U.S. patent application number 10/755521 was filed with the patent office on 2004-11-25 for keel joint arrangements for floating platforms.
Invention is credited to Lyle, Rockford D., McCarty, Jeffery K., Mican, Gilbert P., Munk, Brian N., Pallini, Joseph W., Radi, Amin, Stonesifer, Gary R..
Application Number | 20040234344 10/755521 |
Document ID | / |
Family ID | 26902125 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040234344 |
Kind Code |
A1 |
Munk, Brian N. ; et
al. |
November 25, 2004 |
Keel joint arrangements for floating platforms
Abstract
Keel joint assemblies are described that permit a degree of
rotational movement of a riser within the keel of a floating vessel
and greatly reduce the amount of stress and strain that is placed
upon the riser, as well. Keel joint assemblies described provide a
limiting joint between the riser and the keel opening that permits
some angular rotation of the riser with respect to the floating
vessel. Additionally, the limiting joint permits the riser to move
upwardly and downwardly within the keel opening, but centralizes
the riser with respect to the keel opening so that the riser cannot
move horizontally with respect to the keel opening. In described
embodiments, the limiting joint is provided by a single annular
joint that allows that riser to move angularly with respect to the
can. In some embodiments, the keel joint assembly incorporates a
cylindrical stiffening can that radially surrounds a portion of the
riser and is disposed within the keel opening. In these
embodiments, a flexible joint is provided between the can and the
riser. Supports or guides maybe used to retain the can within the
keel opening.
Inventors: |
Munk, Brian N.; (Houston,
TX) ; Lyle, Rockford D.; (Pinehurst, TX) ;
McCarty, Jeffery K.; (Houston, TX) ; Radi, Amin;
(Nassau Bay, TX) ; Pallini, Joseph W.; (Tomball,
TX) ; Mican, Gilbert P.; (Sealy, TX) ;
Stonesifer, Gary R.; (Pasadena, TX) |
Correspondence
Address: |
Shawn Hunter
Bracewell & Patterson, L.L.P.
P.O. Box 61389
Houston
TX
77208-1389
US
|
Family ID: |
26902125 |
Appl. No.: |
10/755521 |
Filed: |
January 12, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10755521 |
Jan 12, 2004 |
|
|
|
10207296 |
Jul 29, 2002 |
|
|
|
6746182 |
|
|
|
|
60308365 |
Jul 27, 2001 |
|
|
|
Current U.S.
Class: |
405/224 |
Current CPC
Class: |
E21B 17/017 20130101;
E21B 19/004 20130101 |
Class at
Publication: |
405/224 |
International
Class: |
E02D 005/54 |
Claims
What is claimed is:
1. A keel joint for retaining a riser within the keel of a floating
vessel, the keel joint comprising: a keel opening disposed
generally vertically within a floating vessel; a riser disposed
within the keel opening; and a limiting joint securing the riser
with respect the keel opening, the limiting joint precluding
horizontal movement or the riser with respect to the keel opening,
but permitting vertical and angular movement of the riser with
respect to the keel opening.
2. The keel joint of claim 1 wherein the limiting joint comprises:
a generally cylindrical stiffening can that is disposed within the
keel opening; and a collar that annularly surrounds the riser and
is secured to the stiffening can.
3. The keel joint of claim 1 wherein the limiting joint comprises:
a wear sleeve radially surrounding an outer portion of the riser;
an annular ring disposed upon the outer portion of the wear sleeve,
the ring presenting a vertically curved outer surface; an annular
recess formed within the keel opening and presenting an inner
surface that is generally complimentary to the curved outer surface
of the annular ring, the annular recess retaining the annular ring
therewithin to permit angular movement of the wear sleeve within
the keel opening.
4. The keel joint of claim 3 wherein the wear sleeve and collar are
run in with the riser.
5. The keel joint of claim 3 wherein the wear sleeve is seated
within the keel opening using a seating profile.
6. The keel joint of claim 1 wherein the limiting joint comprises:
a wear sleeve radially surrounding an outer portion of the riser;
an annular ring disposed upon the outer portion of the wear sleeve,
the ring presenting a frustoconical outer surface; an annular
recess formed within the keel opening and presenting an inner
surface that is generally complimentary to the frustoconical outer
surface of the annular ring, the annular recess retaining the
annular ring therewithin to permit angular movement of the wear
sleeve within the keel opening.
7. The keel joint of claim 6 wherein the wear sleeve comprises a
tapered portion that assists angular movement of the wear sleeve
within the keel opening.
8. The keel joint of claim 6 wherein the keel opening further
comprises an outwardly flared upper portion.
9. The keel joint of claim 1 wherein the limiting joint comprises
at least one centralizer assembly disposed within the keel opening
and in contact with the riser.
10. The keel joint of claim 9 wherein the centralizer assembly
comprises a piston-type centralizer assembly.
11. The keel joint of claim 9 wherein the centralizer assembly
comprises a hinged centralizer assembly.
12. The keel joint of claim 9 wherein the centralizer assembly is
hydraulically-actuated.
13. The keel joint of claim 9 wherein the centralizer assembly is
mechanically-actuated.
14. The keel joint of claim 1 wherein the limiting joint comprises:
a riser collar that radially surrounds a portion of the riser, the
riser collar having a bulbous central portion; and a guide sleeve
secured within the keel opening to radially surround the riser
collar, the guide sleeve comprising an interior rounded profile
that is shaped and sized to receive the bulbous portion and permit
angular rotation of the bulbous portion therewithin.
15. The keel joint of claim 14 wherein the guide sleeve and riser
collar are run in with the riser.
16. The keel joint of claim 14 wherein the guide sleeve is seated
within the keel opening using a seating profile.
17. The keel joint of claim 14 further comprising a locking flange
that secures the position of the guide sleeve with respect to the
keel opening.
18. The keel joint of claim 17 wherein the locking flange may be
unlocked and retrieved by upward movement of the riser with respect
to the guide sleeve.
19. The keel joint of claim 1 wherein the limiting joint comprises:
an inner, cylindrical riser sleeve that radially surrounds and
engages the riser; an outer, cylindrical keel sleeve that radially
surrounds the riser sleeve and engages the keel opening; and a cage
formed of a plurality of flexible spokes that radiate from the
riser sleeve to the keel sleeve, the spokes being elastically
deformable as needed to accommodate angular movement of the riser
with respect to the keel opening.
20. The keel joint of claim 19 further comprising a locking flange
that secures the position of the guide sleeve with respect to the
keel opening.
21. The keel joint of claim 20 wherein the locking flange may be
unlocked and retrieved by upward movement of the riser with respect
to the guide sleeve.
22. The keel joint of claim 1 wherein the limiting joint comprises:
an open top can riser section that is incorporated into said riser,
the open top can riser section comprising: an elongated,
cylindrical inner tubular member having end connection means for
connecting the inner tubular member to adjoining riser sections; an
outer tubular member that radially surrounds the inner tubular
member and is secured within the keel opening; and an annular
flange adapter that interconnects the inner and outer tubular
members.
23. A keel joint for retaining a riser within the keel of a
floating vessel, the keel joint comprising: a riser; a
substantially cylindrical stiffening can disposed within a keel of
a floating vessel and radially surrounding the riser; a single
joint in contact with the can and the riser, the joint permitting
angular movement of the riser with respect to the can; and a
plurality of supports extending from a keel of a floating vessel
radially inwardly to contact the can, the supports being unaffixed
to the can to permit upward and downward movement of the can within
the keel of the floating vessel.
24. The keel joint of claim 23 wherein the joint comprises a pair
of collars interconnect the can and riser.
25. The keel joint of claim 23 wherein the supports each present a
rounded end for contacting the can.
26. The keel joint of claim 23 wherein the supports each present a
roller for contacting the can.
27. A keel joint for retaining a riser within the keel of a
floating vessel, the keel joint comprising: a keel opening disposed
generally vertically within a floating vessel; a riser disposed
within the keel opening; and a limiting joint securing the riser
with respect to the keel opening, the limiting joint precluding
horizontal movement or the riser with respect to the keel opening,
but permitting vertical and angular movement of the riser with
respect to the keel opening, the limiting joint comprising: a wear
sleeve secured to the riser; a stiffening can disposed radially
within the keel opening; and an annular member joining the wear
sleeve to the stiffening can.
28. The keel joint of claim 27 wherein the annular member comprises
a cage having a plurality of radially extending spokes.
29. The keel joint of claim 27 wherein the annular member comprises
a collar.
30. The keel joint of claim 27 further comprising a plurality of
supports extending radially inwardly from the keel opening to
contact the stiffening can.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of provisional patent
application serial No. 60/308,365 filed Jul. 27, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to methods and devices for
providing a stress-relieving joint between a riser and the keel of
a floating platform.
[0004] 2. Description of the Related Art
[0005] Deep water floating platforms use risers to communicate
production fluid from the sea floor to the floating production
platform. Floating platforms have a portion that lies below the
surface of the sea. For stability of the platform, it is desired
that there be a very deep draft. The spar, for example, is a
popular style of floating platform that has an elongated,
cylindrical hull portion which, when deployed, extends downwardly a
significant distance into the sea. The lowest portion of the
submerged hull is referred to as the keel. Currents in the sea tend
to move the floating platform laterally across the sea surface.
Despite the presence of anchorages, the platform imparts bending
stresses to the riser during lateral movement. Localized, or point,
stresses are particularly problematic for risers.
[0006] One known joint arrangement for use with risers and floating
vessels is described in U.S. Pat. No. 5,683,205 issued to Halkyard.
Halkyard describes an arrangement wherein a joint means is
positioned within a keel opening in the floating vessel to reduce
the amount of stress upon a pipe passing through the keel opening.
The joint means consists of a radially enlarged sleeve member with
an elastomeric annulus at either end that is in contact with both
the sleeve member and the pipe. Halkyard's intent is to reduce
stress upon the pipe that is imposed by lateral movement of the
floating vessel upon the sea. In order to reduce stress, Halkyard
contacts the pipe at two points with an elastomeric annulus, which
is described as providing a resilient, somewhat yieldable
connection. Unfortunately, Halkyard's arrangement is problematic
since it permits almost no angular movement of the pipe within the
sleeve member. While point stresses upon the pipe are reduced, they
are still significant. Further, the pipe is required to bend within
the confines of the sleeve. This bending, together with the induced
point stresses at either end of the sleeve, place significant
strain on the pipe.
[0007] The present invention addresses the problems in the prior
art.
SUMMARY OF THE INVENTION
[0008] Keel joint assemblies are described that permit a degree of
rotational movement of a riser within the keel of a floating
vessel. The assemblies of the present invention greatly reduce the
amount of stress and strain that is placed upon the riser, as well.
The present invention describes keel joint assemblies that provide
a limiting joint between the riser and the keel opening that
permits some angular rotation of the riser with respect to the
floating vessel. Additionally, the limiting joint permits the riser
to move upwardly and downwardly within the keel opening, but
centralizes the riser with respect to the keel opening so that the
riser cannot move horizontally with respect to the keel
opening.
[0009] In described embodiments, the limiting joint is provided by
a single annular joint that allows that riser to move angularly
with respect to the can. In some embodiments, the keel joint
assembly incorporates a cylindrical stiffening can that radially
surrounds a portion of the riser and is disposed within the keel
opening. In these embodiments, a flexible joint is provided between
the can and the riser. Supports or guides may be used to retain the
can within the keel opening.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates an exemplary riser extending upwardly
from the sea floor and through a spar-type floating platform.
[0011] FIG. 2 is a schematic side, cross-sectional view of a first
exemplary keel joint assembly constructed in accordance with the
present invention.
[0012] FIG. 3 is a schematic side, cross-sectional view of a second
exemplary keel joint assembly constructed in accordance with the
present invention.
[0013] FIG. 4 is aschematic side, cross-sectional view of a third
exemplary keel joint assembly constructed in accordance with the
present invention.
[0014] FIG. 5 is a schematic side, cross-sectional view of a fourth
exemplary keel joint constructed in accordance with the present
invention.
[0015] FIG. 6 is a schematic side, cross-sectional view of a fifth
exemplary keel joint assembly constructed in accordance with the
present invention.
[0016] FIG. 7 is a schematic side, cross-sectional view of a sixth
exemplary keel joint assembly constructed in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIG. 1 generally illustrates a subsea wellhead 10 that has
been installed into the sea floor 12. A riser 14 is connected to
the wellhead 10 and extends upwardly through the waterline 16 to a
floating platform 18. The riser 14 is used to transmit production
fluids or as a drilling conduit from the wellhead 10 to production
facilities (not shown) on the floating platform 18. The riser 14 is
used to provide a closed conduit from the wellhead 10 to the
floating platform 18. The floating platform 18 shown is a spar-type
floating vessel that carries production equipment (not shown) on an
upper deck 20. The hull 22 of the platform 18 is a cylinder having
flotation chambers within and a central, vertically-oriented
passage 24 through which the riser 14 is disposed. It is noted that
the configuration for a passage used in floating platforms varies
from platform to platform. Sometimes the passage is lined by a
cylindrical wall that extends substantially the entire length of
the hull. In other platforms, the passage is partially lined by
such a wall, and in still other platforms, there is essentially no
lining for the passage. The keel 26 is located at the lower end of
the hull 22. A keel joint, indicated generally at 28, is used to
permit axial upward and downward motion as well as angular
deflection of the riser 14 with respect to the keel 26. It is
desired that the keel joint 28 be constructed to preclude localized
bending stresses in the riser 14 that could damage it, resulting in
structural failure of the riser 14.
[0018] Referring to FIG. 2, there is shown a first, and currently
most preferred, exemplary keel joint arrangement 30 that can be
used as the keel joint 28 to support the riser 14. The keel joint
arrangement 30 includes a stiff cylindrical can 32 that radially
surrounds a portion of the riser 14. The can 32 is retained within
and disposed away from the walls of the keel opening or passage 24
by supports or guides 34 that are securely affixed with the hull
22. While there are only two upper and two lower supports 34 shown
in FIG. 2, it should be understood that there are actually more
such supports 34, perhaps four or more upper and four or more lower
supports 34 and that the supports are located to surround the
circumference of the riser 14. The supports 34 have rounded,
non-puncturing ends 36 to contact the outer wall of the can 32. It
is noted that the supports 34 are not affixed to the can 32,
thereby permitting the can 32 to move upwardly and downwardly
within the passage 24. The keel joint arrangement 30 may be thought
of an "open can" arrangement since the can 32 is affixed to the
riser 14 by a stress joint (straight or tapered) 38 proximate the
lower end of the can 32 while the upper end 40 of the can 32 is not
secured to or maintained in contact with the riser 14. The
exemplary stress joint 38 illustrated consists of a pair of
radially enlarged collars 42 5 that surround the riser 14 and are
affixed to the inner radial surface of the can 32. The collars 42
are shown to be fashioned of metal. However, the collars 42 may
also be fashioned of a suitable elastomeric material. The collars
42 may be substantially rigid so as to permit a small amount of
angular movement of the riser 14 with respect to the can 32.
Alternatively, the collars 42 may be relatively flexible to permit
additional angular movement.
[0019] In operation, the riser 14 can move angularly to a degree
within the can 32 under bending stresses. Illustrative directions
of such relative angular movement are shown in FIG. 2 by arrows 33
about rotation point 35. During such angular movement, the outer
walls of the riser 14 are moved closer to or further away from the
inner walls of the keel opening 24. The stress joint 38 forms a
fulcrum. The can 32 is stiff enough that it transfers stresses
directly from the stress joint 38 to the supports 34, thereby
preventing any significant stresses from being seen by the upper
portion of the riser 14. Generally, this arrangement allows the
upper portion of the riser 14 to have a smaller cross section than
the stress joint 38.
[0020] FIG. 3 illustrates an alternative embodiment for a keel
joint arrangement 5 that is useful as a keel joint 28. In the keel
joint arrangement 50, a heavy walled wear sleeve 52 radially
surrounds a portion of the riser 14. The wear sleeve 52 may or may
not be secured to the riser 14 in a fixed relation, such as by the
use of welding or retaining rings such as are known in the art. A
central portion of the wear sleeve 52 has an external annular ring
54 that extends radially outwardly and forms the portion of the
sleeve 52 having the largest exterior diameter. The ring 54
presents an outer radial surface that is vertically curved in a
convex manner. The outer radial surface of the ring 54 may also be
frustoconical in shape. Below the annular ring 54 is a lower
inwardly tapered portion 56. Above the ring 54 is an upper inwardly
tapered portion 58. A partially-lined passage, designated as 24',
in the hull 22 of the floating vessel 18 has an open upper end 60
that is outwardly flared for installation purposes. The flare of
the upper end assists in guiding the sleeve 52 and ring 54 into
place when lowering the riser 14 through the hull 22. The lower end
of the passage 24 has an annular recess 62 that is sized and shaped
for the annular ring 54 to reside within. The recess 62 presents an
inner surface that is vertically curved in a concave manner so that
the outer convex surface of the annular ring 54 can be matingly
engaged. If the outer radial surface of the ring 54 is
frustoconical in shape, however, the inner surface of the recess 62
will be made complimentary to that frustoconical shape.
[0021] In operation, the keel joint arrangement 50 helps to prevent
damage to the riser 14 from bending stresses. The wear sleeve 52 is
located at the keel 26 where the primary bending stresses are
imparted to the riser 14 and, therefore, is designed to absorb most
of those stresses and prevent them from being imparted directly to
the riser 14. The interface of the ring 54 and the recess 62
provides a fulcrum wherein the riser 14 can move angularly with
respect to the hull 22. In addition, the elongated upper tapered
portion 58 will tend to bear against the length of the passage 24',
thereby reducing or eliminating localized, or point, stresses.
[0022] Referring now to FIG. 4, there is shown a keel joint
arrangement 70, which is a second alternative embodiment that is
useful as the keel joint 28. The keel joint arrangement 70 employs
centralizer assemblies 72 that are secured within the passage 24 of
the hull 22. Preferably, the centralizer assemblies 72 are spaced
angularly about the circumference of the passage 24. In a preferred
embodiment, the centralizers 72 comprise hydraulically actuated
piston-type assemblies, the piston arrangement being illustrated
schematically by two 72a, 72b. In practice, the two arms 72a, 72b
would be nested one within the other in a piston fashion and would
be selectively moveably with respect to one another. In an
alternative embodiment, the centralizer assemblies 72 comprise
hinged assemblies wherein the two arms 72a, 72b are hingedly
affixed to one another at hinge point 72c. Actuation of the
centralizer assembly in this case would move the arm 72a angularly
with respect to the arm 72b about the hinge point 72c, thereby
permitting the arm 72a to be selectively moved into and out of
engagement with the riser 14. The centralizers 72 are energized via
hydraulic lines (not shown) to urge the riser toward the radial
center of the passage 24 to resist contact between the riser 14 and
the passage 24. The centralizers 72 have rounded, non-puncturing
tips 74 that bear upon the riser 14. Preferably, the non-puncturing
tips comprise either wear pads or rollers for engagement of the
riser 14. It is noted that the piston-type centralizer assemblies
72 may be actuated mechanically rather than hydraulically. Also,
the centralizer assemblies' attachments to the passage 24 may be
softened, such as through use of springs or rubber, in such a way
as to decrease bending stresses by yielding to riser deflection. In
a further alternative embodiment, the centralizers 72 will comprise
members that have a hinged attachment to the passage 24.
[0023] FIG. 5 depicts a third alternative embodiment for the keel
joint 28. Keel joint assembly 90 includes a riser collar 92 that
surrounds a portion of the riser 14 proximate the keel 26. The
collar 92 is not affixed to the riser 14 but instead permits
sliding movement of the riser 14 upwardly and downwardly through
the collar 92. The collar 92 is generally cylindrical but includes
a bulbous central portion 94 and two tapered end portions 96, 98. A
guide sleeve 100 radially surrounds the collar 92 and features an
interior rounded profile 102 that is shaped and sized to receive
the bulbous portion 94 of the collar 92. An exterior landing
profile 104 is located at the lower end of the guide sleeve and is
shaped and sized to form a complementary fit with a landing profile
106 formed into the keel 26. The passage 24' is constructed
identically to the passage 24' described earlier in that it has an
open upper end with an outward flare.
[0024] To assemble the keel joint arrangement 90, the collar 92 and
guide sleeve 100 are assembled onto the riser 14. Then the riser 14
is run through the passage 24' and the landing profile 104 of the
guide sleeve 100 is seated into the matching profile 106 in the
keel 26. In operation, the riser 14 can slide upwardly and
downwardly within the collar 92 as necessary to compensate for
movement of the floating platform 18. Rotation of the platform 18
with respect to the riser 14 is permitted between the riser 14 and
the collar 92 as well as between the collar 92 and the guide sleeve
100. Angular movement of the riser 14 with respect to the platform
18 is accommodated by rotation of the bulbous portion 94 within the
rounded profile 102 of the guide sleeve 100. Alternatively, a
rubberized flex joint of a type known in the art (not shown) might
be used to accommodate angular rotation.
[0025] A fourth alternative exemplary embodiment for the keel joint
28 is shown in FIG. 6. Keel joint assembly 110 incorporates a
flexible cage assembly to permit relative movement between the
riser 14 and the floating vessel 18. A flexible cage assembly 112
is formed of an inner riser sleeve 114 and an outer keel sleeve
116. A central cage 118 adjoins the two sleeves 114, 116. The cage
118 includes an upper ring 120, a central ring 122, and a lower
ring 124. There are a series of upper spokes 126 that radiate
upwardly and outwardly from the central ring 122 to the upper ring
124. There are also a series of lower spokes 128 that radiate
outwardly and downwardly from the central ring 122 to the lower
ring 124. The upper and lower spokes 126, 128 are each arranged in
a spaced relation from one another about the circumference of the
central ring 122. The spokes 126, 128 are fashioned from a material
that is somewhat flexible yet has good strength under both tension
and compression. It is currently preferred that the spokes 126, 128
are fashioned of a steel alloy, although other suitable materials
may be used. The spokes 126, 128 are elastically deformable as
necessary to allow the riser 14 to move angularly within the
passage 24'. Angular deflection of the riser 14 results in
non-uniform deflection of upper spokes 126 and lower spokes 128.
The upper ring 120 affixes the upper spokes 126 to the outer keel
sleeve 116. The lower ring 124 is not affixed to the outer keel
sleeve 116.
[0026] The outer keel sleeve 116 is seated within the passage 24'
by means of a landing profile 130 that is shaped and sized to be
seated within a complimentary seating profile 132 at the lower end
of the passage 24'. Locking flanges 134 are secured onto the lower
side of the keel 26 to secure the outer keel sleeve 116 in place.
In a manner known in the art, the locking flanges 134 may be
selectively disengaged. or unlocked, and subsequently retrieved by
upward movement of the riser 14 with respect to the passage 24',
i.e., by pulling upwardly on the riser string.
[0027] During operation, the cage 118 holds the riser 14 in a
semi-rigid manner that permits some flexibility. The riser 14 can
move angularly with respect to the hull 22 due to the flexibility
of the spokes 126 and 128 of the cage 118. Loading from movement of
the riser 14 is transferred by the upper spokes 126 to the keel
sleeve 116 which, in turn transfers the loading to the hull 22.
Because the keel sleeve 116 engages the passage 24' of the hull 22
along substantially its entire length, point loading is
avoided.
[0028] FIG. 7 depicts a fifth alternative embodiment for use as the
keel joint 28. Keel joint arrangement 130 includes an open top can
structure, which is shown incorporated into the riser 14 as a sub
132 at is affixed at either end to other riser sections 134, 136.
The can sub 132 includes a pair of concentric tubular members. The
inner tubular member 138 has the same interior and exterior
diameters as a standard riser section. The outer tubular member, or
can, 140 is coaxial with the inner tubular member 138 and is
affixed to the inner tubular member 138 by a flange adapter, or
stress joint, 142 that joins the two pieces together proximate the
lower end of the sub 132. While FIG. 7 shows the flange adapter 142
to be an annular metallic collar that is integrally formed into
both the inner and outer tubular members 138, 140, it might also
comprise a separate collar or elastomeric member as well as a
flexible casing.
[0029] A cylindrical guide sleeve 144 radially surrounds the open
top can sub 132. The guide sleeve 144 is securely affixed to the
outer tubular member 140 by, for example, welding. Supports 146 are
used to secure the guide sleeve 144 within the passage 24 of the
hull 22. The supports 146 maintain the guide sleeve 144 a distance
away from the wall of the passage 24 so that the guide sleeve 144
is substantially radially centered within the passage 24. The
supports 146 are preferably formed of structural beams. The
supports 146 are arranged in two tiers, an upper tier and a lower
tier, and each tier surrounds the circumference of the passage 24.
The outer tubular member 140 is stiff enough that it transfers
stresses directly from the flange adapter 142 to the guide sleeve
144. Because the guide sleeve 144 and the outer tubular member 140
are affixed along substantially their entire length, point stresses
are avoided. In addition, the supports transmit loads or stresses
from the guide sleeve 144 to the passage 24 walls. The length of
contact between the outer tubular member 140 and the guide sleeve
144 allows for a longer vertical riser stroke than arrangements
wherein there is less contact area, such as the arrangement 30
shown in FIG. 2.
[0030] While described in terms of preferred embodiments, those of
skill in the art will understand that many modifications and
changes may be made while remaining within the scope of the
invention.
* * * * *