Offshore gangway and lifting system and method

Abstract

An offshore gangway and lifting system, comprising: a base frame adapted to be mounted to the deck of a vessel; a mast which is extendable along its longitudinal axis between an extended position and a retracted position; a gangway supported by the mast; actuators adapted for adjusting an orientation of the longitudinal axis of the mast relative to the base frame, each of said actuators being interconnected between the mast and the base frame; sensors for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller for dynamically controlling the actuators, based on the orientation determined by the sensors, to adjust the orientation of the longitudinal axis of the mast to be substantially vertical; wherein the base frame is provided with a bearing having an at least partially spherical circumferential outer surface, wherein the mast is substantially supported by said outer surface in such a manner that the mast and gangway are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis normal to the longitudinal axis of the mast, and around a second axis normal to the longitudinal axis of the mast and normal to the first axis.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an offshore gangway and lifting system, in particular for transporting personnel from a vessel, e.g. a ship, to an offshore structure, e.g. an offshore structure which is fixed on the seafloor or which is in a floating moored situation. From CN 204507189 a system to be mounted on a ship is known, comprising a base column, a pedestal and a gangway. The base column is vertically arranged and comprises an outer base column and an inner base column, and the inner base column is nested and installed in the outer base column in a liftable manner. The pedestal is installed in a horizontally rotatable manner at a top end of the inner base column. The gangway comprises a first gangway section and second gangway section, wherein the first gangway section is installed on the pedestal in a vertically rotatable manner, and wherein the first and second gangway section are slidably installed. The known system aims to be adaptable to a large range of height differences between the offshore structure and the vessel. A stairs may be provided for boarding the base column, with a distance between the stairs and the base column being 2 meters.

[0002] A drawback of the known system is that it is relatively heavy. It is an object of the invention to provide an offshore gangway and lifting system which at least partially overcomes this drawback.SUMMARY OF THE INVENTION

[0003] To this end, according to a first aspect the present invention provides an offshore gangway and lifting system, comprising: a base frame adapted to be mounted to the deck of a vessel; a mast supported by the base frame, wherein the mast comprises multiple mast segments and is extendable along its longitudinal axis between an extended position and a retracted position; a gangway supported by the mast and comprising one or more gangway sections; actuators adapted for adjusting an orientation of the longitudinal axis of the mast relative to the base frame, each of said actuators being interconnected between the mast and the base frame; one or more sensors for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller for dynamically controlling the actuators, based on the orientation determined by the one or more sensors, to adjust the orientation of the longitudinal axis of the mast to be substantially vertical; wherein the base frame is provided with a bearing having an at least partially spherical circumferential outer surface, wherein the mast is substantially supported by said outer surface in such a manner that the mast and gangway are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis normal to the longitudinal axis of the mast, and around a second axis normal to the longitudinal axis of the mast and normal to the first axis. The controller helps to ensure that the mast will be oriented in a substantially vertical position, e.g. to compensate for roll, heave and / or pitch of the vessel.

[0004] As, during use, the mast and gangway are substantially supported by the bearing, e.g. such that at least 80% of the downward force exerted by the mast and gangway is supported by the bearing, relatively small actuators may be used for maintaining the mast in the substantially vertical orientation. Moreover, as, during use, the system ensures that the mast remains substantially upright, i.e. with its longitudinal axis substantially vertical, typically less force will be exerted by the mast on the actuators during roll and pitch of the vessel, than if the longitudinal axis of the mast were not kept substantially vertical. Thus, the weight of the system of the invention can be kept significantly lower than in prior art systems. The gangway and lifting system of the invention is intended for transfer of personnel and / or a load from the vessel to the offshore structure and vice versa, in particular for transferring personnel and / or a load which enter the gangway from the level of the deck, after which the gangway is lifted and rotated around the longitudinal axis of the mast towards the offshore structure. The bearing may be formed as a truncated bearing, which is truncated at its lower and upper side and comprises a through-opening which extends from the lower to the upper side. A suitable bearing may have an internal diameter of at least 30 cm.

[0005] An example of a suitable sensor for determining an orientation of the mast relative to the horizontal is an inertial measurement unit, which may be mounted to the mast. An example of a suitable sensor for determining an orientation of the base frame relative to the horizontal is a motion reference unit (MRU), which may be mounted to the base frame.

[0006] Advantageously, the invention allows movements such as roll and pitch of a vessel on which the system is mounted, to be compensated for close to the centre of gravity of the vessel. As a result, relatively small movements of the actuators typically suffice to keep the mast and in the vertical position. In turn, any actuators that are connected to the gangway will typically require relatively small movements in order to keep the gangway in a correct orientation.

[0007] In an embodiment, a largest outer diameter of each of the mast segments is less than 4 times the outer diameter of the at least partially spherical surface of the bearing. Preferably, the largest outer diameter of each of the mast segments is less than 3 times the outer diameter of the at least partially spherical surface of the bearing. Typically, that mast segment which is closest to the bearing when the mast is in the extended position will have the largest outer diameter out of all the mast segments.

[0008] In an embodiment the bearing is adapted for supporting the mast and gangway such that, during use of the system, at least 80% of the downward force exerted by the mast and gangway is supported by the at least partially spherical outer surface of the bearing. In an embodiment the system further comprises a pedestal substantially supported on the bearing, wherein the mast is substantially supported on the bearing via the pedestal, wherein one or more of the actuators are connected at one end to the pedestal and at another end to the base frame.

[0009] When seen in projection onto a main plane of the pedestal, the point of connection where the actuators connect to the pedestal typically do not overlap the mast, and preferably are spaced apart from the mast by at least 0,5 to 1,5 m. Typically, the farther the actuators are from the mast, the less force each of the actuators has to apply for maintaining the mast in the substantially vertical orientation.

[0010] In an embodiment the system further comprises a slewing bearing arranged between the pedestal and the mast, and adapted for allowing the mast to rotate around its longitudinal axis relative to the pedestal. Thus, the mast and the gangway can be rotated for instance from a position in which the distal end of the gangway is within the contour of the ship when seen in plane view, e.g. when loading personnel from the vessel to the offshore gangway and lifting system, to a position in which the distal end of the gangway is outside of said contour, e.g. when offloading the personnel from the gangway of the gangway and lifting system to the offshore structure. The slewing bearing is typically attached between an upper surface of the pedestal and a lower side of the mast.

[0011] In an embodiment, during use of the system when the mast is kept in a substantially vertical position, the spherical bearing is arranged below the slewing bearing.

[0012] In an embodiment the bearing, i.e. the bearing having the partially spherical outer surface, is provided with a through-opening at its side which faces the mast, for passage of data cables, power cables, and / or hydraulics cables from below the mast to the interior of the one or more mast segments and / or to the gangway. Thus, power cables and / or hydraulics cables for powering the actuators of the gangway can pass via the through-opening, through the hollow interior of the mast, to the gangway, in particular to actuators of the gangway. The system may further comprise one or more swivels connected to the cable(s) for accommodating rotation of the mast around its longitudinal axis relative to the pedestal and / or the base frame.

[0013] In an embodiment the gangway comprises: a platform attached to the mast and comprising a floor surface for supporting personnel thereon; preferably wherein the one or more gangway sections are supported by the platform and / or by the mast to be rotatable relative to the mast around a third axis normal to the longitudinal axis of the mast. Personnel can thus stand on the floor surface of the platform when the mast is moved from the retracted position to a more extended position. The floor surface of the platform may for instance have an area of between 1,5 m 2< and 6 m 2< . Generally, during lifting or lowering of the platform, the personnel and / or load remain supported on the floor surface, and typically the personnel and / or load will not enter the one or more gangway sections until the gangway is in contact with the offshore structure.

[0014] Preferably, when the mast is in the retracted position, the one or more gangway sections are rotatable around the third axis between a first angle relative to the mast in which the distal end of a most distal one of the one or more gangway sections is arranged below the floor surface of the platform, and a second angle relative to the mast in which said distal end is arranged above said floor surface. This allows personnel on the vessel to enter the platform via the gangway substantially from the level of the deck. The controller may further control an actuator to drive rotation of the one or more gangway sections around the axis normal to the longitudinal axis of the mast, to help compensate for motion of the vessel relative to the offshore structure.

[0015] Preferably, when the mast is in the retracted position, the gangway is rotatable to allow the distal end of the gangway to be at the level of the base frame and / or to contact the deck of the vessel. Thus, no stairs or the like are required for using the offshore gangway and lifting system of the invention.

[0016] In an embodiment the gangway comprises a first gangway section and a second gangway section, wherein the second gangway section is telescopically slidable relative to the first gangway section between an extended position and a retracted position. The gangway may be provided with an actuator connected to both the first and second section, adapted for sliding the first section relative to the second section.

[0017] In an embodiment, the platform is rotationally fixed with respect to the mast. Thus, rotation of the mast around its longitudinal axis relative to the base frame will cause a same rotation of the platform relative to the base frame. No actuators or the like are needed to keep the platform aligned with respect to the mast.

[0018] In an embodiment the longitudinal axis of the mast intersects the floor surface of the platform. The floor surface of the platform directly above the mast thus is also available for supporting personnel thereon.

[0019] In an embodiment the system further comprises one or more actuators for controlling a rotation of the gangway around the third axis relative to the mast. These actuators, typically linear actuators, may be connected at one end to the mast and / or platform, and at another end to a gangway section.

[0020] In an embodiment the system further comprises one or more sensors for detecting a forward force exerted by the distal end of the gangway on the offshore structure, wherein the controller is adapted for controlling movement of the mast and one or more gangway sections to keep the forward force at or above 2000 Newton. This helps ensure that the gangway remains in contact with the offshore structure during relative movement of the vessel and the offshore structure. By forward force is meant a force exerted by the distal end in the longitudinal direction of the gangway section. The force may conveniently be measured using a load cell arranged near the distal end of the gangway, and / or by measuring a force exerted by an actuator which is adapted for driving sliding movement between the at least two gangway sections.

[0021] In an embodiment the system further comprises a linear actuator having a first end attached to a first segment of the mast, and a second end attached to a second segment of the mast, wherein the linear actuator is adapted for driving movement of the mast between the extended and the retracted position. Thus, the second segment of the mast can be moved between an extended and a retracted position relative to the first segment. Typically, the first segment is fixed to pedestal, e.g. via a slewing bearing. The second segment is typically arranged at least partially within the first segment when in the retracted position.

[0022] In an embodiment, the mast segments comprise at least 2, 3, 4 or 5 mast segments, which, when seen in projection onto a plane normal to the longitudinal axis of the mast, are arranged concentrically.

[0023] Preferably, the mast is further provided with extension / retraction members adapted and arranged for extending and retracting one or more further segments of the mast upon extension or retraction of the linear actuator. These extension / retraction members are mechanically driven by relative movement between the first and second segment of the mast. The extension / retraction members are not connected to electrical power cables, hydraulic and / or pneumatic cables. Suitable extension / retraction members are described for instance in US 3,467,217. When seen in cross-section in a plane normal to the longitudinal axis of the mast, the mast segments preferably have a non-circular outer circumference, such as a rounded square outer circumference, to facilitate mounting the extension / retraction members to the mast segments.

[0024] Preferably, the mast is provided with extension / retraction members to allow all mast segments except the mast segment closest to the pedestal, i.e. the first mast segment, to move between the retracted and extended position when the linear actuator changes its length.

[0025] In an alternative embodiment, each mast segment of the mast is provided with a linear actuator for driving movement of said mast segment between the extended and retracted position of the mast.

[0026] In an embodiment the first axis, the second axis and the longitudinal axis of the mast substantially intersect, preferably in a point below the pedestal, more preferably in a point bounded by the partially spherical circumferential outer surface of the bearing.

[0027] In an embodiment the mast is hingeably attached to the pedestal, to allow the mast to hinge to a storage configuration in which the longitudinal axis of the mast extends substantially parallel to the base frame, and such that the mast and base frame, when the mast is in its storage configuration and in its retracted position, fit within an ISO standard 20ft x 8ft x 8 ft container. This allows easy storage and transport of the offshore gangway and lifting system when it is not mounted on the deck of a vessel. Additionally, the hinged connection allows quick installation of the system on a vessel.

[0028] According to a second aspect, the invention provides a method for transferring personnel from a vessel having a deck on which an offshore gangway and lifting system according to the first aspect of the invention is mounted, to an offshore structure, the method comprising: moving the mast to the retracted position, and moving the one or more gangway sections to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to enter the platform via the gangway; when personnel has entered the platform, moving the mast to an extended position, rotating the mast around its longitudinal axis relative to the base frame, and subsequently controlling movement of the gangway towards the offshore structure until a distal end of the gangway contacts the offshore structure. Preferably, after personnel has entered the platform but prior to moving the mast to the extended position, the one or more gangway sections are rotated such that a distal end thereof is arranged above the level of the floor of the platform. Once the distal end of the gangway contacts the offshore structure, extension / retraction of the gangway is typically controlled such that a force exerted by the gangway on the offshore structure in the direction of the one or more gangway sections is at least 2000 Newton.

[0029] According to a third aspect, the invention provides a method for transferring personnel from an offshore structure to a vessel having a deck on which an offshore gangway and lifting system according to the first aspect of the invention is mounted, the method comprising: after personnel has entered the platform, retracting the one or more gangway sections until the gangway is spaced apart from the offshore structure; rotating the mast around its longitudinal axis relative to the base frame, and retracting the mast until the gangway is completely arranged above the vessel; moving the gangway to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to leave the platform via the gangway.

[0030] Again, after personnel has entered the platform but prior to moving the mast to the extended position, the one or more gangway sections are preferably rotated such that a distal end thereof is arranged above the level of the floor of the platform.

[0031] In summary the invention provides an offshore gangway and lifting system and methods for using said system, wherein the system comprises: a base frame adapted to be mounted to the deck of a vessel; a mast which is extendable along its longitudinal axis between an extended position and a retracted position; a gangway supported by the mast; actuators adapted for adjusting an orientation of the longitudinal axis of the mast relative to the base frame, each of said actuators being interconnected between the mast and the base frame; sensors for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller for dynamically controlling the actuators, based on the orientation determined by the sensors, to adjust the orientation of the longitudinal axis of the mast to be substantially vertical; wherein the base frame is provided with a bearing having an at least partially spherical circumferential outer surface, wherein the mast is substantially supported by said outer surface in such a manner that the mast and gangway are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis normal to the longitudinal axis of the mast, and around a second axis normal to the longitudinal axis of the mast and normal to the first axis.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will now be illustrated with reference to the drawings, in which like reference numerals refer to like structures, and wherein Fig. 1A schematically shows a side view of an offshore gangway and lifting system according to the invention, with its mast in an extended position and with the gangway contacting an offshore structure; Fig. 1B schematically shows a side view of the offshore gangway and lifting system of Fig. 1A, with the mast in a retracted position, and with the gangway supported by the vessel; Fig. 2A schematically shows a detail of the pedestal of the system of Figs. 1A and 1B; Fig. 2B shows a partially cut-away view of the pedestal of Fig. 2A; and Fig. 3A shows an isometric view of an offshore gangway and lifting system according to the invention, with its mast in the extended position; Fig. 3B shows a perspective view of an offshore gangway and lifting system of Fig. 3A, with its mast in the retracted position; and Fig. 4 shows the system of the invention stored within a standard ISO 20 feet container. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0033] Fig. 1A schematically shows side view of an offshore structure 1 and of a floating vessel 10 that is provided with an offshore gangway and lifting system 100 according to an embodiment of the present invention.

[0034] The offshore structure 1 of the example is fixedly connected to the sea floor via a monopile 2, and comprises a substantially horizontal terrace 3 which allows personnel access to the structure 1. Typically, the offshore structure will be the base of a wind turbine. The vessel 10 floats on the water, with part of the vessel being submerged below the water surface W. Though not shown here, it will be appreciated that alternatively the offshore structure may float while being moored to the seabed. In such a case, motion of the offshore structure relative to the seabed may be independent from motions of the vessel relative to the seabed.

[0035] The vessel 10 comprises a deck 11 on which the offshore gangway and lifting system 100 is provided. The gangway and lifting system 100 comprises a base frame 110, mounted on the deck 11. Linear actuators, of which linear actuators 121, 122 and 123 are shown in the side view of Fig. 1A, are each fixed at one end to the base frame 110, and at their other end to a pedestal 140. A telescopic mast 160 comprising mast segments 161, 162, 163, 164, 165 is mounted rotationally relative to the pedestal 140 around the longitudinal axis L on a slewing bearing 150 which slewing bearing is shown in more detail in Figs. 2B. A gangway 180 is mounted to the topmost mast segment 165, comprising a platform 185 that is fixed with respect to the topmost mast segment 165. The platform comprises a platform floor 186 for supporting personnel thereon, which floor is intersected by the longitudinal axis L of the mast. The gangway 180 further comprises a first gangway section 181 that is rotatably attached to the platform 185, and a second gangway section 182 that is slidably attached to the first gangway section 181. An electromotor 188 is provided on the first gangway section 181, for driving telescoping movement of the second gangway section 181 relative to the first gangway section. A handrail 187 is arranged at the periphery of the platform floor 186 that is not proximate to the first gangway section 181, to prevent personnel from falling off the platform 185. Likewise, the gangway sections 181, 182, are provided with handrails. When the mast 160 is rotated relative to the pedestal 40 around its longitudinal axis L, the platform 185 and gangway sections 181,182 are rotated around the longitudinal axis L as well.

[0036] The actuators 121,122,123 do not carry the full weight of the mast 160. Instead, most of the weight of the mast is supported by a bearing 130, which is shown in greater detail in Fig. 2B. During use, sensors 200 measure an orientation of the longitudinal axis L of the mast 160 relative to a horizontal plane. Based on the orientation determined by the sensors 200, controller 210 continuously adjusts the orientation of the longitudinal axis L of the mast to be substantially vertical. Thus, even during roll, heave or pitch of the vessel 10, the mast remains substantially vertical. As most of the weight of the mast is exerted on the bearing 130, the actuators do not have to exert as much force on the pedestal 140, and can respond quickly to changes in orientation of the mast.

[0037] By controlling the actuators 121, 122, 123 the mast 160 and slewing bearing 150 are rotatable in conjunction around a first axis and around a second axis (not shown in Fig. 1A, but shown in Fig. 3A), with the first axis and second axis being normal to each other and to the longitudinal axis L of the mast 160.

[0038] In Fig. 1A the mast 160 is shown in an extended position, and the gangway sections 181, 182 are in an extended position and extend upwardly from the mast at an angle α to the longitudinal axis L of the mast. A sensor 220, e.g. a load cell, measures a forward force exerted by distal end of the gangway on the offshore structure in the direction of extension of the gangway sections 181, 182. The controller 210 is adapted for controlling linear actuator 169 and / or motor 188 in such a manner that the forward force measured by sensor 220 remains above 2000 Newton, in order to maintain good contact between the gangway 180 and the offshore structure 1.

[0039] Fig. 1B shows the same system of Fig. 1A, but with the mast 160 in a completely retracted position. With respect to Fig. 1A, the slewing bearing 150 has rotated the mast and gangway 180 degrees relative to the base frame 110 around the longitudinal axis L. The sections of the gangway 180 are in a retracted position as well, and extend downwardly from the mast at an angle β to the longitudinal axis L of the mast, with a distal end of the gangway 180 contacting the deck 11. Personnel may thus walk from the platform 185, across the gangway sections 181, 182 directly onto the deck 11, without having to climb any stairs or use elevators or the like.

[0040] Fig. 2A shows a detail of the outer sides of pedestal 140 and bearing 130 of Fig. 1A, wherein the mast has been omitted for reasons of clarity. The four linear actuators 121 - 124 are each connected via ball joints at one end to the base frame 110, and at the other end to corresponding portions 141 - 144 of the pedestal 140. The pedestal 140 is pivotably supported on the bearing 130. In Fig. 2A the bearing 130 is obscured by the pedestal 140, but it is shown more clearly the partially cut-away view shown in Fig. 2B. The pedestal 140 comprises a plate 146 which is fixedly supported on portions 141 - 144 and is adapted for supporting the mast 160 thereon during use of the gangway and lift system, such that the longitudinal axis of the mast intersects plate 146. The mast is hingeably attached to the pedestal 140 via hinge portion 147, which allows the mast to hinge relative to the pedestal around axis R, to allow the mast to be hinge to a storage configuration in which the longitudinal axis of the mast does not intersect the plate 146. When the mast is in such a storage configuration, the base frame 110, bearing 130, actuators 121 - 124 and mast 160 in retracted position fit within an ISO standard 20ft x 8ft x 8 ft container, as illustrated in Fig. 4. During use, i.e. when the mast is not in the storage configuration but is in a configuration of use as shown in Figs. 1A and 1B, the mast is connected at one side of the pedestal 140 via hinge 147, and is locked to opposite side 148 of pedestal 140 by means of a locking mechanism (not shown).

[0041] Fig. 2B provides a partially cut-away portion of Fig. 2A, showing the partially spherical outer surface 135 of the bearing 130 in contact with a corresponding mating surface 145 of the pedestal, to allow the pedestal to pivot relative to the base frame 110. The bearing 130 is adapted for substantially supporting the weight of the mast 160, gangway and any personnel supported thereon, so that relatively little weight has to be supported by the actuators 121,122,123,124. By actuating the actuators, it is possible to keep the mast in a substantially vertical orientation, while the weight of the mast, gangway and any personnel or load supported thereby, is substantially borne by the bearing 130.

[0042] Additionally, a slewing bearing 150 is shown which is arranged between the bearing 130 and the plate 146 for supporting the mast 160, to allow rotation of the mast around its longitudinal axis relative to the bearing 130 and the base frame 130. The slewing bearing 150 comprises a plurality of rollers 151, for supporting said rotational movement, and is provided with teeth 152 for engaging a toothed gear of an actuator to drive said rotational movement. Though the actuator is not shown here, it will be clear that the actuator may for instance comprise an electro motor or an hydraulically powered motor.

[0043] The bearing 130 is provided at its top end with a through-opening 137 through which power cables and / or hydraulics cables may pass from the lower side of the bearing, through the bearing and to the interior of the mast, e.g. to the gangway. It will be appreciated that in order to allow the cables to pass to the interior of the mast, the plate 146 typically is provided with a through-opening as well, even though such an opening in the plate 146 is not shown in Fig. 2A or 2B.

[0044] Fig. 2B shows a partially cut-away detailed view of the bearing 130 and the slewing bearing 150. The bearing 130 has a partially spherical circumferential outer surface 135, on which a mating surface 145 of pedestal 140 is supported. The bearing 130 thus substantially supports the weight of the mast, and a relatively small portion of the weight of the mast, gangway and any personnel thereon, is supported by the actuators 121,122,123.

[0045] Fig. 3A schematically shows an isometric view of the system according 100 to the invention, intended to show first axis A1 as well as around second axis A2 around which the mast and pedestal can rotate while most of the weight of the mast is supported by the bearing 130. Actuator 190, which is connected on one side to the platform 185, and on another side to the first gangway section 181, can extend or retract in order to rotate the gangway sections 181, 182 around axis B, which axis B is normal to the longitudinal axis L of the mast.

[0046] The mast 160 is further provided with extension / retraction members 172, 174, which are adapted for extending or retracting mast segments 162, 164 when the linear actuator 169 extends or retracts.

[0047] Fig. 3B shows a perspective view of the system of Fig. 3A with the mast 160 in a completely retracted position, and with a distal lower end of gangway section 182 substantially at the level of the base frame 110, so that personnel may reach the platform 185 of the gangway from the deck on which system is mounted.

[0048] Fig. 4 schematically illustrates how the base frame 110 and mast 160 of the system of the invention in a storage configuration in which they can moved along arrow T into a standard 20ft ISO container 400 for transport and / or storage. In Fig. 4 a side of the mast 160 is hingeably connected to the pedestal, and has hinged such that the longitudinal axis of the mast extends substantially parallel to a main plane of the base frame 110. In this manner, the mast 160, base frame 110, and platform floor 186 fit completely in the container 300, when the mast is completely retracted. The railing of the platform, and the gangway sections 181, 182 have been detached from the system and may be transported separately. The actuators 190 for driving rotation of gangway sections 181,182 relative to the platform, have been detached from the platform 185 and from the first gangway section 181, and are stored on the base frame 110.

Examples

Embodiment Construction

[0033]Fig. 1A schematically shows side view of an offshore structure 1 and of a floating vessel 10 that is provided with an offshore gangway and lifting system 100 according to an embodiment of the present invention.

[0034]The offshore structure 1 of the example is fixedly connected to the sea floor via a monopile 2, and comprises a substantially horizontal terrace 3 which allows personnel access to the structure 1. Typically, the offshore structure will be the base of a wind turbine. The vessel 10 floats on the water, with part of the vessel being submerged below the water surface W. Though not shown here, it will be appreciated that alternatively the offshore structure may float while being moored to the seabed. In such a case, motion of the offshore structure relative to the seabed may be independent from motions of the vessel relative to the seabed.

[0035]The vessel 10 comprises a deck 11 on which the offshore gangway and lifting system 100 is provided. The gangway and lifting sys...

FIELD OF THE INVENTION

[0001] The present invention relates to an offshore gangway and lifting system, in particular for transporting personnel from a vessel, e.g. a ship, to an offshore structure, e.g. an offshore structure which is fixed on the seafloor or which is in a floating moored situation. From CN 204507189 a system to be mounted on a ship is known, comprising a base column, a pedestal and a gangway. The base column is vertically arranged and comprises an outer base column and an inner base column, and the inner base column is nested and installed in the outer base column in a liftable manner. The pedestal is installed in a horizontally rotatable manner at a top end of the inner base column. The gangway comprises a first gangway section and second gangway section, wherein the first gangway section is installed on the pedestal in a vertically rotatable manner, and wherein the first and second gangway section are slidably installed. The known system aims to be adaptable to a large range of height differences between the offshore structure and the vessel. A stairs may be provided for boarding the base column, with a distance between the stairs and the base column being 2 meters.

[0002] A drawback of the known system is that it is relatively heavy. It is an object of the invention to provide an offshore gangway and lifting system which at least partially overcomes this drawback.SUMMARY OF THE INVENTION

[0003] To this end, according to a first aspect the present invention provides an offshore gangway and lifting system, comprising: a base frame adapted to be mounted to the deck of a vessel; a mast supported by the base frame, wherein the mast comprises multiple mast segments and is extendable along its longitudinal axis between an extended position and a retracted position; a gangway supported by the mast and comprising one or more gangway sections; actuators adapted for adjusting an orientation of the longitudinal axis of the mast relative to the base frame, each of said actuators being interconnected between the mast and the base frame; one or more sensors for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller for dynamically controlling the actuators, based on the orientation determined by the one or more sensors, to adjust the orientation of the longitudinal axis of the mast to be substantially vertical; wherein the base frame is provided with a bearing having an at least partially spherical circumferential outer surface, wherein the mast is substantially supported by said outer surface in such a manner that the mast and gangway are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis normal to the longitudinal axis of the mast, and around a second axis normal to the longitudinal axis of the mast and normal to the first axis. The controller helps to ensure that the mast will be oriented in a substantially vertical position, e.g. to compensate for roll, heave and / or pitch of the vessel.

[0004] As, during use, the mast and gangway are substantially supported by the bearing, e.g. such that at least 80% of the downward force exerted by the mast and gangway is supported by the bearing, relatively small actuators may be used for maintaining the mast in the substantially vertical orientation. Moreover, as, during use, the system ensures that the mast remains substantially upright, i.e. with its longitudinal axis substantially vertical, typically less force will be exerted by the mast on the actuators during roll and pitch of the vessel, than if the longitudinal axis of the mast were not kept substantially vertical. Thus, the weight of the system of the invention can be kept significantly lower than in prior art systems. The gangway and lifting system of the invention is intended for transfer of personnel and / or a load from the vessel to the offshore structure and vice versa, in particular for transferring personnel and / or a load which enter the gangway from the level of the deck, after which the gangway is lifted and rotated around the longitudinal axis of the mast towards the offshore structure. The bearing may be formed as a truncated bearing, which is truncated at its lower and upper side and comprises a through-opening which extends from the lower to the upper side. A suitable bearing may have an internal diameter of at least 30 cm.

[0005] An example of a suitable sensor for determining an orientation of the mast relative to the horizontal is an inertial measurement unit, which may be mounted to the mast. An example of a suitable sensor for determining an orientation of the base frame relative to the horizontal is a motion reference unit (MRU), which may be mounted to the base frame.

[0006] Advantageously, the invention allows movements such as roll and pitch of a vessel on which the system is mounted, to be compensated for close to the centre of gravity of the vessel. As a result, relatively small movements of the actuators typically suffice to keep the mast and in the vertical position. In turn, any actuators that are connected to the gangway will typically require relatively small movements in order to keep the gangway in a correct orientation.

[0007] In an embodiment, a largest outer diameter of each of the mast segments is less than 4 times the outer diameter of the at least partially spherical surface of the bearing. Preferably, the largest outer diameter of each of the mast segments is less than 3 times the outer diameter of the at least partially spherical surface of the bearing. Typically, that mast segment which is closest to the bearing when the mast is in the extended position will have the largest outer diameter out of all the mast segments.

[0008] In an embodiment the bearing is adapted for supporting the mast and gangway such that, during use of the system, at least 80% of the downward force exerted by the mast and gangway is supported by the at least partially spherical outer surface of the bearing. In an embodiment the system further comprises a pedestal substantially supported on the bearing, wherein the mast is substantially supported on the bearing via the pedestal, wherein one or more of the actuators are connected at one end to the pedestal and at another end to the base frame.

[0009] When seen in projection onto a main plane of the pedestal, the point of connection where the actuators connect to the pedestal typically do not overlap the mast, and preferably are spaced apart from the mast by at least 0,5 to 1,5 m. Typically, the farther the actuators are from the mast, the less force each of the actuators has to apply for maintaining the mast in the substantially vertical orientation.

[0010] In an embodiment the system further comprises a slewing bearing arranged between the pedestal and the mast, and adapted for allowing the mast to rotate around its longitudinal axis relative to the pedestal. Thus, the mast and the gangway can be rotated for instance from a position in which the distal end of the gangway is within the contour of the ship when seen in plane view, e.g. when loading personnel from the vessel to the offshore gangway and lifting system, to a position in which the distal end of the gangway is outside of said contour, e.g. when offloading the personnel from the gangway of the gangway and lifting system to the offshore structure. The slewing bearing is typically attached between an upper surface of the pedestal and a lower side of the mast.

[0011] In an embodiment, during use of the system when the mast is kept in a substantially vertical position, the spherical bearing is arranged below the slewing bearing.

[0012] In an embodiment the bearing, i.e. the bearing having the partially spherical outer surface, is provided with a through-opening at its side which faces the mast, for passage of data cables, power cables, and / or hydraulics cables from below the mast to the interior of the one or more mast segments and / or to the gangway. Thus, power cables and / or hydraulics cables for powering the actuators of the gangway can pass via the through-opening, through the hollow interior of the mast, to the gangway, in particular to actuators of the gangway. The system may further comprise one or more swivels connected to the cable(s) for accommodating rotation of the mast around its longitudinal axis relative to the pedestal and / or the base frame.

[0013] In an embodiment the gangway comprises: a platform attached to the mast and comprising a floor surface for supporting personnel thereon; preferably wherein the one or more gangway sections are supported by the platform and / or by the mast to be rotatable relative to the mast around a third axis normal to the longitudinal axis of the mast. Personnel can thus stand on the floor surface of the platform when the mast is moved from the retracted position to a more extended position. The floor surface of the platform may for instance have an area of between 1,5 m 2< and 6 m 2< . Generally, during lifting or lowering of the platform, the personnel and / or load remain supported on the floor surface, and typically the personnel and / or load will not enter the one or more gangway sections until the gangway is in contact with the offshore structure.

[0014] Preferably, when the mast is in the retracted position, the one or more gangway sections are rotatable around the third axis between a first angle relative to the mast in which the distal end of a most distal one of the one or more gangway sections is arranged below the floor surface of the platform, and a second angle relative to the mast in which said distal end is arranged above said floor surface. This allows personnel on the vessel to enter the platform via the gangway substantially from the level of the deck. The controller may further control an actuator to drive rotation of the one or more gangway sections around the axis normal to the longitudinal axis of the mast, to help compensate for motion of the vessel relative to the offshore structure.

[0015] Preferably, when the mast is in the retracted position, the gangway is rotatable to allow the distal end of the gangway to be at the level of the base frame and / or to contact the deck of the vessel. Thus, no stairs or the like are required for using the offshore gangway and lifting system of the invention.

[0016] In an embodiment the gangway comprises a first gangway section and a second gangway section, wherein the second gangway section is telescopically slidable relative to the first gangway section between an extended position and a retracted position. The gangway may be provided with an actuator connected to both the first and second section, adapted for sliding the first section relative to the second section.

[0017] In an embodiment, the platform is rotationally fixed with respect to the mast. Thus, rotation of the mast around its longitudinal axis relative to the base frame will cause a same rotation of the platform relative to the base frame. No actuators or the like are needed to keep the platform aligned with respect to the mast.

[0018] In an embodiment the longitudinal axis of the mast intersects the floor surface of the platform. The floor surface of the platform directly above the mast thus is also available for supporting personnel thereon.

[0019] In an embodiment the system further comprises one or more actuators for controlling a rotation of the gangway around the third axis relative to the mast. These actuators, typically linear actuators, may be connected at one end to the mast and / or platform, and at another end to a gangway section.

[0020] In an embodiment the system further comprises one or more sensors for detecting a forward force exerted by the distal end of the gangway on the offshore structure, wherein the controller is adapted for controlling movement of the mast and one or more gangway sections to keep the forward force at or above 2000 Newton. This helps ensure that the gangway remains in contact with the offshore structure during relative movement of the vessel and the offshore structure. By forward force is meant a force exerted by the distal end in the longitudinal direction of the gangway section. The force may conveniently be measured using a load cell arranged near the distal end of the gangway, and / or by measuring a force exerted by an actuator which is adapted for driving sliding movement between the at least two gangway sections.

[0021] In an embodiment the system further comprises a linear actuator having a first end attached to a first segment of the mast, and a second end attached to a second segment of the mast, wherein the linear actuator is adapted for driving movement of the mast between the extended and the retracted position. Thus, the second segment of the mast can be moved between an extended and a retracted position relative to the first segment. Typically, the first segment is fixed to pedestal, e.g. via a slewing bearing. The second segment is typically arranged at least partially within the first segment when in the retracted position.

[0022] In an embodiment, the mast segments comprise at least 2, 3, 4 or 5 mast segments, which, when seen in projection onto a plane normal to the longitudinal axis of the mast, are arranged concentrically.

[0023] Preferably, the mast is further provided with extension / retraction members adapted and arranged for extending and retracting one or more further segments of the mast upon extension or retraction of the linear actuator. These extension / retraction members are mechanically driven by relative movement between the first and second segment of the mast. The extension / retraction members are not connected to electrical power cables, hydraulic and / or pneumatic cables. Suitable extension / retraction members are described for instance in US 3,467,217. When seen in cross-section in a plane normal to the longitudinal axis of the mast, the mast segments preferably have a non-circular outer circumference, such as a rounded square outer circumference, to facilitate mounting the extension / retraction members to the mast segments.

[0024] Preferably, the mast is provided with extension / retraction members to allow all mast segments except the mast segment closest to the pedestal, i.e. the first mast segment, to move between the retracted and extended position when the linear actuator changes its length.

[0025] In an alternative embodiment, each mast segment of the mast is provided with a linear actuator for driving movement of said mast segment between the extended and retracted position of the mast.

[0026] In an embodiment the first axis, the second axis and the longitudinal axis of the mast substantially intersect, preferably in a point below the pedestal, more preferably in a point bounded by the partially spherical circumferential outer surface of the bearing.

[0027] In an embodiment the mast is hingeably attached to the pedestal, to allow the mast to hinge to a storage configuration in which the longitudinal axis of the mast extends substantially parallel to the base frame, and such that the mast and base frame, when the mast is in its storage configuration and in its retracted position, fit within an ISO standard 20ft x 8ft x 8 ft container. This allows easy storage and transport of the offshore gangway and lifting system when it is not mounted on the deck of a vessel. Additionally, the hinged connection allows quick installation of the system on a vessel.

[0028] According to a second aspect, the invention provides a method for transferring personnel from a vessel having a deck on which an offshore gangway and lifting system according to the first aspect of the invention is mounted, to an offshore structure, the method comprising: moving the mast to the retracted position, and moving the one or more gangway sections to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to enter the platform via the gangway; when personnel has entered the platform, moving the mast to an extended position, rotating the mast around its longitudinal axis relative to the base frame, and subsequently controlling movement of the gangway towards the offshore structure until a distal end of the gangway contacts the offshore structure. Preferably, after personnel has entered the platform but prior to moving the mast to the extended position, the one or more gangway sections are rotated such that a distal end thereof is arranged above the level of the floor of the platform. Once the distal end of the gangway contacts the offshore structure, extension / retraction of the gangway is typically controlled such that a force exerted by the gangway on the offshore structure in the direction of the one or more gangway sections is at least 2000 Newton.

[0029] According to a third aspect, the invention provides a method for transferring personnel from an offshore structure to a vessel having a deck on which an offshore gangway and lifting system according to the first aspect of the invention is mounted, the method comprising: after personnel has entered the platform, retracting the one or more gangway sections until the gangway is spaced apart from the offshore structure; rotating the mast around its longitudinal axis relative to the base frame, and retracting the mast until the gangway is completely arranged above the vessel; moving the gangway to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to leave the platform via the gangway.

[0030] Again, after personnel has entered the platform but prior to moving the mast to the extended position, the one or more gangway sections are preferably rotated such that a distal end thereof is arranged above the level of the floor of the platform.

[0031] In summary the invention provides an offshore gangway and lifting system and methods for using said system, wherein the system comprises: a base frame adapted to be mounted to the deck of a vessel; a mast which is extendable along its longitudinal axis between an extended position and a retracted position; a gangway supported by the mast; actuators adapted for adjusting an orientation of the longitudinal axis of the mast relative to the base frame, each of said actuators being interconnected between the mast and the base frame; sensors for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller for dynamically controlling the actuators, based on the orientation determined by the sensors, to adjust the orientation of the longitudinal axis of the mast to be substantially vertical; wherein the base frame is provided with a bearing having an at least partially spherical circumferential outer surface, wherein the mast is substantially supported by said outer surface in such a manner that the mast and gangway are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis normal to the longitudinal axis of the mast, and around a second axis normal to the longitudinal axis of the mast and normal to the first axis.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will now be illustrated with reference to the drawings, in which like reference numerals refer to like structures, and wherein Fig. 1A schematically shows a side view of an offshore gangway and lifting system according to the invention, with its mast in an extended position and with the gangway contacting an offshore structure; Fig. 1B schematically shows a side view of the offshore gangway and lifting system of Fig. 1A, with the mast in a retracted position, and with the gangway supported by the vessel; Fig. 2A schematically shows a detail of the pedestal of the system of Figs. 1A and 1B; Fig. 2B shows a partially cut-away view of the pedestal of Fig. 2A; and Fig. 3A shows an isometric view of an offshore gangway and lifting system according to the invention, with its mast in the extended position; Fig. 3B shows a perspective view of an offshore gangway and lifting system of Fig. 3A, with its mast in the retracted position; and Fig. 4 shows the system of the invention stored within a standard ISO 20 feet container. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0033] Fig. 1A schematically shows side view of an offshore structure 1 and of a floating vessel 10 that is provided with an offshore gangway and lifting system 100 according to an embodiment of the present invention.

[0034] The offshore structure 1 of the example is fixedly connected to the sea floor via a monopile 2, and comprises a substantially horizontal terrace 3 which allows personnel access to the structure 1. Typically, the offshore structure will be the base of a wind turbine. The vessel 10 floats on the water, with part of the vessel being submerged below the water surface W. Though not shown here, it will be appreciated that alternatively the offshore structure may float while being moored to the seabed. In such a case, motion of the offshore structure relative to the seabed may be independent from motions of the vessel relative to the seabed.

[0035] The vessel 10 comprises a deck 11 on which the offshore gangway and lifting system 100 is provided. The gangway and lifting system 100 comprises a base frame 110, mounted on the deck 11. Linear actuators, of which linear actuators 121, 122 and 123 are shown in the side view of Fig. 1A, are each fixed at one end to the base frame 110, and at their other end to a pedestal 140. A telescopic mast 160 comprising mast segments 161, 162, 163, 164, 165 is mounted rotationally relative to the pedestal 140 around the longitudinal axis L on a slewing bearing 150 which slewing bearing is shown in more detail in Figs. 2B. A gangway 180 is mounted to the topmost mast segment 165, comprising a platform 185 that is fixed with respect to the topmost mast segment 165. The platform comprises a platform floor 186 for supporting personnel thereon, which floor is intersected by the longitudinal axis L of the mast. The gangway 180 further comprises a first gangway section 181 that is rotatably attached to the platform 185, and a second gangway section 182 that is slidably attached to the first gangway section 181. An electromotor 188 is provided on the first gangway section 181, for driving telescoping movement of the second gangway section 181 relative to the first gangway section. A handrail 187 is arranged at the periphery of the platform floor 186 that is not proximate to the first gangway section 181, to prevent personnel from falling off the platform 185. Likewise, the gangway sections 181, 182, are provided with handrails. When the mast 160 is rotated relative to the pedestal 40 around its longitudinal axis L, the platform 185 and gangway sections 181,182 are rotated around the longitudinal axis L as well.

[0036] The actuators 121,122,123 do not carry the full weight of the mast 160. Instead, most of the weight of the mast is supported by a bearing 130, which is shown in greater detail in Fig. 2B. During use, sensors 200 measure an orientation of the longitudinal axis L of the mast 160 relative to a horizontal plane. Based on the orientation determined by the sensors 200, controller 210 continuously adjusts the orientation of the longitudinal axis L of the mast to be substantially vertical. Thus, even during roll, heave or pitch of the vessel 10, the mast remains substantially vertical. As most of the weight of the mast is exerted on the bearing 130, the actuators do not have to exert as much force on the pedestal 140, and can respond quickly to changes in orientation of the mast.

[0037] By controlling the actuators 121, 122, 123 the mast 160 and slewing bearing 150 are rotatable in conjunction around a first axis and around a second axis (not shown in Fig. 1A, but shown in Fig. 3A), with the first axis and second axis being normal to each other and to the longitudinal axis L of the mast 160.

[0038] In Fig. 1A the mast 160 is shown in an extended position, and the gangway sections 181, 182 are in an extended position and extend upwardly from the mast at an angle α to the longitudinal axis L of the mast. A sensor 220, e.g. a load cell, measures a forward force exerted by distal end of the gangway on the offshore structure in the direction of extension of the gangway sections 181, 182. The controller 210 is adapted for controlling linear actuator 169 and / or motor 188 in such a manner that the forward force measured by sensor 220 remains above 2000 Newton, in order to maintain good contact between the gangway 180 and the offshore structure 1.

[0039] Fig. 1B shows the same system of Fig. 1A, but with the mast 160 in a completely retracted position. With respect to Fig. 1A, the slewing bearing 150 has rotated the mast and gangway 180 degrees relative to the base frame 110 around the longitudinal axis L. The sections of the gangway 180 are in a retracted position as well, and extend downwardly from the mast at an angle β to the longitudinal axis L of the mast, with a distal end of the gangway 180 contacting the deck 11. Personnel may thus walk from the platform 185, across the gangway sections 181, 182 directly onto the deck 11, without having to climb any stairs or use elevators or the like.

[0040] Fig. 2A shows a detail of the outer sides of pedestal 140 and bearing 130 of Fig. 1A, wherein the mast has been omitted for reasons of clarity. The four linear actuators 121 - 124 are each connected via ball joints at one end to the base frame 110, and at the other end to corresponding portions 141 - 144 of the pedestal 140. The pedestal 140 is pivotably supported on the bearing 130. In Fig. 2A the bearing 130 is obscured by the pedestal 140, but it is shown more clearly the partially cut-away view shown in Fig. 2B. The pedestal 140 comprises a plate 146 which is fixedly supported on portions 141 - 144 and is adapted for supporting the mast 160 thereon during use of the gangway and lift system, such that the longitudinal axis of the mast intersects plate 146. The mast is hingeably attached to the pedestal 140 via hinge portion 147, which allows the mast to hinge relative to the pedestal around axis R, to allow the mast to be hinge to a storage configuration in which the longitudinal axis of the mast does not intersect the plate 146. When the mast is in such a storage configuration, the base frame 110, bearing 130, actuators 121 - 124 and mast 160 in retracted position fit within an ISO standard 20ft x 8ft x 8 ft container, as illustrated in Fig. 4. During use, i.e. when the mast is not in the storage configuration but is in a configuration of use as shown in Figs. 1A and 1B, the mast is connected at one side of the pedestal 140 via hinge 147, and is locked to opposite side 148 of pedestal 140 by means of a locking mechanism (not shown).

[0041] Fig. 2B provides a partially cut-away portion of Fig. 2A, showing the partially spherical outer surface 135 of the bearing 130 in contact with a corresponding mating surface 145 of the pedestal, to allow the pedestal to pivot relative to the base frame 110. The bearing 130 is adapted for substantially supporting the weight of the mast 160, gangway and any personnel supported thereon, so that relatively little weight has to be supported by the actuators 121,122,123,124. By actuating the actuators, it is possible to keep the mast in a substantially vertical orientation, while the weight of the mast, gangway and any personnel or load supported thereby, is substantially borne by the bearing 130.

[0042] Additionally, a slewing bearing 150 is shown which is arranged between the bearing 130 and the plate 146 for supporting the mast 160, to allow rotation of the mast around its longitudinal axis relative to the bearing 130 and the base frame 130. The slewing bearing 150 comprises a plurality of rollers 151, for supporting said rotational movement, and is provided with teeth 152 for engaging a toothed gear of an actuator to drive said rotational movement. Though the actuator is not shown here, it will be clear that the actuator may for instance comprise an electro motor or an hydraulically powered motor.

[0043] The bearing 130 is provided at its top end with a through-opening 137 through which power cables and / or hydraulics cables may pass from the lower side of the bearing, through the bearing and to the interior of the mast, e.g. to the gangway. It will be appreciated that in order to allow the cables to pass to the interior of the mast, the plate 146 typically is provided with a through-opening as well, even though such an opening in the plate 146 is not shown in Fig. 2A or 2B.

[0044] Fig. 2B shows a partially cut-away detailed view of the bearing 130 and the slewing bearing 150. The bearing 130 has a partially spherical circumferential outer surface 135, on which a mating surface 145 of pedestal 140 is supported. The bearing 130 thus substantially supports the weight of the mast, and a relatively small portion of the weight of the mast, gangway and any personnel thereon, is supported by the actuators 121,122,123.

[0045] Fig. 3A schematically shows an isometric view of the system according 100 to the invention, intended to show first axis A1 as well as around second axis A2 around which the mast and pedestal can rotate while most of the weight of the mast is supported by the bearing 130. Actuator 190, which is connected on one side to the platform 185, and on another side to the first gangway section 181, can extend or retract in order to rotate the gangway sections 181, 182 around axis B, which axis B is normal to the longitudinal axis L of the mast.

[0046] The mast 160 is further provided with extension / retraction members 172, 174, which are adapted for extending or retracting mast segments 162, 164 when the linear actuator 169 extends or retracts.

[0047] Fig. 3B shows a perspective view of the system of Fig. 3A with the mast 160 in a completely retracted position, and with a distal lower end of gangway section 182 substantially at the level of the base frame 110, so that personnel may reach the platform 185 of the gangway from the deck on which system is mounted.

[0048] Fig. 4 schematically illustrates how the base frame 110 and mast 160 of the system of the invention in a storage configuration in which they can moved along arrow T into a standard 20ft ISO container 400 for transport and / or storage. In Fig. 4 a side of the mast 160 is hingeably connected to the pedestal, and has hinged such that the longitudinal axis of the mast extends substantially parallel to a main plane of the base frame 110. In this manner, the mast 160, base frame 110, and platform floor 186 fit completely in the container 300, when the mast is completely retracted. The railing of the platform, and the gangway sections 181, 182 have been detached from the system and may be transported separately. The actuators 190 for driving rotation of gangway sections 181,182 relative to the platform, have been detached from the platform 185 and from the first gangway section 181, and are stored on the base frame 110.

Examples

Embodiment Construction

[0033]Fig. 1A schematically shows side view of an offshore structure 1 and of a floating vessel 10 that is provided with an offshore gangway and lifting system 100 according to an embodiment of the present invention.

[0034]The offshore structure 1 of the example is fixedly connected to the sea floor via a monopile 2, and comprises a substantially horizontal terrace 3 which allows personnel access to the structure 1. Typically, the offshore structure will be the base of a wind turbine. The vessel 10 floats on the water, with part of the vessel being submerged below the water surface W. Though not shown here, it will be appreciated that alternatively the offshore structure may float while being moored to the seabed. In such a case, motion of the offshore structure relative to the seabed may be independent from motions of the vessel relative to the seabed.

[0035]The vessel 10 comprises a deck 11 on which the offshore gangway and lifting system 100 is provided. The gangway and lifting sys...

Claims

1. An offshore gangway and lifting system (100), comprising: a base frame (110)adapted to be mounted to the deck (11) of a vessel (10); a mast (160) supported by the base frame, wherein the mast comprises multiple mast segments (161 - 165) and is extendable along its longitudinal axis (L) between an extended position and a retracted position; a gangway (180) supported by the mast and comprising one or more gangway sections (181, 182); actuators (121, 122, 123, 124) adapted for adjusting an orientation of the longitudinal axis (L) of the mast (160) relative to the base frame (110), each of said actuators being interconnected between the mast and the base frame; one or more sensors (200) for determining an orientation of the longitudinal axis of the mast relative to a horizontal plane and / or for determining an orientation of the base frame relative to the horizontal; a controller (210) for dynamically controlling the actuators (121, 122, 123, 124), based on the orientation determined by the one or more sensors, to adjust the orientation of the longitudinal axis (L) of the mast to be substantially vertical; wherein the base frame (110) is provided with a bearing (130) having an at least partially spherical circumferential outer surface (135), wherein the mast is substantially supported by said outer surface (135) in such a manner that the mast (160) and gangway (180) are rotatable in conjunction relative to the base frame and relative to the bearing around a first axis (A1) normal to the longitudinal axis (L) of the mast, and around a second axis (A2) normal to the longitudinal axis (L) of the mast and normal to the first axis (A1).

2. System according to claim 1, wherein the bearing (130) is adapted for supporting the mast and gangway such that, during use of the system, at least 80% of the downward force exerted by the mast (160) and gangway (180) is supported by the at least partially spherical outer surface of the bearing.

3. System according to claim 1 or 2, further comprising a pedestal (140) substantially supported on the bearing (130), wherein the mast (160) is substantially supported on the bearing via the pedestal, wherein one or more of the actuators (121, 122, 123) are connected at one end to the pedestal (140) and at another end to the base frame (110), the system further comprising a slewing bearing (150) arranged between the pedestal (140) and the mast (160), and adapted for allowing the mast to rotate around its longitudinal axis (L) relative to the pedestal (140).

4. System according to any one of the preceding claims, wherein the longitudinal axis of the mast (L) extends through each of the one or more mast segments (161 - 165); and / or wherein the one or more mast segments, when seen in projection onto a plane normal to the longitudinal axis (L) of the mast, are arranged concentrically.

5. System according to any one of the preceding claims, wherein the bearing (130) is provided with a through-opening at its side which faces the mast, for passage of power cables and / or hydraulics cables from below the mast to the interior of the one or more mast segments, and / or to the gangway; and / or wherein the bearing (130) is formed as a truncated bearing, which is truncated at its lower and upper side and comprises a through-opening which extends from the lower to the upper side.

6. System according to any one of the preceding claims, wherein the gangway (180) comprises a platform (185) attached to the mast and comprising a floor surface (186) for supporting personnel thereon; and wherein said one or more gangway sections are supported by the platform and / or by the mast to be rotatable relative to the mast around a third axis (B) normal to the longitudinal axis (L) of the mast, preferably wherein the gangway sections are rotatable around the third axis (B) between a first angle relative to the mast in which the distal end of a most distal one of the one or more gangway sections is arranged below the floor surface of the platform, and a second angle relative to the mast in which said distal end is arranged above said floor surface.

7. System according to claim 6, wherein the floor surface of platform is intersected by the longitudinal axis (L) of the mast.

8. System according to anyone of the preceding claims, wherein the mast segments comprise at least 2, 3, 4 or 5 mast segments, which, when seen in projection onto a plane normal to the longitudinal axis of the mast, are arranged concentrically.

9. System according to any one of the preceding claims, further comprising one or more sensors (220) for, when the distal end of the gangway is in contact with the offshore structure, detecting a forward force exerted by the distal end of the gangway on the offshore structure, wherein the controller is adapted for controlling movement of the mast and one or more gangway sections to keep the forward force at or above 2000 Newton.

10. System according to any one of the preceding claims, further comprising a linear actuator (169) having a first end attached to a first segment (161) of the mast, and a second end attached to a second segment (162) of the mast, wherein the linear actuator is adapted for driving movement of the mast between the extended and the retracted position, preferably wherein the linear actuator (169) is arranged on an outer side of the multiple mast segments.

11. System according to claim 10, wherein the mast (160) is further provided with extension / retraction members (172, 174) adapted and arranged for extending and retracting one or more further segments (163, 164, 165) of the mast upon extension or retraction of the linear actuator (169).

12. System according to any one of the preceding claims, wherein the first axis, the second axis and the longitudinal axis (L) of the mast substantially intersect, preferably in a point below the pedestal, more preferably in a point bounded by the partially spherical circumferential outer surface of the bearing.

13. System according to any one of the preceding claims, wherein the mast is hingeably attached to the pedestal, to allow the mast to hinge to a storage configuration in which the longitudinal axis of the mast extends substantially parallel to the base frame, and such that the mast (160) and base frame (110), when the mast is in its storage configuration and in its retracted position, fit within an ISO standard 20ft x 8ft x 8 ft container (400).

14. Method for transferring personnel from a vessel having a deck on which an offshore gangway and lifting system according to any one of claims 1-13 is mounted, to an offshore structure, the method comprising: moving the mast to the retracted position, and moving the one or more gangway sections to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to enter the platform via the gangway; when personnel has entered the platform, moving the mast to an extended position, rotating the mast around its longitudinal axis relative to the base frame, and subsequently controlling movement of the gangway towards the offshore structure until a distal end of the gangway contacts with the offshore structure.

15. Method for transferring personnel from an offshore structure to a vessel having a deck on which an offshore gangway and lifting system according to any one of claims 1-13is mounted, the method comprising: after personnel has entered the platform, retracting the one or more gangway sections until the gangway is spaced apart from the offshore structure; rotating the mast around its longitudinal axis relative to the base frame, and retracting the mast until the gangway is completely arranged above the vessel; moving the gangway to be at an angle of between 10 and 20 degrees to the deck and such that a distal end of the gangway is in contact with the deck to allow personnel to leave the platform via the gangway.

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