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.

We claim: 
     
         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.