Subsea remotely operated chain tensioning and slacking system

Abstract

A mooring line tension adjusting system comprises a connecting device, connecting and locking two adjacent chain sections of a mooring line, and an operating device, moving one of the chain sections inside the connecting device to change the tension of the mooring line. The system has the inventive feature that the operating device is remotely attachable to the connecting device before a tensioning operation and detachable from the connecting device after the tensioning operation. The invention discloses also a method how to use the tensioning system.

1 . A mooring line tension adjusting system, comprising
 a. a connecting device, connecting and locking two adjacent chain sections of a mooring line, and   b. an operating device, moving one of the chain sections inside the connecting device to increase or relax a tension on the mooring line,   wherein the operating device is remotely attachable to the connecting device using docking elements provided on both the connecting device and the operating device before a tensioning operation and the operating device is detachable from the connecting device after a tension adjustment operation.   
     
     
         2 . A connecting device for use in the mooring line tension adjusting system according to  claim 1 , comprising a first connection arrangement for a first chain and a second connection arrangement for a second chain wherein the first connection arrangement provides a permanently fixed connection of said first chain and the second connection arrangement provides a connection which can be modified by an operating device, wherein the connecting device comprising a first docking element enables the operating device to firmly attach to the connecting device prior to performing a tension adjusting operation. 
     
     
         3 . An operating device for use in the mooring line tension adjusting system according to  claim 1 , comprising a second docking element being compatible with a first docking element on a connecting device comprising a first connection arrangement for a first chain and a second connection arrangement for a second chain wherein the first connection arrangement provides a permanently fixed connection of said first chain and the second connection arrangement provides a connection which can be modified by an operating device, wherein the connecting device comprising a first docking element enables the operating device to firmly attach to the connecting device prior to performing a tension adjusting operation, enabling the operating device to firmly attach to the connecting device to perform a tension adjustment operation. 
     
     
         4 . A method for tensioning a mooring line with the tension adjusting system according to  claim 1 , said system comprising a connecting device connecting two chains and an operating device, the method comprising the steps of
 a. positioning a surface vessel above the mooring line, slightly to the side of a connecting device, where two sections of the mooring line are connected by the connecting device;   b. attaching one end of a first chain to one of two attachment points provided on a guide at an lower end of the operating device and attaching a first weight bar to the second end of the first chain;   c. attaching a second chain, longer than the first chain to a second attachment point on the guide at the lower end of the operating device and attaching a second weight bar to the second end of the second chain;   d. attaching a lifting/handling equipment to a third attachment point at an upper end of the operating device;   e. connecting an umbilical to a power system of the operating device, and to an power supply system on board of the surface vessel;   f. overboard the operating device with the umbilical and accessories and lower it to slightly above the same depth as the connecting device mounted into the mooring line;   g. moving the vessel such that the second chain hits the connecting device, and by moving the vessel slightly passed but without the second chain jumping over the operating device should rotate such that it orients correctly relative to the connecting device;   h. lowering the operating device such that the connecting device is between the first and the second chain;   i. continuing to lower the operating device until it sits on top of the connecting device;   j. after the lower end of the operating device has docked onto the connecting device, sliding it down along the connecting device until it stops against a first docking element, a second docking element on the operating device connecting to the first docking element;   k. operating the operating device via the umbilical for pushing the mooring line in a tensioning direction; repeating this step until a requested tension is achieved; and   l. lifting the operating device off the connecting device, unhooking from the first docking element.