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CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to Provisional Application Serial No. 60/419,992, filed on Oct. 21, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    In certain offshore applications, keel guides are mounted to various vessels or platforms to guide risers extending to subsea locations. The keel guides restrain the upper end of the risers against lateral motion, thus preventing the risers from interfering with each other or with the vessel or platform. Generally, a keel guide comprises a cylindrical member or “can” which is attached to the hull of the vessel or platform with an appropriate bracket.  
           [0003]    Risers are permitted to move vertically within the keel guide to compensate for motion of the vessel or platform. Each riser is equipped with a keel joint designed to ride within the keel guide. Generally, the keel joint comprises a pipe section of increased thickness to withstand the bending loads exerted on the joint by the keel guide. The keel joint may be provided with an outer wear sleeve along the portion of the joint which contacts the keel guide.  
           [0004]    In many applications, a tieback connector is coupled to a lower end of the riser and moved to the seabed as the riser is lowered. However, such connectors may tend to be too large to pass through the keel guide of nominal size. Accordingly, the riser is run outside of or offset from the keel guide and moved into the keel guide in a later procedure. In some applications, for example, the keel guide is formed with a slot, and once the connector has passed the keel guide, the vessel or platform is translated toward the riser until the riser passes through the slot and into the keel guide. The riser is then moved vertically until the keel joint enters the keel guide. The outer diameter of the keel joint is larger than the width of the slot to restrain the keel joint within the keel guide.  
           [0005]    In some applications, the riser is lowered until the tieback connector is below the keel guide. At this point, the vessel or platform is translated, until the riser moves through the slot in the keel guide. The riser is then lowered and positioned until the keel joint is within the keel guide, the riser is tensioned and the keel joint remains positioned in the keel guide.  
           [0006]    Translation of the vessel or platform to the riser coupled with subsequent movement of the keel joint into the keel guide is a costly and time-consuming process. Additionally, such an approach typically requires the cutting of a slot into the platform structure of sufficient width to permit the passing of the riser from a position external to the keel guide to a position within the keel guide.  
         SUMMARY  
         [0007]    The present invention relates generally to a technique for guiding a riser in an offshore environment. The technique utilizes a bushing assembly that may be selectively landed within a keel guide. The bushing assembly also comprises an opening sufficient to permit relative linear movement of the riser therethrough. The bushing assembly allows the use of a keel guide with a larger diameter, e.g. sufficient to permit the passing of a tieback connector, while still guiding linear movement of the riser within the keel guide. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Certain exemplary embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:  
         [0009]    [0009]FIG. 1 is a front elevational view of a riser being installed in a keel guide, according to an embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a top view of a keel guide, according to one embodiment of the present invention;  
         [0011]    [0011]FIG. 3 is a cross-sectional view taken generally along line  3 - 3  of FIG. 2;  
         [0012]    [0012]FIG. 4 is a partial cross-sectional view taken generally along line  4 - 4  of FIG. 2;  
         [0013]    [0013]FIG. 5 illustrates one embodiment of a bushing being installed in a keel guide;  
         [0014]    [0014]FIG. 6 is a cross-sectional view taken generally along line  6 - 6  of FIG. 5;  
         [0015]    [0015]FIG. 7 is a top view of an embodiment utilizing several keel guides arranged on a hull;  
         [0016]    [0016]FIG. 8 is a top view of another embodiment of a keel guide having retractable pins for retaining a bushing;  
         [0017]    [0017]FIG. 9 is a side cross-sectional view taken generally along line  9 - 9  of FIG. 8;  
         [0018]    [0018]FIG. 10 illustrates a guide bushing being installed in a keel guide as illustrated in FIG. 8;  
         [0019]    [0019]FIG. 11 is a cross-sectional view of a plumb mounted lock-down pin assembly taken generally along line  11 - 11  of FIG. 9;  
         [0020]    [0020]FIG. 12 is a cross-sectional view similar to FIG. 11, but showing an obliquely mounted lock-down pin assembly;  
         [0021]    [0021]FIG. 13 is a top view of a plurality of keel guides of the type illustrated in FIG. 8, arranged on a hull;  
         [0022]    [0022]FIG. 14 is a side cross-sectional view of another embodiment of a keel guide having spring-loaded retaining pins;  
         [0023]    [0023]FIG. 15 is a side view of the guide bushing illustrated in FIG. 14 being installed in a keel guide;  
         [0024]    [0024]FIG. 16 is an expanded view of a spring-loaded retaining pin illustrated in FIG. 15;  
         [0025]    [0025]FIG. 17 is a side cross-sectional view of another embodiment of a bushing disposed within a keel guide;  
         [0026]    [0026]FIG. 18 is a cross-sectional view taken generally along line  18 - 18  of FIG. 17;  
         [0027]    [0027]FIG. 19 is a top view of another embodiment of a keel guide having a lock-down pin assembly;  
         [0028]    [0028]FIG. 20 is a side cross-sectional view taken generally along line  20 - 20  of FIG. 19;  
         [0029]    [0029]FIG. 21 is an expanded view of an embodiment of a lock-down pin assembly illustrated in FIG. 20;  
         [0030]    [0030]FIG. 22 is a cross-sectional view taken generally along line  22 - 22  in FIG. 21;  
         [0031]    [0031]FIG. 23 is a cross-sectional view taken generally along line  23 - 23  in FIG. 21;  
         [0032]    [0032]FIG. 24 is a top view of an embodiment of a keel guide system having a band-type locking device;  
         [0033]    [0033]FIG. 25 is a side partial cross-sectional view of the keel guide system illustrated in FIG. 24;  
         [0034]    [0034]FIG. 26 is a cross-sectional view taken generally along line  26 - 26  of FIG. 25; and  
         [0035]    [0035]FIG. 27 is a cross-sectional view taken generally along line  27 - 27  of FIG. 24. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0036]    Referring generally to FIG. 1, an exemplary embodiment of a keel guide system  30  is illustrated. Keel guide system  30  comprises a keel guide  32 , a riser assembly  34  and a bushing  36  to be selectively landed in keel guide  32 . In at least one embodiment, riser assembly  34  comprises a keel joint  38 , and bushing  36  is temporarily coupled to riser assembly  34  at or below keel joint  38 . As riser assembly  34  is moved downwardly through keel guide  32 , bushing  36  lands in keel guide  32  and is released from riser assembly  34  to permit keel joint  38  to slide in a linear direction within an opening  39  formed axially through bushing  36 .  
         [0037]    In the embodiment illustrated, keel guide system  30  also comprises a connector  40 , such as a tieback connector. Keel guide  32  is sized to permit the passage of connector  40  as riser assembly  34  is fed downwardly towards the subsea floor. Additionally, keel guide  32  may be attached to a structure  42  which, by way of example, comprises a hull of a vessel or a platform used in an offshore application. Keel guide  32  is attached to the vessel or platform via an appropriate bracket  44 .  
         [0038]    One embodiment of keel guide system  30  is illustrated in FIG. 2. In this embodiment, keel guide  32  is mounted to a vessel or platform by bracket  44 . An inner diameter  46  of keel guide  32  is sufficiently large to allow passage of tieback connector  40  or other component attached to the bottom of riser assembly  34 .  
         [0039]    As illustrated, keel guide  32  comprises a side opening  48  that extends the longitudinal length of keel guide  32 . Side opening  48  allows keel guide  32  to be opened and closed a slight amount to increase or decrease the effective internal diameter  46  of keel guide  32 . A locking device  50 , such as a band-type locking device, is coupled to keel guide  32  to open or close the keel guide  32 .  
         [0040]    One exemplary locking device  50  is illustrated in cross-section in FIG. 3. In this embodiment, locking device  50  comprises a pivot bracket  52  attached to keel guide  32  by, for example, welding or other appropriate fastener, on one side of opening  48 . Pivot bracket  52  comprises a pair of slots  54  for receiving corresponding pins  56  extending from a pivot sleeve  58 .  
         [0041]    A second bracket  60  is attached to keel guide  32  by welding or other appropriate fastener on a side of opening  48  opposite pivot bracket  52 . Second bracket  60  comprises a remote operated vehicle (“ROV”) bucket  62 . A stem  64  is coupled between pivot sleeve  58  and bucket  62  and extends across side opening  48 . Stem  64  may be threadably engaged with pivot sleeve  58  and retained against movement relative to ROV bucket  62  by a shoulder  66  and a retaining ring  68 . Stem  64  further comprises a head  70  that extends into ROV bucket  62 . Head  70  is adapted for engagement and rotation by an ROV manipulator to selectively increase or decrease the width of side opening  48  and thus the diameter  46  of keel guide  32 .  
         [0042]    Referring generally to FIG. 4, in this embodiment, bushing  36  comprises a wear bushing assembly  72  disposed in an annular space between keel guide  32  and keel joint  38 . Wear bushing assembly  72  has a bushing member  74  and a plurality of wear members  76 . Wear members  76  may be attached to bushing member  74  by fasteners, such as screws  78  and are oriented to bear against keel joint  38 , as illustrated. Thus, wear members  76  may be replaced due to, for example, sacrificial wear. In other embodiments, wear members  76  may comprise coatings or other types of hardened surfaces, e.g. hard facing, to reduce the detrimental effects of wear. The coating may be formed of a hardened metal or a nonmetallic material applied to bushing member  74 .  
         [0043]    Bushing  36  is selectively received and held within keel guide  32  by a retention or landing mechanism  80 . An exemplary landing mechanism  80  comprises a landing feature  82 , e.g. a groove, defined by a lower shoulder  84  and an upper shoulder  86 . Bushing member  74  is received in landing feature  82  and is retained against axial movement by lower shoulder  84  and upper shoulder  86 .  
         [0044]    To facilitate landing of bushing  36  in keel guide  32 , bushing  36  may be temporarily attached to riser assembly  34  by a mounting mechanism  88  as illustrated in FIG. 5. One exemplary mounting mechanism  88  comprises a clamp connector  90  which connects wear bushing assembly  72  to riser assembly  34  generally at the junction between keel joint  38  and a next lower riser section  92 . A lower clamp  94  is secured below a flange  96  disposed on lower riser section  92 . An upper clamp  98  is secured above flange  96  on keel joint  38 . Lower clamp  94  is secured to upper clamp  98  by a plurality of tie rods  100  and corresponding fasteners, such as nuts  102 .  
         [0045]    As illustrated in FIG. 6, lower clamp  94  and upper clamp  98  may each comprise semicircular halves  104  and  106  that are secured around riser assembly  34  by one or more appropriate fasteners  108 , such as screws. Clamp connector  90  is secured to wear bushing assembly  72  by posts  110 . In the specific embodiment illustrated, posts  110  extend from wear bushing assembly  72  to upper clamp  98  and are secured to upper clamp  98  by shear pins  112  (see FIG. 5).  
         [0046]    Prior to running riser assembly  34 , the locking device  50  on keel guide  32  is actuated via, for example, an ROV to open keel guide  32  to a position where the inner diameter  46  above landing feature  82  is slightly larger than the outside diameter of bushing  36 . The inside diameter below landing feature  82  remains slightly smaller that the outside diameter of bushing  36 . As bushing  36  is lowered into keel guide  32 , bushing assembly  72  lands on lower shoulder  84 . As the riser assembly  34  is further lowered, the weight of the riser assembly causes the shearing of shear pins  112 . The riser assembly  34  then continues downward and leaves bushing  36  retained in keel guide  32 . Locking device  50  may then be actuated to close keel guide  32  such that upward, linear movement of bushing  36  is prevented by the interfering engagement of upper shoulder  86  with bushing member  74 .  
         [0047]    In an exemplary application, a plurality of keel guides  32  are attached to a structure such as a hull  114  of a vessel or platform, as illustrated in FIG. 7. The locking devices  50  on each keel guide are oriented for accessibility by an ROV. By using bushings  36  in each keel guide  32 , connectors or components can be moved downwardly through the center of each keel guide during installation, and the corresponding keel guides  32  and bushings  36  cooperate to prevent the riser assemblies  34  from interfering with each other or hull  114  upon installation.  
         [0048]    Another embodiment of keel guide system  30  is illustrated in FIGS. 8 through 10. A keel guide  32 ′ is coupled to a structure, such as the hull of a vessel or a platform, via bracket  44 . As described above, the inner diameter of the keel guide is large enough to allow passage of a tieback connector or other component attached to the bottom of riser assembly  34 . In this embodiment, bushing  36  is landed on a shoulder  116  formed along an interior surface  118  of keel guide  32 ′. Interior surface  118  has a slightly greater diameter than the remainder of keel guide  32 ′ to permit bushing  36  to move downwardly to shoulder  116  without the use of an expandable side opening.  
         [0049]    In the embodiment illustrated, wear bushing assembly  72 , and specifically bushing members  74 , is held against shoulder  116  by one or more lock-down assemblies  120 . Lock-down assemblies  120  may be mounted in a variety of orientations, such as the exemplary plumb mounted lock-down assembly  122  and the obliquely mounted assemblies  124 , illustrated best in FIG. 8. Lock-down assemblies  120  may be used selectively to prevent upward linear motion of bushing  36  once landed against shoulder  116 , as illustrated in FIGS. 9 and 10. Specifically, once bushing  36  is landed in keel guide  32 ′, either or both lock-down assemblies  122  and  124  may be actuated by, for example, an ROV to retain bushing  36  against linear motion within keel guide  32 ′. As illustrated best in FIG. 10, a temporary mounting mechanism  88  and corresponding clamp connector  90  may be used to temporarily hold bushing  36  in place with respect to riser assembly  34  while being lowered into keel guide  32 ′.  
         [0050]    Exemplary embodiments of a plumb mounted lock-down assembly  122  and an obliquely mounted lock-down assembly  124  are illustrated in FIGS. 11 and 12, respectively. Each lock-down assembly comprises a sleeve  126  which is attached to keel guide  32 ′ by an appropriate fastening method, such as welding. Each lock-down assembly further comprises an ROV bucket  128  attached to an end of sleeve  126  generally opposite keel guide  32 ′. A lock-down pin  130  is threadably engaged with sleeve  126  at an internal threaded region  132 . A first end  134  of lock-down pin  130  extends into a keel guide opening  136 . As pin  130  is threaded inwardly, the first end  134  moves into the interior of keel guide  32 ′ to prevent upward movement of bushing  36 . In the plumb mounted lock-down assembly  122 , opening  136  is generally radially directed, while opening  136  of obliquely mounted lock-down assembly  124  is oriented at an angle with respect to the radius, as illustrated in FIG. 12. First end  134  may have a variety of configurations, but one exemplary configuration is a conical tip.  
         [0051]    An opposite end  138  of lock-down pin  130  extends into ROV bucket  128  and terminates at a head  140 . Head  140  is adapted for engagement by an external device, such as an ROV manipulator.  
         [0052]    One exemplary application of keel guide system  30  in which keel guide  32 ′ is utilized is illustrated in FIG. 13. In this example, a plurality of keel guides  32 ′ are attached to hull  114  by appropriate brackets  44 . Each of the keel guides comprises a plurality of lock-down assemblies  120  oriented for access by an ROV. Thus, the riser assemblies  34  with attached connectors or other components may be run through corresponding keel guides  32 ′ until each bushing  36  is landed therein. Upon release, e.g. fracturing, of the temporary mounting mechanism  88 , each riser assembly slides linearly downward through its surrounding bushing  36 .  
         [0053]    Another embodiment of keel guide system  30  is illustrated in FIGS. 14 through 16. In this embodiment, a keel guide  32 ″ is coupled to bracket  44  for connection to an appropriate structure, such as the hull of a vessel or platform. As with previously described embodiments, the inner diameter of keel guide  32 ″ may be large enough to allow passage of a connector, such as a tieback connector, or other component attached to the bottom of riser assembly  34 .  
         [0054]    In this embodiment, bushing  36  is landed in a landing feature  142  that is in the form of bowl  144  defined by an upper interior surface of keel guide  32 ″ (see FIG. 15). Bowl  144  is shaped to receive a wear bushing assembly  146  of bushing  36 . Specifically, the exemplary wear bushing assembly  146  comprises one or more radially extending bearing members  148  having interior wear inserts  150 . Wear inserts  150  are positioned to bear against keel joint  38 . Additionally, wear bushing assembly  146  also comprises a plurality of retention members  152  that retain bushing  36  against upward movement within keel guide  32 ″. In other words, the shape of bowl  144  allows wear bushing assembly  146  to move downwardly into keel guide  32 ″ until further movement is blocked by landing feature  142 . Once positioned against landing feature  142 , retention members  152  may be actuated to impede upward movement of bushing  36 , as illustrated in FIG. 14.  
         [0055]    In this embodiment, bushing  36  also may comprise a temporary retention mechanism  154  by which bushing  36  is temporarily coupled to riser assembly  34  during installation of bushing  36  into keel guide  32 ″. One exemplary retention mechanism  154  comprises a clamp connector  156  that may be clamped around riser assembly  34 . Clamp connector  156  is coupled to wear bushing assembly  146  via posts  158  and shear pins  160 . As riser assembly  34  is lowered through the interior of keel guide  32 ″, bushing  36  moves with riser assembly  34  until landed in landing feature  142 . The weight of riser assembly  34  shears shear pins  160 , and riser assembly  34  continues downward movement through keel guide  32 ″ while bushing  36  is retained within the keel guide. Subsequently, retention members  152  may be actuated to impede upward movement of bushing  36  with respect to keel guide  32 ″.  
         [0056]    One exemplary embodiment of retention mechanism  152  is illustrated in FIG. 16. In this embodiment, retention member  152  comprises a plurality of spring-loaded assemblies  162 . Each spring-loaded assembly has a pin that is biased outwardly by a spring  166 . Pin  164  and spring  166  may be mounted in a corresponding bore  168  formed in bearing member or members  148 . Spring  166  biases pin  164  towards a retention groove  170  formed in the interior wall of keel guide  32 ″. Once pin  164  is biased into engagement with groove  170 , upward movement of bushing  36  is inhibited. A retainer, such as a screw  172 , may be used to partially block bore  168  and thereby retain pin  164  within bore  168 .  
         [0057]    As illustrated in FIGS. 17 and 18, an external wear sleeve  174  may be utilized between bushing  36  and keel joint  38 . The wear sleeve  174  may be attached to keel joint  38  by, for example, press fitting, shrink fitting or other suitable techniques. Wear sleeve  174  protects keel joint  38  from wear and damage as keel joint  38  moves within keel guide  32 . In one example, wear sleeve  174  may comprise a radially inward backup ring  176  coupled to an external wear layer  178  by, for example, welding. In this example, backup ring  176  comprises a feature  180 , such as a split in the material. Feature  180  can be engaged with a corresponding feature  182  on keel joint  38  to limit relative movement between keel guide  38  and wear sleeve  174 . Alternatively, backup ring  176  may comprise or may be replaced with a thicker elastomeric material to enable greater flexibility within the keel guide. The thicker elastomeric material may comprise, for example, a poured or castable material, such as a foam.  
         [0058]    Another embodiment of keel guide system  30  is illustrated in FIGS. 19 through 23. In this embodiment, a keel guide  32 ′″ is mounted to a structure, such as the hull of a vessel or platform by a bracket  44 . Again, the inner diameter of keel guide  32 ′″ may be large enough to allow the passage of a connector, such as a tieback connector, or other component attached to the bottom of riser assembly  34 . Bushing  36  is landed within the interior of keel guide  32 ′″ to limit radial movement of riser assembly  34  while allowing relative linear movement between riser assembly  34  and keel guide  32 ′″. Bushing  36  comprises a bushing assembly  184  having at least one and typically a plurality of wear inserts  186  that bear against keel joint  38  of riser assembly  34 . Additionally, a retention mechanism  188  is used to retain bushing  36  within keel guide  32 ′″, as illustrated in FIGS. 19 and 20.  
         [0059]    One exemplary retention mechanism  188  comprises a plurality of swinging lock-down pin assemblies  190  (see FIG. 19). Additionally, a temporary retention mechanism may be used to hold bushing  36  to riser assembly  34  during installation of bushing  36  in keel guide  32 ′″, as with the embodiments described above. In this embodiment, the plurality of pin assemblies  190 , e.g. four pin assemblies, cooperate to restrain bushing  36  against linear movement with respect to keel guide  32 ′″ once the bushing is landed within the keel guide.  
         [0060]    As illustrated in FIGS. 21 through 23, one exemplary type of pin assembly  190  comprises a body  192  having a bore or other type of opening  194  to slidably receive a lock-down pin  196 . Lock-down pin  196  is biased radially outwardly by a spring  198  disposed within bore  194 . Each lock-down pin  196  is retained in its corresponding bore  194  by a retaining screw  200 .  
         [0061]    Pin assemblies  190  may be mounted at a lower region of bushing  36  beneath a wear bushing assembly  202 . Each pin assembly  190  may be coupled to the underside of wear bushing assembly  202  by sets of brackets and pins. For example, a pair of outer brackets  204  are attached to wear bushing assembly  202  at a radially outlying region by, for example, welding or other suitable attachment technique (see FIG. 22). A second set of brackets  206  are similarly attached below wear bushing assembly  202  radially inward from the set of brackets  204  (see FIG. 23). Body  192  is secured to the second, inward set of brackets  206  via a pin  208 . Additionally, body  192  is secured to the first, radially outward set of brackets  204  via shear pins  210 , which are threaded into outer brackets  204 . An undercut  212  is formed, e.g. machined, to an underside of wear bushing assembly  202  proximate each second, radially inward set of brackets  206 .  
         [0062]    During deployment, bushing  36  is run into keel guide  32 ′″ in a manner similar to that of the embodiments described above. When the wear bushing assembly  202  enters keel guide  32 ′″, the outer end of each lock-down pin  196  contacts a tapered surface  214  formed along the interior surface of keel guide  32 ′″. The lock-down pins  196  ride against tapered surface  214  and are cammed inward into their corresponding bores  194  against the biasing force of the corresponding spring  198 . As wear bushing assembly  202  is moved downwardly into keel guide  32 ′″, the lock-down pins  196  are moved past tapered surface  214  and into proximity with a groove  216 . The springs  198  force corresponding lock-down pins  196  outwardly into groove  216 . An upper edge or shoulder  218  that defines the upper extent of groove  216  forms a locking taper with the lock-down pins  196 . This prevents pins  196  from being cammed inward by moderate upwardly directed loads on the bushing  36 .  
         [0063]    If bushing  36  is to be retrieved, riser assembly  34  is raised until the installation clamps, e.g. clamp connector  154 , contacts wear bushing assembly  202 . When sufficient upward force is applied to bushing  36 , shear pins  210  are sheared. This allows each pin assembly  190  to swing about pin  208  so the lock-down pin  196  clears groove  216 . The undercut region  212  formed in wear bushing assembly  202  provides clearance for the pivoting of body  192 . Upon retrieval of bushing  36 , shear pins  210  may be replaced.  
         [0064]    Another embodiment of keel guide system  30  is illustrated in FIGS. 24 through 27. In this embodiment, a keel guide  32 ″″ may be mounted to a structure, such as the hull of a vessel or platform. As with the embodiments described above, the inner diameter of keel guide  32 ″″ may be made large enough to allow passage of a connector, such as a tieback connector, or other component attached to the bottom of riser assembly  34 . In this embodiment, keel guide  32 ″″ has a longitudinal side opening  222  that extends along the length of the keel guide. Side opening  222  allows the diameter of the keel guide to be increased and decreased a small amount by expanding and contracting, respectively, side opening  222 . A locking device  224 , such as a band-type locking device, is used to expand or contract side opening  222 . An exemplary bushing  36  may be designed similar to that described with reference to FIGS. 2 and 5.  
         [0065]    Locking device  224  comprises a first set of brackets  226  and  228  (see FIGS. 26 and 27) that are attached to an exterior of keel joint  32 ″″ by, for example, welding or other suitable attachment technique. The first set of brackets  26 ,  28  are located on one side of opening  222 . A first pivot pin  230  is rotatably mounted in brackets  226 ,  228  and is retained by a suitable mechanism, such as a washer  232  and a screw  234 .  
         [0066]    A second set of brackets  236  and  238  are attached to the exterior of the keel joint, on a side of opening  222  opposite brackets  226 ,  228 , by welding or other suitable technique. A second pivot pin  240  is rotatably mounted in brackets  236 ,  238  and is retained by an appropriate mechanism, such as a washer  242  and a screw  244 . The first set of brackets  226 ,  228  is provided with notches, such as notches  246 , and the second set of brackets  236 ,  238  is provided with comparable notches, such as notches  248  (see FIG. 24). Notches  246  and  248  are designed for engagement by an ROV clamping tool of the type used in subsea operations.  
         [0067]    A stud  250  (see FIGS. 26 and 27) is disposed through a hole  252  in first pivot pin  230  and through a second hole  254  disposed through second pivot pin  240 . The rotation of stud  250  is prevented by, for example, a screw  256  which engages a slot  258  in a head  260  of stud  250 . The other end of stud  250  is threaded into a blind bore  262  of a locking device bushing  264 . After stud  250  is threaded partially into bore  262 , a retaining screw  266  is screwed transversely into the side of stud  250 . Screw  266  prevents inadvertent separation of stud  250  from locking device bushing  264 .  
         [0068]    An open end  268  of locking device bushing  264  is disposed proximate to or bears on pivot pin  240  to prevent further separation of locking device  224 . Opposite open end  268 , locking device bushing  264  is attached to an actuator  270 , such as a T-handle. The T-handle is attached via a fastener, such as a bolt  272 . By way of example, actuator  270  may comprise a cross-bar  274  adapted to be gripped for rotation by an ROV tool.  
         [0069]    To adjust locking device  224  and increase or decrease the effective diameter of the keel guide, notches  246 ,  248  are engaged by an ROV, and the two sides of the locking device are squeezed more closely together. Another ROV tool is then utilized to rotate actuator  270 , e.g. a T-handle, to turn bushing  264  relative to stud  250 . Depending on the direction of rotation, the distance between the head of stud  250  and locking device bushing  264  can be increased or decreased. Because the ROV is squeezing the locking device together, the spring force of keel guide  32 ″″ is not bearing on stud  250  and locking device bushing  264 . Accordingly, a smaller amount of torque is required to rotate the locking device bushing  264 .  
         [0070]    Once the bushing  264  has been adjusted as desired, the ROV releases the sides of the locking device  224 , and the keel guide expands to its adjusted diameter. Accordingly, the diameter of the keel guide can be decreased or increased to hold or release the bushing  36 , as described with respect to the embodiment illustrated in FIGS. 2 and 5.  
         [0071]    It should be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, the keel guide system may be utilized in a variety of environments with a variety of riser assemblies; the size and shape of the keel guide may be adjusted depending on the size and shape of connectors or other components that pass through the keel guide; the configuration of the landing mechanisms, retention mechanisms and locking devices may be changed; and the size and configuration of various components can be adjusted according to a desired application. These and other modifications may be made in the design and arrangement of certain elements without departing from the scope of the invention as expressed in the appended claims.

Summary:
A technique for guiding a riser in an offshore environment. The technique utilizes a keel guide that permits the passage of connectors or other components therethrough. A bushing is mounted within the keel guide to guide the relative linear motion of the riser assembly through the keel guide.