Patent Publication Number: US-10766579-B1

Title: Passive heave compensated davit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/655,018 filed Apr. 9, 2018, which is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The following description was made in the performance of official duties by employees of the Department of the Navy, and, thus the claimed invention may be manufactured, used, licensed by or for the United States Government for governmental purposes without the payment of any royalties thereon. 
    
    
     TECHNICAL FIELD 
     The following description relates generally to a passive heave compensation arrangement that compensates for heave events in the open water, when loading or offloading/launching objects. The arrangement is part of a system that includes a water vessel that is operating on open water, a davit, and an object to be loaded/offloaded. 
     BACKGROUND 
     Larger parent ships often recover smaller surface water vessels, such as manned or unmanned surface water vessels (USVs), and other water-bound objects to perform maintenance operations, to store, or to transport to other locations. Typically, the recovery of a smaller vessel or object is accomplished by positioning the smaller vessel alongside a stationary larger/parent ship and lifting the smaller vessel or object by davit into the parent ship. Similarly, the davit may be used to offload the smaller vessel or object, from the larger/parent ship into the open water 
     These operations are affected by the elements of the sea environment and mooring arrangements. Even relatively small waves can induce large motions between the parent ship and davit, and the object/vessel being recovered from the open water. Without some sort of compensation for these environmental conditions in which waves induce relative motion between the larger/parent ship and the object being loaded, the safety and performance of loading and offloading operations may be severely limited. 
     Throughout the years, different solutions have been sought to solve the problem of heave-compensation during different sea states. Computer models have been used to accommodate for the dynamic properties of system elements. Equipment have incorporated mechanical stabilizers to adjust for wave motion. However, these attachments tend to add undesired bulk and complexity to the system apparatus. It is desired to have a davit device that captures, loads and unloads objects onto the parent ship, and passively compensates for heave motions triggered by the environmental conditions of the open water. 
     SUMMARY 
     In one aspect, the invention is a passive heave compensation system for the at-sea loading and unloading of objects on a water vessel. In this aspect, the system includes a water vessel having a bow and a stem, and a vessel centerline extending in a bow-to-stern direction. The water vessel has an upper deck. The water vessel is afloat in a body of water. The passive heave compensation system also includes, an object having a centerline, to be loaded and/or unloaded onto or from the water vessel. The passive heave compensation system also includes a passive heave compensation arrangement. The passive heave control arrangement includes a slewing gear attached to the upper deck of the water vessel and a stanchion extending axially in the vertical direction. The stanchion has a deck-attachment end and a boom-attachment end. At the deck-attachment end the stanchion is attached to the upper deck via the slewing gear so as to be rotatable about the vertical axis. The passive heave control arrangement also includes a boom extending axially and generally in a horizontal direction or at an angle to the horizontal direction. The boom has a stanchion-attachment end with an elbow thereat, and a head-attachment end. The passive heave control arrangement further includes a first pin having an elongated first pin axis, wherein the boom is attached to the stanchion via the first pin, the boom pivotable with respect to the stanchion about the first pin axis Z 1 . The passive heave control arrangement further includes a capture head attached to the head end of the boom for capturing and cradling the object. There is a first winch on the stanchion, the first winch including a first winch cable connected to the elbow of the boom, whereat the first winch manipulates the pivoting motion of the boom about the first pin axis Z 1 . There is a second winch on the boom, the second winch including a second winch cable that extends into the capture head and is connectable to the object, whereat the second winch manipulates capturing and cradling of the object from either the upper deck or the body of water, and wherein the in the at-sea capturing and cradling of the object that is floating in the body of water, the vertical distance between the capture head and the object is a Reel Distance R d . Furthermore, during a heave event a Heave Distance H d  is the vertical displacement distance, with respect to the water vessel, the object moves under the force of the water. According to this aspect, the vertical displacement distance may be an upward displacement or a downward displacement. The passive heave compensation arrangement also includes an elongatable and retractable gas spring extending from the stanchion to the elbow of the boom. During a heave event the gas spring provides passive heave compensation by elongating if the Heave Distance H d  moved by the object is a downward displacement or retracting if the Heave Distance H d  moved by the object is an upward displacement, to negate the vertical displacement distance H d  applying a force to move the boom by the Heave Distance H d , thereby keeping the Reel Distance a constant during the heave event. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features will be apparent from the description, the drawings, and the claims. 
         FIGS. 1A and 1B  are exemplary perspective views of a passive heave compensation system for the open-water loading and unloading of objects on a water vessel, according to an embodiment of the invention. 
         FIGS. 2A and 2B  are perspective illustrations of the passive heave control arrangement, according to an embodiment of the invention. 
         FIGS. 3A, 3B, and 3C  are perspective illustrations of the passive heave control arrangement  200 , showing the mechanical linkage  400 , according to an embodiment of the invention. 
         FIG. 4  is an exemplary explanatory illustration of the passive heave compensation system, according to an embodiment of the invention. 
         FIGS. 5A-5F , are exemplary explanatory illustrations of the passive heave compensation arrangement, as it goes through the different stages of capturing and recovering an object, according to an embodiment of the invention. 
         FIG. 6A  is an exemplary top view of the loading or offloading of an object, onto or off the water vessel, according to an embodiment of the invention. 
         FIG. 6B  is an explanatory illustration, showing the rotation about the vertical axis through the stanchion, and the rotation about the vertical axis through the swivel plate, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  are exemplary perspective views of a passive heave compensation system  100  for the open-water loading and unloading of objects  50  on and off a water vessel/parent ship  150 , according to an embodiment of the invention. Objects  50  may be manned or unmanned surface water vessels (USVs), manned or unmanned undersea vessels (UUVs) and any other water-bound objects. As outlined below, the system  100  operates in the open water, and includes a passive heave control arrangement  200  which includes a davit  300 . The passive heave control arrangement  200  accommodates for the heave events associated with the sea states of the open water. 
     As shown in  FIGS. 1A and 1B , the passive heave compensation system  100  includes the water vessel/parent ship  150 .  FIG. 1B  shows the water vessel  150  having a bow  151  and a stem  153 , and a vessel centerline  155  extending in a bow-to-stern direction.  FIG. 1A  shows the water vessel  150  having an upper deck  160 .  FIG. 1A  also shows the water vessel  150  afloat on a body of water  10 . The body of water  10  may be the sea, a river, a lake, or the like.  FIGS. 1A and 1B  also show an object  50 , which according to an embodiment of the invention, may have a substantially cylindrical shape. The object  50  may also include a centerline  55  (shown in  FIG. 1B ) extending axially through the object. As outlined below, according to the invention, during the at-sea loading and offloading of objects on and off a water vessel/parent ship  150 , the centerline  55  of the object  50  is kept substantially parallel to the vessel centerline  155 . 
       FIGS. 1A and 1B  also show a passive heave compensation arrangement  200 .  FIG. 1A  shows the davit  300  which forms a part of the overall passive heave compensation arrangement  200 . The davit  300  will be outlined in greater detail below, but as shown in  FIG. 1A , includes a stanchion extending axially in the vertical direction Y, and a boom extending axially in the horizontal direction X. In the illustrations of  FIGS. 1A and 1B , the passive heave compensation arrangement  200 , including the davit  300  is arranged in the stowed position. 
       FIGS. 2A and 2B  are perspective illustrations of the passive heave control arrangement  200 , which includes the davit  300 , according to an embodiment of the invention. The illustrations of  FIGS. 2A and 2B  show the arrangement  200  in identical position, but for clarity, shows the elements from different perspectives.  FIGS. 2A and 2B  show davit  300 , having a stanchion  320 , a boom  340 , and a capture head  360 , which are the primary linking arms/members for capturing, loading, and off-loading objects onto and off the water vessel  150  (not shown). 
       FIG. 2A  is a side view perspective of the passive heave control arrangement  200 .  FIG. 2A  shows a slewing gear  210 , which may be driven by any known driving device, which may include motors, gears, transmission elements, and the like. The slewing gear  210  is positioned at the upper deck  160  (not shown) of the water vessel  150  (not shown).  FIG. 2A  shows the stanchion  320  extending axially in the vertical direction Y 1 . As shown, the stanchion  320  has a deck-attachment end  322 , having a slewing gear attachment  310 .  FIG. 2A  also shows a boom-attachment end  324 . The deck-attachment end  322  is attached to the upper deck via the mating connection between the slewing gear  210  and the slewing gear attachment  310 . Through this attachment between the slewing gear  210  and the slewing gear attachment  310 , the stanchion  320  is rotatable about the vertical axis Y 1 , as indicated by arrow A. 
       FIG. 2A  also shows the boom  340  extending axially generally horizontally in a direction X. However as outlined below, the boom  340  may pivot downwards at an angle to the horizontal. The boom  340  has a stanchion-attachment end  342  with an elbow  343  thereat, and a head-attachment end  344 .  FIG. 2A  shows a first pin  350  having an elongated first pin axis Z 1  (going into the page). The axis Z 1  is illustrated in  FIG. 2B . The boom  340  is attached to the stanchion  320  via the first pin  350 . The boom  340  is pivotable with respect to the stanchion  320  about the first pin axis Z 1 . The axis Z 1  is illustrated in  FIG. 2B , with arrow B showing how the boom  340  rotates with respect to the stanchion.  FIGS. 2A and 2B  show the capture head  360  attached to the head-attachment end  344  of the boom for capturing and cradling an object. 
       FIGS. 2A and 2B  also show a head-attachment assembly  355  that is attached to the head-attachment end  344  of the boom  340 . As shown, the head-attachment assembly includes a first plate  357  and a second plate  359 , wherein each of the first plate  357  the second plate  359  has a common pivot axis Z 2  through which the capture head  360  freely pivots to maintain the horizontal orientation of the object.  FIGS. 2A and 2B  also show a swivel disk  361 , which is structured to rotate about a vertical axis Y 2 . As shown, both the first plate  357  and the second plate  359  are attached to the swivel disk  361 , through which the capture head swivels about the vertical axis Y 2  in the direction shown by arrow C. 
       FIGS. 2A and 2B  also show the passive heave control arrangement  200  having a first winch  370  on the stanchion  320 . The first winch  370  has a first winch cable  371  connected to the elbow  343  of the boom. As outlined below, the first winch  370  is actually a boom winch and it manipulates the pivoting motion of the boom  340  about the first pin axis Z 1 , shown by arrow B. Thus, depending on the stage of operation as outlined below, when the first winch  370  reels in the cable  371 , the boom  340  pivots about the first pin axis Z 1  in an anti-clockwise direction, thereby lifting the boom  340  upwards. As outlined below, it should be noted that when the first winch  370  releases the cable  371 , the boom  340  does not pivot about the first pin axis Z 1  in a clockwise direction. A gas spring  250  (outlined below) keeps the boom  340  in the up position allowing slack cable  371  to come off of first winch  370 . This slack cable  371  is necessary for heave compensation. 
       FIGS. 2A and 2B  show a second winch  380  on the boom  340 , the second winch including a second winch cable  381  that extends into the capture head  360  and is connectable to the object (not shown). A hook (not shown) may be connected to the end of the cable/line  381  for securing the object with the cable  381 . The second winch  380 , which is a line winch, reels in and releases the cable  381  to manipulate the capturing and cradling of the object from either the upper deck  160  (not shown) or from the body of water  10  (not shown) during loading and off-loading/launching operations.  FIGS. 2A and 2B  show an elongatable and retractable gas spring  250  extending from the deck-attachment end  322  of the stanchion  320  to the elbow  343  of the boom  340 . It should be noted that the gas spring  250  may alternatively be affixed to and extend from other locations along the stanchion  320 , such as more central locations along the stanchion. As outlined below, during heave events in the open water  10  (not shown), the gas spring  250  operates to provide passive heave compensation. It should also be noted that the stanchion  320  may include a stop (not shown) that stops the boom  340  from rotating upwards beyond a predetermined angle. 
       FIGS. 3A, 3B, and 3C  are perspective illustrations of the passive heave control arrangement  200 , showing the mechanical linkage  400 , according to an embodiment of the invention. The illustrations of  FIGS. 3A, 3B, and 3C  show the arrangement  200  in identical position, but for clarity, shows the elements from different perspectives.  FIG. 3C  shows the mechanical linkage  400  being laterally displaced in direction z from the stanchion  320  and boom  340  of the davit  300 . As outlined below, according to this embodiment, the mechanical linkage  400  helps to keep the centerline of the object parallel to the vessel centerline. 
     The mechanical linkage  400  is a 3D parallelogram system that keeps the capture head  360  parallel to centerline while rotating about the Y 1  axis while still allowing the boom  340  rotate up and down about the Z 1  axis.  FIGS. 3A, 3B, and 3C  show the mechanical linkage  400  having a first arm  420  that extends axially, generally in the vertical direction, the first arm  420  has a deck attachment end  422  and an outer end  421 .  FIG. 3A  also shows a curved portion  430  to which the outer end  421  is attached. 
       FIGS. 3A, 3B, and 3C  show a second arm  440  that extends axially in a direction that is generally the same as the boom  340 , which may be horizontal, or at an angle with respect to horizontal. The second arm  440  has a head attachment end  442  and an inner end  444 . The second arm  440  head attachment end  442  swivels and rotates about the Z 4  and Y 3  axes to maintain the parallel to centerline and vertical alignment. Second arm  440  inner end  444  is attached to the curved portion  430 , and therefore also rotates about the Z 3  axis, via the curved portion  430 . It should be noted that the inner end  444  of the second arm  440  is pivotally attached to the curved portion  430  so that the second arm is pivotable about a horizontal axis Z 3 . It should be noted that the entire arm structure, i.e., the first arm  420 , the second arm  440 , and the curved portion  430 , as a unit, rotates about the vertical Y 4  axis. 
     As shown, the second arm  440  of the mechanical linkage  400  is attached to the swivel disk  361  of the capture head  360 . As outlined above, the swivel disk  361  is structured to rotate about a vertical axis Y 2 . As outlined below, in operation when an object is captured in the capture head  360  and the stanchion rotates about a vertical axis Y 1  via the slewing gear (not shown) and slewing gear attachment  310 , the capture head  360  rotates about vertical axis Y 1 , the complementary rotations about the vertical axes Y 1  and Y 2 , keep the object centerline parallel to the vessel centerline, with the assistance of the mechanical linkage  400 , which restrains and controls the rotation about vertical axis Y 2 , keeping the object in the desired orientation. 
       FIG. 3C  also shows more structure of the capture head  360 . As shown the capture head includes a first gripper  372 , a second gripper  374 , and a plurality of elongated cradle bars  376  between the grippers. In operation, the object is held by the first gripper  372  and the second gripper  374 , and is cradled by the cradle bars  376 . The first the second grippers ( 372 ,  374 ) and the cradle bars  376  help to maintain the object in an orientation so that said object centerline is maintained substantially parallel to the vessel centerline. 
       FIG. 4  is an exemplary explanatory illustration of the passive heave compensation system  100  for open-water loading and offloading objects on and off the water vessel/parent ship  150 , according to an embodiment of the invention.  FIG. 4  is an explanatory illustration showing heave event variables and the adjustments made by the passive heave compensation system  100  during heave events.  FIG. 4  shows the water vessel  150  in open water  10 , the system including the passive heave control arrangement  200  which includes the davit  300 . The passive heave control arrangement  200  accommodates for the heave events such as waves associated with the sea states of the open water. 
       FIG. 4  shows the heave control arrangement  200  during the recovery process in a position in which the object is captured, as outlined with respect to  FIG. 5C  below.  FIG. 4  shows the davit  300  and other elements hanging off a side of the water vessel  150 , with the boom  340  angled downwards. The capture head  360  is above the water, with the cable  381  engaging the object  50 .  FIG. 4  also shows the open water  10  having a waterline region  11  that coincides with the level at which the water vessel  150  floats in the water, and according to this embodiment generally represents the level of the water. 
       FIG. 4  also shows the object  50  floating in the water  10 . The object  50  is held by the second winch cable  381 , which extends from the second winch  380 , through the capture head  360 , and downwards to the object  50 .  FIG. 4  shows the vertical distance between the capture head  360  and the object  50  is a Reel Distance R d .  FIG. 4  also shows a Heave Distance H d , which is the vertical displacement distance the object  50  moves under the force of the water, wherein this Heave Distance H d  is a vertical displacement with respect to the water vessel  150 . A heave event will be caused by a wave or the like, which moves the object  50  upwards or downwards, with respect to the water vessel  150 , from its initial resting position on the water represented by the level of the waterline  11 . 
     The heave distance H d  has a direct correlation to the gas spring  250  elongation. As waves cause the object to move up and down in relation to the water vessel  150 , the tension in the gas spring  250  causes the boom  340  to rotate to maintain the reel distance R d . The lift created by the gas spring  250  is only enough to overcome the weight of the boom  340  and other davit components plus a small margin for inertia. The gas spring  250  does not lift the object  50 , and thus compensates for the H d , by maintaining the R d . 
       FIGS. 5A-5F , are exemplary explanatory illustrations of the passive heave compensation arrangement  200 , as it goes through the different stages of capturing and recovering an object  50 , according to an embodiment of the invention. Each of the figures, i.e.,  FIGS. 5A, 5B, 5C, 5D, 5E, and 5F , shows the passive heave compensation arrangement  200  at a different stage of the process. Although the overall system  100  is not shown, it should be understood that the davit  300  and other elements of the arrangement  200  is positioned on the deck of the water vessel, which is in open water. It  5 F should also be understood that  FIGS. 5A-5F  outline only one mode of operation of the passive heave compensation arrangement  200  within the system  100  (shown in  FIGS. 1A and 1B ), and other modes of operation are possible, such as off-loading or launching an object from the deck of the vessel to the water. However, it should be noted that the function of passively compensating for heave events is consistent, regardless of the specific functions being carried out, i.e., loading, offloading/launching, etc. 
       FIGS. 5A-5F  show davit elements including the stanchion  320 , the boom  340 , and the capture head  360 .  FIGS. 5A-5F  also show, the first winch (boom winch)  370  positioned on the stanchion  320 , and the first winch cable  371 .  FIGS. 5A-5F  also show, the second winch (line winch)  380  positioned on the boom  340 , and the second winch cable/line  381 , which extends through the capture head  360 . A hook  363  is attached at the end of the cable/line  381  for securing the object  50  thereto.  FIGS. 5A-5F  also show a stop  330  on the stanchion  320  that contacts the elbow region of the boom  340 , preventing upward rotation of the boom  340  beyond a desired angle. Also shown in the gas spring  250 , which according to this embodiment is positioned at a central part of the stanchion  320 , and extends and is connected at the elbow of the boom  320 . 
       FIG. 5A  shows the passive heave compensation arrangement  200  in a stowed position. In operation the arrangement  200  may be positioned in the stowed position when the water vessel/parent ship  150  is transiting from one location to another. In the stowed position the boom winch  370  has put the tension in the line  371  to pull the boom  340  down on the up stop  330 . The gas spring  250  is fully retracted. The line winch  380  retracts the line  381  so that the hook is secure. 
       FIG. 5B  shows the passive heave compensation arrangement  200  in a recover position. In the recover position the arrangement  200  including the davit  300  is ready to recover the object  50 . In the recovered position the boom winch  370  pays out the cable/line  371  so that the boom  340  can articulate. It should be noted that although the line is paid out, articulation does not occur until prompted by the force/weight of the object  50 . The line winch  380  pays out the cable  381  so that the object could be captured with the hook  363 . As shown the cable  381  is not under tension. At this stage the object is floating in the open water. The tension in the gas spring  250  keeps the boom  340  up against the up stop  330 . 
       FIG. 5C  shows the passive heave compensation arrangement  200  in a recovering position. This is a stage at which the gas spring  250  compensates for heave events. In the recovering position the object  50  is still afloat in the open water, but has been hooked. The line winch  380  retrieves and continues to retrieve the cable  381  to the point at which the cable  381  is taut. The weight of the object  50  extends the gas spring  250 . The retrieving cable/line  381  pulls the boom  340  and capture head down  360  towards the object  50 . In this position, heave events may cause a vertical displacement distance H d  (the vertical displacement distance the object  50  moves under the force of the water with respect to the water vessel  150 ), which is compensated for. This is accomplished by the gas spring  250  elongating if the object  50  goes down or retracting if the object  50  goes up, to negate the vertical displacement distance H d . As shown in  FIG. 3C , the cable line  371  is paid out and loose, and thus articulation of the boom  340  at this stage is effected by the gas spring  250  and the weight of the object, and not the first winch  371 .  FIG. 5D  shows the passive heave compensation arrangement  200  in a captured position. This is also a stage at which the gas spring  250  compensates for heave events. In the captured position the line winch  380  has retrieved the cable/line  381  till the boom  340  and capture head  360  are pulled completely down to the object  50  so that the object  50  is secured into the capture head  360 . As state above, this position is still heave compensated by the gas spring  250  which is extended further than the previous position. Thus, even though the reel distance R d  is zero, the gas spring  250  effect adjusts for heave events and the accompanying vertical displacement distance H d . 
       FIG. 5E  shows the passive heave compensation arrangement  200  in a lifting position. In the lifting position the boom winch  370  retrieves cable  371  to begin lifting the object  50  from the water. After the object  50  is lifted, there is no need for heave compensation as the object is no longer directly affected by heave events. FIG.  5 F shows the passive heave compensation arrangement  200  in a recovered position. In the recovered position, the boom winch  370  has retrieved cable  371  until the boom  340  is against the up stop  330 . 
       FIG. 6A  is an exemplary top view of the loading or offloading of an object, onto or off the water vessel, according to an embodiment of the invention.  FIG. 5A  shows the water vessel  150  having a vessel centerline  155  extending in a bow-to-stern direction.  FIG. 6A  shows the upper deck  160 . According to the illustration, the water vessel  150  is afloat on a body of water  10 .  FIG. 6A  shows the object  50  in a launch/recovery position  601  when captured on the water  10 , and in a stowed position  603  on the upper deck  160 . The object centerline  55 , extends axially through the object  50  when the object  50  is in the launch/recovery position. The object centerline  552  extends axially through the object  50  when the object  50  is in the stowed position. As shown, in positions  601  and  603 , the object centerline  55 , and  552  is maintained parallel to the vessel centerline  155 . 
     Throughout the process of moving from the loading or offloading position to the stowed position and vice versa, the object centerline is maintained parallel to the vessel centerline  155 .  FIG. 6B  is an explanatory illustration, showing the rotation about the vertical axis through the stanchion  320  Y 1 , and the rotation about the vertical axis through the swivel plate  361 , and axis Y 1 , according to an embodiment of the invention.  FIG. 5B  shows a first arc  610 , an unadjusted arc at 90 degrees, and the adjusted second arc  620 . The second arc  620  shows the adjustment in rotation about the swivel plate  361 , and axis Y 2  caused by the mechanical linkage  400 , which controllably restrains the rotation about Y 2 , so that the centerlines  55  and  155  are parallel to each throughout the entire arc of movement, i.e., from the loading/offloading position to the stowed position. 
     Returning to  FIGS. 3A-3C , the apparatus and process involved in maintaining the centerlines  55  and  155  parallel to each other is illustrated. As stated above, during the loading or offloading/launching process when an object is captured in the capture head  360 , the stanchion  320  may rotate about a vertical axis Y 1  via the operation of the slewing gear. Because the capture head  360  is attached to the boom  340 , the capture head rotates with the stanchion  320  about a vertical axis Y 1  as well. As shown, the capture head  360  rotates about vertical axis Y 2 , via the operation of the swivel disk  361 . However, the rotation about vertical axis Y 2  is restrained and controlled by the second arm  440  of the mechanical linkage  400 , which is connected to the swivel disk  361 . The object centerline  55  is kept parallel to the vessel centerline  155  (as shown in  FIG. 5 ) by the mechanical linkage&#39;s control of the rotation of the capture head  360  about vertical axis Y 2  while the stanchion  320  rotates about axis Y 1 . 
     What has been described and illustrated herein are preferred embodiments of the invention along with some variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention, which is intended to be defined by the following claims and their equivalents, in which all terms are meant in their broadest reasonable sense unless otherwise indicated.