Abstract:
A chain support, hinged on two perpendicular axes to allow chain movement in two perpendicular planes is disclosed. The apparatus provides an improved arrangement to allow chain to be pulled at an angle above the chain support while maintaining straight pull across a stopper mechanism.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to mooring systems for offshore structures such as platforms and vessels and in particular, to a device which supports the mooring chain in such systems. 
         [0003]    2. Description of the Prior Art 
         [0004]      FIG. 1  illustrates a prior art mooring line connector from U.S. Pat. No. 6,663,320 (published Dec. 16, 2003). The known connector allows the mooring line to rotate in two perpendicular planes relative to the offshore structure to which it is attached. The mooring line is connected using a rod and a latch mechanism. Adjustment of the length of the mooring line, which is often desired before and sometimes after installation of the mooring line, will have to take place before the rod is connected, most likely on board of another vessel. 
         [0005]      FIG. 2  illustrates a prior art mooring line connector from UK Patent Application GB2351058 (published Dec. 12, 2000). This chain stopper provides two axes of rotation, and as a result reduced chain wear, but the construction is not designed to minimize so called out-of-plane bending, which occurs when the chain is under tension and one chain link (the captive link) is fixed by the chain stopper while the adjacent link below the captive link is allowed to rotate relative to the captive link. Also, during chain installation and tensioning, an uplift force is produced in the connector that must be resolved by bending the line of chain or by other means. 
         [0006]      FIG. 3  illustrates a prior art mooring line connector from U.S. Pat. No. 7,926,436 (published Jul. 15, 2010). This chain support provides two axes of rotation, allows adjustment of the length of the mooring line and minimizes so called out-of-plane bending. The use of a trunnion block instead of a gimbal body forces the chain retainer mechanism to be located below the two axes of rotation which makes operation and maintenance of the chain retainer mechanism more challenging and requires the hawse pipe to be a load carrying member. 
         [0007]    3. Identification of Objects of the Invention 
         [0008]    A primary object of this invention is to provide a chain support in which fatigue damage due to out-of-plane bending is reduced. 
         [0009]    Another object of this invention is to provide a chain support that allows rotation about two perpendicular axes, such that the maximum total rotation about the first axis is at least 90 degrees and the rotation about the second axis is ±15 degrees. 
         [0010]    Another object of this invention is to provide a chain support that allows the upper end of the mooring line to be pulled up vertically through the assembly while at the same time allowing large vertical angle variations of the lower end of the assembly, without inducing objectionable vertical or lateral misalignment of the assembly with the mooring line. 
         [0011]    Another object of this invention is to provide a chain support that allows adjustment of the mooring line length at any time by pulling in or letting out chain links with the capacity of latching into every other chain link. 
         [0012]    Another object of this invention is to provide a chain support with an arrangement of components that minimizes the overall width of the assembly. 
         [0013]    Another object of this invention is to provide a chain support with an integrated chain retainer guide that ensures that the chain maintains a straight line as it is pulled through the chain retainer mechanism. 
         [0014]    Another object of this invention is to provide a chain support with an option of using either a dual chain retainer of the latch mechanism or a single chain retainer of the latch mechanism. 
       SUMMARY OF THE INVENTION 
       [0015]    The objects identified above, along with other features and advantages result from providing a chain support with two axes of rotation and an elongated hawse pipe. The length of the hawse pipe is chosen such that even very small angles between the captive chain link on the chain retainer and the first free chain link below the captive link generates enough torque to rotate the hawse pipe around either one of the axes. This ensures that the bending stresses in the first free link are kept at low levels and the accrual of fatigue damage can be controlled. 
         [0016]    An elongated hawse pipe is pivotally connected to a structure such as a vessel or buoy by using a gimbal body. The upper end of the elongated hawse pipe is fitted with one or two spring loaded chain retainers that function passively. The use of the gimbal body allows placement of the chain retainer mechanism at the upper end of the hawse pipe where it is accessible for operation and maintenance. In most existing chain support designs, the chain retainer mechanism relies on gravity to close the chain retainer. By incorporating a passive, spring actuated chain retainer mechanism, operation of the chain retainer mechanism is assured regardless of the orientation of the hawse pipe and without the need for human contact. 
         [0017]    The chain retainer mechanism of this type provides a dual retainer of the latch mechanism. For this reason, a spring for actuation of the latch is preferred. A chain retainer with a single retainer may be provided so that a spring is not needed, such that the chain retainer relies on gravity to close. 
         [0018]    The inside of the elongated hawse pipe is fitted with a chain guide including grooves which, when projected onto a plane that is perpendicular to the longitudinal direction of the chain, describe a cruciform. The cruciform slot aligns the chain rotationally around its longitudinal axis such that alternating links of the chain are oriented parallel or perpendicular to the chain retainer mechanism and makes possible the use of the passive chain retainer mechanism. 
         [0019]    The gimbal body is fitted at its upper end with a chain guide which ensures that when the chain is pulled in and goes from slack to taut, the chain is pulled in a straight line across the chain retainer mechanism, even as the orientation of the hawse pipe undergoes a large change in an angle due to tensioning of the chain. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a prior art mooring line connector with two axes of rotation where the connection is established by latching a rod into a tube; 
           [0021]      FIG. 2  shows a prior art mooring line connector with two axes of rotation where the mooring line length can be adjusted by pulling up outside of the universal joint assembly; 
           [0022]      FIG. 3  shows a prior art mooring line connector with two axes of rotation where the mooring line length can be adjusted by pulling the line up through a trunnion block that is fitted with two pairs of trunnions that are mutually perpendicular; 
           [0023]      FIG. 4  shows a mooring buoy where each of the mooring lines is connected to the floating structure using the dual axis chain support/chain guide of the present invention; 
           [0024]      FIGS. 5   a  and  5   b  show two perspective views of the chain support of the present invention with a mooring chain extending from both ends of the chain supports, with the view of  FIG. 5   b  rotated clockwise from that of  FIG. 5   a;    
           [0025]      FIGS. 6   a  and  6   b  present views of the chain support view of  FIG. 6   b  rotated clockwise from the views of  FIG. 6   a;    
           [0026]      FIGS. 7   a  and  7   b  are sectional views of the chain support showing its connection to a floating structure; 
           [0027]      FIGS. 8   a  and  8   b  present perspective views of the chain support with the gimbal body partially removed so that chain retainers of the latch mechanism and a self-lubricating bushing between a trunnion and the gimbal body of the connection can be seen; 
           [0028]      FIG. 9  is a perspective view of the gimbal body; and 
           [0029]      FIGS. 10   a  and  10   b  illustrate the connection of trunnions to the tubular member. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]      FIG. 4  shows a floating structure  1  that is moored with a plurality of mooring lines. The upper end of each mooring line includes a section of chain  4  which is connected to the floating structure  1  through a chain support  3  of this invention. 
         [0031]      FIGS. 5   a  and  5   b  are perspective views of the chain support  3 .  FIG. 5   b  shows a view where the chain support  3  is rotated clockwise from the view of  FIG. 5   a . The chain support  3  allows rotation of the chain  4  around a first pivot axis  5  and a second pivot axis  6 . The mooring chain  4  is pulled through guide mouth  13  and through the interior of an elongated tubular member  11 . The chain  4  exits the chain support  3  through gimbal body  8 . 
         [0032]    Since the direction of pull is often different from the orientation of the tubular member  11 , the gimbal body  8  is fitted with an upper chain guide  7 . The gimbal body  8  is rotatably connected to the structure  1  via trunnions  10  and bearing blocks  20 /bearing caps  12 . See  FIGS. 7   a ,  7   b.    
         [0033]    As shown in  FIGS. 8   a  and  8   b , the elongated tubular member  11  is rotatably connected to gimbal body  8  with a first pair of trunnions  9  and a bearing cap  12 .  FIGS. 8   a  and  8   b  show the chain support  3  with the gimbal body  8  partially “cut away” and bearing caps  12  removed so that self-lubricating bushings  18  can be seen placed between the pair of trunnions  9  and the gimbal body  8 . The gimbal body  8  is secured to structure  1  ( FIG. 4 ) as illustrated in  FIGS. 7   a ,  7   b  for operation of the chain support assembly  3 . 
         [0034]      FIG. 9  illustrates the gimbal body  8  with the chain guide  7  and trunnions  10 .  FIGS. 10   a  and  10   b  show the trunnions  9  which are secured to tubular  11  and which are placed in the orthogonal slots  19  of the gimbal body  8 . Low friction, self-lubricating bushings are also placed between the first pair of trunnions  9  and the bearing cap  12 . See  FIGS. 6   b.    
         [0035]    The first and second pair of trunnions  9 ,  10  are arranged to form two mutually perpendicular pivot axes  5  and  6 . The second pair of trunnions  10  is pivotally connected to the structure  1  with structure bearing blocks  20  and caps  12  and low friction self-lubricating bushings  18  ( FIGS. 7   a ,  7   b ) placed between the second pair of trunnions  10  and the structure bearing blocks and caps  12 . 
         [0036]    The chain  4  enters the elongated tubular member  11  through a guide mouth  13 . A latch mechanism is mounted at the upper end of the elongated tubular member  11  to latch the chain  4  once the desired amount of chain has been pulled through the chain support. Optionally, the latch mechanism consists of dual retainers  14  (see  FIGS. 6   a  and  8   a ) mounted on opposing sides of the chain  4 . Alternatively the latch mechanism includes a single retainer  21  mounted on one side of the first pair of trunnions  9  (see  FIGS. 6   b ,  7   b , and  8   b ). If there is a need to let out chain  4 , a cable (not shown) can be attached to the latch mechanism to keep the latch in the open position so that the chain  4  can be lowered. 
         [0037]      FIGS. 6   a  and  6   b  show views of the chain support  3  with the lower part of the elongated tubular member  11  removed for clarity. During operation of the chain support  3 , as the mooring chain  4  is being pulled upward through the elongated tubular member  11 , the orientation of the chain will change, leading to a rotation of the elongated tubular member  11  around the second pair of trunnions  10 . Upper chain guide  7  guides chain  4  in a straight line through the latch mechanism, thereby preventing misalignment between the chain  4  and the latch mechanism while ensuring proper operation of the retainers  14  ( FIGS. 8   a ) and  21  ( FIG. 7   b ) of the latch mechanism. 
         [0038]    Two elastomeric springs  16  (for the retainer  14  of  FIG. 8   a ) are mounted on the gimbal body  8  to actuate the latch mechanism. The springs provide a passive closing system for the retainers  14  ( FIGS. 6   a ,  8   a ) of the latch mechanism, regardless of the orientation of the elongated tubular member  11 . 
         [0039]      FIGS. 7   a  and  7   b  present a section view of the chain support  3  with part of the elongated tubular member  11  removed for clarity. The inside of the elongated hawse pipe  11  is fitted with a chain guide  15  consisting of grooves which, when projected onto a plane that is perpendicular to the longitudinal direction of the chain describe a cruciform. The function of the chain guide  15  is to orient alternating links of the chain parallel or perpendicular to the first pivot axis  5  (see  FIGS. 5   a  and  5   b ) while the chain is being pulled through the tubular member  11  so that every other link is aligned with the latch mechanism. The latch mechanism is designed to fit around every other chain link. During operation of the chain support, the chain  4  is pulled upward through the elongated tubular member  11 . The latch mechanism ( 14 ,  21 ) is actuated by slacking off the pull on the chain. 
         [0040]    In the preferred embodiment, the first and second pair of trunnions  9 ,  10  are arranged such that the first pivot axis and the second pivot axis intersect. The arrangement can be modified to a further embodiment of the invention whereby the first and second pair of trunnions are arranged such that the first and second pivot axes do not intersect but are separated along the direction of the chain. 
         [0041]    An item list of reference numbers used to describe the invention follows:
     1  floating structure     3  chain support assembly     4  mooring chain     5  primary pivot axis     6  secondary pivot axis     7  upper chain guide     8  gimbal body     9  first pair of trunnions (on elongated tubular element)     10  second pair of trunnions (on gimbal body)     11  elongated tubular member     12  bearing caps     13  guide mouth     14  latch mechanism     15  chain guide     16  springs     17  (not used)     18 . self-lubricating bushing     19 . orthogonal slots in gimbal body     20 . bearing block     21 . single retainer