels or smooths vertical movement of the vessel beneath the pedestal. The interface is substantially free to move. The base of the pedestal is fixed. The system compensates for pitch and ensures constant, firm contact with the structure, without providing active roll compensation.

The ram or rams additionally ensure that the interface is directed at a single point of the structure and movement of the gangway distal end is accommodated for as the vessel moves. A horizontally aligned ram provides compensation for pitch motion to ensure firm interface contact through constant force on the structure.

The pedestal may include electronic means to compensate for vessel movement and maintain the gangway within a predetermined orientation range and the interface on the structure.

The pedestal may include automatically adjusting rams to compensate for vessel movement in respect of the structure.

Typically, a ram may provide active compensation for vertical motion of the vessel. The ram may be a hydraulic cylinder acting on the gangway.

The gangway may comprise two plates typically with an uppermost plate defined at the distal end, wherein said plates allow free extension and retraction of the uppermost plate and gangway to accommodate changes in distance from the proximal inboard root to the interface contact. Such gangway plates may be provided with or may comprise flooring which is high grip and/or self-draining. The gangway may comprise high tension side netting.

Traffic lights may be provided to be clearly visible from the gangway to identify when it is safe to transfer from the gangway. The gangway plates may be moved by means of a hydraulic ram, wherein said ram is typically powered and controlled by a motor and control within the pedestal. Said control may be enabled to maintain constant extension of the ram and extension plates, in order to ensure that the interface is maintained with the structure. The vessel is typically kept butted up against the structure in use, and limited force is ideally exerted against the structure.

The pedestal control may include electronic components, wherein said components act to compensate for movement of the vessel in maintaining the interface at a fixed height.

The control may further include apparatus for user definition of settings, such as on and off control and emergency shutdown and degree of automatic vertical and horizontal gangway adjustment.

The electronic components may interact or interface with sensors located at the gangway end or at the interface, said sensors enabling measurement of height and/or positioning. An acce!erometer could be used for example. The interface may be formed by a plurality of rollers, said rollers being formed of or covered with, for example, rubber or another elastomer, in order that the rollers freely roll on the structure. This is particularly advantageous where the structure presents an arcuate surface, for example being a cylindrical turbine pile. Other plural rolling interfaces may be used, such as multiple balls and/or bearings. Low friction (e.g. PTFE) pads could alternatively or additionally be used. Using two rollers reduces the torsion experienced by the gangway during use as the vessel rolls compared to an arrangement with a single roller.

The interface may be provided with a flexible, deformable or adaptable face for interfacing with the structure closely and flexibly. For example in some embodiments the rollers or balls may be sprung biased.

The interface may be adaptable with a variety of different heads providing different faces for interface with varying structures. In this way a modular format may be envisaged that is capable of fitting to a plurality of vessels and structures. The hinged attachment of the pedestal to the gangway root may include hinging in at least two orthogonal directions, enabling roll of the vessel to be accommodated for, as well as pitch of the vessel, although no active roll compensation is provided. The hinging could be arranged by separate pivots.

The pedestal may additionally include hinging with respect to the vessel.

The hinging may combine with springs or resiliently deformable parts, which combine to maintain a more steady or balanced root as forces counteract.

Thus the gangway is pivoted onto or about the pedestal, wherein the system allows for roll motion of the vessel through at least one pivot and the gangway is protected from shearing forces indicated by the interface with the structure, and a stable interface is provided. Hinging, resiliently deformable parts, springs etc. may be provided within the gangway itself or parts thereof, so as to allow twisting of the gangway or parts of the gangway under roll.

Said springs, hinges and at least one ram may be coordinated and controlled by the pedestal control to provide active vertical motion compensation for the gangway.

The pedestal may be provided with a universal fitting so that it can be attached to a number of different vessels.

The pedestal and the gangway when retracted may be arranged so as not to block an operator's view during docking. The gangway may for example be kept in a stowed position, i.e. at its lowest point, during the docking manoeuvre to ensure visibility.

Figure 1 shows an example gangway system in use. A vessel 101 abuts a marine structure 102 to which personnel aboard the vessel require access. Such access is provided by an extending gangway or brow (e.g. of aluminium) 103, pivotable atop a pedestal 104 which may for example be centrally mounted on the foredeck of the vessel 101. This provides a means to safely transfer personnel between floating vessel 101 , typically an offshore wind farm support vessel, and marine structure 102 (which may be fixed) such as a wind turbine tower, in a range of sea conditions. For wind farm operators this will significantly improve the operating conditions envelope, with the benefit of higher turbine generating availability and improvements in technician safety.

The gangway or brow 103 is automatically controlled to compensate for heave and pitch of the vessel, in order that a technician 105 at the end of the brow may be supported in a position substantially stationary relative to the structure 102, despite motion of the vessel 101 on the waves beneath him. The gangway end has an interface 106, wherein the brow is arranged to automatically extend to maintain firm contact with the structure at the interface. The interface 106 may have interchangeable modular heads. Such modular design allows use with a variety of access ladders/towers on various structures 102. The proximal root of the brow is pivoted on pedestal 104 mounted on the vessel 101 to allow the up and down movement and hinged to permit a degree of side to side movement to allow for, but not actively compensate for, roll of the vessel.

The automatic gangway is arranged to remain more or less stationary against vertical tubes on a wind turbine tower, allowing safer transfer of personnel to and from the tower, in seas with significant wave-heights up to e.g. 3.0 metres (dependent on vessel type).

The system is suitable for various support vessels operating offshore. There are various vessel foredeck mounting options.

The system has a modular design, with interchangeable heads to create variance in interface with differing towers. This allows use with most access ladders/towers. The system facilitates simple external safety inspection and maintenance.

The system can have a cheap and simple construction, suitable for volume production. The system is significantly safer, cheaper and more reliable than alternative transfer methods. Some components may be multifunctional. For example the brow structure 103 may also provide a handrail 107 and the pedestal 104 may also provide a housing and mounting for the hydraulics system used by horizontal ram 108 and/or vertical ram 109.

In use the interface 106 pushes against the structure 102 hard enough to absolutely ensure contact is maintained, but not so hard as to prevent vertical motions. These motions are damped, smoothed motions, with no risk of sudden movement when the friction of the brow contact is overcome by hydrodynamic/gravitational forces. This smoothing reduces the demands on the gangway for longitudinal strength.

The pedestal 104 supports the brow 103 at the pivoted root, and provides height to minimise the brow angle during operation. The pivot point may be located substantially at the far aft end of the pedestal to maximise the length of the gangway while minimising its footprint. The upper surface of the pedestal may be sloped to permit the gangway to be stowed at a lower position when not in use. The pedestal may also provide mounting for vertical ram 109, and dry enclosed space for the hydraulics system valves and control system components.

Access stairs may be provided to reach the inboard end of the gangway. Such stairs could be to the port, starboard or aft side of the pedestal if the gangway system is mounted on the foredeck as shown. The brow may be constructed from two parallel plates or Warren girders that provide a gangway from the pedestal to the brow end, head, and in use interface with the marine structure, and mounting for the horizontal ram 108 that controls the horizontal motion of the brow 103 relative to the vessel 101. The brow is typically mounted centrally, but could be off-centreline on some vessels.

The brow head provides interface 106 between the brow 103 and the structure 102 and is designed to fit tightly against the structure access (e.g. ladder), and be the exit/entry point from the structure. A control system controls the hydraulics system, based on user input mode selection, and acts as the interlock to ensure sensible and safe operation of the brow. The control system may be reprogrammable. Figure 2 illustrates schematically the various stages of a process used to transfer personnel from a vessel 201 to a marine structure 202 via a brow or gangway 203. in a manual control mode, the operator has full manual control of a vertical ram 209 and a horizontal ram (not shown). The main purpose of manual control is to move the brow to and from a storage state, in which a brow extension 203b is fully retracted, and the brow is stowed as low as possible, resting on the foredeck of the vessel 201 as shown in Figure 2(a).

In a pre-transfer mode, illustrated in Figure 2(b), the brow 203 is raised such that the brow is in the nominal mid operating position, and the vertical cylinder is actively controlled to maintain the brow head in a vertically stationary position, but with the brow extension 203b still retracted.

In a transfer mode, illustrated in Figure 2(c), the brow is as per the pre-transfer mode, but with the brow extension 203b extended such that it is firm contact with the tower, with the horizontal cylinder pushing with constant force, to counteract the effect of vessel pitching, and ensuring constant, firm contact.

In extremely rough seas the vessel motion may exceed the range which the rams are able to compensate for. In that case an additional smoothing mode could be implemented in which the motion of the interface is smoothed rather than halted.

Figure 3 is a flowchart setting out an example procedure for use of gangway systems such as those shown in Figures 1 and 2.

At step 301 , a vessel is docked with (e.g. its prow is butted up to) a marine structure, with the gangway system stowed, for example as shown in Figure 2(a), and its control system switched off. At step 302, the control system is switched on in manual mode. Manual operation could be tested by an operator at this point. At step 303, the control system is switched to pre-transfer mode and the vertical ram is automatically actuated to raise the gangway to the position shown in Figure 2(b). At step 304, the control system is switched to transfer (or, if available and necessitated by conditions, smoothing) mode and the horizontal ram is automatically actuated to extend the gangway extension so as to create and maintain an interface with the marine structure as shown in Figure 2(c). At step 305, personnel transfer between the vessel and the marine structure via the gangway.

These steps may be reversed when all required transfers have been completed. During transfer, or if required smoothing, mode the brow is actively controlled to maintain the brow head in firm contact with the tower (to prevent the brow coming away from tower, and to minimise vertical motion up and down the tower, thus providing a safe environment for transfer of personnel. Two types of emergency stop may be provided as follows.

Crash stop may be provided by a stand-alone hardware system that immediately stops all ram motion, and hence brow motion, relative to the vessel, by cutting power to the hydraulic system. The crash stop intervention is designed to allow for situations where there is imminent danger of impacts (albeit creating risks from sudden deceleration) or if the control system is not responding.

Soft stop may be a control system driven approach to bring the brow to a stop in a controlled manner. Once activated, the control system sounds a klaxon and after a predetermined time period (e.g. 5 seconds) to give the transferee time to decide on his course of action will simultaneously withdraw the brow head and reduce vertical cylinder motion over a further 10 second period to bring the brow to a halt.

An example control panel with operator input devices and operator feedback mechanisms is shown in Figure 4. An activation key 401 may be provided for switching the system on and off. A mode selection switch 402 may be provided for switching between modes, e.g. "off', "manual", "pre-transfer", "transfer" and "smoothing". A manual control panel 403a may be provided with up and down manual controls for the vertical ram 403a and 403b respectively and out and in manual controls for the horizontal ram 403c and 403d respectively. Buttons 404 and 405 may be provided to activate crash stop and soft stop respectively. A communications unit 406 may be provided for an operator to communicate with a transferee. This may be switched on and off using a button 406a and the operator may receive audio from a microphone on the brow or worn by the transferee via a headphone jack 406b or speaker 406c. Red and green traffic lights on the brow may be activated using buttons 407a and 407b respectively. The current state of the traffic lights may be indicated by the state of indicator lights 408a and 408b for red and green respectively. The extent of the horizontal and vertical rams may be indicated by light panel 409. Figure 5 shows an example gangway 503 in stowed position mounted on a pedestal 504 on a vessel 501. Pedestal 504 has a sloping top to allow the gangway 503 to be stowed in such a way that it does not block the forward view from the cab 510.

Figure 6 shows an example gangway 603 mounted on a pedestal 604 and provided with access stairs 611. Interface 606 on the gangway distal end is provided with rollers 606a and 606b. The gangway is formed of main gangway part 603a and gangway extension 603b which can be extended telescopically from the main gangway part using horizontal cylinder 608. Vertical motion of the gangway can be actuated using vertical cylinder 609. The access stairs and/or gangway are provided with traffic lights 612.

The brow may be shorter than shown in the various figures to cope with more restricted foredeck space. The brow may be longer than shown to cope with larger sea states, or to reduce maximum slope.

The pedestal may be lower to cope with differing wheelhouse and hull configurations.

The mounting may be off-centre to allow space for containers to the other side. The pedestal may be collapsible to reduce visual intrusion of the brow when not in use.

The control system may be configured such that an operator can adjust the standard height that the brow is seeking to maintain to optimise the exact technician transfer point.

Lighting may be provided, e.g. in red and green, to visually emphasize the operational state to users.

The control system may be provided with additional reporting functions using the information from the brow data processes, for example calculating and logging vessel motions and acceleration. Improved compensation could be provided using a combination of accelerometer readings and a wheel sensor when in contact. This could be further improved by predictive motion analysis.

Additional external sensing and warning systems may be provided, for example a large wave warning.

The invention has been described by way of examples only and it will be appreciated that variation may be made to the above-mentioned embodiments without departing from the scope of invention.

With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person ski!led in the art that various modifications may be made within the scope of the invention.

Claims

A gangway system for providing passage between a structure and an independent vessel, comprising:

a pedestal for mounting to said vessel;

an elongatedly extendable gangway comprising:

an inboard root hingedly mounted to said pedestal, and an outboard end for interfacing with said structure;

a processor;

one or more sensors configured to report to said processor;

a control system responsive to signals from the processor;

a ram responsive to signals from the control system and mounted on the pedestal for adjusting the vertical position of said gangway outboard end; and

a ram responsive to signals from the control system and mounted on the gangway for adjusting the horizontal position of said gangway outboard end;

wherein the system is arranged to allow for roll of the vessel without active roll compensation.

A gangway system according to claim 1 , further comprising hinging in at least two orthogonal directions of the gangway inboard root with respect to the pedestal, enabling heave, pitch and roll of the vessel to be accommodated.

A gangway system according to any preceding claim, further comprising hinging of the pedestal with respect to the vessel.

A gangway system according to any preceding claim, further comprising: hinging and/or

one or more resiliently deformable parts and/or

one or more springs

within the gangway, arranged to allow twisting of the gangway or parts thereof under roll of the vessel.

A gangway system according to any preceding claim, wherein the ram for adjusting the horizontal position of the gangway outboard end is arranged to ensure firm interface contact through substantially constant force on the structure in order to compensate for pitch motion of the vessel.

6. A gangway system according to any preceding claim, wherein the gangway comprises two plates, an uppermost plate of the two plates being at the outboard end of the gangway, wherein said plates allow free extension and retraction at least of the uppermost plate to accommodate changes in distance from the gangway inboard root to an interface contact point with the structure.

7. A gangway system according to any preceding claim, having a modular design with interchangeable heads for the gangway outboard end to create variance in interface with differing structures.

8. A gangway system according to any preceding claim, wherein the gangway outboard end comprises a flexible, deformable or adaptable face for interfacing with the structure closely and flexibly.

9. A gangway system according to claim 8, wherein said face comprises sprung biased rollers or balls.

10. A method for providing passage between a structure and an independent vessel via an elongated ly extendable gangway, said gangway comprising an inboard root hingedly mounted to a pedestal mounted on said vessel, and an outboard end for interfacing with said structure, the method comprising:

sensing data indicating the position of the outboard end with respect to the structure; and

processing said data to determine appropriate control signals to control the vertical position of the gangway outboard end by adjusting a ram mounted on the pedestal and the horizontal position of the gangway outboard end by adjusting a ram mounted on the gangway such that the gangway outboard end maintains an interface with the structure while allowing for roll of the vessel without active roll compensation.

11. A computer program comprising code means adapted to perform the steps of claim 10 when the program is run on processor apparatus.

12. A computer program embodied on a computer-readable medium, configured to control the method of claim 10.