OFFSHORE TRANSFER SYSTEM WITH A DOCKING POSITION ON A TRANSFER VESSEL THAT COMPRISES A MOTION COMPENSATED MOORING ELEMENT

Abstract

An offshore transfer system for transferring persons and/or cargo between a transfer vessel and an offshore object, includes the transfer vessel having a docking position with a mooring element. The offshore object includes a docking arm, in particular a gangway, that at a free end is provided with a coupling device. The docking position on the transfer vessel has its mooring element at least partly compensated for transfer vessel motions, at least during a docking operation, and includes one or more force actuators for moving the mooring element relative to the transfer vessel, one or more sensors for detecting motions of the transfer vessel, and a control unit for driving the one or more force actuators such that the motions of the transfer vessel get at least partly compensated for the mooring element.

Claims

1. An offshore transfer system for transferring persons and/or cargo between a transfer vessel and an offshore construction, floating platform or other vessel, wherein the transfer vessel comprises: a docking position with a mooring element, wherein the offshore construction, floating platform or other vessel comprises: a docking arm, in particular a gangway, that at a free end is provided with a coupling device, wherein the mooring element is configured to have the coupling device at the free end of the docking arm coupled thereto during a docking operation, wherein the docking position on the transfer vessel has its mooring element at least partly compensated for transfer vessel motions, at least during the docking operation, and comprises: one or more force actuators for moving the mooring element relative to the transfer vessel; one or more sensors for detecting one or more of pitch, roll and/or heave motions of the transfer vessel; and a control unit for driving the one or more force actuators such that the one or more detected motions of the transfer vessel get at least partly compensated for the mooring element of the docking position.

2. The offshore transfer system according to claim 1, wherein the mooring element is supported by and connected to the transfer vessel by means of a hinge connection designed to allow the transfer vessel to rotate relative to the mooring element in a rotation direction around a y-axis, wherein the y-axis extends substantially horizontal, and wherein a first one of the one or more force actuators acts between the transfer vessel and the mooring element for swivelling the mooring element around the hinge connection relative to the transfer vessel at least in the rotation direction around said y-axis.

3. The offshore transfer system according to claim 2, wherein the hinge connection is designed to allow the transfer vessel to also rotate relative to the mooring element in a rotation direction around an x-axis, wherein the x- and y-axis extend substantially horizontal and orthogonal relative to each other, and wherein a second one of the one or more force actuators acts between the transfer vessel and the mooring element for swivelling the mooring element around the hinge connection relative to the transfer vessel at least in the rotation direction around said x-axis.

4. The offshore transfer system according to claim 3, wherein the hinge connection comprises two substantially horizontal orthogonal pivot pins.

5. The offshore transfer system according to claim 4, wherein the two pivot pins form part of a Universal joint, Cardan joint or a Gimbal assembly.

6. The offshore transfer system according to one claim 1, wherein the mooring element is supported by and connected to the transfer vessel by means of a z-guidance designed to allow the transfer vessel to move relative to the mooring element in a translation direction along a z-axis, wherein the z-axis extends substantially vertical, and wherein a third one of the one or more force actuators acts between the transfer vessel and the mooring element for translating the mooring element along the z-guidance relative to the transfer vessel at least in the translation direction along said z-axis.

7. The offshore transfer system according to claim 1, wherein the mooring element is supported by and connected to the transfer vessel by means of a x- and/or y-guidance designed to allow the transfer vessel to move relative to the mooring element in a translation direction along an x- and/or y-axis, wherein the x- and/or y-axis extend substantially horizontal and orthogonal relative to each other, and wherein a fourth and/or fifth one of the one or more force actuators acts between the transfer vessel and the mooring element for translating the mooring element along the x- and/or y-guidance relative to the transfer vessel at least in the translation direction along said x- and/or y-axis.

8. The offshore transfer system according to claim 1, wherein the docking position further comprises: an upright column extending upwards from the transfer vessel, wherein the mooring element is provided on an upper portion of the column.

9. The offshore transfer system according to claim 8, wherein lever arms are provided which are fixedly connected to the column and extend in a substantially sideways direction from it, the force actuators being provided in between the transfer vessel and the lever arms.

10. The offshore transfer system according to claim 1, wherein the one or more sensors comprise: a position sensor for sensing deteriorations from an aimed orientation of the mooring element, wherein the control unit is configured for driving the force actuators in dependence of sensed deteriorations by the position sensor such that the force actuators bring the mooring element back to its aimed orientation.

11. The offshore transfer system according to claim 1, wherein the force actuators are hydraulic cylinders.

12. The offshore transfer system according to claim 1, wherein the docking arm is telescopingly extendable, wherein drive means are provided for retracting or extending the docking arm during mooring, and/or wherein the docking arm is mounted on the offshore construction, floating platform or other vessel movable around a horizontal and/or vertical shaft, wherein drive means are provided for retracting or extending the docking arm during a docking operation.

13. A transfer vessel for an offshore transfer system according to claim 1, comprising a mooring element that is at least partly compensated for transfer vessel motions.

14. A method for coupling the transfer vessel with the docking arm on the offshore construction, floating platform or other vessel, according to one of the preceding claims, comprising the steps: sailing the transfer vessel to a position close to the offshore construction, floating platform or other vessel; and coupling the coupling device at the free end of the docking arm to the mooring element on the transfer vessel, wherein during and/or after the coupling has been made, the force actuators are operated for getting or keeping the mooring element positioned in an aimed orientation independent of motions of the transfer vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] An example of the transfer system according to the invention shall be explained in more detail below with reference to the accompanying drawings in which:

[0038] FIG. 1 schematically shows a perspective view of a motion compensated mooring element on a transfer vessel together with part of a gangway to be coupled thereto;

[0039] FIG. 2 shows a first variant hereof; and

[0040] FIGS. 3a and 3b show a second variant hereof preceding and after coupling.

DETAILED DESCRIPTION OF THE INVENTION

[0041] In FIG. 1 a transfer vessel, of which merely a small portion is shown, is given the reference TV. The transfer vessel TV has a longitudinal direction along an x-axis and a transverse direction along a y-axis. The transfer vessel TV is provided with an upper deck on top of which a docking position DP is provided that comprises a supporting column SC and a mooring element ME on top thereof. The column SC extends upwardly in a vertical direction along a z-axis.

[0042] Between the column SC and the transfer vessel TV a Cardan joint 4 is provided. The Cardan joint 4 forms a hinge connection which has two pivot pins 4a, 4b extending in the horizontal directions x and y and allowing the transfer vessel TV and the column SC to rotate relative to each other around those x- and y-axes. An angle of 90 degrees is enclosed between the two pivot pins 4a, 4b.

[0043] The pivot pin 4b is supported by brackets 5 which are fixedly connected to the transfer vessel TV. The pivot pin 4a is supported by brackets 6 which are fixedly connected to a lower end of the column SC. The column SC projects upwardly in the vertical direction along a z-axis and encloses angles of 90 degrees with both pivot pins 4a, 4b.

[0044] The lower end of the column SC includes two lever arms 10, a first one 10a extending in the x-direction, and a second one 10b extending in the y-direction. Between outer ends of the lever arms 10 and the transfer vessel TV, first and second hydraulic cylinders 11a, 11b are placed. Those cylinders 11 may be pivotally mounted with one side to the lever arms 10 and at their other side to the transfer vessel TV. When operated, the hydraulic cylinders 11 are lengthened or shortened and force the column SC, together with the mooring element ME on top thereof, to rotate/swivel around the x- and/or y-axis relative to the transfer vessel TV.

[0045] The column SC has a lower column part SCa and an upper column part SCb. The upper column part SCb is guided telescopingly relative to the lower column part SCa such that it is movable up and down along the z-axis. Between the lower and upper column parts SCa and SCb, a third hydraulic cylinder 20 is placed. When operated, the hydraulic cylinder 20 is lengthened or shortened and forces the upper column part SCb, together with the mooring element ME on top thereof, to translate along the z-axis relative to the transfer vessel TV.

[0046] The mooring element ME is configured to have a complementary coupling device CD that is provided at a free end of a gangway GW coupled thereto during a docking operation of the transfer vessel TV with an offshore object (not shown in FIG. 1) on which the gangway GW is provided. In the embodiment shown in FIG. 1 the mooring element ME comprises a coupling surface 22 and two upwardly projecting pins 23, whereas the coupling device CD comprises a coupling surface 24 with two through going openings 25 that are dimensioned slightly larger than the pins 23.

[0047] Between the mooring element ME and the top of the column SC, a first guidance member 30 is provided that is movably guided relative to the upper column part SCb such that it is movable back and forth along the x-axis. Between the first guidance member 30 and the upper column part SCb, a fourth hydraulic cylinder 31 is placed. When operated, the hydraulic cylinder 31 is lengthened or shortened and forces the mooring element ME to translate along the x-axis relative to the transfer vessel TV.

[0048] Between the mooring element ME and the top of the column SC, furthermore a second guidance member 34 is provided that is movably guided relative to the first guidance member 30 such that it is movable between starboard and port side along the y-axis. Between the first guidance member 30 and the second guidance member 34, a fifth hydraulic cylinder 35 is placed. When operated, the hydraulic cylinder 35 is lengthened or shortened and forces the mooring element ME to translate along the y-axis relative to the transfer vessel TV.

[0049] Between the mooring element ME and the top of the column SC, furthermore a turntable 38 is provided that is rotatable relative to the second guidance member 34 such that it is rotatable clockwise and counter-clockwise around the z-axis. Between the second guidance member 34 and the turntable 38, a toothed gear 39 is placed. When operated, the toothed gear 39 is rotated in either direction and forces the mooring element ME to rotate around the z-axis relative to the transfer vessel TV.

[0050] A possible method for docking the transfer vessel TV to the offshore object shall now be explained with reference to FIG. 1. In FIG. 1 it is shown that the vessel TV has already been sailed to a position alongside the offshore object such that the mooring element ME is positioned in the neighbourhood of the gangway GW that projects sideways of the offshore object. The transfer vessel TV than be kept at that position, for example by being dynamically positioned.

[0051] The gangway GW is of a type that is telescopingly extendable and that can be turned around a vertical axis and that can swivel around a horizontal axis. Thus if necessary the gangway GW can be manoeuvred to point with its outer end towards the mooring element ME. If necessary, for example depending on the water level of the sea, it is also possible to raise or lower the gangway GW in such a way that the gangway GW gets to point towards the mooring element ME. Subsequently the gangway GW can be extended until the coupling device CD comes to lie straight above the mooring element ME. By subsequently lowering the gangway GW, the coupling device CD automatically gets to grip with its openings 25 over the pins 23.

[0052] During the entire docking operation cq coupling process the mooring element ME can be kept in a stable orientation and position relative to the offshore object.

[0053] As soon as the coupling is made, the gangway GW can be given the full freedom to extend or retract such that the distance between the transfer vessel TV and the offshore object can change somewhat. At the same time the swivelling of the gangway GW can also be set free such that the gangway GW is free to alter its angle of inclination, which gives the transfer vessel TV the freedom to rise up and downwards somewhat together with the waves. Furthermore, the turning of the gangway GW can also be set free such that the gangway GW is given the full freedom to turn such that the transfer vessel TV is given the freedom to turn left or right.

[0054] According to the invention the column SC with the mooring element ME on top thereof maintains to be vertically orientated both during coupling and after the coupling has been made. For this, operation of the hydraulic cylinders 11 may be necessary. Depending on the amount and direction of rolling or pitching movements the transfer vessel TV makes, the hydraulic cylinders 11 need to be adjusted in length in order to have the column SC maintain its vertical orientation. This is obtained by means of a control unit which receives sensor signals of a position sensor which is built into the mooring element ME. Whenever the control unit receives a signal of the sensor that the column SC has left its vertical orientation, it immediately sends out corresponding signals to the hydraulic cylinders 11 to change their length(s) and with this exert suitable forces to the column SC in order to have it move back towards its aimed vertical orientation.

[0055] The hydraulic cylinders 11 can be operated over and over again each time that it is necessary to make a correction in order to have the column SC maintain its vertical orientation.

[0056] In a similar manner to the abovementioned automated compensation of the orientation of the mooring element ME for rolling and pitching movements of the transfer vessel TV, also an automated compensation of the position of the mooring element ME for x-y-z-translational motions, movements or displacements of the transfer vessel TV can take place, both during coupling and after the coupling has been made. For this, operation of the hydraulic cylinders 20, 31, 35 may be necessary. Depending on the amount and direction of the translational movements the transfer vessel TV makes, the hydraulic cylinders 20, 31, 35 need to be adjusted in length in order to have the mooring element ME maintain not only its orientation but also its position. This is also obtained by means of the control unit receiving the sensor signals of the position sensor. Whenever the control unit receives a signal of the sensor that the mooring element has left its position, it immediately sends out corresponding signals to the hydraulic cylinders 20, 31, 35 to change their length(s) and with this exert suitable forces to the mooring element ME in order to have it move back towards its aimed position.

[0057] In addition thereto or in the alternative, the operation of the hydraulic cylinders 20, 31, 35 also can be used for docking the transfer vessel's mooring element ME onto a gangway with less DOF's, for example a gangway that is not telescopingly extendable and/or not turnable and/or not swivable. After the transfer vessel TV has been sailed to the proximity of such a more rigid gangway GW, the mooring element ME subsequently can be accurately manoeuvred towards the coupling device CD by means of operation of the hydraulic cylinders 20, 31, 35. During this accurate manoeuvring, the mooring element ME is advantageously controlled by the control unit to substantially maintains its orientation by means of the automated pitch and roll compensations. The accurate manoeuvring can be done manually but also can be automated by equipping the mooring element ME and the coupling device CD with suitable sensors that are configured to send signals to the control unit. If it is then detected that the pins on the mooring element ME are not properly aligned with the openings in the coupling device CD on the gangway GW, then the mooring element ME can even be rotated around the z-axis by operation of the toothed gear 39. Thus a coordination of the mooring element ME with the stationary or moving tip of the gangway GW is possible.

[0058] In FIG. 2 a variant is shown in which the mooring element ME is only compensated for pitch and roll motions as well as for up and down motions. For that the docking position (DP) still comprises a telescopingly extendable support column SC that is rotatable around a hinge connection with two horizontal orthogonal pivot pins 4a, 4b.

[0059] The mooring element ME here comprises an upwardly projecting bar 50 above a dish-shaped coupling surface 51.

[0060] It can be seen here that the gangway GW is mounted with a base 52 to an offshore object that here is formed by a Floating Production, Storage and Offloading (FPSO) platform. Between the base 52 and the gangway GW a hinge connection is provided which has a single pivot pin 54 which extends in a horizontal direction and which allows the gangway GW to swivel around this horizontal axis. The gangway GW comprises a fixed gangway section GWa and a telescoping gangway section GWb. The telescoping gangway section GWb can slide in and out of the fixed gangway section GWa in a direction A. Between the two sections (hydraulic) drive means can be provided for actively lengthening or shortening the gangway GW whenever desired, in particular during a coupling action to the mooring element ME on the transfer vessel TV. The gangway GW is hung to the base by means of cables 55 which are run over a hoisting device. Thus the angle of inclination of the gangway GW can actively be altered whenever desired, in particular during a coupling action to the mooring element ME on the transfer vessel TV. Between the base 52 and the offshore object a turnable connection is provided which allows the base 52 together with the gangway GW to turn around a vertical axis.

[0061] At its outer free end the gangway GW is provided with the coupling device CD that here is formed by a hook 52 which is complementary to the bar 50 and that is operable between an open and closed position.

[0062] In FIG. 3 a variant is shown in which the mooring element ME is only compensated for pitch motions. For that the docking position comprises a support column SC that now is merely rotatable around a hinge connection with one horizontal pivot pins 4a.

[0063] The mooring element ME here comprises a sideways projecting connection surface. The gangway GW here is of a similar type as the one shown in FIG. 2, that is to say that it is telescopingly extendable, turnable and swivable relative to the offshore object it is mounted to. At its outer free end the gangway GW is provided with a coupling device CD that is complementary to the mooring element ME, for example by means of electromagnetic attraction forces.

[0064] Thus an economic simple version of the transfer system is provided that still makes use of the inventive pitch compensation for its mooring element on the transfer vessel. The other transfer vessel motions can be dealt with by the slewing/luffing/telescoping provisions that are already provided in the gangway GW on the other offshore object.

[0065] Besides the embodiments shown numerous variants are possible. For example the dimensions and shapes of the various parts can be varied, and instead of hydraulic cylinders other types of force actuators can be used. Also all kinds of other types of coupling means can be provided at or near the free end of the gangway and on the mooring element. Instead of gangway it is also possible to use other types of docking arms along or via which the transfer of persons and/or cargo can take place after docking.

[0066] Thus the invention provides for an effective, user-friendly and save transfer system with which persons and all kinds of cargo can be quickly transferred from a transfer vessel towards a stationary or floating offshore object even at heavy sea or otherwise difficult conditions.

[0067] It should be understood that various changes and modifications to the presently preferred embodiments can be made without departing from the scope of the invention, and therefore will be apparent to those skilled in the art. It is therefore intended that such changes and modifications be covered by the appended claims.