Subsea carrier

Abstract

A subsea carrier ( 100 ) for transporting a fluid, e.g. CNG or crude, comprises a main body ( 101 ) for containing the fluid at a predetermined internal pressure, wherein the main body ( 101 ) preferably is made of concrete and designed to operate at a water depth where the external pressure substantially counteracts the internal pressure. The subsea carrier has a floating element ( 102 ) connected to the main body ( 101 ) by a stabilising cable ( 132 ), wherein the stabilising cable ( 132 ) comprises a first rope ( 321 ) for transmitting force and is attached to a first connector ( 134 ) that is movable with respect to the main body ( 101 ). A system wherein the subsea carrier is towed by a surface vessel ( 3 ) or is self-propelled and controlled remotely is also disclosed. The subsea carrier ( 100 ) reduces operational costs relative to subsea carriers with traditional control surfaces and ballasting systems at large cargo volumes, e.g. 150 000 m 3 or more.

1 - 17 . (canceled) 
     
     
         18 . A subsea carrier for transporting a fluid comprising:
 a main body for containing the fluid at a predetermined internal pressure, wherein the main body is designed to operate at a water depth where the external pressure substantially counteracts the internal pressure;   a stabilising cable; and   a floating element connected to the main body by the stabilising cable, wherein the stabilising cable comprises a first rope for transmitting force and is attached to a first connector that is movable with respect to the main body.   
     
     
         19 . The subsea carrier according to  claim 18 , wherein the length of the stabilising cable exceeds the water depth. 
     
     
         20 . The subsea carrier according to  claim 18 , further comprising a bridle for distributing a towing and lifting force. 
     
     
         21 . The subsea carrier according to any  claim 18 , wherein the main body comprises a ballast element connected under a tank element. 
     
     
         22 . The subsea carrier according to  claim 18 , wherein the main body comprises a first cargo compartment separated from a second cargo compartment by a movable gas tight sealing element. 
     
     
         23 . The subsea carrier according to  claim 22 , wherein the gas tight sealing element is a flexible membrane. 
     
     
         24 . The subsea carrier according to  claim 18 , further comprising at least one ballast tank for trimming and depth control. 
     
     
         25 . The subsea carrier according to  claim 18 , wherein the main body comprises a control surface and/or a thruster for causing rotation of the main body about at least one of three mutually perpendicular axes of rotation. 
     
     
         26 . The subsea carrier according to  claim 18 , wherein the main body comprises at least one thruster for causing translation of the main body along at least one of tree mutually perpendicular axes. 
     
     
         27 . A system for transporting a fluid comprising a subsea carrier according to  claim 24 , further comprising:
 a communication line for conveying control related signals between a controller at the surface and the main body; and   a power line supplying electrical power from an electric generator at the surface to the main body.   
     
     
         28 . The system according to  claim 27 , further comprising a surface vessel with the controller and the electric generator, and a control cable with the communication line and the power line. 
     
     
         29 . The system according to  claim 28 , wherein the control cable further comprises a second rope for transmitting force. 
     
     
         30 . The system according to  claim 28 , wherein the control cable further comprises a fuel line from the main body to the surface vessel. 
     
     
         31 . The system according to  claim 28 , wherein the floating element comprises the controller and the electric generator, and the stabilising cable comprises the communication line and the power line. 
     
     
         32 . The system according to  claim 28 , wherein the stabilising cable further comprises a fuel line from the main body to the floating element. 
     
     
         33 . A method for operating a subsea carrier according to  claim 22 , comprising the steps of:
 filling the first cargo compartment with a cargo fluid at the predetermined internal pressure;   transporting the cargo fluid from a subsea loading point to a subsea unloading point;   expelling the cargo fluid from the first cargo compartment;   filling the first cargo compartment with a return fluid at a second internal pressure;   transporting the return fluid from the unloading point to the loading point, wherein expelling the cargo fluid involves allowing water to flow into the second cargo compartment, and filling the first cargo compartment with a return fluid involves pumping water out from the second cargo compartment.   
     
     
         34 . The method according to  claim 33 , wherein the subsea loading point and/or the subsea unloading point comprises a subsea platform serving as a foundation for the main body during loading and/or unloading, wherein expelling the cargo fluid involves allowing the water to flow from a storage tank in the platform, and filling the first cargo compartment with a return fluid involves pumping the water back into the storage tank.