Abstract:
An uplift spring assembly to compensate for hull deflection at a main bearing of a mooring turret is disclosed. Elastomeric pads are used to react turret uplift because of their properties of large deflections and resistance to cold weather. Tie rods are provided to transmit the uplift loads into the elastomeric pads. The elastomeric pads react the uplift loads in compression. The assembly arrangement prevents the elastomeric pads from reacting tension loads.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application 60/158,001 filed Oct. 6, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an uplift spring assembly for the main bearing of a mooring turret to compensate for the hull deflection or distortion of the moored vessel. 
     2. Description of the Prior Art 
     Heretofore, springs have been provided for supporting the upper bearing of a mooring turret for a moored vessel. The mooring turret is usually mounted for rotation within a moon pool in the body or hull of the vessel. The vessel weathervanes about the turret which is anchored to the sea floor. 
     U.S. Pat. No. 5,306,186 dated Apr. 26, 1994 illustrates a mooring system including a turret supported within a moon pool on a main upper bearing mounted on the hull of the moored vessel. An upper turret support ring on the body of the vessel has a plurality of elastomeric pads equally spaced about the outer periphery of the turret for absorbing vertical shocks between the turret and the vessel. The elastomeric pads function to minimize moment load imbalances between the turret and vessel and to compensate for manufacturing tolerances of the upper bearing supports. The elastomeric pads are placed in compression upon downward movement of the turret relative to the body of the vessel. 
     3. Identification of Object of the Invention 
     A principal object of the invention is to provide an elastomeric spring assembly for the upper bearing of a mooring turret which includes a first elastomeric spring which is placed in compression upon an upward movement or uplifting of the turret relative to the vessel and a second elastomeric spring which is placed in compression upon a downward movement of the turret relative to the vessel. 
     SUMMARY OF THE INVENTION 
     The object identified above as well as other objects and features of the invention are provided in a spring assembly for the upper main bearing between a mooring turret and a vessel. An elastomeric spring is provided to react against turret uplift loads and downlift loads. A load applying horizontal ring connected to the main upper bearing has upper and lower elastomeric pads positioned on opposed sides thereof. A tie-rod extends through the load applying ring and the opposed elastomeric pads. The tie-rod is anchored at its lower end to a base support on the vessel. The upper end of the tie-rod is anchored an upper retaining plate. Upon an upward or uplifting movement of the turret, the tie-rod is effective to prevent movement of the retaining plate for transmitting a compressive force against the upper elastomeric pad thereof to permit the absorbing of the uplifting force by compression of the upper elastomeric pad. The lower elastomeric pad is compressed against the base support on the vessel by the load applying ring and is effective to absorb a downward force from the turret and load applying ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a spring assembly which embodies the present invention and which is positioned between the vessel and the upper main bearing for a turret mounted in a moon pool of the vessel. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a vessel shown at  10  has a hull  12  with a moon pool generally indicated at  14  extending through the hull or body  12  of vessel  10 . A horizontal base support ring  16  on hull  12  adjacent moon pool  14  is mounted on vessel hull  12  and supports a spring assembly generally indicated at  20  for turret  22  mounted within moon pool  14 . Turret  22  is anchored to the sea floor by a plurality of mooring lines or anchor legs (not shown). The vessel  10  weatherwanes about turret  22  in a manner that is well known. 
     A plurality of spring assemblies  20 , such as twenty, for example, are equally spaced about the outer periphery  24  of turret  22 . FIG. 1 shows a single spring assembly  20  according to the invention for illustration. Turret  22  includes an upper turret shear ring  26  which extends outwardly from the outer periphery  24  of turret  22 . Shear ring  26  supports turret  22  on a main upper bearing generally indicated at  28  which includes an inner ring  30  mounted on bearings within outer rings  32 . Suitable studs  34  secure turret shear ring  26  to inner bearing ring  30 . Outer bearing rings  32  are secured by studs  33  to an upper load applying support ring  35  of spring assembly  20 . Spring assembly  20  includes lower load applying support ring  36 . Annular vertical member  38  is secured between load applying support rings  35  and  36 . A flanged plate  44  is secured between support rings  35  and  36  at the position for each radial spring assembly  40  about the periphery of the turret  22 . 
     Spring assembly  20  includes a radial spring subassembly generally indicated at  40  mounted between an abutment  42  on hull  12  and a vertical member  44  secured between rings  35  and  36 . Radial spring subassembly  40  includes an elastomeric pad  46  between the flanged plate  44  and an opposed plate  47  and is adapted to absorb or dampen radial loads from turret  22 . Telescoping cylinders  49 ,  51 , which are slidable relative to each other, prevent tensioning of elastomeric pad  46 . 
     Spring assembly  20  also includes a vertical uplift spring assembly shown generally at  50  which embodies this invention. Vertical uplift spring assembly  50  is supported on base support ring  16  of hull  12  adjacent moon pool  14 . Assembly  50  includes a lower elastomeric pad  52  below a load applying ring  36  and an upper elastomeric pad  54  above load applying ring  36 . 
     A lower annular ring  56  extends upwardly from base plate support  16 . Suitable leveling plates or shims  58  including a layer of epoxy (if needed) are positioned within ring  56  for leveling spring assembly  50 . A lower plate  75  is attached by bolts  61  to ring  77  of the lower elastomeric pad  52  and slides with pad  52  inside ring  56  to prevent application of tension in pad  52 . An upper plate  63  is secured by bolts  79  to ring  60  of lower elastomeric pad  52 . Metallic rings  60 ,  77  are molded into lower pad  52 . Metallic rings  64 ,  65  are molded into upper pad  54 . Bolts  68  secure upper plate  63  and lower elastomeric pad  52  to the load applying ring  36 . Bolts  68  also secure ring  71  of the upper elastomeric spring to load applying ring  36  as described below. A horse-shoe shaped spacer  62  is positioned between plate  60  and load applying ring  36  for in-service replacement of a single elastomeric pad  52 . 
     Upper elastomeric pad  54  is secured by means of bolts  69  to a lower plate  71  via ring  64  which is also secured to the vertical load applying ring  36  by bolts  68 . Upper elastomeric pad  54  has its molded ring  65  fixed to retaining plate  66  by bolts  67 . 
     A central tie rod or threaded bolt  70  anchors vertical spring assembly  50  on base support ring  16  and vertical load applying ring  36 . The upper end of tie rod  70  includes a suitable nut  72  washers abutting above retaining plate  66 . The lower end of rod  70  has a suitable nut  74  washers abutting beneath base support  16 . Tie rod  70  is arranged to slide downwardly when ring  36  moves downwardly (with ring  66  and elastomeric pad  54 ), through a hole  17  in plate  58  and ring  16 . Thus, ring  66  is prevented from moving up more than a distance of the tie rod  70  between nuts  72 ,  74 , yet ring  66  can move down with respect to ring  16  because rod  70  can slide down through hole  17 . Ring  36  and ring  66  move down as a unit, but ring  36  can move upwardly with respect to ring  66 . 
     Operation 
     Vertical spring subassembly  50  is operable upon relative downward movement of turret  22  with respect to vessel  12  to compress lower elastomeric pad  52  between base support plate  16  and load applying ring  36 . Elastomeric pad  54  is not placed in tension during such downward movement of turret  22  and load applying ring  36  from the neutral position shown in FIG. 1, because the tie rod  70  slides through a hole  17  in base support ring  16 . Thus, lower elastomeric pad  52  is put in compression effective to absorb or dampen vertical loads exerted in a downward direction by turret  22  and load applying ring  36 , while upper elastomeric pad  54 , moving downwardly with load applying ring  36  and retaining plate  66 , is not placed in tension. 
     However, elastomeric pad  52  is not adapted to absorb any substantial upwardly directed vertical or uplifting loads. For this purpose, elastomeric pad  54  is provided. Upon relative upward movement of turret  22  with respect to vessel  12  from the position shown in FIG. 1, upward movement of load applying ring  36  relative to base support  16  and retaining plate  66  compresses elastomeric pad  54  between retaining plate  66  and load applying ring  36 . Retaining plate  66  is held against upward movement by nut  72  on tie rod  70  anchored to support ring  16 . Elastomeric pad  52  is not placed in tension upon upward movement of load applying ring  36  from the position of FIG. 1, because pad  52  is fixed to plate  36  by bolts  68  and plate  60 , and because plate  75  slides upwardly within ring  56 . The uplifting of turret  22  is transmitted by shear ring  26  to inner bearing ring  30 , thence to outer bearing rings  32  and upper ring  35 , and thence to vertical members  38 ,  44  and load applying ring  36  for exerting a compression load against upper elastomeric pad  54 , and ultimately via plate  66  and tie rod  70  to support ring  16  on vessel  12 . 
     From the above, an elastomeric spring assembly  50  has been provided in which upwardly directed vertical or uplifting loads exerted by the turret are absorbed or cushioned by an elastomeric element  54 . Downwardly exerted movements by the turret are absorbed or cushioned by an elastomeric element  52 . 
     While a preferred embodiment of the present invention has been illustrated in detail it is apparent that modifications and adaptations of the preferred embodiment will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.