U.S. patent number 3,835,800 [Application Number 05/161,865] was granted by the patent office on 1974-09-17 for twin hull semi-submersible derrick barge.
This patent grant is currently assigned to Santa Fe Drilling Company. Invention is credited to Yorman Goren, Samuel Harry Lloyd, III.
United States Patent |
3,835,800 |
Lloyd, III , et al. |
September 17, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
TWIN HULL SEMI-SUBMERSIBLE DERRICK BARGE
Abstract
The derrick barge comprises a pair of laterally spaced elongated
hulls having a plurality of upstanding columns spaced therealong
supporting a working platform and a heavy duty derrick or crane in
spaced relation above the hulls. The hulls bouyantly support the
vessel including its deck load in the floating condition with the
hulls having freeboard. The hulls have ballast compartments to
submerge the hulls and portions of the stabilizing columns to a
distance of approximately one-half the effective height of the
stabilizing columns to maintain the vessel in a semisubmerged
floating condition with the platform and derrick elevated above the
waterline. However, the vessel also may be ballasted or deballasted
to submerge or emerge to a greater or lesser extent from the
semisubmerged condition such that the distance between the mean
water surface and either the underside of the deck or top side of
the hull is not less than 0.75 of the mean wave height. The columns
stabilize the vessel in the semisubmerged condition about roll and
pitch axes. The heavy duty derrick is located adjacent the stern
portion of the vessel with its vertical axis of rotation
intersecting the vessel centerline. This novel twin hull column
stabilized derrick barge arrangement has excellent motion
minimizing characteristics under wave action in operations at
sea.
Inventors: |
Lloyd, III; Samuel Harry (Mill
Valley, CA), Goren; Yorman (Los Angeles, CA) |
Assignee: |
Santa Fe Drilling Company
(Santa Fe Spring, CA)
|
Family
ID: |
26858185 |
Appl.
No.: |
05/161,865 |
Filed: |
July 9, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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705175 |
Feb 13, 1968 |
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Current U.S.
Class: |
114/265; 114/125;
212/308; 212/310 |
Current CPC
Class: |
B63B
1/107 (20130101); B66C 23/52 (20130101); B63B
35/44 (20130101); B63B 2001/044 (20130101) |
Current International
Class: |
B63B
1/00 (20060101); B63B 1/10 (20060101); B63B
35/44 (20060101); B66C 23/00 (20060101); B66C
23/52 (20060101); B63b 035/02 (); B63b
027/10 () |
Field of
Search: |
;114/.5D,.5R,43.5,61
;61/46.5 ;212/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
National Science Foundation; Project Mohole Six Column Platform
Design, April 1963. .
The Society of Naval Architects and Marine Engineers, Vol. 73,
1965, pages 50-99..
|
Primary Examiner: Halvosa; George E. A.
Assistant Examiner: Frankfort; Charles E.
Attorney, Agent or Firm: LeBlanc & Shur
Parent Case Text
The present application is a continuation of copending application
Ser. No. 705,175 filed Feb. 13, 1968, now abandoned, for Twin Hull
Semisubmersible Derrick Barge.
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A column stabilized semi-submersible derrick barge
comprising:
a pair of elongated hulls disposed in spaced side-by-side
relation;
a working platform spaced above said hulls a predetermined
height;
means for supporting said platform in fixed spaced relation above
said hulls including columns connected to said hulls and said
platform;
the distance between the extremities of said barge along the
longitudinal centerline of said barge being substantially greater
than the distance between the extremities of said barge along the
transverse centerline of said barge;
a heavy duty crane located adjacent one end of said barge and
mounted for rotation about a substantially vertical axis, said
crane having a rated capacity and a boom of sufficient length
capable of performing lifting operations off both barge beams and
off the end of the barge adjacent to which said crane is
mounted;
said hulls having ballast compartments for ballasting said barge to
alter its draft between a low draft hull supported floating
condition and a high draft semi-submerged column stabilized
floating condition;
said columns having predetermined cross-sectional areas and being
located on the hulls to provide righting moments about the pitch
and roll axes of said barge when in high draft condition;
the area of said columns, the number thereof and the distance of
said columns from the longitudinal and transverse centerlines of
said barge being such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge is in high draft
semi-submerged condition.
2. A derrick barge according to claim 1 wherein:
said crane load capacity and boom outreach length are such that
when said crane is rotated in high draft condition of the barge
with load and outreach of predetermined values the resultant moment
with respect to the roll axis causes substantial heel of said barge
about said axis which if uncorrected would exceed the maximum slew
limiting angle of said crane;
said barge having ballast means for counteracting such angle of
heel caused by such crane operations to provide a counter-righting
moment for said barge about its roll axis sufficient to maintain
the angle of heel of the barge during crane operations within said
slew limiting angle of said crane.
3. A derrick barge according to claim 2 wherein:
said ballast means is operable to transfer ballast from one hull to
the other hull in a manner to achieve said counter-righting moment
to maintain the heel of said barge within the crane slew limiting
angle, with said ballast being transferable as the crane slews
during load operating conditions.
4. A derrick barge according to claim 2 wherein:
said ballast means is operable to transfer ballast between said
hulls in relation to the moment caused by operation of said crane
to provide sufficient counter-righting moment to maintain the heel
of said barge within the predetermined crane slew limiting
angle.
5. A derrick barge according to claim 2 further including:
ballast means for counteracting the angle of trim caused when said
crane boom extends outwardly away from the end of said barge in the
direction of the barge's longitudinal axis with load and boom
outreach of high magnitude causing a high resultant moment with
respect to the pitch axis of said barge so that the latter
mentioned ballast means may provide a counter-moment for reducing
the angle of trim of the barge about its pitch axis.
6. A derrick barge according to claim 1 wherein:
at least one column on each hull is located adjacent the end of
said barge at substantially the same longitudinal position at which
said crane is mounted and at a distance from the transverse
centerline of said barge at least substantially the same as the
distance between said transverse centerline and the crane's axis of
rotation.
7. A derrick barge according to claim 1 further including:
additional structural support means adjacent said crane for
increased support of said heavy duty crane both in unloaded and
loaded condition.
8. A derrick barge according to claim 7 wherein:
said additional structural support means includes support members
directly connecting between the base of said crane and each of said
pair of hulls for at least partially structurally supporting said
crane from said hulls.
9. A derrick barge according to claim 1 wherein:
at least one of said columns on each of said hulls has a cross
section whereby the column dimension extending in the direction of
the barge roll axis is greater than the transverse dimension of the
column.
10. A derrick barge according to claim 1 further including:
a plurality of longitudinally spaced structural means for
reinforcing the structural relationship of said hulls, platform and
columns.
11. A derrick barge according to claim 1 including:
additional structural supporting means adjacent said crane for
increased support of said heavy duty crane in loaded and unloaded
operations;
a plurality of longitudinally spaced structural members for
reinforcing the structural relationship of said hulls, platform,
and columns;
said structural members including substantially transversely
extending members interconnecting said hulls adjacent the uppermost
portions of said hulls and restraining said hulls against lateral
displacement relative to one another;
at least one column on each hull being located adjacent the end of
the barge at substantially the same longitudinal position at which
said crane is mounted at a distance from the transverse centerline
of said barge at least substantially the same as the distance
between said transverse centerline and the crane's axis of
rotation.
12. A derrick barge according to claim 1 wherein:
there are at least three columns connecting with each of said hulls
and with said platform, said columns being located at spaced
intervals along each of the hulls;
at least one column on each hull being located adjacent the end of
said barge at substantially the same longitudinal position at which
said crane is mounted and at a distance from the transverse barge
centerline at least substantially the same as the distance between
said transverse barge centerline and the crane axis of rotation,
another of said columns on each hull being located adjacent the
opposite end of the barge, with at least one additional column at
an intermediate position on each hull;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of the hulls, platform and columns;
said structural means including substantially transversely
extending members interconnecting said hulls adjacent the uppermost
portions thereof and restraining said hulls against lateral
displacement relative to one another;
said barge including additional structural support means adjacent
said heavy duty crane for increased support of said heavy duty
crane both in unloaded and loaded condition.
13. A derrick barge according to claim 1 wherein:
said barge is elongated so that it has a length to width ratio such
that the barge length is at least a plural number of times as great
as the barge width.
14. A derrick barge according to claim 13 wherein:
the barge's length to width ratio is approximately 400 to 100.
15. A derrick barge according to claim 13 wherein:
the boom of the crane is of such length that it reaches beyond the
transverse centerline of the barge when the crane boom is disposed
in a rest position.
16. A derrick barge according to claim 13 wherein:
the boom of the crane is of such length that the end of the boom
reaches to adjacent the end of said barge opposite the end at which
said crane is mounted when said boom is disposed in the rest
position.
17. A derrick barge according to claim 1 wherein:
said crane has a predetermined angle of inclination from the
crane's normal substantially vertical axis of rotation beyond which
said crane cannot slew;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft semisubmerged condition with
stabilizing characteristics with respect to inclination about the
roll and pitch axes for enabling the barge to maintain an attitude
keeping the axis of rotation of said crane within said
predetermined slew limiting angle for predetermined magnitudes of
load and boom outreach.
18. A derrick barge according to claim 1 wherein:
the upper and lower surfaces of each of said hulls have a
non-streamlined configuration to provide increased added mass and
thereby increased resistance to movement of said hulls through
water in a vertical direction when said barge is in said high draft
column stabilized semisubmerged condition;
said crane having a predetermined angle of inclination from said
crane's normal substantially vertical axis beyond which said crane
cannot slew;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft semisubmerged condition with
stabilizing characteristics with respect to inclination about the
roll and pitch axes sufficient for enabling the barge to maintain
an attitude keeping the axis of rotation of said crane within said
predetermined slew limiting angle for predetermined magnitudes of
load and boom outreach;
the crane load capacity and boom outreach length being such that
when the crane is rotated in high draft condition of the barge with
load and outreach of predetermined values the resultant moment with
respect to the roll axis causes substantial heel of said barge
about said roll axis which if uncorrected would exceed the maximum
slew limiting angle of said crane;
said barge having ballast means for counteracting excessive angle
of heel caused by such crane operation with beam outreach to
provide a counter-righting moment for said barge about its roll
axis sufficient to maintain the angle of heel of said barge during
crane operations within said slew limiting angle of said crane;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of said hulls, platform and columns
with said structural means including substantially transversely
extending members interconnecting said hulls adjacent the uppermost
portions of said hulls and restraining said hulls against lateral
displacement relative to one another;
said vessel including additional structural supporting means
adjacent said crane for increased support of the heavy duty crane
in both loaded and unloaded condition.
19. A column stabilized semi-submersible derrick barge
comprising:
a pair of elongated hulls disposed in spaced side-by-side
relation;
a working platform spaced above said hulls a predetermined
height;
means for supporting said platform in fixed spaced relation above
said hulls including columns connected to said hulls and said
platform;
the distance between the extremities of the barge along its
longitudinal centerline being substantially greater than the
distance between the extremities of the barge along its transverse
centerline;
a heavy duty crane located adjacent one end of said barge and
mounted for rotation about a substantially vertical axis, said
crane having a rated capacity and a boom of sufficient length
capable of performing lifting operations off both barge beams and
off the end of said barge adjacent to which it is mounted;
said barge hulls having ballast compartments for ballasting said
barge to alter its draft between a low draft hull supported
floating condition and a high draft semisubmerged column stabilized
floating condition;
said crane having a predetermined angle of inclination from said
crane's normal substantially vertical axis of rotation beyond which
said crane cannot slew;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft condition with stabilizing
characteristics with respect to inclination about the roll and
pitch axes sufficient for enabling the barge to maintain an
attitude keeping the axis of rotation of said crane within said
predetermined crane slew limiting angle for predetermined
magnitudes of load and boom outreach;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of said hulls, platform and
columns;
said structural means including substantially transversely
extending members interconnecting said hulls adjacent the uppermost
portions thereof and restraining said hulls against lateral
displacement relative to one another.
20. A derrick barge according to claim 19 wherein:
the crane load capacity and boom outreach length are such that when
the crane is rotated in the high draft condition of the barge with
load and outreach of predetermined values the resultant moment with
respect to the roll axis causes substantial heel of said barge
about said axis which if uncorrected would exceed the maximum slew
limiting angle of said crane;
said barge having ballast means for counteracting excessive angle
of heel caused by such crane operations with boom outreach to
provide a counter-righting moment for the barge about its roll axis
sufficient to maintain the angle of heel of said barge during crane
operations within said slew limiting angle of said crane.
21. A derrick barge according to claim 19 wherein:
at least one column on each said hull is located adjacent the end
of the barge at substantially the same longitudinal position at
which said crane is mounted and at a distance from the transverse
centerline of said barge at least substantially the same as the
distance between said transverse barge centerline and the crane
axis of rotation.
22. A derrick barge according to claim 19 including:
additional structural supporting means adjacent said crane for
increased support of said heavy duty crane both in loaded and
unloaded condition.
23. A derrick barge according to claim 19 wherein:
at least one of the columns on each said hull has a longitudinal
dimension greater than its transverse dimension whereby the
cross-sectional dimension of each such column is greater in length
than in width.
24. A derrick barge according to claim 19 wherein:
the area of said columns, the number thereof, and the distance of
said columns from the longitudinal and transverse centerlines of
said barge are such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge is in high draft
semi-submerged condition.
25. A derrick barge according to claim 19 wherein:
the upper and lower surfaces of each hull have a non-streamlined
configuration such as to provide increased added mass providing
higher resistance to movement of the hulls and portions thereof
through the water in a vertical direction when said barge is in
high draft semi-submerged condition;
the area of said columns, the number thereof, and the distance of
said columns from the longitudinal and transverse centerlines of
said barge being such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge is in high draft
semi-submerged condition.
26. A derrick barge according to claim 25 wherein:
each hull is of generally rectangular cross section with the longer
axis of the hull cross section extending in like direction as the
transverse barge centerline.
27. A derrick barge according to claim 19 wherein:
there are at least three columns connecting with each of said hulls
and with said platform, said columns being located at spaced
intervals along each of the hulls;
at least one column on each hull being located adjacent the end of
said barge at substantially the same longitudinal position at which
said crane is mounted and at a distance from the transverse barge
centerline at least substantially the same as the distance between
said transverse barge centerline and the crane axis of rotation,
another of said columns on each hull being located adjacent the
opposite end of the barge, with at least one additional column at
an intermediate position on each hull;
said barge including additional structural support means adjacent
said heavy duty crane for increased support of said heavy duty
crane both in unloaded and loaded condition.
28. A column stabilized semi-submersible derrick barge
comprising:
a pair of elongated hulls disposed in spaced side-by-side
relation;
a working platform spaced above the hulls a predetermined
height;
means supporting the platform in fixed spaced relation above the
hulls and including columns connected to the hulls and the
platform;
the distance between the extremities of the barge along its
longitudinal centerline being substantially greater than the
distance between the extremities of the barge along its transverse
centerline;
a heavy duty crane located adjacent one end of said barge and
mounted for rotation about a substantially vertical axis, said
crane having a rated capacity and a boom of sufficient length
capable of performing lifting operations off both barge beams and
off the end of said barge adjacent to which it is mounted;
said barge hulls having ballast compartments for ballasting the
barge to alter its draft between a low draft hull supported
floating condition and a high draft semisubmerged column stabilized
floating condition;
said columns having predetermined cross-sectional areas and being
located to provide righting moments about pitch and roll axes, when
said vessel lies in high draft condition;
the upper and lower surfaces of each said hull having a
non-streamlined configuration to provide increased added mass to
provide higher resistance to movement of the hulls and portions
thereof through the water in vertical direction when said barge
lies in high draft condition;
the area of said columns, the number thereof, and the distance of
said columns from the longitudinal and transverse centerlines of
the barge being such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge lies in high draft
semi-submerged condition;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of the hulls, platform and columns;
said structural means including substantially transversely
extending members interconnecting the hulls adjacent the uppermost
portions thereof and restraining said hulls against lateral
displacement relative to one another.
29. A derrick barge according to claim 28 wherein:
said crane has a predetermined angle of inclination from the
crane's normal substantially vertical axis of rotation beyond which
said crane cannot slew;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft semi-submerged condition with
stabilizing characteristics with respect to inclination about the
roll and pitch axes for enabling the barge to maintain an attitude
keeping the axis of rotation of said crane within said
predetermined crane slew limiting angle for predetermined
magnitudes of load and boom outreach;
said barge having ballast means for counteracting excessive angle
of heel caused by crane operation with beam outreach to provide a
counter-righting moment for said barge about its roll axis
sufficient to maintain the angle of heel of the barge during crane
operations within said slew limiting angle of said crane.
30. A derrick barge according to claim 29 wherein:
said ballast means is operable to transfer ballast from one hull
into the other hull in a manner to achieve said counter-righting
moment to maintain the heel of said barge within said crane slew
limiting angle, with said ballast being transferable as said crane
slews during load operating conditions.
31. A derrick barge according to claim 29 wherein:
said ballast means is operable to transfer ballast between said
hulls in relation to the moment caused by operation of said crane
to provide sufficient counter-righting moment to maintain the heel
of said barge within the slew limiting angle of said crane.
32. A derrick barge according to claim 29 further including:
ballast means for counteracting the angle of trim caused when said
crane boom extends outwardly away from the end of said barge in the
direction of said barge's longitudinal axis with load and boom
outreach of high magnitude causing a high resultant moment with
respect to the pitch axis so that the latter ballast means may
provide a counter moment for reducing the angle of trim of said
barge about its pitch axis.
33. A derrick barge according to claim 28 wherein:
at least one of said columns on each said hull has a cross section
whereby the column dimension in direction of the barge longitudinal
axis is greater than the transverse dimension of such column.
34. A derrick barge according to claim 28 wherein:
the cross section of each hull is generally rectangular with the
longer axis of the hull cross section extending in like direction
as the barge's transverse centerline.
35. A derrick barge according to claim 28 wherein:
at least three columns connect with each of said hulls and with
said platform, said columns being located at spaced intervals along
each of the hulls;
at least one column on each said hull being located adjacent the
end of said barge at substantially the same longitudinal position
at which said crane is mounted and at a distance from the
transverse centerline at least substantially the same as the
distance between the transverse barge centerline and the crane axis
of rotation, another of said columns on each hull being located
adjacent the opposite end of the barge, with at least one
additional column at an intermediate position on each hull.
36. A derrick barge according to claim 35 wherein:
the upper and lower surfaces of each hull are substantially planar
for at least most of their length and substantially perpendicular
to a vertical plane through the barge's longitudinal axis.
37. A derrick barge according to claim 28 wherein:
said barge is elongated so that it has a length to width ratio such
that the barge length is at least a plural number of times as great
as the barge width.
38. A derrick barge according to claim 37 wherein:
the boom of the crane is of such length that the end of the boom
reaches to adjacent the end of said barge opposite the end at which
said crane is mounted when said boom is disposed in the rest
position.
39. A derrick barge according to claim 28 wherein:
each of said hulls has a streamlined bow portion for minimizing
resistance to movement through water in the low draft
condition.
40. A column stabilized semi-submersible barge comprising:
a pair of elongated hulls disposed in spaced side-by-side
relation;
a working platform spaced above said hulls a predetermined
height;
means for supporting the platform in fixed spaced relation above
the hulls and including at least three columns connecting with each
of the hulls and with said platform;
the distance between the extremities of the platform along the
barge's longitudinal centerline being substantially greater than
the distance between the extremities of the platform along the
barge's transverse centerline, with the barge length being at least
a plural number of times as great as the barge width;
means located adjacent one end of said platform for mounting a
heavy duty crane which rotates about a substantially vertical axis
and has a rated capacity and a boom of sufficient length capable of
performing lifting operations off at least one beam of the barge
and off said end of said barge adjacent which said crane mounting
means is located;
said hulls having ballast compartments for ballasting the barge to
alter its draft between a low draft hull supported floating
condition and a high draft semisubmerged column stabilized floating
condition;
said columns having predetermined cross-sectional areas and being
located on said hulls to provide righting moments about pitch and
roll axes of said barge when in high draft semi-submerged
condition;
the area of said columns, the number thereof, and the distance of
the columns from the longitudinal and transverse centerline of the
barge being such as to provide a greater righting moment about the
transverse pitch axis than the righting moment about the
longitudinal roll axis when the barge is in high draft
semi-submerged condition;
the upper and lower surfaces of each said hull having a
non-streamlined configuration to provide increased added mass
providing higher resistance to movement of the hulls through the
water in vertical direction when said barge is in said high draft
semi-submerged condition;
at least one column on each said hull being located adjacent the
end of said barge at substantially the same longitudinal position
of said crane mounting means and located at a distance from the
transverse centerline of said barge at least substantially the same
as the distance between said transverse centerline and the center
of said crane mounting means, another of said columns on each hull
being located adjacent the opposite end of the barge, with at least
one additional column at an intermediate position on each hull;
said structural means including substantially transversely
extending members interconnecting said hulls adjacent the uppermost
portions thereof and restraining said hulls against lateral
displacement relative to one another;
said barge including additional structural supporting means
adjacent said mounting means for increased support of the crane
when mounted and operated on said barge.
41.
41. A barge according to claim 40 wherein:
said additional structural supporting means includes support
members directly connected between said crane mounting means and
said hulls for at least partially structurally supporting said
mounting means and the crane when mounted and operated on said
latter means.
42. A barge according to claim 40 wherein:
at least one of the columns on each said hull has a cross section
with longitudnally extending dimension greater than its
transversely extending dimension.
43. A barge according to claim 40 wherein:
the centroid of the cross-section of at least one column on each
hull lies outboard of the longitudinal centerline of the associated
hull.
44. A barge according to claim 40 wherein:
said barge has ballast means for counteracting angle of heel caused
by operation of a crane having a slew limiting angle and disposed
on said mounting means so as to provide a counter-righting moment
for said barge about its roll axis sufficient to maintain the angle
of heel of the barge during crane operations within the slew
limiting angle of such crane;
said ballast means being operable to transfer ballast from one hull
to the other hull in a manner to achieve such counter-righting
moment to maintain the heel of said barge within said slew limiting
angle, with said ballast being transferable as such crane slews
during load operating conditions.
45. A barge according to claim 44 further including:
ballast means operable for counteracting the angle of trim caused
by operation of a crane on said mounting means with its boom
extending outwardly away from the end of said barge in the
direction of the barge's longitudinal axis so that the
latter-mentioned ballast means may provide a counter-moment for
reducing the angle of trim of the barge about its pitch axis.
46. A column stabilized semisubmersible derrick barge
comprising
a pair of elongated hulls disposed in spaced side by side
substantially parallel relation with each hull having substantially
parallel planar top and bottom horizontal surfaces disposed
substantially perpendicular to a vertical plane through the
longitudinal centerline of the barge and extending substantially
the length of each hull, with the transverse horizontal dimension
of each hull being greater than its vertical dimension;
a working platform spaced above said hulls a predetermined
height;
means for supporting said platform in fixed spaced relation above
said hulls including at least three columns connecting with each of
said hulls and said platform and located at spaced intervals along
said hulls;
the distance between the extremities of said barge along the
barge's longitudinal centerline being substantially greater than
the distance between the extremities of said barge along the
barge's transverse centerline, with the barge length being at least
a plural number of times as great as the barge width;
a heavy duty crane located adjacent one end of said barge and
mounted for rotation about a substantially vertical axis, said
crane having a rated capacity and a boom of sufficient length
capable of performing lifting operations off both barge beams and
off the end of the barge adjacent to which said crane is mounted,
the boom of said crane being of such length that it reaches beyond
the transverse centerline of the barge when the crane boom is
disposed in a rest position, and said crane having a predetermined
angle of inclination from the crane's normal substantially vertical
axis of rotation beyond which said crane cannot slew;
at least one column on each hull being located adjacent the end of
said barge at substantially the same longitudinal position at which
said crane is mounted and at a distance from the transverse barge
centerline at least substantially the same as the distance between
said transverse barge centerline and the crane axis of rotation,
another of said columns on each hull being located adjacent the
opposite end of the barge, with at least one additional column at
an intermediate position on each hull;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of the hulls, platform and columns;
said barge including additional structural supporting means
adjacent the crane for increased support of the heavy duty crane in
both loaded and unloaded condition;
said hulls having ballast compartments for ballasting said barge to
alter its draft between a low draft hull supported floating
condition and a high draft semisubmerged column stabilized floating
condition;
said columns having predetermined cross-sectional areas and being
located on the hulls to provide righting moments about the pitch
and roll axes of said barge when in high draft semi-submerged
condition;
the area of said columns, the number thereof and the distance of
said columns from the longitudinal and transverse centerlines of
said barge being such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge is in high draft
semi-submerged condition;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft semisubmerged condition with
stabilizing characteristics with respect to inclination about the
roll and pitch axes for enabling the barge to maintain an attitude
keeping the axis of rotation of said crane within said
predetermined crane slew limiting angle;
said barge having ballast means for counteracting excessive angle
of heel caused by crane operation with beam outreach to provide a
counter righting moment for said barge about its roll axis
sufficient to maintain the angle of heel of the barge during crane
operations within the slew limiting angle of said crane;
additional ballast means for counteracting the angle of trim caused
when said crane boom extends outwardly away from the end of said
barge in the direction of said barge's longitudinal axis with load
and boom outreach of high magnitude causing a high resultant moment
with respect to the pitch axis so that the latter ballast means may
provide a countermoment for reducing the angle of trim of said
barge about its pitch axis.
47. A barge according to claim 46 wherein said ballast means is
operable to transfer ballast from one hull to the other hull in a
manner to achieve said counter-righting moment to maintain the heel
of said barge within the crane's slew limiting angle, with said
ballast being transferable as the crane slews during load operating
conditions.
48. A barge according to claim 46 wherein said structural
reinforcing means includes substantially transversely extending
members interconnecting said hulls adjacent the uppermost portions
thereof and restraining said hulls against lateral displacement
relative to one another.
49. A barge according to claim 46 wherein said structural support
means adjacent the crane includes support members directly
connected between the base of said crane and said hulls for at
least partially structurally supporting said crane from said
hulls.
50. A barge according to claim 46 wherein:
the barge's length-to-width ratio is approximately 400 to 100.
51. A derrick barge according to claim 46 having at least eight
stabilizing columns and wherein:
there are at least four columns connecting with each of said hulls
and with said platform, with at least one pair of columns on each
hull located adjacent opposite ends of said barge as above-stated
and with at least one additional pair of columns at two
intermediate positions on each hull.
52. A derrick barge according to claim 51 wherein the
last-mentioned pair of additional columns are longitudinally
positioned on each hull so that the centroid of each of said latter
columns is located on opposite sides of the barge's transverse
pitch axis.
53. A derrick barge according to claim 46 wherein:
at least one of said columns on each of said hulls has a cross
section whereby the column dimension extending in the direction of
the barge roll axis is greater than the transverse dimension of the
column.
54. A derrick barge according to claim 46 wherein:
each of said hulls has a streamlined bow portion for minimizing
resistance to movement through water in the low draft
condition.
55. A column stabilized semi-submersible derrick barge
comprising:
a pair of elongated hulls disposed in spaced side by side
substantially parallel relatiOn with each hull having a
substantially right quadrilateral cross section with substantially
planar top and bottom horizontal surfaces disposed substantially
perpendicular to a vertical plane through the longitudinal
centerline of the barge, and extending substantially the length of
each hull;
a working platform spaced above said hulls a predetermined
height;
means for supporting said platform in fixed spaced relation above
said hulls including at least three columns connecting with each of
said hulls and said platform and located at spaced intervals along
said hulls;
the distance between the extremities of said barge and its platform
along the barge's longitudinal centerline being substantially
greater than the distance between the extremities of said barge and
its platform along the barge's transverse centerline, with the
barge length being at least a plural number of times as great as
the barge width;
a heavy duty crane located adjacent one end of said barge and
mounted for rotation about a substantially vertical axis, said
crane being mounted and having a rated capacity and a boom of
sufficient length capable of performing lifting operations off at
least one beam and one end of the barge, with the boom of said
crane being of such length that it reaches beyond the transverse
centerline of the barge when the crane boom is disposed in a rest
position;
said crane having a predetermined angle of inclination from the
crane's normal substantially vertical axis of rotation beyond which
said crane cannot slew;
at least one column on each hull being located adjacent the end of
said barge at substantially the same longitudinal position at which
said crane is mounted and at a distance from the transverse barge
centerline at least substantially the same as the distance between
said transverse barge centerline and the crane axis of rotation,
another of said columns on each hull being located adjacent the
opposite end of the barge, with at least one additional column at
an intermediate position on each hull;
a plurality of longitudinally spaced structural means reinforcing
the structural relationship of the hulls, platform and columns;
said structural reinforcing means including substantially
transversely extending members interconnecting said hulls adjacent
the uppermost portions thereof and restraining said hulls against
lateral displacement relative to one another;
said barge including additional structural supporting means
adjacent the crane for increased support of the heavy duty crane in
both loaded and unloaded condition, such means including support
members directly connected between the base of said crane and said
hulls for at least partially structurally supporting said crane
from said hulls;
said hulls having ballast compartments for ballasting said barge to
alter its draft between a low draft hull supported floating
condition and a high draft semisubmerged column stabilized floating
condition;
said columns having predetermined cross-sectional areas and being
located on the hulls to provide righting moments about the pitch
and roll axes of said barge when in high draft semi-submerged
condition;
the area of said columns, the number thereof and the distance of
said columns from the longitudinal and transverse centerlines of
said barge being such as to provide a greater righting moment about
the transverse pitch axis than the righting moment about the
longitudinal roll axis when said barge is in high draft
semi-submerged condition;
the configurations, areas and locations of said columns being such
as to provide the barge in high draft semisubmerged condition with
stabilizing characteristics with respect to inclination about the
roll and pitch axes for enabling the barge to maintain an attitude
keeping the axis of rotation of said crane within said
predetermined crane slew limiting angle;
said barge having ballast mens for counteracting excessive angle of
heel caused by crane operation with beam outreach to provide a
counter righting moment for said barge about its roll axis
sufficient to maintain the angle of heel of the barge during crane
operations within the slew limiting angle of said crane, said
ballast means being operable to transfer ballast from one hull to
the other hull in a manner to achieve said counter-righting moment
as the crane slews during load operating conditions;
additional ballast means for counteracting the angle of trim caused
when said crane boom extends outwardly away from the end of said
barge in the direction of said barge's longitudinal axis with load
and boom outreach of high magnitude causing a high resultant moment
with respect to the pitch axis so that the latter ballast means may
provide a countermoment for reducing the angle of trim of said
barge about its pitch axis.
56. A barge according to claim 55, wherein:
the barge's length-to-width ratio is approximately 400 to 100.
57. A method for transferring loads between horizontally spaced
locations utilizing a variable draft derrick barge of the type
characterized by a pair of spaced elongated hulls, a working
platform spaced above the hulls a predetermined height at least
equal to the height of the maximum anticipated wave, a derrick
having a generally vertically extending axis of rotation
substantially coincident with the centerline of the barge, and a
plurality of stabilizing columns connecting between the hulls and
the platform and upstanding from the hulls a distance at least
equal to said predetermined height comprising the steps of:
moving the barge in a low draft condition with the hulls having
freeboard to a work site; ballasting the barge to respectively
submerge the hulls and portions of the columns below the waterline
to provide a high draft floating condition with the mean waterline
located a distance above the hulls at substantially one-half the
height of said stabilizing columns, lifting a load at one location,
slewing the derrick and the load carried thereby to transfer the
load from said one location to another location, depositing the
load at said other location, the steps of lifting, slewing and
depositing being performed when the barge lies in said high draft
floating condition, and deballasting the barge to return the barge
to the low draft condition with the hulls having freeboard.
58. A method of claim 57 including the step of ballasting and
deballasting the barge to vary its submergence when in the high
draft floating condition such that the distance between the mean
waterline and either the underside of the platform or the topside
of the hulls is not less than 0.75 of the mean wave height for wave
heights less than the maximum anticipated wave to preclude
amplification of barge motion due to interaction of wave and barge
motions.
59. A method according to claim 57 wherein each of said hulls
includes a plurality of ballast compartments and including the
further step of selectively ballasting the compartments in each of
the hulls to alter the natural period of the barge about at least
one of its pitch and roll axes.
60. The method according to claim 57 wherein the derrick includes
an elongated boom and a counterweight and including the steps of
ballasting one of the hulls to incline the barge to one side about
its roll axis, slewing the derrick such that the boom lies outboard
of the barge on said one side thereof whereby the counterweight
inclines the barge about the roll axis in the opposite direction,
and lifting the load on said one side thereof.
Description
BACKGROUND OF THE INVENTION
This invention relates to a twin hull, semisubmersible floating
vessel and more specifically to a semisubmersible barge mounting a
heavy duty derrick or crane for use in offshore, particularly deep
water, construction including, for example the erection and
dismantling of oil drilling and production platforms as well as
other offshore lifting and transfer functions.
Offshore activities, such as current attempts to drill and exploit
oil wells at sea, have led to the development and construction of
various special purpose marine structures capable of operations in
the offshore environment over extended periods of time. For
example, one such structure employed in offshore oil drilling
operations comprises a fixed, self-contained drilling platform
erected on piles driven into the sea floor, with the platform
mounting a drilling rig, auxiliary equipment and crew's quarters. A
variation of the foregoing structure provides a somewhat smaller
platform similarly erected on piles and having a drilling rig
located thereon, the auxiliary equipment and crew being located on
a tender tied alongside.
To erect structures in the offshore environment as well as to
dismantle the same as in the case of discontinued oil drilling and
production platforms and other structures, barges mounting heavy
duty derricks or cranes have been employed to lift, transfer and
set into place the parts forming such structures. For example,
current methods of offshore construction, particularly the
construction of oil drilling and production platforms, employ such
barges to drive piles at the construction site on which the
platform is mounted. Present practice provides for the assembly on
land of the component parts of the platforms to form subassemblies
which are then loaded aboard derrick or crane barges for transport
to the construction site. At the site, these barges provide a work
deck from which the subassemblies are offloaded by the heavy duty
derricks or cranes mounted on the barges and assembled to form the
completed structure.
Present derrick or crane barges employed for this purpose comprise
single hull surface floating vessels which are either towed or
self-propelled to and anchored at the construction site. Platform
erecting and dismantling operations conducted from barges of this
type are, however, highly restricted by sea state conditions, since
excessive vessel motion in heave, pitch and roll precludes crane or
derrick operations. For example, surface floating derrick or crane
barges currently employed for offshore construction can operate in
sea states having wave heights up to about 5 feet or in special
cases 6 feet. The wave action against the vessel caused by sea
states having wave heights in excess of these limits normally
causes excessive vessel motion precluding derrick or crane
operations. Construction operations utilizing present day barges
are thus normally halted when these high sea state conditions are
encountered and are resumed only when the sea state subsides to
within the above-noted limits.
The main problems that present day vessels of this type encounter
are (1) their natural period in roll, pitch and heave is inherently
low and (2) their GM (distance between center of gravity and
metacenter GM) is inherently high. The low natural periods are more
apt to be close to the period of the waves thus causing motion
amplification. The high GM values result in abrupt correcting
motions when the vessels are submitted to roll or pitch
excitations. This may damgage the equipment, bring about structural
or wire failures of the derrick due to excessive acceleration
forces and cause discomfort to personnel.
Accordingly, it is a primary object of the present invention to
provide a derrick barge or crane barge which minimizes the
above-discussed and other shortcomings of prior vessels employed
for like purposes and provides various advantages in construction,
mode of operation and result over prior vessels. [The terms
"derrick" or "crane" are employed hereinafter interchangeably and
the vessel or barge mounting either one or the other is herein
referred to as a derrick barge.]
It is another object of the present invention to provide a twin
hull, semisubmersible barge mounting a heavy duty derrick for
offshore construction work.
It is still another object of the present invention to provide a
semisubmersible twin hull derrick barge which, particularly when in
floating semisubmerged condition, has the characteristic of
minimizing vessel motion due to excitation forces caused by wave
action (hereinafter called "motion minimizing characteristics"). It
is a related object to provide such a derrick barge affording
improved motion minimizing characteristics in vessel pitch, roll
and heave as well as minimizing sideslip and surge.
It is yet another object of the invention to provide a derrick
barge comprising a platform and a derrick mounted in spaced
relation above a pair of hulls and which can be selectively
ballasted or deballasted from its normal semisubmerged floating
condition to obtain even better motion minimizing characteristics
when the period of the waves is the same or close to the natural
period of the vessel, thereby tending to produce vessel motion
amplification.
It is another related object of the present invention to provide a
twin hull semisubmersible derrick barge having long natural periods
in roll, pitch and heave and a lower GM in the semisubmerged
condition as compared with its GM in the surface floating condition
(low draft).
It is a further object of the present invention to provide a
semisubmersible derrick barge having rapid mobility in transit, the
ability to carry large deck loads in the surface floating condition
and a beam providing for transit of the barge through the Panama
Canal.
It is a still further object of the present invention to provide,
in a barge mounting a heavy duty derrick, a method of coordinating
operation of the derrick and the ballasting of the barge as to
enable operation of the derrick when its permissible slew angle
would otherwise be exceeded, and also to maintain heel angle of the
vessel within limits acceptable for comfort of the crew.
These and other related objects and advantages of the present
invention will become more apparent from the following
specification, claims and appended drawings wherein:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a twin hull semisubmerged derrick
barge constructed in accordance with the present invention;
FIG. 2 is a side elevational view of the derrick barge with the
waterline being illustrated relative to the barge in both the
surface and semisubmerged floating conditions;
FIG. 3 is a plan view of the derrick barge with portions broken out
for ease of illustration;
FIG. 4 is a cross-sectional view thereof taken on lines 4--4 in
FIG. 3;
FIG. 5 is a cross-sectional view thereof taken on lines 5--5 in
FIG. 3;
FIG. 6 is a fragmentary plan view of the barge with portions broken
away, illustrating the derrick support structure;
FIG. 7 is an aft end elevational view thereof illustrating the
derrick support structure;
FIG. 8 is a schematic plan view of the hulls of the derrick barge
illustrating a ballast system therefor;
FIG. 9 is a fragmentary side elevational view of the derrick barge
illustrating the operating limits when in the semisubmerged
floating condition;
FIGS. 10a-10d are schematic aft end elevational views of the
derrick barge hereof illustrating the various angular positions
thereof in exaggerated form when operating the derrick to pick up
load with the crane to beam; and using ballast transfer.
FIG. 11 is a diagrammatic horizontal cross-sectional view between
deck and hull illustrating another embodiment of the derrick barge
hereof.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to the drawings, particularly FIGS. 1 and 2, there is
shown a semisubmersible derrick barge or vessel generally indicated
at 10 comprising a pair of transversely spaced, elongated hulls 12
extending in spaced parallel relation and providing sufficient
displacement to support vessel 10 in the floating condition with
the hulls having freeboard indicated at f in FIG. 2. [Each hull 12
has a substantially rectangular cross section as seen in FIGS. 4
and 5, an arcuate bow portion 14 and a round stern bottom portion
16. Hulls 12 are thus sufficiently streamlined in shape to minimize
resistance to towing when vessel 10 is entirely supported by hulls
12 in the floating condition.]
A platform P comprising a main deck 20 and a lower deck 22 is
supported a predetermined height above hulls 12 by support
structure including a plurality of longitudinally spaced,
transversely extending truss formations generally indicated at 24
and a plurality of longitudinally spaced pairs of transversely
spaced stabilizing columns 26 hereinafter referred to as columns. A
plurality of truss formations 24 are longitudinally spaced between
longitudinally spaced pairs of columns 26 and each truss includes
as best seen in FIG. 4 two outermost support members 28 upstanding
from each hull 12 to the outer edges of lower deck 22. Each truss
24 includes a plurality of diagonally and transversely extending
beams 38 secured between hulls 12 and lower deck 22 providing for
platform P. Trusses 24 include transversely extending, horizontal
cross braces 39 joining the upper inner sides of hulls 12. Similar
diagonally and transversely extending truss formations 40 connect
between hulls 12 in the area between columns 26 as seen in FIG.
5.
As discussed more fully hereinafter, the support structure also
includes stabilizing columns 26 extending upwardly from the upper
surface of hulls 12 to platform P an effective height h (FIG. 2)
which may be equal to and preferably greater than the maximum
anticipated wave height, the vertical distance between wave crest
and trough. In the preferred embodiment, four pairs of columns 26
are equally longitudinally spaced one from the other along hulls 12
with the column arrangement on each hull being symmetrical with
respect to the other hull. As shown by the dashed lines in FIG. 3,
columns 26 preferably are generally oblong shaped with
longitudinally elongated vertical sides and semicylindrical fore
and aft vertical end sections 42. It will be understood, however,
that columns 26 may have circular, square or other cross-sectional
configurations as desired. Use of columns 26 provides motion
minimizing characteristics when the vessel is in the floating
semisubmerged condition. Stabilizing columns 26 are preferably
constant in cross-sectional area throughout their effective length.
It will be understood that either or both the upper and lower ends
of the columns may be reduced in cross section, for example, to
form frustro-conical sections, to provide mechanical connection
between the columns and the hulls and platform which do not
substantially affect the effective height or make the latter
subject thereto.
As seen in FIG. 2, the lower ends of the legs 44 of a shear leg
generally indicated at 46 are pivotally mounted to bow portions of
hulls 12 as at 48. The vertical inclination of shear leg 46 is
controlled by a hoist cable 50 connected to a block, not shown,
located at the upper end of shear leg 46 and to a pulley block 52
at its lower end which connects with a power-driven drum apparatus
54 whereby the inclination of shear leg 46 may be selectively
altered.
A heavy duty derrick or crane, generally indicated at 56 and
hereinafter referred to as derrick, comprises a boom 58 and a
housing 60, derrick 56 being pivotally mounted on a support
structure including girders extending upwardly from stern portions
of hulls 12 locating the base structure B of derrick 56 at a level
coincident with lower deck 22 of platform P. As seen in FIGS. 6 and
7, the support girders may comprise four inwardly and upwardly
directed columns formed by girders 57 with foot or base portions 59
of each lateral pair of girder columns 57 being secured to the
inboard sides of stern portions of hulls 12. The upper ends of
girder columns 57 converge to support a base structure B on which
derrick 56 may be rotated. Obviously, other types of supporting
structures may be formed and the foregoing is considered exemplary
only.
It will be understood that derrick 56 is secured to the vessel such
that the pivotal axis thereof extends vertically when the vessel
lies in calm water, i.e., its equilibrium position. Also, the
derrick is mounted such that the pivotal axis thereof lies in the
vertical plane intersecting the horizontal centerline of the vessel
whereby the weight of the derrick is equally distributed to each of
hulls 12. The crane 56 more particularly comprises a counterweight
59, a mast structure 61 carrying tackle 62 and load blocks and
hooks 64 arranged in a conventional manner. A Dutch pintle crane,
known to the art, is preferably employed herein, but it will be
understood that derrick 56 may comprise any commercially available
heavy duty crane. For example, a tub type crane may be employed. In
the preferred form hereof, a crane having a capacity of 500 tons in
slewing is provided.
Columns 26, in the preferred form, are disposed along outboard
portions of hulls 12 as shown in FIGS. 3 and 5. The outboard sides
of columns 26 are in vertical alignment with and form continuations
of the outboard sides of the associated hulls. The displacement and
stability requirements of columns 26 are such that their
longitudinal axes preferably are spaced laterally outwardly of the
centerline of the hulls. The centroids of the water plane areas
defined by the cross sections of the columns 26 are located an
extended distance from the centerline of the vessel on opposite
sides thereof to develop large moments of inertia of the water
plane areas about the roll axis.
As seen in FIG. 2, anchor winches 35 are disposed in the forward
and stern pairs of columns 26 and carry anchor lines 36 disposed
about suitable mooring pulleys. Lines 36 carry anchors, not show,
whereby vessel 10 can be moored at the construction site. Also, as
seen in FIG. 1, suitable fenders 37 may be provided hulls 12 and
columns 26.
As seen in FIG. 8, hulls 12 are each divided into compartments 66
forming a plurality of ballast chambers for submerging and
refloating the vessel, and it will be understood that any number of
compartments 66 may be provided as desired to perform the intended
ballasting function. While only the starboard hull and ballast
system therefor is illustrated in FIG. 8, it will be understood
that the port hull is similarly arranged and ballasted but on the
opposite hand. Also, the port hull and bilge system therefor is
illustrated in FIG. 8, and it will be understood that the starboard
hull is similarly arranged and of the opposite hand. Ballast
chambers 66 are selectively and independently ballasted and
deballasted whereby the vessel may be submerged with the platform P
remaining substantially level throughout the submergence thereof
and any attitude deviation of the vessel in both heel and trim may
be corrected during submergence and retention of the vessel at the
semisubmerged depth. Ballast chambers 66 may also be selectively
and independently or dependently ballasted and deballasted when the
vessel is semisubmerged to provide a transverse vessel inclination
about its heel axis to enhance the comfort, safety and
effectiveness of the operating personnel and to assist derrick
operations when necessary and in a manner described hereinafter. To
these ends, a plurality of conduits 68 extend from a pump room PR
in each of hulls 12 in opposite longitudinal directions to the
several ballast compartments 66, there being multiple compartments
in the forward and aft portions, respectively, of each hull.
Pump room PR is provided with a sea-suction inlet indicated at 70
and an overboard discharge indicated at 72 controlled by suitable
power operated gate valves 74 and 76 respectively, the hull side
being indicated by the dashed lines in FIG. 8. A pair of pumps 78
and 80 are connected in parallel via lines 79 and 81 respectively
across conduits 82 and 84, conduit 82 connecting with inlet 70 and
conduit 84 connecting with discharge 72. Conduits 82 and 84 connect
with a conduit 86 and it will be seen that, with valves 88 and 90
closed, pumps 78 and 80 suction sea water through inlet 70 past
suitable valves 92 located in the parallel pump lines 79 and 81,
and into conduit 84 which, with valves 76 closed, communicates with
a main ballast conduit 94. Opposite ends of main conduit 94 are
connected in parallel with ballast conduits 68 through a pair of
power operated valves 96 located on opposite sides of feed conduit
84, ballast conduits 68 each having a suitable power operated valve
98. Thus, with valves 74, 92, 96 and 98 open and valve 76 closed,
the 12 ballast compartments may be simultaneously ballasted with
sea water at an equal rate to maintain the platform substantially
level when the vessel is being submerged or the valves 98 may be
selectively operated to control the ballasting of the individual
compartments 66 whereby the trim of the vessel may be corrected or
altered during submergence, retention of the vessel in the
semisubmerged condition, and during operation of derrick 56 as
hereinafter described. Line 86 is used to transfer ballast between
one hull and the other.
Conduit 82 connects with a deballasting conduit 100 having suitable
power operated valves 102 on opposite sides of the connection,
opposite ends of deballasting conduit 100 connecting across
ballasting conduit 94 between valves 96 and the first of the
parallel connected conduits 68. To refloat the vessel with the
hulls 12 having freeboard, valves 74 and 96 are closed and valves
76 and 102 are opened. Pumps 78 and 80 operated to pump water in
the same direction as before and accordingly suction main
deballasting conduit 100 via conduit 82, thereby suctioning ballast
conduits 68 and withdrawing ballast water from compartments 66 via
conduits 68, 100 and 82, the pump lines 79 and 81, open valve 76
and outlet 72. With all of valves 98 open, compartments 66 may be
simultaneously deballasted as desired to effect refloatation of the
vessel to the surface floating condition with hulls 12 having
freeboard f. Selected operation of valves 98 with valves 76 and 102
open and valve 74 closed deballasts selected compartments 66 as
desired to alter the attitude of the vessel about the heel and trim
axes an to assist in the operation of derrick 56 when necessary as
hereinafter described. It is thus readily seen that compartments 66
may be simultaneously ballasted and deballasted or selectively
ballasted and deballasted or having ballast transferred between the
port and starboard hulls by selected operation of the various
valves and that this can be accomplished when the vessel is in any
operating condition, for example, floating with the hulls having
freeboard, semisubmerged floating or any intermediate position
during submerging or refloating operations wherein the attitude of
the vessel about heel and trim axes is to be altered. Note also
that the various valves, conduits, etc. of the foregoing ballast
system are provided each hull 12 whereby one or both hulls may be
ballasted or deballasted alone or together, or ballast
transferred.
It is a significant feature of the present invention that vessel 10
can be towed or self-propelled, by means not shown, between work
sites at speeds in the order of 8 to 10 knots providing the present
vessel with a mobility heretofore unavailable in prior
semisubmersible type vessels (with the exception of the vessel
disclosed in the aforementioned parent application Ser. No.
705,175. To this end, hulls 12 have a displacement when deballasted
to support the entire weight of the vessel, including derrick 56,
crew, auxiliary equipment and the like as well as a heavy deck
load, with the hulls 12 having freeboard f. When in the latter
surface floating condition, vessel 10 has the great righting
stability and decreased roll angles characteristic of a twin hull
type vessel. It will be seen that the support structure for
platform 20 including truss formations 24 and stabilizing columns
26 are disposed above the waterline and accordingly do not present
a frontal area to the water to offer resistance to passage
therethrough. In the floating condition, only twin hulls 12
displace water and the substantially streamline shape thereof as
well as the absence of support structure in contact with the water
permit movement of the vessel at significantly higher speeds than
heretofore possible with prior semisubmersible vessels (with the
exception of the vessel disclosed in the aforementioned parent
application Ser. No. 705,175.
When vessel 10 reaches the work or construction site for the
purpose of erecting or dismantling a marine structure such as an
oil drilling or production platform or other offshore marine
structure, anchors, not shown, are deployed to maintain vessel 10
in proper position. It is understood that a dynamic position
keeping system could be employed in lieu of the conventional
anchoring system mentioned herein.
For normal wave conditions and with the vessel in the surface
floating condition with hulls 12 having freeboard f, derrick 56
could be operated to lift and transfer loads up to its full tonnage
capacity when servicing adjacent structure. In moderate or heavier
sea states, for example wave heights in excess of 5 or 6 feet,
servicing operations with a conventional derrick barge would at
this point cease because of excessive vessel motions in roll, pitch
and heave and not be continued until a sea state prevailed which
would preclude such vessel motions. However, a semisubmersible
vessel constructed in accordance with the present invention can
continue to perform its function even in sea states having wave
heights exceeding 5 or 6 feet in a manner as will now be
described.
When vessel 10 is at the work site and derrick operations in the
semisubmerged condition are to be conducted, hulls 12 are ballasted
preferably by simultaneously ballasting the compartments 66 in each
hull in the previously described manner to submerge hulls 12 below
the waterline. Vessel 10 is preferably submerged to the extent that
columns 26 are submerged for approximately half their effective
height h, thereby locating the mean waterline above the upper
surfaces of hulls 12 at a distance of approximately half the
distance between lower deck 22 and the upper surface of hulls 12.
The displacement of the submerged portions of columns 26 and the
residual displacement of hulls 12 are adequate to maintain the
vessel in the floating semisubmerged condition at such
predetermined height. In this manner, the maximum anticipated wave
is prevented from acting against hulls 12 and platform P and acts
only on the columns 26 and in the open frame area between the hulls
and the platform. This reduces the adverse effect of wave action on
the vessel which now has excellent motion minimizing
characteristics in the floating semisubmerged condition. When the
vessel is in the semisubmerged condition, anchor lines 36 are made
taut to maintain the vessel in proper servicing position relative
to the construction site.
It will be noted that the primary purpose of the semisubmersible
vessel is to minimize vessel motion due to wave action. Ideally,
this is accomplished by submerging the vessel to approximately
one-half the effective height of columns 26 thus precluding wave
action against the deck structure as well as the hull structure so
that only the exposed columns 26 and trusses 24 between platform P
and hulls 12 are exposed to the wave action. The present
semisubmersible derrick barge can accordingly operate efficiently
in much higher sea states than derrick barges of known types, for
example, in sea states having waves 11 and 12 feet in height or
higher. (Of course, there is an upper limit as to the wave height
in which even the present semisubmersible barge can operate
efficiently, and beyond that derrick operations must be suspended
until the sea subsides.) However, even when this semisubmersible
vessel is operating within design limits in the semisubmerged
condition with motion minimizing characteristics afforded by the
described vessel construction, there is some vessel response to
wave action, i.e., the wave action against columns 26 and trusses
24. Because of this, when the natural period of the ship is the
same as or close to the period of the waves according to existent
sea conditions, there is amplification of vessel motion which may
become so excessive as to interfere with derrick operations, even
though the vessel is semisubmerged to the usual operating condition
wherein the mean waterline is at approximately one-half the
effective height h of stabilizing columns 26. It is thus necessary
and desirous to alter the motion of the vessel when such motion
amplification occurs and this can be accomplished by either
ballasting or deballasting the vessel within certain predetermined
limits to submerge or emerge the vessel to a greater or lesser
extent from the ideal submergence which locates the mean water
surface one-half the effective height h. The maximum variation of
submergence of the vessel from the ideal submergence by ballasting
or deballasting the vessel is, however, limited to distances within
a range which do not reorient the vessel to a position wherein wave
action against the vessel causes excessive impact. Thus, to
preclude excessive vessel motion and impact caused by the
interaction of vessel and wave motion, the maximum variation, i.e.,
submergence or emergence of vessel 10 as by ballasting or
deballasting, respectively, from the ideal submergence of one-half
h, is such that the distance between the mean water surface and
either the underside of the lower deck 22 or the top side of hulls
12 is not less than 0.75 of the mean wave height. FIG. 9
illustrates a pair of permissible mean waterlines relative to the
vessel for a particular wave height under this criteria. The
preferred variation from the ideal submergence provides for
deballasting the vessels such that there is less splash against the
lower deck 22. In addition to ballasting and deballasting the
natural period of the vessel in pitch and roll may be varied by
redistribution of the ballast within the vessel. This can be
accomplished through ballast transfer between compartments, toward
or away from, the ship's extremities, as the conditions may
necessitate, i.e., transversely or longitudinally of the vessel. In
this manner, all vessel motions caused by wave action can be
minimized.
It is a significant feature hereof that the foregoing vessel has
optimal stability characteristics in the floating submerged
condition. The columns are designed to provide a large water plane
area at all the aforementioned depths of submergence to afford an
adequate righting moment to return the vessel to a level position.
The vessel is designed such that there are long periods of roll,
pitch ahd heave. Particularly, the columns provide a roll
sufficiently slow as to preclude tossing about of operating
personnel on platform P and a roll rate sufficiently fast to
provide adequate stability about the roll axis. The vessel attitude
about heel and trim axes can be corrected by selected ballasting of
compartments 66. The stability characteristics and motion
minimizing characteristics thus afforded the vessel are optimum for
a vessel of the foregoing construction.
Since the displacement of hulls 12 is considerably larger than the
displacement of the submerged portions of columns 26, the lifting
of a like load when the crane is similarly oriented in the floating
and semisubmerged conditions causes the vessel to roll to a greater
load induced heel angle in the semisubmerged condition than in the
floating condition. The operational capacity of crane 56 when
vessel 10 is semisubmerged is thus limited to predetermined values
expressed in the net moment caused by load W so as to preclude
excessive load induced heel angles. It has been found statistically
that the vast majority of marine construction operations of the
type contemplated herein require a crane lifting capacity of 250
tons or less. The capacity of the present derrick in the preferred
form is 500 tons slewing and 800 tons fixed and this capability is
fully obtained when the vessel lies in the surface floating (low
draft) condition. The vessel is configured, i.e., the hulls and
columns are designed and located to maintain the vessel within a
permissible range of heel angles when operating in the
semisubmerged condition for loads up to 250 tons disposed at a
maximum predetermined radius normal to the vessel centerline. The
range of weights and distances thereof from the centerline of the
vessel, i.e., the operating limits of the derrick barge in the
semisubmerged condition, are dependent upon the physical
configuration of the vessel's hulls and columns and in an
illustrative preferred embodiment hereof, vessel 10 has an overall
length of 400 feet at hulls 12 with each hull having a beam of 38
feet and an inside spacing of 30 feet one from the other, providing
an overall hull beam of 106 feet. The effective height h of the
stabilizing columns 26 is 23.0 feet. The centroids of bottles 26
are equally spaced 39 feet from the vessel's longitudinal
centerline. The pairs of columns 26 are longitudinally spaced one
from the other 63.25 feet with the bow pair of columns being spaced
19.75 feet from the bow of hulls 12. The length of each column 26
is 46 feet and the width is 28 feet with the ends thereof being
formed cylindrical in shape providing an overall area of
approximately 1119.5 square feet per column.
To refloat the vessel, the anchor lines, not shown, are loosened or
the anchors shipped aboard and ballast compartments 66 are pumped
to evacuate the water therein as hereinbefore described. The
combined hull displacement and the submerged column displacement is
sufficient to raise the vessel to the surface floating condition
with hulls 12 having freeboard indicated as f in FIG. 2, the
stabilizing columns 26 acting continuously to stabilize the vessel
during refloating operations.
The vessel is self-contained in that crew's quarters, auxiliary
equipment, and the like are all on board and can provide these
facilities to the serviced vessel or structure, as well as to
auxiliary accompanying vessels. Particularly, the crew's quarters
are located on lower deck 22 leaving ample space on main deck 20
for locating other heavy equipment and carrying large deck loads.
Auxiliary equipment, crew's quarters, etc. may be located within
columns 26 in addition to being located on platform P. As seen in
FIGS. 1 and 2, a control house 110 is disposed on main deck 20
adjacent the foreward end and port side of vessel 10 and a boom
rest is provided for boom 58 while vessel 10 is in transit.
It will be noted that the vessel may be ballasted in the
semisubmerged condition to compensate for and minimize transverse
inclinations about the heel axis caused by crane operations. For
example, slewing of crane 56 in either the loaded or unloaded
conditions induces an inclination about the heel axis of the vessel
due to the asymmetrical location of the load and/or counterweight.
For those derrick barges employing a crane having a small
permissible heeling angle d (the angle between true vertical and
the vertical axis of rotation of the crane) beyond which the crane
will not rotate, such induced heel angle in combination with the
dynamic rolling characteristics of the vessel may provide a total
inclination of vessel 10 exceeding the permissible crane angle d
thereby precluding derrick operations.
Accordingly, to provide for the comfort and safety of the operating
personnel and to retain crane slewing capability wherein the latter
described cranes are employed, the vessel may be ballasted in a
predetermined manner in accordance with the rotational movement of
the crane to maintain the vessel heel angle within predetermined
limits. To this end and referring to FIGS. 10a-d wherein vessel 10
is illustrated in the onloading semisubmerged floating condition,
the port hull 12P may be ballasted to incline the vessel from the
even keel crane to aft position illustrated in FIG. 10a to the
ballasted condition illustrated in FIG. 10b providing a heel angle
e. To pick up a load W off the port side, the unloaded crane is
slewed to the port side and counterweight 59 causes the vessel to
incline about its heel axis in the opposite direction assuming a
heel angle of e'. A load W may then be picked up by means of load
blocks 64 whereupon the vessel inclines counterclockwise about its
heel axis to the position illustrated in FIG. 10d assuming a heel
angle g. Note that the ballast, ballasted counterweight and
ballasted load induced heel angles e, e' and g respectively incline
the vessel to smaller heel angles than would otherwise be the case
if the vessel were not ballasted in the foregoing manner. Such
induced angles also lie within the permissible heeling angle d
where such cranes are employed whereby slewing capability is
retained. To offload the vessel, i.e., to transfer load W from the
vessel to a point outboard thereof, the operation is reversed and,
of course, onloading or offloading may be conducted from either the
port or starboard sides of the vessel with the port or starboard
hull being ballasted as the case may be. The above illustrates one
set of conditions. The ballast system may assist in any case where
loads should be balanced and heel angles reduced. Also, when
employing shear leg 46 near or at its full capacity of 2000 tons,
compartments 66 located in the stern portion of the vessel may be
ballasted to offset and minimize the load induced trim angle.
While the preferred form of the vessel described herein provides an
even number of pairs of columns on opposite sides of the pitch and
roll axes in a generally symmetrical relation thereabout, an odd
number of pairs of columns can be provided as illustrated in FIG.
10. It is seen in this form that a pair of columns are spaced on
opposite sides of the pitch axes adjacent fore and aft portions of
the vessel with a central pair located such that the pitch axis
preferably intersects the same, the columns being symmetrically
arranged on opposite sides of the roll axis.
Certain basic principles are employed in the construction of the
present vessel:
1. A pair of elongated, laterally spaced hulls 12 in substantially
parallel relation are employed to provide greater towing speeds as
well as high stability.
2. The hulls have sufficient displacement to float the vessel
having a large deck load and a heavy duty crane of the
aforementioned type with the hulls having freeboard.
3. The hulls are compartmented for ballasting and selected
compartments in both hulls may be ballasted and deballasted to
submerge the vessel and to induce predetermined heel or trim angles
in the semisubmerged condition. Ballast may also be transferred
between the hulls.
4. The vessel should have at least four stabilizing columns 26,
with half of the columns being disposed on each hull on opposite
sides of the roll axis RA. When six columns are provided, a first
and second pair of such columns are located on opposite sides of
the pitch axis PA (passing through the center of flotation), with
the third middle pair of such columns located adjacent or
intersected by the pitch axis. When eight stabilizing columns are
employed, the same number of pairs are located generally
symmetrically on opposite sides of and spaced from the pitch
axis.
4b. More specifically, if an odd number of pairs of stabilizing
columns are employed, the middle pair should be adjacent the pitch
axis PA and the other pairs of columns should be disposed in equal
numbers on opposite sides of the pitch axis PA and in a generally
symmetrical relation; whereas when an even number of pairs of
stabilizing columns are employed, the same number of pairs are
located on the opposite sides of the pitch axis PA in a generally
symmetrical relation thereto.
5. To stabilize the vessel, each of the columns 26 should have a
predetermined area which is constant in cross section throughout
the effective height thereof.
6. The stabilizing columns 26 are constructed so that their lower
halves provide a combined displacement together with the residual
displacement of the partially ballasted hulls 12 so as to float the
vessel in a semisubmerged condition.
7. The effective height of the stabilizing bottles 26, which is
defined by the distance h between the upper surfaces of hulls 12
and the underside of platform P, may be equal to and preferably
greater than the maximum anticipated wave height from crest to
trough, such height being substantially unaffected by any slight
changes in configuration for the mechanical connection between the
columns and either of the hulls and platform.
8. The vessel is ballasted to a submergence of approximately
one-half the effective height of the stabilizing columns to
maintain the vessel in a semisubmerged floating condition. To
minimize vessel motion amplification under such conditions when
necessary, ballast is redistributed and/or the vessel is ballasted
to submerge or emerge to a greater or lesser extent from the ideal
semisubmerged condition such that the distance between the mean
water surface and either the underside of the deck or top side of
the hull is not less than 0.75 of the mean wave height, i.e., the
effective height h is at least equal to and preferably greater than
1.5 times the mean wave height.
9. When semisubmerged and inclined about the heel axis in the load
and/or ballast induced condition, the stabilizing columns provide
righting moments about the roll axis RA in proportion to their
cross sectional area and the square of their distance from the roll
axis.
10. The hulls 12 in the semisubmerged floating condition can be
selectively ballasted to compensate for and minimize crane induced
vessel inclination providing for increased comfort and
effectiveness of the operating personnel and retaining crane
slewing capability in those instances where cranes having small
permissible heeling angles are employed.
11. When shear leg 46 operates at or near its capacity, the stern
portion of the vessel may be ballasted to minimize excessive shear
leg load induced trim angles.
SUMMARY OF CONSTRUCTION AND OPERATION
Thus, the present invention provides a twin hull, semisubmersible
derrick barge having a plurality of spaced connecting members
including upstanding stabilizing columns 26 fixed at their lower
ends to a pair of laterally spaced, elongated parallel hulls 12.
The members support a platform P including crew's quarters and
machinery spaces, and a heavy duty crane above hulls 12 a distance
at least as great as the effective height h of columns 26. The
spaced hulls are compartmented to provide ballast tanks 66 which
are deballasted when the semisubmersible is towed to and from work
sites to provide sufficient hull displacement to support the
semisubmersible vessel (including the heavy duty crane, crew's
quarters, machinery spaces and deck load) with the hulls having
freeboard. At the work site and with mild sea conditions, the crane
may be operated in the usual manner lifting and transferring loads
up to its capacity, in this instance 500 tons slewing and 800 tons
fixed or the shear leg may be operated to its maximum lift
capacity, in this case 2000 tons. Upon encountering heavy seas,
tanks 66 are ballasted to submerge the hulls normally to a distance
about one-half the effective height of stabilizing columns 26 which
is about one-half the height of the maximum anticipated wave
whereby platform P and the derrick remain supported above the
maximum anticipated wave height. The displacement required to
support the vessel in the semisubmerged floating condition is
provided by the hulls and portions of the stabilizing columns 26,
the vessel in this condition being otherwise unsupported. The hulls
and bottles are configured and located to provide excellent motion
minimizing characteristics under wave action in the semisubmerged
condition. When vessel and wave motion interact to amplify the
vessel motion in the semisubmerged condition, the vessel may be
ballasted or deballasted to a greater or lesser extent from the
ideal semisubmerged condition, i.e., one-half the effective height
of columns 26, such that the distance between either the underside
of the deck or top side of the hull is not less than 0.75 of the
mean wave height.
The ability of the present semisubmersible vessel to provide a
substantially stable and limited motion floating base in the
semisubmerged condition for various wave states is highly
significant as it permits operation of the vessel's derrick in
heavy sea states whereas prior derrick barges are incapable of
derrick operations due to excessive vessel motion. By submerging
the twin hulls to half the effective height of columns 26 or within
the foregoing limits to preclude vessel motion amplification, wave
action against hulls 12 and work platform P is substantially
eliminated, and waves act only against the relatively small area of
the columns, open support structure and framework between work
platform P and hulls 12 and the derrick support structure, thus
minimizing vessel motion due to wave action. The hulls 12 may also
be selectively ballasted to counter derrick induced heel angles,
thereby minimizing transverse inclinations of the vessel and
enhancing the safety, comfort and effectiveness of the operating
personnel. The columns are located such that the hydrodynamic
forces act to establish righting moments proportional to the
volumetric displacement of the submerged portions of the
stabilizing columns about the roll and pitch axes to locate and
maintain the metacenter above the center of gravity of the vessel
for all of the foregoing floating semisubmerged positions of the
vessel.
When the construction work is completed, compartments 66 are
deballasted to refloat the vessel with hulls 12 having freeboard f.
The boom 58 is positioned in a substantially horizontal position
resting on the boom rest and the vessel is ready for transit in the
surface floating condition to other construction sites.
It will be appreciated that the foregoing described vessel may be
employed in virtually any type of marine construction operation and
is in no way limited to the erection and dismantling of offshore
drilling and production platforms. For example, the present vessel
may be employed to lay pipe, build bridges, construct offshore oil
storage tanks, and the like, and may even be employed in the
construction of other vessels.
This invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof.
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