Abstract:
A lifting tool for opposing twisting of generally submerged ropes. The lifting tool includes a body with a center axis, an operable lock configured to selectively limit movement of a rope connector through the body, and a structure coupled to the body and configured to couple to a hoist or crane. The lifting tool also includes at least one rudder positioned at a radial distance from the center axis to oppose rotation of the lifting tool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is the U.S. National Stage filing made under 35 U.S.C. §371 of International Application No. PCT/NO2011/000308 filed Nov. 2, 2011, which claims priority to Norwegian Patent Application No. 20101540 filed Nov. 3, 2010, entitled “Lifting Tool For Opposing Twisting Of Generally Submerged Ropes.” 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]    Not applicable. 
       BACKGROUND  
       [0003]    The present disclosure relates to a lifting tool for opposing twisting of generally submerged ropes. More precisely, the present disclosure relates to a lifting tool for opposing twisting of generally submerged ropes where the lifting tool comprises a body having an operable lock that is adapted to catch a rope connector, and a structure that is designed to be connected to a hoist or a crane. 
         [0004]    During hoisting operations at sea where heavy items having weights on the order of several hundred tons are to be disposed on the seabed, the availability of steel ropes having sufficient combined strength and length has become a limiting factor for the size of items that can be handled. The seabed may be located several kilometers below sea level, and the weight of the steel rope therefore becomes significant. 
         [0005]    It may therefore be necessary to use fiber ropes that have a density close to that of water, to allow the largest items to be submerged into deep waters. 
         [0006]    The use of fiber ropes for operations of this type requires consideration of conditions not normally problematic when using steel ropes. For example, the effective life of a fiber rope, which includes a significant proportion of carbon fiber, depends directly on the number of load-related flexures that the fiber rope is exposed to. 
         [0007]    Oftentimes, hoisting operations of this type are heave-compensated, and the lifting rope will therefore be continuously reeled in and out from a winch due to the heave motion of the lifting vessel. Even if the item being lifted is stationary relative to the seabed, the lifting rope will still be reeled in and out, whereby the effective life of a fiber rope is reduced relatively quickly. 
         [0008]    Norwegian Patent Application 20090729 discloses a method for paying out a relatively long fiber rope, which carries a load, by means of a shorter steel rope. The method, which includes the use of parallel ropes, is explained in detail in that application document. 
         [0009]    A problem when utilizing parallel ropes is the tendency of the rope to twist and to get entangled in each other. As the ropes have to be moved independently of each other in the sea, an entanglement may in a worst case lead to cutting of the ropes and loss of a valuable item. 
       SUMMARY  
       [0010]    An object of the present disclosure is to remedy or reduce at least one of the disadvantages associated with the prior art. 
         [0011]    In accordance with various embodiments, a lifting tool is provided for opposing twisting of generally submerged ropes. The lifting tool comprises a body with a center axis, an operable lock configured to catch a rope connector, and a structure that is configured to connect to a hoist or a crane. The lifting tool is equipped with at least one water flow inducing means positioned at a radial distance from the center axis. 
         [0012]    The water flow inducing means may be adjustable and include one or more of a thruster, a nozzle or a rudder. 
         [0013]    When lifted or lowered through the sea, the thruster, the nozzle or rudder may be adjusted to oppose a torque from one or both ropes. By measuring one or more physical features such as the rotational acceleration or inclination using various sensors, the thruster, the nozzle or the rudder may be adjusted autonomously by a control unit and actuator, remotely by an operator, or by a combination thereof to counteract such a torque. 
         [0014]    The lifting tool may include a pair of thrusters, nozzles and rudders where the thrusters, nozzles or rudders are positioned on opposite sides of the lifting tool. When adjusting the pair of thrusters, nozzles or rudders properly, a couple acting about the central axis of the payload carrying rope may be generated. 
         [0015]    The rudder may be turnable about an axis laid out in the direction of the span of the rudder. Thus the rudder may be balanced so that less torque is needed in adjusting the rudder. 
         [0016]    The thrusters, nozzle or rudder may be connected to an actuator for the adjustment about said axis. Energy for operation of the actuator and for the thrusters may be stored on the lifting tool. 
         [0017]    The energy may for instance be stored in the form of a pressurized fluid or an electrical charge (e.g., in a battery). 
         [0018]    Water flow for the nozzle may be generated from the speed of the lifting tool through the sea. The nozzle inlet may be positioned in the lifting direction, while the outlet of the nozzle may be directed tangentially relative the lifting tool body. 
         [0019]    It may be advantageous to combine a thruster for use when the lifting tool is stationary in the sea, and a rudder for use when the lifting tool is at speed, this in order to conserve energy. While in motion, a thruster may be used for generating energy. The thruster and rudder may be one unit or separate items 
         [0020]    The lifting tool may, when it is connected to the steel rope and either moving along, or carrying the fiber rope, oppose the rotational forces typically generated by torque from the ropes, sea current and vortex shredding, and acting on the lifting tool. Thus, the lifting tool may, when having a speed through the sea, largely prevent the twisting and entanglement between parallel ropes in the sea. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    Non-limiting examples of various embodiments of the present disclosure are described in the following and are depicted in the accompanying drawings, in which: 
           [0022]      FIG. 1  shows an exemplary layout of a lifting operation in accordance with various embodiments of the present disclosure; 
           [0023]      FIG. 2  shows an enlarged, perspective view of a lifting tool in accordance with various embodiments of the present disclosure; and 
           [0024]      FIG. 3  shows a partial cross-section, side view of the lifting tool shown in  FIG. 2  in accordance with various embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION  
       [0025]    Referring to  FIGS. 1-3 , the reference number  1  denotes a lifting tool that is connected to a crane  2  on a vessel  4  by a steel rope  6  and a lifting hook  8 . The lifting hook  8  includes a swivel, which is not shown. 
         [0026]      FIG. 1  shows a first fiber rope section  10  of a fiber rope  12  passing through the lifting tool  1 . The first fiber rope section  10  is partly connected at its lower end to an item  14  (e.g., a payload) via a first rope connector  16  and an intermediate rope  18 . At its opposite upper end the first fiber rope section  10  is connected to a second fiber rope section  20  via a second rope connector  22 . 
         [0027]    The second fiber rope section  20  extends over a sheave  24  on the crane  2 , to a feed mechanism  26  on the vessel  4 . 
         [0028]    In  FIG. 1 , the second rope connector  22  is shown in a locked position in a hanger  28  on the crane  2 . The lifting force generated by the item  14  is thus carried by the first fiber rope section  10  and the crane  2 , and not by the second fiber rope section  20 . 
         [0029]    Turning to  FIG. 2 , the lifting tool  1  includes a generally pipe formed body  30  having an operable lock  32  that is adapted to catch a rope connector  10 ,  22  as the fiber rope  12  passes through the body  30 . 
         [0030]    Referring to the lifting tool  1  of  FIGS. 2 and 3 , the lock  32  is shown including a first lock party  34  that is fixed to a first shaft  36 , and a second lock party  38  that is fixed to a second shaft  40 . Other forms of locking mechanisms may be applicable. 
         [0031]    The two shafts  36 ,  40  are rotationally interconnected by toothed sectors  42 . The lock parties  34 ,  38  are movable by a lock actuator, not shown, between an active locked position as shown in  FIG. 3 , where the lock parties  34 ,  38  rest on a protrusion  44  in the body  30 , and an open position, not shown, where the lock parties  34 ,  38  are turned upward so the rope connector  10  may pass through the body  30 . 
         [0032]    An upper structure  46  is pinned to the body  30  and allowed to swing a limited amount out from the center axis  48 . The structure  46  includes a padeye  50  for a shackle  52 . 
         [0033]    The body  30  is equipped with a first rudder  54  and a second rudder  56  protruding with their span  58  in a radial direction of the body  30 . As the first and second rudders  54 ,  56  are connected to the body  30  by bearings  60 , the first rudder  54  may be turned about a first axis  62  by a first actuator  64  while the second rudder  56  may be turned about a second axis  66  by a second actuator  68 . In some embodiments, a rudder control unit (not shown) receives data indicating a value of rotational acceleration or inclination of the body  30  from one or more sensors. The rudder control unit may communicate with the first and second actuators  64 ,  68  to cause the actuators  64 ,  68  to alter a characteristic of the first and second rudders  54 ,  56 , such as their position about the first axis  62  and the second axis  66 . Additionally, although not shown, a nozzle may be used to oppose rotational motion of the body  30  by positioning an inlet of the nozzle in the lifting direction and directing water flow for the nozzle through an outlet of the nozzle tangentially relative the lifting tool body  30 . A control unit may similarly communicate with an actuator to cause the actuator to alter a characteristic of the nozzle, such as fluid flow rate through the nozzle. 
         [0034]    The rudders  54 ,  56  of the present embodiment are substantially symmetrical about the respective axis  60 ,  64 . The axes  60 ,  64  are generally parallel with the span  58  and the rudder&#39;s  54 ,  56  root chords  70  are longer than their tip chords  72 . Energy for operation of the actuators  64 ,  68  may be stored on the lifting tool  1 , for example as pressurized drive fluid stored in containers  74 . 
         [0035]    Various equipment, cables, and pipes for the operation of the actuators  62 ,  66  are not shown on the drawings. 
         [0036]    When an item  14  is to be lowered into the sea  76  and down to the sea floor  78 , the first rope connector  16  is prevented from passing through the body  30  by the lock  32  as shown in  FIG. 3 . 
         [0037]    The first fiber rope section  10  is paid out from the feed mechanism  26  while the crane  2  is bearing the load of the item  14  via the steel rope  6 , the lifting tool  1 , the first rope connector  16 , and the intermediate rope  18 . 
         [0038]    As the lifting tool  1  descends through the sea  76 , the rudders  54 ,  56  are adjusted to oppose torques from the sources described above, preventing the steel rope  6  from becoming entangled with the first fiber rope section  10 . 
         [0039]    When the second rope connector  22  interlocks with the hanger  28 , the payload is taken over from the steel rope  6  by the first fiber rope section  10 . 
         [0040]    The lifting tool  1  is released from the first rope connector  10  by moving the lock parties  34 ,  38  to their open position. The lifting tool  1  may be moved upwardly along the first fiber rope section  10  as shown in  FIG. 1 , the rudders opposing rotation of the lifting tool  1 , continuing to prevent the steel rope  6  from becoming entangled with the first fiber rope section. The lifting tool  1  then latches in with the second rope connector  22 . When the hanger  28  unlatches from the second rope connector  22 , the crane  2  may lower the first fiber rope section  10 , now carrying the payload, while the second fiber rope section  20  is paid out over the sheave  24  largely unloaded.