Arrangement for positioning a fall pipe end

Abstract

An arrangement for positioning a fall pipe end (414) during subsea rock installation includes a submersible frame (400) adapted to be lowered towards an underwater structure. The submersible frame has a first (401) frame structure carrying propulsion equipment (415) and a second frame structure (402) carrying survey equipment (406, 407), a channel structure (410), and a rotation system with an actuator (403). The actuator (403) has a first (411) and a second element (412) and being adapted to convert an energy input into a rotation of the second element (412) when holding the first element (411). The second element (412) is connected to the second frame structure (402), such that in suspended condition of the submersible frame (400), the survey equipment (406, 407) can be rotated about a vertical axis (409) by energizing the actuator (403), without using the propulsion equipment (415).

1 . An arrangement suitable for positioning a fall pipe end, during subsea rock installation from a vessel, the arrangement comprising:
 a submersible frame adapted to be lowered towards an underwater structure, while being suspended from the vessel, the submersible frame comprising:
 a first and a second frame structure; 
 a channel structure adapted to receive the fall pipe end or to be joined to the fall pipe end; 
   propulsion equipment adapted for moving the submersible frame in a horizontal plane, thereby controlling the position of the submersible frame independently from the vessel, the propulsion equipment being mounted to the first frame structure;   survey equipment adapted for subsea sensing or inspection, the survey equipment being mounted to the second frame structure;
 wherein the arrangement comprises a rotation system operable independently from the propulsion equipment, 
 wherein: 
 the rotation system comprises an actuator, the actuator comprising a first and a second element adapted to mutually engage or interact, and the actuator being adapted to convert an energy input into a rotation of the second element when holding the first element, the rotation being about a vertical axis; 
   the second element of the actuator is connected to the second frame structure carrying the survey equipment,   
       such that in suspended condition of the submersible frame, the survey equipment can be rotated about the vertical axis by energizing the actuator, without using the propulsion equipment. 
     
     
         2 . The arrangement according to  claim 1 , wherein the first element of the actuator is adapted to be connected to the vessel, via a hoisting system for suspending the submersible frame, or due to the first element being fixed directly to the deck of the vessel, thereby allowing for a rotation of the second element relatively to the first element upon energizing the actuator. 
     
     
         3 . The arrangement according to  claim 1 , wherein the first element of the actuator is connected to the vessel via a hoisting system, and the second element of the actuator is connected to the submersible frame, such that during use, the actuator is submerged into the water together with the submersible frame. 
     
     
         4 . The arrangement according to  claim 3 , wherein the first frame structure carrying the propulsion equipment and the second frame structure carrying the survey equipment are joined, such that by energizing the actuator, the survey equipment and propulsion equipment are rotated together about the vertical axis. 
     
     
         5 . The arrangement according to  claim 3 , wherein the second frame structure carrying the survey equipment is mounted rotatably with respect to the first frame structure carrying the propulsion equipment, such that by energizing the actuator, the survey equipment is rotated about the vertical axis without rotating the propulsion equipment. 
     
     
         6 . The arrangement according to  claim 1 , wherein the first element of the actuator is fixed directly to the deck of the vessel, and the second element of the actuator is connected to the submersible frame via a hoisting system, such that during use, the actuator is found at deck level and is not submerged into the water. 
     
     
         7 . The arrangement according to  claim 1 , wherein the second frame structure comprises one or more elongated arms, the survey equipment being mounted to the one or more elongated arms, the one or more elongated arms being rigidly connected to the rest of the second frame structure, or being collapsible with respect to the rest of the second frame structure. 
     
     
         8 . The arrangement according to  claim 7 , wherein the second frame structure comprises a set of two elongated arms, each of the arms mounted at opposite sides of the submersible frame, wherein
 the two elongated arms are rigidly connected to the rest of the second frame structure and are in line, or   the two elongated arms are collapsible with respect to the rest of the second frame structure, and are in line in unfolded condition.   
     
     
         9 . The arrangement according to  claim 1 , wherein the vertical rotation axis corresponds to the central axis of the channel structure, such that the survey equipment can be rotated about the central axis of the channel structure. 
     
     
         10 . The arrangement according to  claim 1 , wherein the first element comprises a ring having a central axis extending in vertical direction, and the actuator is adapted to move the second element along a ring-shaped trajectory coaxially with the ring, such that the second element is rotated about the central axis of the ring,
 or   the second element comprises a ring having a central axis extending in vertical direction, and the actuator is adapted to rotate the ring about its central axis.   
     
     
         11 . The arrangement according to  claim 1 , wherein the first or second element respectively is a slewing ring comprising a toothed rack along its circumference, and the second or first element respectively is a pinion adapted to engage with the toothed rack. 
     
     
         12 . The arrangement according to  claim 3 , wherein the first element or the second element respectively comprises a slewing ring having a central axis corresponding to the vertical rotation axis,
 and the rotation system comprises multiple bearing assemblies distributed over the circumference of the slewing ring, each of the bearing assemblies adapted to retain the slewing ring in vertical direction with respect to the submersible frame, while allowing for a rotation of the slewing ring relatively to the second or first frame structure respectively.   
     
     
         13 . The arrangement according to  claim 12 , wherein each of the bearing assemblies comprises three individual bearings, of which the first bearing engages with the upper surface of the slewing ring, the second bearing engages with the bottom surface of the slewing ring, and the third bearing engages with the side surface of the slewing ring. 
     
     
         14 . The arrangement according to  claim 1 , wherein the propulsion equipment comprises multiple thrusters, distributed along the circumference of the first frame structure. 
     
     
         15 . A method for positioning a fall pipe end during subsea rock installation from a vessel, the method comprising:
 providing a vessel suitable for subsea rock installation;   providing a fall pipe;   providing an arrangement according to  any of the preceding claims ;   arranging an end portion of the fall pipe in the channel structure, or joining the fall pipe end to the channel structure;   lowering the submersible frame into the water, towards an underwater structure, while being suspended from the vessel;   operating the rotation system, by energizing the actuator, such that the second element is rotated about the vertical rotation axis relatively to the first element, thereby rotating the survey equipment about the vertical rotation axis.