U.S. patent number RE29,167 [Application Number 05/577,674] was granted by the patent office on 1977-04-05 for twin hull variable draft drilling vessel.
This patent grant is currently assigned to Santa Fe International Corporation. Invention is credited to Samuel Harry Lloyd, III.
United States Patent |
RE29,167 |
Lloyd, III |
April 5, 1977 |
Twin hull variable draft drilling vessel
Abstract
The vessel comprises a pair of laterally spaced elongated hulls
having a plurality of upstanding columns spaced therealong
supporting a working platform in spaced relation above the hulls a
distance slightly greater than the maximum anticipated wave height.
The hulls buoyantly support the vessel in a low draft 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 half the effective height of
the stabilizing columns which is slightly greater than maximum
anticipated wave height, to maintain the vessel in a high draft
floating condition with the platform elevated above the waterline.
The columns stabilize the vessel in the high draft condition about
roll and pitch axes. The working platform mounts either a drilling
rig or a heavy duty crane or like operational equipment along the
centerline of the vessel. .[.This application is a
continuation-in-part of application Ser. No. 666,395, filed Sept.
8, 1967 and now abandoned..]..Iadd.
Inventors: |
Lloyd, III; Samuel Harry (Mill
Valley, CA) |
Assignee: |
Santa Fe International
Corporation (Los Angeles, CA)
|
Family
ID: |
27077309 |
Appl.
No.: |
05/577,674 |
Filed: |
May 15, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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221769 |
Jan 8, 1972 |
|
|
|
Reissue of: |
766662 |
Sep 4, 1968 |
03616773 |
Nov 2, 1971 |
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Current U.S.
Class: |
114/264 |
Current CPC
Class: |
B63B
1/107 (20130101); B63B 35/4413 (20130101); B63B
2001/128 (20130101) |
Current International
Class: |
B63B
1/10 (20060101); B63B 1/00 (20060101); B63B
35/44 (20060101); B63B 035/00 () |
Field of
Search: |
;114/.5D,.5R,43.5R,43.5VC,43.5AC,125 ;61/46.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Halvosa; George E. A.
Assistant Examiner: Goldstein; Stuart M.
Attorney, Agent or Firm: LeBlanc & Shur
Parent Case Text
This is a copending continuation of application Ser. No. 221,769
filed Jan. 8, 1972 as an application for reissue of U.S. Pat. No.
3,616,773 issued on Nov. 2, 1971, said application Ser. No. 221,769
now abandoned in favor of this application. Said U.S. Pat. No.
3,616,773 issued from application Ser. No. 766,662 filed Sept. 4,
1968, said Ser. No. 766,662 being a continuation-in-part of
application Ser. No. 666,395 filed Sept. 8, 1967 (abandoned).
.Iaddend.
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A variable draft vessel comprising:
a pair of elongated hulls disposed in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
means connected to said hulls and said platform to support said
platform in spaced relation above said hulls;
said connecting means including at least six upstanding stabilizing
columns disposed on said hulls, a pair of said columns being
located adjacent opposite ends of said hulls on opposite sides of
the pitch axis of the vessel, at least three columns being located
on each hull and on opposite sides of the roll axis of the
vessel;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the hulls and portions of said connecting
means below said platform below the waterline thereby to provide a
high draft condition and refloat the vessel with the hulls having
freeboard, the displacement of the submerged hulls and portions of
said connecting means being sufficient to maintain the vessel
buoyant in the high draft condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said hulls;
the cross sectional area and configuration of said columns, the
weight distribution of the vessel, and the geometry of the
submerged hulls and portions of said connecting means being such as
to maintain the natural period of the vessel in the high draft
condition no less than six seconds;
said vessel having a length to width ratio of at least 2 to 1;
said stabilizing columns being connected to said hulls on the
outboard sides thereof with the distance between the pitch axis and
the centroid of the stabilizing columns on opposite sides of the
pitch axis being greater than the transverse distance between the
roll axis and the centroid of the stabilizing columns on opposite
sides of the roll axis, said stabilizing columns having outboard
portions thereof which extend transversely beyond the outboard
sides of the respective hulls thereby providing increased moment
for stabilizing action about the roll axis.
2. A variable draft vessel comprising:
a pair of elongated hulls disposed in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
means connected to said hulls and said platform to support said
platform in spaced relation above said hulls; said connecting means
including at least four stabilizing columns located on said hulls
with a pair of said columns on each of the opposite sides of the
respective pitch and roll axes of the vessel;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the hulls and portions of said connecting
means below said platform below the waterline thereby to provide a
high draft condition and refloat the vessel with the hulls having
freeboard, the displacement of the submerged hulls and portions of
said connecting means being sufficient to maintain the vessel
buoyant in the high draft condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof, and between said
hulls and said platform;
the cross sectional area and configuration of the columns, the
weight distribution of the vessel, and the geometry of the
submerged hulls and portions of said connecting means being such as
to maintain the natural period of the vessel in the high draft
condition no less than 6 seconds; said stabilizing columns being
connected to said hulls on the outboard sides thereof with the
distance between the pitch axis and the centroid of the stabilizing
columns on opposite sides of the pitch axis being greater than the
transverse distance between the roll axis to the centroid of the
stabilizing columns on opposite sides of the roll axis, said
stabilizing columns having outboard portions thereof which extend
transversely beyond the outboard sides of the respective hulls
thereby providing increased moment for stabilizing action about the
roll axis.
3. A variable draft vessel comprising:
a pair of elongated hulls disposed-in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
a plurality of elements upstanding from said hulls with at least a
portion of said elements being connected to said platform to
support the platform in spaced relation above the hulls a
predetermined height at least equal to the height of the maximum
anticipated wave; at least a portion of said upstanding elements
including at least six stabilizing columns disposed on said hulls
and upstanding therefrom a predetermined effective height at least
equal to the height of the maximum anticipated wave, a pair of said
columns being located adjacent opposite ends of said hulls on
opposite sides of the pitch axis of the vessel, at least three
columns being located on each hull and on opposite sides of the
roll axis of the vessel;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the hulls and portions of said elements below
the waterline thereby to provide a high draft condition and refloat
the vessel with the hulls having freeboard, the displacement of the
submerged hulls and portions of said elements being sufficient to
maintain the vessel buoyant in the high draft condition;
said elements being spaced one from the other to provide an open
frame area therebetween and between said platform and hulls;
the cross sectional area and configuration of the columns, the
weight distribution of the vessel and the geometry of the submerged
hulls and portions of said elements being such as to maintain the
natural period of the vessel in the high draft condition no less
than 6 seconds;
said vessel having a length to width ratio of at least 2 and 1;
the displacement of the submerged hulls and portions of said
elements being sufficient to maintain the vessel buoyant in the
high draft condition with the mean waterline located a distance
above the hulls at substantially one-half the effective height of
said stabilizing columns;
said stabilizing columns being connected to said hulls on the
outboard sides thereof with the distance between the pitch axis and
the centroid of the stabilizing columns on opposite sides of the
pitch axis being greater than the transverse distance between the
roll axis and the centroid of the stabilizing columns on opposite
sides of the roll axis, said stabilizing columns having outboard
portions thereof which extend transversely beyond the outboard
sides of the respective hulls thereby providing increased moment
for stabilizing action about the roll axis.
4. A variable draft vessel comprising: no more than two hulls
disposed in side-by-side spaced substantially parallel relation one
to the other;
a working platform;
means connected to said hulls and said platform to support said
platform in spaced relation above said hulls a predetermined height
at least equal to the height of the maximum anticipated wave, said
connecting means including at least six upstanding stabilizing
columns disposed on said hulls and upstanding therefrom a
predetermined effective height of at least equal to the height of
the maximum anticipated wave, a pair of said columns being located
adjacent opposite ends of said hulls on opposite sides of the pitch
axis of the vessel, at least three columns being located on each
hull and on opposite sides of the roll axis of the vessel;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the hulls and portions of the connecting
means below said platform below the waterline thereby to provide a
high draft condition and refloat the vessel with the hulls having
freeboard, the displacement of the submerged hulls and portions of
said connecting means being sufficient to maintain the vessel
buoyant in the high draft condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said hulls;
said vessel having a length to width ratio of at least 2 to 1;
said stabilizing columns being connected to said hulls on the
outboard sides thereof with the distance between the pitch axis and
the centroid of the stabilizing columns on opposite sides of the
pitch axis being greater than the transverse distance between the
roll axis and the centroid of the stabilizing columns on opposite
sides of the roll axis, said stabilizing columns having outboard
portions thereof which extend transversely beyond the outboard
sides of the respective hulls thereby providing increased moment
for stabilizing action about the roll axis.
5. A variable draft vessel comprising:
no more than two hulls disposed in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
means connected to said hulls and to said platform to support said
platform in spaced relation above said hulls a predetermined height
at least equal to the height of the maximum anticipated wave, said
connecting means including at last six upstanding stabilizing
columns disposed on said hulls and upstanding therefrom a
predetermined effective height at least equal to the height of the
maximum anticipated wave, a pair of said columns being located
adjacent opposite ends of said hulls on opposite sides of the pitch
axis of the vessel, at least three columns being located on each
hull and on opposite sides of the roll axis of the vessel with the
cross sectional area of said columns being substantially constant
throughout the effective height thereof;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the hulls and portions of said connecting
means below the waterline thereby to provide a high draft condition
and refloat the vessel with the hulls having freeboard, the
displacement of the submerged hulls and portions of said connecting
means being sufficient to maintain the vessel buoyant in the high
draft condition with the mean waterline located a distance above
the hulls at substantially one-half the effective height of said
stabilizing columns;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said hulls;
the cross sectional area and configuration of said columns, the
weight distribution of the vessel and the geometry of the submerged
hulls and portions of said connecting means being such as to
maintain the natural period of the vessel in the high draft
condition no less than 6 seconds;
said vessel having a length to width ratio of at least 2 to 1;
said stabilizing columns being connected to said hulls on the
outboard sides thereof with the distance between the pitch axis and
the centroid of the stabilizing columns on opposite sides of the
pitch axis being greater than the transverse distance between the
roll axis and the centroid of the stabilizing columns on opposite
sides of the roll axis, said stabilizing columns having outboard
portions thereof which extend transversely beyond the outboard
sides of the respective hulls thereby providing increased moment
for stabilizing action about the roll axis.
6. A variable draft vessel comprising:
a base structure having hydrostatic and hydrodynamic
characteristics;
a working platform;
a plurality of elements upstanding from said base structure with at
least a portion of said elements being connected to said platform
to support said platform in spaced relation about said base
structure, at least a portion of said upstanding elements including
at least six stabilizing columns disposed on said base structure
with a pair of said columns being located adjacent opposite ends of
said base structure on opposite sides of the pitch axis of the
vessel, at least three columns being located on said base structure
on opposite sides of the roll axis of the vessel;
said base structure having displacement sufficient to float the
vessel in a low draft condition with the base structure having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the base structure and portions of said
elements below the waterline thereby to provide a high draft
condition and refloat the vessel with the base structure having
freeboard;
said elements being spaced one from the other to provide an open
frame area therebetween and between said platform and said
hulls;
the cross sectional area and configuration of said columns, the
weight distribution of the vessel, and the geometry of the
submerged base structure and portions of said elements being such
as to maintain the natural period of the vessel in the high draft
condition no less than 6 seconds;
said vessel having a length to width ratio of at least 2 to 1;
said stabilizing columns being connected to said base structure on
the outboard sides thereof with the distance between the pitch axis
and the centroid of the stabilizing columns on opposite sides of
the pitch axis being greater than the transverse distance between
the roll axis and the centroid of the stabilizing columns on
opposite sides of the roll axis, said stabilizing columns having
outboard portions thereof which extend transversely beyond the
outboard sides of the base structure thereby providing increased
moment for stabilizing action about the roll axis. .[.7. A variable
draft vessel comprising:
a pair of elongated flotation members disposed in side-by-side
spaced substantially parallel relation one to the other;
a working platform;
means connected to said flotation members and said platform to
support said platform in fixed spaced relation above said
members;
said connecting means including at least six upstanding stablizing
columns disposed on said members, a pair of said columns being
located adjacent opposite ends of said members on opposite sides of
the pitch axis of the vessel, at least three columns being located
on each member and on opposite sides of the roll axis of the
vessel;
said platform being spaced above said members a predetermined
height at least equal to the height of the maximum anticipated
wave, said columns upstanding from said members a predetermined
effective height at least equal to the height of the maximum
anticipated wave, the cross sectional area of said columns being
substantially constant throughout the effective height thereof;
said members having a combined displacement sufficient to float the
vessel in a low draft condition with the members having
freeboard;
means for ballasting and deballasting the vessel to respectively
submerge the members and portions of said connecting means below
said platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return the vessel to
the low draft condition with the members having freeboard, the
displacement of the submerged members and portions of said
connecting means being sufficient to maintain the vessel buoyant in
the high draft floating condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said members;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional area and configuration of said columns, the
weight distribution of the vessel, and the geometry of the
submerged members and portions of said connecting means being such
that the vessel obtains motion minimizing characteristics in the
high draft condition;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition;
said vessel having a length to width ratio of about 2 to 1..].
.[.8. A vessel according to claim 7 wherein the natural periods in
pitch and roll of the vessel in the high draft condition lie within
a range of 6 to 40 seconds..]. .[.9. A vessel according to claim 7
wherein the displacement of said submerged members and portions of
said connecting means is sufficient to maintain the vessel buoyant
in the high draft condition with the mean waterline located a
distance above said members at substantially one-half the effective
height of said stabilizing columns;
said ballasting and deballasting means being operable to vary the
submergence of the vessel when in the high draft condition such
that the distance between the mean waterline and either the
underside of the platform or the topside of said members is not
less than 0.75 of the mean wave height for wave heights less than
the maximum anticipated wave to preclude amplification of vessel
motion due to interaction of wave and vessel motion..]. .[.10. A
vessel according to claim 7 including a stabilizing column on each
member located adjacent the transverse axis through the center of
flotation of the vessel, said connecting means including a
plurality of support members forming trusses extending between said
member and said platform at spaced longitudinal positions along the
vessel, said trusses including transversely extending elements
connecting one member to the other with said elements lying above
the uppermost portions of said flotation members..]. .[.11. A
vessel according to claim 7 wherein at least one of said
stabilizing columns on each said member has a cross section
elongated in a direction substantially parallel to the roll axis of
the vessel..]. .[.12. A vessel according to claim 7 wherein at
least one of said stabilizing columns on each said member is
substantially oblong in cross section and extends longitudinally
parallel to said member a distance greater than its width..].
.[.13. A vessel according to claim 7 wherein said drilling means
includes a drilling rig mounted on said platform over the space
between said members..]. .[.14. A vessel according to claim 7
wherein each of said members has bow and stern designs to minimize
resistance to movement through the water in said low draft
condition..]. .[.15. A vessel according to claim 7 wherein the
centroids of said columns are transversely spaced from vertical
planes containing the longitudinal centerlines of said members..].
.[.16. A vessel according to claim 7 wherein the centroids of said
columns are spaced outboard of vertical planes passing through the
longitudinal centerlines of said members..]. .[.17. A vessel
according to claim 7 including a crane for transferring loads
between horizontally spaced positions..]. .[.18. A vessel according
to claim 7 wherein said ballasting and deballasting means includes
at least two ballast compartments in each of said members, said two
ballast compartments being horizontally spaced one from the other,
and means for selectively ballasting and deballasting said two
compartments in each said member to alter the natural period of
said vessel..]. .[.19. A vessel according to claim 18 wherein said
ballasting and deballasting means includes at least four ballast
compartments in each of said members, a pair of said ballast
compartments in each member being transversely spaced one from the
other, another pair of said ballast compartments in each member
being longitudinally spaced one from the other and means for
effecting ballast transfer into and out of the ballast compartments
of each said pair thereof to alter the natural period of said
vessel about roll and pitch axes..]. .[.20. A variable draft vessel
comprising: a pair of elongated hulls disposed in side-by-side
spaced substantially parallel relation one to the other;
a working platform;
means connected to said hulls and said platform to support said
platform in fixed spaced relation above said hulls;
said connecting means including at least four stabilizing columns
located on said hulls with a pair of said columns on each of the
opposite sides of the respective pitch and roll axes of the
vessel;
the cross sectional area of said columns being substantially
constant throughout the height thereof;
said hulls having combined displacement sufficient to float the
vessel in a low draft condition with the hulls having freeboard,
each of said hulls having bow and stern designs to minimize
resistance to movement through the water in said low draft
condition;
means for ballasting and deballasting the vessel to respectively
submerge the hulls and portions of said connecting means below said
platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return the vessel to
the low draft condition with the hulls having freeboard, the
displacement of the submerged hulls and portions of said connecting
means being sufficient to maintain the vessel buoyant in the high
draft floating condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof, and between said
hulls and said platform;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional area and configuration of the columns, the
weight distribution of the vessel, and the geometry of the
submerged hulls and portions of said connecting means being such
that the vessel obtains moton minimizing characteristics in the
high draft condition;
and means carried by the vessel for conducting drilling operations
while
the vessel is maintained in the high draft floating condition..].
.[.21. A vessel according to claim 20 wherein said connecting means
includes at least 6 upstanding stabilizing columns disposed on said
hulls, a pair of said columns being located adjacent opposite ends
of said hulls on the opposite sides of the pitch axis of the
vessel, at least 3 columns being located on each hull and on
opposite sides of the roll axis of the vessel..]. .[.22. A vessel
according to claim 20 having a length to width ratio of at least 2
to 1..]. .[.23. A vessel according to claim 20 wherein said
platform is spaced above said hulls a predetermined height at least
equal to the height of the maximum anticipated wave, said columns
upstanding from said hulls a predetermined effective height at
least equal to the height of the maximum anticipated wave..].
.[.24. A vessel according to claim 20 wherein the natural periods
in pitch and roll of the vessel in the high draft condition lies
within a range of 6 to 40 seconds..]. .[.25. A vessel according to
claim 23 wherein the displacement of said submerged hulls and
portions of said connecting means is sufficient to maintain the
vessel buoyant in the high draft condition with the mean waterline
located a distance above said hulls at substantially one-half the
effective height of said stabilizing columns;
said ballasting and deballasting means being operable to vary the
submergence of the vessel when in the high draft condition such
that the distance between the mean waterline and either the
underside of the platform or the topside of said hulls is not less
than 0.75 of the mean wave height to preclude amplification of
vessel motion due to interaction of wave and vessel motion..].
.[.26. A vessel according to claim 20 wherein said drilling means
includes a drilling rig mounted on said platform over the space
between the hulls..]. .[.27. A vessel according to claim 24 wherein
said ballasting and deballasting means include a plurality of
compartments in each of said hulls together with means for
selectively ballasting and deballasting said compartments..].
.[.28. A vessel according to claim 20 wherein the centroids of said
columns are transversely spaced from vertical planes passing
through the longitudinal centerlines of said hulls..]. .[.29. A
vessel according to claim 20 wherein said platform is spaced above
said hulls a predetermined effective height at least equal to the
height of the maximum anticipated wave, said columns upstanding
from said hulls a predetermined effective height at least equal to
the height of the maximum anticipated wave, said ballasting and
deballasting means including a plurality of compartments in each of
said hulls together with means for selectively ballasting and
deballasting said compartments, the displacement of the submerged
hulls and portions of said connecting means being sufficient to
maintain the vessel buoyant in the high draft condition with the
mean waterline located a distance above the hulls at substantially
one-half the effective height of said stabilizing columns..].
.[.30. A vessel according to claim 20 wherein said ballasting and
deballasting means includes at least two ballast compartments in
each of said hulls, said two ballast compartments being
horizontally spaced one from the other, and means for selectively
ballasting and deballasting said two compartments in each said hull
to alter the natural period of said vessel..]. .[.31. A variable
draft vessel comprising: a pair of elongated flotation members
disposed in side-by-side spaced substantially parallel relation one
to the other;
a working platform;
a plurality of elements upstanding from said members with at least
a portion of said elements being connected to said platform to
support the platform in spaced relation above the members; at least
a portion of said upstanding elements including at least six
stabilizing columns disposed on said members and upstanding
therefrom a predetermined height, a pair of said columns being
located adjacent opposite ends of said members on opposite sides of
the pitch axis of the vessel, at least three columns being located
on each member and on opposite sides of the roll axis of the
vessel;
the cross sectional area of said columns being substantially
constant throughout the predetermined height thereof;
said flotation members having a combined displacement sufficient to
float the vessel in a low draft condition;
means for ballasting and deballasting the vessel to respectively
submerge the members and portions of said elements below the
waterline thereby to provide a high draft, otherwise unsupported,
floating condition and return the vessel to a low draft condition;
the displacement of the submerged members and portions of said
elements being sufficient to maintain the vessel buoyant in the
high draft floating condition;
said elements being spaced one from the other to provide an open
frame area therebetween and between said platform and members;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional area and configuration of the columns, the
weight distribution of the vessel and the geometry of the submerged
members and portions of said elements being such that the vessel
obtains motion minimizing characteristics in the high draft
condition;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition;
said vessel having a length to width ratio of at least 2 to 1..].
.[.32. A vessel according to claim 31 including a crane for
transferrng loads between horizontally spaced positions..]. .[.33.
A vessel according to claim 31 wherein the displacement of the
submerged members and portions of said elements is sufficient to
maintain the vessel buoyant in the high draft condition with the
mean waterline located a distance above the members at
substantially one-half the predetermined height of said stabilizing
columns..]. .[.34. A vessel according to claim 31 wherein the
natural periods in pitch and roll of the vessel in the high draft
condition lie within a range of 6 to 40 seconds..]. .[.35. A vessel
according to claim 33 wherein said columns upstand from said
members a predetermined height at least equal to the height of the
maximum anticipated wave; said ballasting and deballasting means
being operable to vary the submergence of the vessel when in the
high draft condition such that the distance between the mean
waterline and either the underside of the platform or the topside
of said members is not less than 0.75 of the mean wave height for
wave heights less than the maximum anticipated wave to preclude
amplification of vessel motion due to interaction of wave and
vessel motion..]. .[.36. A vessel according to claim 33 including a
stabilizing column on each member located adjacent the transverse
axis through the center of flotation of the vessel, said connecting
means including a plurality of trusses extending between said
members and said platform at spaced longitudinal positions along
the vessel, said trusses including transversely extending elements
connecting one member to the other with said elements lying
adjacent the uppermost portions of said members..]. .[.37. A vessel
according to claim 31 wherein at least one of said stabilizing
columns on each said member has a cross section elongated in a
direction substantially parallel to the roll axis of the vessel..].
.[.38. A vessel according to claim 37 wherein the centroid of said
one stabilizing column on each said member is spaced outboard of
the vertical plane containing the longitudinal centerline of the
corresponding member..]. .[.39. A vessel according to claim 31
wherein the members have freeboard in the low draft condition of
the vessel..]. .[.40. A vessel according to claim 31 wherein said
platform is fixed in spaced relation above said members each of
said members having bow and stern designs to minimize resistance to
movement through the water in said low draft condition..]. .[.41. A
vessel according to claim 31 wherein said ballasting and
deballasting means includes at least two ballast compartments in
each of said members, said two ballast compartments being
horizontally spaced one from the other, and means for selectively
ballasting and deballasting said two compartments in each said
member to alter the natural period of said vessel..]. .[.42. A
variable draft vessel comprising: no more than two hulls disposed
in side-by-side spaced substantially parallel relation one to the
other;
a working platform;
means connected to said hulls and said platform to support said
platform in spaced relation above said hulls, said connecting means
including at least six upstanding stabilizing columns disposed on
said hulls and upstanding therefrom a predetermined effective
height, a pair of said columns being located adjacent opposite ends
of said hulls on opposite sides of the pitch axis of the vessel, at
least three columns being located on each hull and on opposite
sides of the roll axis of the vessel;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having
freeboard;
the cross sectional area of said columns being substantially
constant throughout the effective height thereof;
means for ballasting and deballasting the vessel to respectively
submerge the hulls and portions of the connecting means below said
platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return the vessel to
the low draft condition with the hulls having freeboard, the
displacement of the submerged hulls and portions of said connecting
means being sufficient to maintain the vessel buoyant in the high
draft floating condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said hulls;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition;
said vessel having a length to width ratio of at least 2 to 1..].
.[.43. A vessel according to claim 42 including a crane for
transferring loads between horizontally spaced positions..]. .[.44.
A vessel according to claim 42 wherein the displacement of the
submerged hulls and portions of said connecting means is sufficient
to maintain the vessel in the high draft condition with the mean
waterline located a distance above the hulls at substantially
one-half the effective height of said stabilizing columns..].
.[.45. A vessel according to claim 42 wherein the cross sectional
area and configuration of the columns, the weight distribution of
the vessel and the geometry of the submerged hulls and portions of
said connecting means are such that the vessel obtains a natural
period in the high draft condition no less than 6 seconds..].
.[.46. A vessel according to claim 44 wherein said ballasting and
deballasting means is operable to vary the submergence of the
vessel when in the high draft condition such that the distance
between the mean waterline and either the underside of the platform
or the topside of said 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 vessel motion due to interaction of wave
and vessel motion..]. .[.47. A vessel according to claim 42 wherein
said stabilizing columns are substantially oblong in cross section
and extend longitudinally parallel to said hulls a distance greater
than their width..]. .[.48. A vessel according to claim 42 wherein
said drilling means includes a drilling rig mounted on said
platform over the space between the hulls..]. .[.49. A vessel
according to claim 42 wherein said platform is fixed in spaced
relation above said hulls, each of said hulls having bow and stern
designs to minimize resistance to movement through the water in
said low draft condition..]. .[.50. A vessel according to claim 42
wherein said ballasting and deballasting means includes at least
two ballast compartments in each of said hulls, said two ballast
compartments being horizontally spaced one from the other, and
means for selectively ballasting and deballasting said two
compartments in each said hull to alter the natural period of said
vessel..]. .[.51. A vessel according to claim 42 wherein the cross
sectional area and configuration of said columns, the weight
distribution of the vessel and the geometry of the submerged hulls
and portions of said connecting means being such as to provide
motion minimizing characteristics to the vessel..]. .[.52. A
variable draft vessel comprising: a base structure having
hydrostatic and hydrodrynamic characteristics;
a working platform;
a plurality of elements carried by said base structure with at
least a portion of said elements upstanding therefrom and being
connected to said platform to support said platform in spaced
relation above said base structure, at least a portion of said
elements including at least four stabilizing columns carried by
said base structure and extending vertically a predetermined
effective height between generally horizontal planes containing
said platform and said base structure, a pair of said columns being
located adjacent opposite ends of said base structure on opposite
sides of the pitch axis of the vessel, at least two columns being
located on opposite sides of the roll axis of the vessel;
the cross sectional area of said columns being substantially
constant throughout the effective height thereof;
said base structure having a displacement sufficient to float the
vessel in a low draft condition with the base structure having
freeboard;
means for ballasting and deballasting the vessel to respectively
submerge the base structure and portions of said elements below the
waterline thereby to provide a high draft, otherwise unsupported,
floating condition and return the vessel to the low draft condition
with the base structure having freeboard;
said elements being spaced one from the other to provide an open
frame area therebetween and between said platform and said base
structure;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional areas and configuration of said columns, the
weight distribution of the vessel, and the geometry of the
submerged base structure and portions of said elements being such
that the vessel obtains a natural period in the high draft
condition no less than 6 seconds;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition;
said vessel having a length to width ratio of at least 2 to 1..].
.[.53. A vessel according to claim 52 including a crane for
transferring loads between horizontally spaced positions..]. .[.54.
A vessel according to claim 52 wherein said platform is spaced
above said base structure a predetermined height at least equal to
the height of the maximum anticipated wave, said columns extending
vertically a predetermined effective height at least equal to the
height of the maximum anticipated wave..]. .[.55. A vessel
according to claim 52 wherein the natural periods in pitch and roll
of the vessel lie within a range of 6 to 40 seconds..]. .[.56. A
vessel according to claim 52 wherein said ballasting and
deballasting means includes at least two ballast compartments
carried by said base structure on each of the opposite sides of the
centerline of said vessel, said two ballast compartments being
horizontally spaced one from the other, and means for effecting
ballast transfer into and out of said two compartments on each side
of said vessel to alter the natural period of said vessel..].
.[.57. A vessel according to claim 52 wherein at least one column
on eah of the opposite sides of the roll axis is oblong with its
long axis extending substantially parallel to the longitudinal
centerline of said vessel..]. .[.58. A variable draft column
stabilized vessel comprising: a pair of elongated flotation members
disposed in side-by-side spaced substantially parallel relation one
to the other;
a working platform;
means connected to said members and said platform to support said
platform in fixed spaced relation above said members;
said connected means including at least six stabilizing columns
disposed on said members and upstanding therefrom a predetermined
height;
a pair of said columns being located adjacent opposite ends of said
members on opposite sides of the pitch axis of said vessel, at
least three columns being located on each member and on opposite
sides of the roll axis of said vessel, at least one column on each
member being substantially oblong in cross section and disposed
such that its long axis extends substantially parallel to the
longitudinal axes of the members;
the cross sectional area of said columns being substantially
constant throughout the height thereof;
said members having a combined displacement sufficient to float the
vessel in a low draft condition with the members having
freeboard;
means for ballasting and deballasting said vessel to respectively
submerge the members and portions of said connecting means below
said platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return said vessel to
the low draft condition with the members having freeboard, the
displacement of the submerged members and portions of said
connecting means being sufficient to maintain said vessel buoyant
in the high draft floating condition;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said members;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition..]. .[.59. A vessel according to claim 58 including a
crane for transferring loads between horizontally spaced
positions..]. .[.60. A vessel according to claim 58 wherein the
cross sectional area and configuration of said columns, the weight
distribution of the vessel and the geometry of the submerged
members and portions of said connecting means are such as to
provide motion minimizing characteristics to said vessel in roll,
pitch and heave in the high draft condition..]. .[.61. The vessel
according to claim 58 wherein said members are connected one to the
other by said connecting means with the area between said members
below a horizontal plane extending through said members adjacent
their upper surfaces being open and substantially unobstructed..].
.[.62. A variable draft vessel according to claim 58 wherein said
platform is supported in spaced relation above said members a
predetermined height at least equal to the height of the maximum
anticipated wave, said columns upstanding from said members an
effective height at least equal to the height of the maximum
anticipated wave, the displacement of said submerged members and
portions of said connecting means being sufficient to maintain said
vessel buoyant in the high draft condition with the mean waterline
located a distance above said members at substantially one-half the
effective height of said stabilizing columns..]. .[.63. A vessel
according to claim 58 wherein said connecting means includes a
plurality of support members forming trusses extending between said
members and said platform at spaced longitudinal positions along
said vessel, said trusses including transversely extending members
lying adjacent the uppermost portions of said members..]. .[.64. A
vessel according to claim 58 wherein each of said members has
streamlined bow and stern portions to minimize resistance to
movement through the water in said low draft condition..]. .[.65. A
vessel according to claim 58 wherein said ballasting and
deballasting means includes at least two ballast compartments in
each of said members, said two ballast compartments being
horizontally spaced one from the other, and means for selectively
ballasting and deballasting said two compartments in each said
member..]. .[.66. A vessel according to claim 58 wherein said
drilling means includes a drilling mast disposed substantially
along the longitudinal centerline of the vessel for supporting a
drill string extending between said members..]. .[.67. A vessel
according to claim 58 wherein said vessel has a length to width
ratio of at least 2 to 1..]. .[.68. A vessel according to claim 58
wherein said platform is supported in spaced relation above said
members a predetermined height at least equal to the height of the
maximum anticipated wave, said columns upstanding from said members
an effective height at least equal to the height of the maximum
anticipated wave, the displacement of said submerged members and
portions of said connecting means being sufficient to maintain said
vessel buoyant in the high draft condition with the mean waterline
located a distance above said members at substantially one-half the
effective height of said stabilizing columns, said connecting means
including a plurality of support members forming trusses extending
between said members and said platform at spaced longitudinal
positions along said vessel, said trusses including transversely
extending members connectng one flotation member to the other and
lying adjacent the uppermost portions of said flotation members,
said ballasting and deballasting means including at least two
ballast compartments in each of said flotation members, said two
ballast compartments being horizontally spaced one from the other,
and means for selectively ballasting and deballasting the
compartments in each said member..]. .[.69. A vessel according to
claim 58 wherein the centroids of said columns are spaced outboard
of vertical planes containing the longitudinal axes of said
members..]. .[.70. A variable draft vessel comprising: a pair of
elongated flotation members disposed in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
means connected to said members and said platform to support said
platform in fixed spaced relation above said members;
said connecting means including at least six upstanding stabilizing
columns disposed on said members, a pair of said columns being
located adjacent opposite ends of said members on opposite side of
the pitch axis of the vessel, at least three columns being located
on each member and on opposite sides of the roll axis of the
vessel, the centroids of said columns being spaced outboard of
vertical planes containing the longitudinal axes of said
members;
the cross sectional area of said columns being substantially
constant throughout the height thereof;
said members having a combined displacement sufficient to float the
vessel in a low draft condition with the members having
freeboard;
means for ballasting and deballasting the vessel to respectively
submerge the members and portions of said connecting means below
said platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return the vessel to
the low draft condition with the members having freeboard, the
displacement of the submerged members and portions of said
connecting means being sufficient to maintain the vessel buoyant in
the high draft floating condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof and between said
platform and said members;
the combined water plane area of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional area and configuration of said columns, the
weight distribution of the vessel, and the geometry of the
submerged members and portions of said connecting means being such
as to provide motion minimizing characteristics to said vessel in
roll, pitch and heave in the high draft condition;
and means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition..]. .[.71. A vessel according to claim 70 including a
crane for transferring loads between horizontally spaced
positions..]. .[.72. A vessel according to claim 70 wherein the
cross sectional area of said columns is substantially constant
throughout the predetermined height thereof..]. .[.73. A variable
draft vessel according to claim 70 wherein said platform is
supported in spaced relation above said members a predetermined
height at least equal to the height of the maximum anticipated
wave, said columns upstanding from said members an effective height
at least equal to the height of the maximum anticipated wave, the
displacement of said submerged members and portions of said
connecting means being sufficient to maintain said vessel buoyant
in the high draft condition with the mean waterline located a
distance above said members at substantially one-half the effective
height of said stabilizing columns..]. .[.74. A vessel according to
claim 70 wherein said ballasting and deballasting means includes at
least two ballast compartments in each of said members, said two
ballast compartments being horizontally spaced one from the other,
and means for selectively ballasting and deballasting said two
compartments in each said member..]. .[.75. A vessel according to
claim 70 wherein said drilling means includes a drilling mast
disposed substantially along the longitudinal centerline of the
vessel for supporting a drill string extending between said
members..]. .[.76. A vessel according to claim 70 wherein each of
said members has streamlined bow portions to minimize resistance to
movement through the water in said low draft condition..]. .[.77. A
vessel according to claim 70 wherein said platform is supported in
spaced relation above said members a predetermined height at least
equal to the height of the maximum anticipated wave, said columns
upstanding from said members an effective height at least equal to
the height of the maximum anticipated wave, the displacement of
said submerged members and portions of said connecting means being
sufficient to maintain said vessel buoyant in the high draft
condition with the mean waterline located a distance above said
members at substantially one-half the effective height of said
stabilizing columns, said ballasting and deballasting means
including at least two ballast compartments in each of said
members, said two ballast compartments being horizontally spaced
one from the other, and means for selectively ballasting and
deballasting said two compartments in each said member, each of
said members having streamlined bow portions to minimize resistance
to movement through the water in said low draft condition..].
.[.78. A variable draft vessel comprising:
a pair of discrete elongated flotation members disposed in
side-by-side spaced substantially parallel relation one to the
other;
a working platform;
means for supporting said platform in fixed spaced relation above
said members;
said connecting means including at least six stabilizing columns
disposed on said members and upstanding therefrom, a pair of said
columns being located adjacent opposite ends of said members on
opposite sides of the pitch axis of said vessel, at least three
columns being located on each member and on opposite sides of the
roll axis of said vessel;
the cross sectional area of said columns being substantially
constant throughout the height thereof;
at least one of said columns on each said member being
substantially oblong in cross section and disposed such that its
long axis extends substantially parallel to the longitudinal axes
of said members;
means for ballasting and deballasting said vessel to selectively
obtain high and low draft, otherwise unsupported, floating
conditions with said members and portions of said connecting means
below said platform located below the waterline in the high draft
floating condition, the displacement of said members and portions
of said connecting means being sufficient to maintain said vessel
buoyant in the high draft floating condition;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition; and
means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition..]. .[.79. A variable draft vessel comprising:
a pair of discrete elongated flotation members disposed in
side-by-side spaced substantially parallel relation one to the
other;
a working platform;
means for supporting said platform in fixed spaced relation above
said members;
said connecting means including at least six stabilizing columns
disposed on said members and upstanding therefrom, a pair of said
columns being located adjacent opposite ends of said members on
opposite sides of the pitch axis of said vessel, at least three
columns being located on each member and on opposite sides of the
roll axis of said vessel;
at least one of said columns on each of said member being
substantially oblong in cross section and disposed such that its
long axis extends substantially parallel to the longitudinal axes
of said members;
and means for ballasting and deballasting said vessel to
selectively obtain high and low draft conditions with said members
and portions of said connecting means below said platform located
below the waterline in the high draft condition, the displacement
of said members and portions of said connecting means being
sufficient to maintain said vessel buoyant in the high draft
condition;
said columns being substantially constant in cross sectional area
throughout their height, said vessel having a length to width
ratio
greater than 2 to 1..]. .[.80. The vessel according to claim 79
wherein the centroid of said oblong column on each said member lies
outboard of vertical planes passing through the longitudinal
centerlines of said member..]. .[.81. The vessel according to claim
79 wherein said ballasting and deballasting means includes at least
two ballast compartments in each of said members, said two ballast
compartments being horizontally spaced one from the other, and
means for selectively ballasting and deballasting said two
compartments in each said member..]. .[.82. The vessel
according
to claim 79 including a derrick..]. 83. A variable draft vessel
comprising:
a base structure having hydrostatic and hydrodynamic
characteristics;
a working platform;
a plurality of elements carried by said base structure with at
least a portion of said elements upstanding therefrom and being
connected to said platform to support said platform in spaced
relation above said base structure, at least a portion of said
elements including at least four stabilizing columns carried by
said base structure and extending vertically a predetermined
effective height between generally horizontal planes containing
said platform and said base structure, a pair of said columns being
located adjacent opposite ends of said base structure on opposite
sides of the pitch axis of the vessel, at least two columns being
located on opposite sides of the roll axis of the vessel;
said base structure having displacement sufficient to float the
vessel in a low draft condition with the base structure having
freeboard;
and means for ballasting and deballasting the vessel to
respectively submerge the base structure and portions of said
elements below the waterline thereby to provide a high draft
condition and return the vessel with the base structure having
freeboard;
said elements being spaced one from the other to provide an open
frame area therebetween and between said platform and said base
structure;
the cross sectional areas and configuration of said columns, the
weight distribution of the vessel and the geometry of the submerged
base structure and portions of said elements being such that the
vessel obtains a natural period in the high draft condition no less
than 6 seconds;
said vessel having a length to width ratio of at least 2 to 1;
said stabilizing .[.column.]. .Iadd.columns .Iaddend.having
portions thereof which extend transversely beyond the outboard
sides of said base structure thereby providing increased moment for
stabilizing action about the roll axis. .[.84. A variable draft
vessel comprising:
a pair of elongated hulls disposed in side-by-side spaced
substantially parallel relation one to the other;
a working platform;
means connected to said hulls and said platform to support said
platform in fixed spaced relation above said hulls;
said connecting means including at least four stabilizing columns
located on said hulls with a pair of said columns on each of the
opposite sides of the respective pitch and roll axes of the
vessel;
said platform being spaced above said hulls a predetermined height
at least equal to the height of the maximum anticipated wave, said
columns upstanding from said hulls a predetermined effective height
at least equal to the height of the maximum anticipated wave, the
cross sectional area of said columns being substantially constant
throughout the effective height thereof;
said hulls having a combined displacement sufficient to float the
vessel in a low draft condition with the hulls having freeboard,
each of said hulls having bow and stern designs to minimize
resistance to movement through the water in said low draft
condition;
means for ballasting and deballasting the vessel to respectively
submerge the hulls and portions of said connecting means below said
platform below the waterline thereby to provide a high draft,
otherwise unsupported, floating condition and return the vessel to
the low draft condition with the hulls having freeboard, the
displacement of the submerged hulls and portions of said connecting
means being sufficient to maintain the vessel buoyant in the high
draft floating condition;
said connecting means being spaced one from the other to provide an
open frame area between the components thereof, and between said
hulls and said platform;
the combined water plane areas of said columns forming at least the
major portion of the total water plane area of said vessel in the
high draft condition;
the cross sectional area and configuration of the columns, the
weight distribution of the vessel, and the geometry of the
submerged hulls and portions of said connecting means being such
that the vessel obtains motion minimizing characteristics in the
high draft condition; and
means carried by the vessel for conducting drilling operations
while the vessel is maintained in the high draft floating
condition..]. .Iadd. 85. A vessel according to claim 83 wherein
said base structure includes a pair of elongated hulls disposed in
side-by-side spaced substantially parallel relation one to the
other, at least a portion of said elements including a plurality of
trusses extending between said hulls and said platform and in
spaced longitudinal positions along said vessel, said trusses
including substantially horizontally extending members disposed
adjacent uppermost portions of said hulls and restraining the hulls
against lateral displacement with respect to each other..Iaddend.
.Iadd. 86. A column stabilized semisubmersible vessel consisting of
a pair of elongated hulls disposed in substantially parallel spaced
side-by-side relation with each of said hulls spaced from and lying
on an opposite side of the longitudinal centerline of said vessel,
said vessel further comprising:
a working platform spaced above said hulls a predetermined height
and normally lying in a generally horizontal plane;
means for supporting said platform in fixed spaced relation above
said hulls including at least three pairs of upstanding columns
connecting with each of said hulls and said platform; each of said
columns having a substantially constant cross sectional area over
the effective height of the column between the platform and
associated hull;
each of said hulls having, over substantially the entire length
thereof, a substantially rectangular transverse cross section with
its breadth greater than its height;
a plurality of longitudinally spaced structural truss means
interconnecting and reinforcing the structural relationship of the
hulls, platform and columns, with such truss means including
substantially transversely extending members structurally
interconnecting uppermost portions of the hulls;
said vessel being generally rectangular in plan with the length of
said vessel along its longitudinal centerline and roll axis being
at least 2.5 times greater than the width of said vessel along its
transverse centerline and pitch axis;
at least three of said columns being located on each of said two
hulls on opposite sides of the vessel's roll axis with pairs of
such columns being located near opposite ends of each of said hulls
on opposite sides of the vessel's pitch axis and another pair of
said columns being located at an intermediate position on each of
said hulls;
each of said columns having an oblong cross section with a
dimension extending in the direction of the vessel's longitudinal
axis greater than the column's dimension extending transversely of
the vessel;
the centroid of the cross section of each column on said hulls
lying outboard of the longitudinal centerline of the associated
hull;
the configuration and cross-sectional areas of said columns
throughout effective height thereof and the distances of said
columns from the vessel's longitudinal roll axis and transverse
pitch axis being such that said columns maintain the vessel's
metacenter above the vessel's center of gravity for all high draft
semisubmerged operating positions of the vessel and also being such
that said columns provide righting moment about the longitudinal
roll axis which is less than righting moment provided about said
transverse pitch axis when the vessel is in semisubmerged column
stabilized operating positions;
said hulls having ballast compartments;
means for ballasting said vessel when required to alter its draft
between a low draft hull-supported floating condition in which the
hulls have freeboard with said transversely extending members
structurally interconnecting uppermost portions of the hulls being
disposed above the mean waterline and a high draft semisubmerged
column stabilized floating and operating condition in which the
mean waterline is located along intermediate portions of said
columns above said hulls and below the underside of said
platform;
said means for ballasting including means for adjusting vessel
angle of heel change caused during semisubmerged operations to
provide a reduction of the vessel's angle of heel about its roll
axis when required during semisubmerged column stabilized
operations; and
said means for ballasting including means for adjusting vessel
angle of trim change caused during semisubmerged operations to
provide a reduction of the vessel's angle of trim about its pitch
axis when required during
semisubmerged column stabilized operations..Iaddend..Iadd. 87. A
vessel according to claim 86, wherein the ballast compartment of
each of said rectangular twin hulls includes at least two separate
ballast compartments spaced transversely within each hull and a
plurality of separate ballast compartments spaced longitudinally
within each hull..Iaddend..Iadd. 88. A vessel according to claim 86
wherein said vessel ballast means includes means for transferring
ballast directly from one of said rectangular twin hulls directly
to the other of said rectangular twin hulls for controlling heel of
said vessel about its roll axis when required during semisubmerged
column stabilized operations..Iaddend..Iadd. 89. A vessel according
to claim 86, wherein: the ballast compartments of each of said
rectangular twin hulls includes at last two separate ballast
compartments spaced transversely within each hull and a plurality
of separate ballast compartments spaced longitudinally within each
hull; and said vessel ballast means also includes means for
transferring ballast from at least one compartment in one hull
directly to at least one compartment in the other hull for
controlling the heel of said vessel about its roll axis when
required during semisubmerged column stabilized
operations..Iaddend. .Iadd. 90. A column stabilized semisubmersible
drilling vessel comprising a vessel according to claim 86 and
further comprising:
a drilling rig carried by said platform;
means carried by said vessel for accommodating sufficient drilling
equipment for conducting offshore drilling operations in column
stabilized semisubmerged high draft condition;
said vessel ballast means including means for counteracting change
in vessel angle of trim caused when said vessel is in said high
draft column stabilized semisubmerged condition for drilling
operations and is subjected to load change of such location and
magnitude with respect to the pitch axis so that such ballast means
provides when required a reduction of the vessel's angle of trim
about its pitch axis during semisubmerged column stabilized
drilling operations; and
said vessel ballast means also including means for similarly
counteracting angle of heel caused when said vessel is in said high
draft semisubmerged condition for drilling and is subjected to load
change of such location and magnitude with respect to the roll axis
so that such ballast means provides when required a reduction of
the vessel's angle of heel about its roll axis during high draft
semisubmerged column stabilized drilling operations. .Iaddend.
.Iadd. 91. A vessel as in claim 86 wherein: said transversely
extending members have opposite end portions overlying top surfaces
of said hulls with their opposite ends connected to columns on each
of said hulls near said top surfaces..Iaddend..Iadd. 92. A vessel
according to claim 91 wherein: said opposite end portions of said
transversely extending members are secured to said top surfaces of
said hulls..Iaddend. .Iadd. 93. A column stabilized semisubmersible
vessel consisting of a pair of elongated hulls disposed in
substantially parallel spaced side-by-side relation with each of
said hulls spaced from and lying on an opposite side of the
longitudinal centerline of said vessel, said vessel further
comprising:
a working platform spaced above said hulls a predetermined height
and normally lying in a generally horizontal plane;
means for supporting said platform in fixed spaced relation above
said hulls including at least three pairs of upstanding columns
connecting with each of said hulls and said platform; each of said
columns having a substantially constant cross sectional area over
the effective height of the column between the platform and
associated hull;
each of said hulls having an oblong transverse cross section with a
breadth greater than its height and having top and bottom
substantially planar parallel surfaces extending substantially the
entire length of each hull, whereby such hulls configuration
provides increased mass resistance to movement of said hulls and
vessel through water in a vertical direction when the vessel is in
high draft semisubmerged column stabilized operating condition;
a plurality of longitudinally spaced structural truss means
interconnecting and reinforcing the structural relationship of the
hulls, platform and columns, with such truss means including
substantially transversely extending members structurally
interconnecting uppermost portions of the hulls;
said vessel being generally rectangular in plan with the length of
said vessel along its longitudinal centerline and roll axis being
at least plural times as great as the width of said vessel along
its transverse centerline and pitch axis;
at least three of said columns being located on each of said two
hulls on opposite sides of the vessel's roll axis with pairs of
such columns being located near opposite ends of each of said hulls
on opposite sides of the vessel's pitch axis and another pair of
said columns being located at an intermediate position on each of
said hulls;
at least one of said columns on each said hull having an oblong
cross section with a dimension extending in the direction of the
longitudinal vessel axis greater than the columns' transversely
extending dimension; the centroid of the cross section of such
oblong columns lying outboard of the longitudinal centerline of
each associated hull;
the configuration and cross-sectional areas of said columns
throughout effective height thereof and the distances of said
columns from the vessel's longitudinal roll axis and transverse
pitch axis being such that said columns maintain the vessel's
metacenter above the vessel's center of gravity for all high draft
semisubmerged operating positions of the vessel and also being such
that said columns provide righting moment about the longitudinal
roll axis which is less than righting moment provided about said
transverse pitch axis when the vessel is in semisubmerged column
stabilized operating position;
said hulls having ballast compartments;
means for ballasting said vessel when required to alter its draft
between a low draft hull-supported floating condition in which the
hulls have freeboard with said transversely extending members
structurally interconnecting uppermost portions of the hulls being
disposed above the mean waterline and a high draft semisubmerged
column stabilized floating and operating condition in which the
mean waterline is located along intermediate portion of said
columns above said hulls and below the underside of said
platform;
the ballast compartments of each of said oblong twin hulls
including at least two separate ballast compartments spaced
transversely within each hull and a plurality of separate ballast
compartments spaced longitudinally within each hull.
.Iaddend..Iadd. 94. A vessel according to claim 93, wherein said
means for ballasting includes means for adjusting vessel angle of
heel change caused during semisubmerged operations to provide a
reduction of the vessel's angle of heel about its roll axis when
required during semisubmerged column stabilized
operations..Iaddend..Iadd. 95. A vessel according to claim 93,
wherein said means for ballasting includes means for adjusting
vessel angle of trim change caused during semisubmerged operations
to provide a reduction of the vessel's angle of trim about its
pitch axis when required during operations of said vessel in
semisubmerged column stabilized operations..Iaddend..Iadd. 96. A
vessel according to claim 93, wherein said vessel ballast means
includes means for transferring ballast directly from one hull to
the other hull to control heel of said vessel about its roll axis
during semisubmerged column stabilized operations..Iaddend..Iadd.
97. A vessel according to claim 93, wherein all of said columns
have such an oblong cross section with greater dimension extending
in direction of the vessel's longitudinal axis..Iaddend..Iadd. 98.
A vessel according to claim 97 wherein the centroid of all of said
columns lies outboard of the longitudinal centerline of each
associated hull..Iaddend. .Iadd. 99. A vessel according to claim
93, wherein each of said hulls is generally rectangular in cross
section..Iaddend..Iadd. 100. A vessel according to claim 93,
wherein said vessel has a length to width ratio of at least 2.5 to
1..Iaddend..Iadd. 101. A vessel according to claim 93, wherein said
vessel has a length which is at least 2.5 times as great as its
width; each of said columns has an oblong cross section with a
dimension extending in the direction of the longitudinal vessel
axis greater than the column's dimension extending transversly of
the vessel; the centroid of the cross section of each column on
each hull lies outboard of the longitudinal centerline of the
associated hull; each of said hulls is generally rectangular in
cross section; and said transversely extending members structurally
interconnect said hulls adjacent uppermost portions
thereof..Iaddend..Iadd. 102. A vessel according to claim 101
wherein said vessel ballasting means includes means operable to
transfer ballast from at least one compartment in one hull directly
to at least one compartment in the other hull to control the heel
of said vessel about its roll axis when required during column
stabilized semisubmerged operations..Iaddend..Iadd. 103. A column
stabilized semisubmersible drilling vessel comprising a vessel
according to claim 93 and further comprising:
a drilling rig carried by said platform;
means carried by said vessel for accommodating sufficient drilling
equipment for conducting offshore drilling operations in column
stabilized semisubmerged high draft condition;
said vessel ballast means including means for counteracting change
in vessel angle of trim caused when said vessel is in said high
draft column stabilized semisubmerged condition for drilling
operations and is subjected to load change of such location and
magnitude with respect to the pitch axis so that such ballast means
provides when required a reduction of the vessel's angle of trim
about its pitch axis during semisubmerged column stabilized
drilling operations; and
said vessel ballast means also including means for similarly
counteracting angle of heel caused when said vessel is in said high
draft semisubmerged condition for drilling and is subjected to load
change of such location and magnitude with respect to the roll axis
so that such ballast means provides when required a reduction of
the vessel's angle of heel about its roll axis during high draft
semisubmerged column stabilized drilling operations..Iaddend.
.Iadd. 104. A vessel as in claim 93 wherein: said transversely
extending members have opposite end portions overlying top surfaces
of said hulls with their opposite ends connected to columns on each
of said hulls near said top surfaces..Iaddend..Iadd. 105. A vessel
according to claim 104 wherein: said opposite end portions of said
transversely extending members are secured to said top surfaces of
said hulls..Iaddend. .Iadd. 106. A column stabilized
semisubmersible vessel consisting of a pair of elongated hulls
disposed in substantially parallel spaced side-by-side relation
with each of said hulls spaced from and lying on an opposite side
of the longitudinal centerline of said vessel, said vessel further
comprising;
a working platform spaced above said hulls a predetermined height
and normally lying in a generally horizontal plane;
means for supporting said platform in fixed spaced relation above
said hulls including at least three pairs of upstanding columns
connecting with each of said hulls and said platform, each of said
columns having a substantially constant cross sectional area over
the effective height of the column between the platform and
associated hull;
each of said hulls having an oblong transverse cross section with a
breadth greater than its height and having top and bottom
substantially planar parallel surfaces extending substantially the
entire length of each hull;
a plurality of longitudinally spaced structural truss means
interconnecting and reinforcing the structural relationship of the
hulls, platform and columns, with such truss means including
substantially transversely extending members structurally
interconnecting uppermost portions of the hulls;
said vessel being generally rectangular in plan with the length of
said vessel along its longitudinal centerline and roll axis being
at least plural times as great as the width of said vessel along
its transverse centerline and pitch axis;
at least three of said columns being located on each of said two
hulls on opposite sides of the vessel's roll axis with pairs of
such columns being located near opposite ends of each of said hulls
on opposite sides of the vessel's pitch axis and another pair of
said columns being located at an intermediate position on each of
said hulls;
the configuration and cross-sectional areas of said columns
throughout effective height thereof and the distances of said
columns from the vessel's longitudinal roll axis and transverse
pitch axis being such that said columns maintain the vessel's
metacenter above the vessel's center of gravity for the high draft
semisubmerged operating positions of the vessel and also being such
that said columns provide righting moment about the longitudinal
roll axis which is less than righting moment provided about said
transverse pitch axis when the vessel is in semisubmerged column
stabilized operating position;
said hulls having ballast compartments; and
means for ballasting said vessel when required to alter its draft
between a low draft hull-supported floating condition in which the
hulls have freeboard with said transversely extending members
structurally interconnecting uppermost portions of the hulls being
disposed above the mean waterline and a high draft semisubmerged
column stabilized floating and operating condition in which the
mean waterline is located along intermediate portion of said
columns above said hulls and below the underside of said
platform..Iaddend..Iadd. 107. A vessel according to claim 106,
wherein: said means for ballasting includes means for adjusting
vessel angle of heel change caused during semisubmerged operations
to provide a reduction of the vessel's angle of heel about its roll
axis when required during semisubmerged column stabilized
operations; and
said means for ballasting also includes means for adjusting vessel
angle of trim change caused during semisubmerged operations to
provide a reduction of the vessel's angle of trim about its pitch
axis when required during operations of said vessel in
semisubmerged column stabilized
operations..Iaddend..Iadd. 108. A vessel according to claim 106,
wherein the ballast compartment of each of said hulls includes at
least two separate ballast compartments spaced transversely within
each hull and a plurality of separate ballast compartments spaced
longitudinally within each hull..Iaddend..Iadd. 109. A vessel
according to claim 106, wherein said vessel ballast means includes
means for transferring ballast directly from one hull to the other
hull to control heel of said vessel about its roll axis when
required during semisubmerged column stabilized floating
operations..Iaddend..Iadd. 110. A vessel according to claim 106
wherein at least one of the columns on each said hull has an oblong
cross section with a dimension extending in the direction of the
longitudinal vessel axis greater than the column's transversely
extending dimension..Iaddend..Iadd. 111. A vessel according to
claim 110 wherein all of said columns have such an oblong cross
section with greater dimension extending in direction of the
vessel's longitudinal axis..Iaddend..Iadd. 112. A vessel according
to claim 106 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..Iaddend..Iadd. 113. A vessel
according to claim 112 wherein the centroid of all of said columns
lies outboard of the longitudinal centerline of the associated
hull..Iaddend..Iadd. 114. A vessel according to claim 106, wherein:
each of said columns has a cross section with a dimension extending
in the direction of the vessel's longitudinal axis greater than the
column's dimension extending transversely of the vessel, with the
centroid of the cross section of each column on each hull lying
outboard of the longitudinal centerline of the associated
hull..Iaddend..Iadd. 115. A vessel according to claim 106, wherein
each of said hulls is generally rectangular in cross
section..Iaddend..Iadd. 116. A vessel according to claim 106,
wherein said vessel has a length to width ratio of at least 2.0 to
1..Iaddend..Iadd. 117. A vessel according to claim 106, wherein:
said vessel has a length which is at least 2.5 times as great as
its width; each of said columns has an oblong cross section with a
dimension extending in the direction of the longitudinal vessel
axis greater than the column's dimension extending transversely of
the vessel; the centroid of the cross section of each column on
each hull lies outboard of the longitudinal centerline of the
associated hull; each of said hulls is generally rectangular in
cross section; and said transversely extending members structurally
interconnect said hulls adjacent uppermost portions
thereof..Iaddend..Iadd. 118. A vessel according to claim 117,
wherein: the ballst compartment of each of said hulls includes at
least two separate ballast compartments spaced transversely within
each hull and a plurality of separate ballast compartments spaced
longitudinally of the hull; said means for ballasting includes
means for adjusting vessel angle of heel change caused during
semisubmerged operations to provide a reduction of the vessel's
angle of heel about its roll axis when required during
semisubmerged columns stabilized operations; said means for
ballasting also includes means for adjusting vessel angle of trim
change caused during semisubmerged operations to provide a
reduction of the vessel's angle of trim about its pitch axis when
required during operations of said vessel in semisubmerged column
stabilized operations; and said vessel ballast means also includes
means operable to transfer ballast from at least one compartment in
one hull directly to at least one compartment in the other hull to
control the heel of said vessel about its roll axis during
semisubmerged operations..Iaddend..Iadd. 119. A vessel according to
claim 106 wherein at least the upper end of said columns is
modified in cross section to provide mechanical connection between
the columns and the platform..Iaddend..Iadd. 120. A vessel
according to claim 119, wherein said modified column cross section
includes a frustoconical section..Iaddend..Iadd. 121. A vessel
according to claim 106 wherein at least the lower end of said
columns is modified in cross section to provide mechanical
connection between the columns and the associated
hulls..Iaddend..Iadd. 122. A vessel according to claim 121 wherein
said modified column cross section includes a frustoconical
section..Iaddend..Iadd. 123. A column stabilized semisubmersible
drilling vessel comprising a vessel according to claim 106 and
further comprising:
a drilling rig carried by said platform;
means carried by said vessel for accommodating sufficient drilling
equipment for conducting offshore drilling operations in column
stabilized semisubmerged high draft condition;
said vessel ballast means including means for counteracting change
in vessel angle of trim caused when said vessel is in said high
draft column stabilized semisubmerged condition for drilling
operations and is subjected to load change of such location and
magnitude with respect to the pitch axis so that such ballast means
provides when required a reduction of the vessel's angle of trim
about its pitch axis during semisubmerged column stabilized
drilling operations; and
said vessel ballast means also including means for similarly
counteracting angle of heel caused when said vessel is in said high
draft semisubmerged condition for drilling and is subjected to load
change of such location and magnitude with respect to the roll axis
so that such ballast means provides when required a reduction of
the vessel's angle of heel about its roll axis during high draft
semisubmerged column stabilized drilling operations..Iaddend..Iadd.
124. A vessel as in claim 106, wherein the centroids of the water
plane areas defined by the cross sections of the columns are
located outboard of the centerlines of the hulls an extended
distance from the centerline of the vessel on opposite sides of the
longitudinally extending roll axis to develop larger moments of
intertia of the water plane area about the roll axis (than would
otherwise be the case if the longitudinal centerlines of said hulls
and their associated columns were coincident)..Iaddend..Iadd. 125.
A vessel as in claim 106, wherein the vessel has six columns
including three columns on each hull, with one middle pair of
columns located adjacent the vessel's transverse pitch axis and
with two other pairs of columns located adjacent the vessel's
transverse pitch axis and with two other pairs of columns on
opposite sides of the vessel pitch axis in generally symmetrical
relation thereto near opposite ends of the associated
hulls..Iaddend..Iadd. 126. A vessel as in claim 106, wherein: the
vessel has a total odd number of pairs of columns and the middle
pair of columns is located adjacent the vessel's pitch axis, with
the remaining pairs of columns being disposed in equal numbers on
opposite sides of the vessel pitch axis and with two pairs of
columns located near opposite ends of said hulls..Iaddend..Iadd.
127. A vessel as in claim 106, wherein: the vessel has a total even
number of pairs of columns and the middle two pairs of columns are
located on opposite sides of and near the transverse pitch axis;
the remaining pairs of said columns being located outwardly of said
middle pairs of columns and including two pairs of each columns on
the hulls near opposite ends of said hulls..Iaddend..Iadd. 128. A
vessel as claimed in claim 106, wherein said stabilizing columns
have outboard portions thereof which extend transversely beyond the
outboard sides of the respective hulls..Iaddend. .Iadd. 129. A
vessel as in claim 106 wherein: said transversely extending members
have opposite end portions overlying top surfaces of said hulls
with their opposite ends connected to columns on each of said hulls
near said top surfaces..Iaddend..Iadd. 130. A vessel according to
claim 129 wherein: said opposite end portions of said transversely
extending members are secured to said top surfaces of said
hulls..Iaddend. .Iadd. 131. A column stabilized semisubmersible
vessel consisting of a pair of elongated hulls disposed in
substantially parallel spaced side-by-side relation with each of
said hulls spaced from and lying on an opposite side of the
longitudinal centerline of said vessel, said vessel further
comprising:
a working platform spaced above said hulls a predetermined height
and lying in a generally horizontal plane;
means for supporting said platform in fixed spaced relation above
said hulls including at least three pairs of upstanding columns
connecting with each of said hulls and said platform;
each of said columns having a substantially constant cross
sectional area over the effective height of the column between the
platform and associated hull;
each of said hulls having an oblong transverse cross section with a
breadth greater than its height and having top and bottom
substantially planar parallel surfaces extending substantially the
entire length of each hull, whereby such hull's configuration
provides increased mass resistance to movement of said hulls and
vessel through water in a vertical direction when the vessel is in
high draft semisubmerged column stabilized operating condition;
a plurality of longitudinally spaced structural truss means
interconnecting and reinforcing the structural relationship of the
hulls, platform and columns, with such truss means including
substantially transversely extending members structurally
interconnecting uppermost portions of the hulls;
said vessel being generally rectangular in plan with the length of
said vessel along its longitudinal centerline and roll axis being
substantially greater than the width of said vessel along its
transverse centerline and pitch axis;
at least three of said columns being located on each of said two
hulls on opposite sides of the vessel's roll axis with pairs of
such columns being located near opposite ends of each of said hulls
on opposite sides of the vessel's pitch axis and another pair of
said columns being located at an intermediate position on each of
said hulls;
the configuration and cross-sectional areas of said columns
throughout effective height thereof and the distances of said
columns from the vessel's longitudinal roll axis and transverse
pitch axis being such that said columns maintain the vessel's
metacenter above the vessel's center of gravity for all high draft
semisubmerged operating positions of the vessel and also being such
that said columns provide righting moment about the longitudinal
roll axis which is less than righting moment provided about said
transverse pitch axis when the vessel is in semisubmerged column
stabilized operating position;
said hulls having ballast compartments;
means for ballasting said vessel when required to alter its draft
between a low draft hull-supported floating condition in which the
hulls have freeboard with said transversely extending members
structurally interconnecting uppermost portions of the hulls being
disposed above the mean waterline and a high draft semisubmerged
column stabilized floating and operating condition in which the
mean waterline is located along intermediate portion of said
columns above said hulls and below the underside of said
platform;
said means for ballasting including means for adjusting vessel
angle of heel change caused during semisubmerged operations to
provide a reduction of the vessel's angle of heel about its roll
axis when required during semisubmerged column stabilized
operations; and
said means for ballasting including means for adjusting vessel
angle of trim change caused during semisubmerged operations to
provide a reduction of the vessel's angle of trim about its pitch
axis when required during
semisubmerged column stabilized operations. .Iaddend..Iadd. 132. A
vessel according to claim 131, wherein the ballast compartment of
each of said hulls includes at least two separate ballast
compartments spaced transversely within each hull and a plurality
of separate ballast compartments spaced longitudinally within each
hull. .Iaddend..Iadd. 133. A vessel according to claim 131, wherein
said vessel ballast means includes means for transferring ballast
directly from one hull to the other hull to control heel of said
vessel about its roll axis when required during semisubmerged
column stabilized floating operations. .Iaddend..Iadd. 134. A
vessel according to claim 131 wherein each of said columns on said
hulls has an oblong cross section with a dimension extending in the
direction of the longitudinal vessel axis greater than the column's
transversely extending dimension. .Iaddend..Iadd. 135. A vessel
according to claim 131, wherein the centroid of the cross section
of each of the columns on each hull lies outboard of the
longitudinal centerline of the associated hull. .Iaddend. .Iadd.
136. A vessel according to claim 131, wherein each of said columns
has a cross section with a dimension extending in the direction of
the vessel's longitudinal axis greater than the column's dimension
extending transversely of the vessel; with the centroid of the
cross section of each column on each hull lying outboard of the
longitudinal centerline of the associated hull. .Iaddend..Iadd.
137. A vessel according to claim 131, wherein each of said hulls is
generally rectangular in cross section. .Iaddend..Iadd. 138. A
vessel according to claim 131, wherein said vessel has a length to
width ratio of at least 2.5 to 1. .Iaddend..Iadd. 139. A vessel
according to claim 131, wherein said vessel has a length which is
at least plural times as great as its width; each of said columns
has an oblong cross section with a dimension extending in the
direction of the longitudinal vessel axis greater than the column's
dimension extending transversely of the vessel; the centroid of the
cross section of each column on each hull lies outboard of the
longitudinal centerline of the associated hull; each of said hulls
is generally rectangular in cross section; and said transversely
extending members structurally interconnect said hulls adjacent
uppermost portions thereof. .Iaddend..Iadd. 140. A vessel according
to claim 139, wherein the ballast compartments of each of said
hulls includes at least two separate ballast compartments spaced
transversely within each hull and a plurality of separate ballast
compartments spaced longitudinally of the hull; and said vessel
also includes ballast means operable to transfer ballast from at
least one compartment in one hull directly to at least one
compartment in the other hull to control the heel of said vessel
about its roll axis during semisubmerged operations. .Iaddend.
.Iadd. 141. A column stabilized semisubmersible drilling vessel
comprising a vessel according to claim 131 and further
comprising:
a drilling rig carried by said platform;
means carried by said vessel for accommodating sufficient drilling
equipment for conducting offshore drilling operations in column
stabilized semisubmerged high draft condition;
said vessel ballast means including means for counteracting change
in vessel angle of trim caused when said vessel is in said high
draft column stabilized semisubmerged condition for drilling
operations and is subjected to load change at such location and
magnitude with respect to the pitch axis so that such ballast means
provides when required a reduction of the vessel's angle of trim
about its pitch axis during semisubmerged column stabilized
drilling operations, and
said vessel ballast means also including means for similarly
counteracting angle of heel caused when said vessel is in said high
draft semisubmerged condition for drilling and is subjected to load
change of such location and magnitude with respect to the roll axis
so that such ballast means provides when required a reduction of
the vessel's angle of heel about its roll axis during high draft
semisubmerged column stabilized drilling operations. .Iaddend.
.Iadd. 142. A vessel as in claim 131 wherein: said transversely
extending members have opposite end portions overlying top surfaces
of said hulls with their opposite ends connected to columns on each
of said hulls near said top surfaces. .Iaddend..Iadd. 143. A vessel
according to claim 142 wherein: said opposite end portions of said
transversely extending members are secured to said top surfaces of
said hulls.
Description
BACKGROUND OF THE INVENTION
This invention relates to a variable draft vessel having twin hulls
for use with a drilling platform and other deck load and which is
adapted for deep water drilling and other operations.
In attempts to locate new oil fields, an increasing and significant
quantity of well drilling has been conducted in offshore sea and
like locations where a substantial body of water overlies the oil
field. This has generated considerable interest and effort in
offshore and deep water drilling. One current method of offshore
drilling utilizes a fixed drill platform mounted on legs resting on
or driven into the sea floor. These, however, are feasible for use
only in relatively shallow depths of water normally not greater
than about 300 feet, which is a realistic depth limit for practical
commerical operations. Deep water drilling has heretofore been
accomplished with the employment of specifically designed and
constructed vessels or rigs which have certain inherent
disadvantages and limitations noted hereinafter. A brief review of
both offshore and deep water drilling methods heretofore practiced
and the vessels or rigs employed therewith will provide a more
clear appreciation and understanding of the present invention, as
well as a clear distinction between those vessels or rigs employed
in offshore drilling and those employed in deep water drilling.
An early method of offshore drilling, still currently employed,
provides for the erection of a self-contained fixed platform which
is supported by pilings driven into the sea floor and has a
drilling rig, auxiliary equipment and crew's quarters located on
the platform. At the conclusion of the drilling, a tender is
brought to dismantle and remove the drilling equipment and, in the
case of a dry hole, the entire self-contained platform is
dismantled and removed by tender. A variation of the foregoing
method provides a somewhat smaller platform similarly erected on
piles and having a drilling rig located thereon while the
auxiliaries, equipment and crew are located in a tender tied
alongside. At the conclusion of the drilling, the platform is
likewise either left for oil production or is dismantled and
removed in the case of a dry hole. Another method employs a
self-elevating barge which is towed to the drilling site and
provided with columns or legs which are then lowered and embedded
in the sea floor. The barge is then jacked up so as to clear the
water surface and serves as a platform on which the drilling rig,
crew, and auxiliary equipment are subsequently positioned for
drilling operation. At the conclusion of the drilling, in the event
of a producing well, a fixed platform generally is erected for
continuing oil production and the self-elevating barge is towed to
another drilling site. The foregoing methods are each feasible for
use in relatively shallow water depths of normally 300 feet or
less. The factors governing construction and operation of the
vessels or rigs utilizing any of the foregoing arrangements are not
significantly concerned with stability and other problems involved
in conducting a drilling operation from a floating platform, as in
deep water drilling, since the above-discussed rigs and vessels are
constructed for sea bottom engagement.
Deep water and exploratory drilling has been accomplished by means
of surface floating drilling vessels which are either towed or
self-propelled to the drilling site and are self-contained in that
the drilling rig, auxiliary equipment and crew's quarters form an
integral part of the vessel. These floating drilling vessels are
anchored over the drilling site and are normally provided with a
central opening through which the drilling rig is operated.
Drilling operations from these floating vessels are, however,
highly restricted by sea state conditions, since excessive vessel
motion in heave, pitch and roll can and does damage the drilling
equipment as well as aggravate the problem of maintaining the
vessel anchored directly over the drilling site. The stability
characteristics of such a single-hulled drilling vessel are
accordingly not conducive to efficient oil drilling operations. A
catamaran type oil drilling vessel has been constructed; however,
while that type vessel affords greater stability than a
single-hulled vessel, it involves substantial problems which
include excessive vessel motion due to wave action, no substantial
motion minimizing characteristics, overstability and resultant
"snapping" action which tosses personnel about and may endanger the
drilling string and other equipment. Accordingly, while these
vessels are not geographically limited to offshore drilling
operations, they are limited to use in restricted or calm
waters.
Deep water and exploratory drilling operations have also employed
semisubmersible platforms which, like the floating vessels, are
completely self-contained. In this latter type, the platform is
supported on a plurality of structural members including
stabilizing columns joined at their lower ends to a base flotation
structure which, when in unballasted condition, floats the entire
structure above the surface of the water with the base structure
having freeboard. After being towed in freeboard condition to the
drilling site, the base flotation structure is deballasted to
submerge the same. To maintain the drilling platform above water in
a relatively stabilized condition, the platform support structure
includes a plurality of columns which extend between the platform
and the base structure and are partially submerged to the extent
that the displacement of such columns in conjunction with any
residual displacement of the base structure supports the overall
semisubmerged structure.
In one type of these prior semisubmersible platforms, the
stabilizing patterns of the stabilizing columns form substantially
symmetrical equilateral polygons with the columns located at the
apices of the respective polygons which are normally square or
triangular in shape. The equilateral symmetrical polygonal
arrangement provides substantially identical righting moments about
the roll and pitch axes, as well as any intermediate axes,
regardless of wave direction. Another form of similar
semisubmersible vessel includes a plurality of stabilizing columns
interconnected adjacent their upper ends so that only the columns
float in the water, with the columns again being arranged in a
symmetrical equilateral polygon. In general, while such prior
vessels of this type provide adequate stability for well drilling
operations, they have an inherent disadvantage of very low mobility
between drilling sites due to the shape and frontal area of the
polygonally arranged columns and/or base structure presented to the
water surface when such vessels are towed; their towing speed often
does not exceed 2 knots. Additionally, to achieve the necessary
displacement for supporting the full weight of drilling rig, deck
load, etc., for such a vessel having a symmetrical equilateral
polygonal configuration of base structure and stabilizing columns,
such prior type vessels are of such large dimension that they
cannot pass through narrow waterways like the Panama and Suez
Canals, whereby their use is accordingly restricted.
Accordingly, it is a primary object of this invention to provide a
new improved twin hull variable draft vessel which minimizes
above-discussed and other shortcomings of prior offshore and deep
water drilling rigs and vessels, and provides various advantages in
construction, mode of operation and result over prior systems.
It is another object of the present invention to provide a variable
draft vessel which, particularly in column stabilized floating
condition, has the characteristic of minimizing vessel motion due
to excitation forces caused by wave action (hereafter called
"motion minimizing characteristic"). It is a related object to
provide such a vessel affording improved motion minimizing
characteristics in vessel pitch, roll and heave.
It is a related object of the present invention to provide a
variable draft column stabilized vessel having rapid mobility in
transit.
It is still another object of the present invention to provide a
twin hull variable draft column stabilized vessel which is operable
in great depths of water as a self-contained drilling vessel.
It is further object of the present invention to provide a variable
draft vessel having twin hulls which has a drilling platform
mounted on a deck which is above the hulls an effective height
slightly greater than the maximum anticipated wave height.
It is still a further object of the present invention to provide a
variable draft drilling vessel having stabilizing columns
configured to reduce displacement of the vessel in heave in the
high draft floating condition due to the inertia thereof and to
provide reduced pitch and roll angles.
It is still a further object of the present invention to provide a
deep water drilling vessel having twin hulls the draft of which is
variable by ballasting and deballasting of the twin hulls to
selectively orient the vessel in a low draft floating condition
with the hulls having freeboard and a high draft column stabilized
floating condition.
It is a related object of the present invention to provide a
variable draft deep water drilling vessel having twin hulls
including separate ballast compartments in each hull together with
ballasting means for selectively ballasting and deballasting the
several compartments in each hull thereby selectively correcting
the heel and trim angles.
It is another object of the present invention to provide an
improved variable draft vessel usable as a tender for other
vessels, or as a platform for a heavy duty crane, dredge or other
equipment, as well as for a drill rig.
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 side elevational view of the twin hull drilling
platform and tender barge or vessel according to the present
invention, with the vessel illustrated in the low draft towing
condition;
FIG. 2 is a side elevational view of the vessel similar to that of
FIG. 1 and illustrating the vessel in the high draft, column
stabilized, floating condition;
FIG. 3 is a plan view of the vessel, with portions broken out for
ease of illustration;
FIG. 4 is a horizontal sectional view taken about on line 4--4 of
FIG. 1;
FIG. 5 is a transverse sectional view taken about on line 5--5 of
FIG. 4;
FIG. 6 is a transverse sectional view taken about on line 6--6 of
FIG. 4;
FIG. 7 is a bow end elevational view of the vessel in the column
stabilized high draft condition;
FIG. 8 is an aft end elevational view of the vessel in the column
stabilized high draft condition;
FIG. 9 is a schematic view of one of the hulls of the vessel
illustrating the ballast system therefor; and
FIGS. 10A and 10B are elevational and plan diagrammatic
illustrations respectively of another embodiment of the vessel
hereof.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to the drawings, there is shown a variable draft drilling
platform (hereinafter referred to as a 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 low draft floating
condition with the hulls having freeboard indicated at f. Hulls 12
are substantially identical one with the other, each hull having a
substantially rectangular cross section as seen in FIGS. 5 and 6.
Each hull 12 has designed hydrostatic properties and hydrodynamic
characteristics, including being streamlined for minimum resistance
in motion. Each hull has freeboard f and a bow 14 and stern 16 with
midbody between. Inwardly curved outboard side formations at bow
portions 14 are indicated at 18. Hulls 12 are thus formed
substantially streamlined in shape to minimize resistance to towing
through the water when vessel 10 is entirely supported by hulls 12
in the low draft floating condition as illustrated in FIG. 1.
A platform or main deck 20 is supported in spaced relation above
hulls 12 a predetermined height h (FIG. 1) which is at least equal
to and preferably slightly greater than the maximum anticipated
wave height, i.e., the vertical distance between wave crest and
trough, by support structure comprising a plurality of
longitudinally spaced, transversely extending truss formations
generally indicated at 22 and a plurality of spaced stabilizing
columns 24. The first, second, third and fifth truss formulations
22, looking aft in FIG. 4, each includes a lower transversely
extending base tubular member 26 having opposite end portions
overlying and secured to hulls 12 to maintain the latter in
predetermined spaced relation preferably a distance at least equal
to a hull beam. The length of the members 26 of the first, third,
and fifth truss formations 22 are identical while the base member
26 of the second truss formation is extended to the longitudinal
centerline of the centrally located stabilizing columns 24. A
plurality of diagonally and upwardly extending columns 28 are
suitably secured at their lower ends to base members 26 and at
their upper ends to platform 20 to form a pair of transversely
extending V-shaped truss formations as best seen in FIGS. 5, 6, and
8. The fourth truss formation 22 comprises a pair of V-shaped
formations without a lower base member. The first, third, and
fourth truss formations 22 have outboard columns 30 joined at their
lower ends to the outboard edges of hulls 12 and which extend
upwardly and inwardly to the outboard edges of platform 20. A
plurality of inboard columns 32 extend from the inner edges of
hulls 12 upwardly to intermediate portions of platform 20 at
longitudinally spaced positions along the hulls between transverse
truss formations 22 to provide additional support for platform 20.
It will be noted that the forwardmost truss formation 22 is spaced
a considerable distance aft of the forward ends of hulls 12 to
provide a substantial open area 33, unencumbered by support
structure, between forward portions of the hulls. It will be
apparent to one skilled in the art in light of the disclosure
herein that other specific support constructions and column and
truss arrangements can be used in a vessel according to this
invention.
As discussed more fully hereinafter, the support structure also
includes stabilizing columns 24 extending upwardly from the upper
surface of hulls 12, a distance which may be equal to and is
preferably at least slightly greater than the maximum anticipated
wave height, the vertical distance between wave crest and trough.
In the preferred illustrated embodiment, the columns 24 extend
upward to platform 20 and form a part of the structural support
therefor whereby their effective height is equal to the height h
between the upper surface of hulls 12 and the underside of platform
20. In the preferred embodiment, columns 24 are located adjacent
opposite ends of each hull 12 with a third column being provided on
each hull intermediate the ends thereof. As seen in section in FIG.
4, columns 24 preferably are generally oval shaped with
longitudinally elongated vertical sides and cylindrical fore and
aft vertical end sections 34. Besides providing streamlining in the
direction of the vessel's longitudinal axis, this provides
increased vessel stability. Use of columns 24 provides better
motion minimizing characteristics when the vessel is in the
floating high draft condition. Stabilizing columns 24 are
preferably constant in cross sectional area throughout their
effective height h. 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 frusto-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.
A drilling platform 35 is spaced above main deck 20 adjacent the
forward end of the vessel by a plurality of support beams 36
secured at their lower ends to platform 20. A house 38 is provided
adjacent the forward end of drill platform 35 adjacent the forward
edge thereof. Truss formations 40 have a pair of transversely
spaced legs 42 secured at their lower ends to mounting members 44
fixed to platform 35 adjacent the aft edge thereof, legs 42
providing the aft support for trusses 40. There is supported on
drill platform 35, a drill rig or derrick 46, having a pair of
transversely spaced base truss formations 48 forming diverging legs
which are pivotally secured at their lower ends to mounting members
44, whereby drill rig or derrick 46 can be pivotally moved between
a vertically extending drill operating position seen in FIG. 2, and
a lowered inoperative position seen in FIG. 1. The base portion 48
of derrick 46 seats against and is suitably secured by means not
shown to truss formations 40 to maintain the same in a vertical
position whereby a drill string 50 can be supported from the upper
end 52 of the derrick 46 so that string 50 extends between hulls 12
on the center line of the vessel forward of the first truss
formation 22 into open area 33. Main deck 20 has a deck
superstructure 54 supporting a weather deck 56 mounting a pair of
transversely spaced, upstanding beams 58 carrying a transverse beam
60 at the upper ends thereof for supporting the upper end of
derrick 46 when the latter is pivoted to the lowered horizontal
position shown in FIG. 1. The main deck superstructure 54 houses
the machinery, crews quarters, and additional drilling equipment
while weather deck 56 supports an after deckhouse 62 and a
plurality of transversely extending pipe racks 64. A longitudinally
extending catwalk 66 is positioned intermediate pipe racks 64 to
provide access to any portion along the racks. The top deck of
deckhouse 62 supports a heliport 70 and ballast control house
71.
In a preferred form hereof, particularly as seen in FIGS. 4, 7, and
8, columns are disposed along the outboard sides of hulls 12 such
that the inner faces of columns 24 lie parallel to and in vertical
alignment with the center line of the associated hull. The
displacement and stability requirements of columns 24 are such that
these columns have a transverse dimension locating an outboard
portion 72 of each column 24 in overhanging relation to the outer
hull sides, with the longitudinal axes of columns 24 being spaced
laterally outwardly of the center line of the hulls and located
inwardly of and adjacent the outer hull sides. The centroids of the
water plane areas defined by the cross sections of the columns 24
are thus located an extended distance from the center line of the
vessel on opposite sides thereof to develop larger moments of
inertia of the water plane areas about the roll axis than would
otherwise be the case if the longitudinal center lines of each of
the hulls and their associated stabilizing columns were coincident.
The upper surfaces of the outer overhanging portions 72 of columns
24 form a continuation of main deck or platform 20 as seen in FIGS.
3 and 7 and each such upper surface adjacent the corners of the
vessel mounts a pair of mooring pulleys 76, which forms a part of
the vessel positioning or station keeping system. A pair of mooring
winches 78 are located in a machinery space adjacent the bottom of
each of the four corner stabilizing columns 24 and carry anchoring
cables 80 which extend over pulleys 76 through chocks 84. Winches
78, pulleys 76, and cables 80 provide an 8-point mooring to anchors
system which serves to hold and maintain the vessel in fixed
position over the drilling site when the vessel is floating in the
high draft column stabilized condition. Other types of positioning
or station keeping devices, such as dynamic positioning devices,
mooring to piles and the like, may be employed with equal facility
and the foregoing described anchoring system is representative only
of a preferred form thereof.
A pair of cranes 84 and 86 are mounted on opposite sides of the
vessel and may be of any conventional design, including the usual
booms 88 and operating cabs 90. Cranes 84 and 86 may have any
desired capacity, for example, 50 tons, crane 84 having an 80 foot
boom and crane 86 having a 100 foot boom. The smaller crane 84 is
preferably employed to service the self-contained drilling rig
aboard vessel 10 such as for example raising or lowering the drill
rig or loading and unloading pipes from pipe racks 64. The heavier
crane 86 is preferably employed when vessel 10 is utilized as a
tender, for example, in erecting or dismantling and generally
servicing other drilling rigs. Crane 84 is pivotally mounted on a
supporting column member 92 fixed at its lower end adjacent the
outboard side of one of the hulls while crane 86 is pivotally
supported on a columnar member 94 spaced from intermediate column
24 and fixed at its lower end to the outboard side of the other
hull 12.
As seen in FIG. 9, hulls 12 are each divided into compartments 96
forming a plurality of ballast chambers for varying the draft of
the vessel. While only the starboard hull and ballast system
therefor are illustrated in FIG. 9, it will be understood that the
port hull is similarly arranged and ballasted but is of the
opposite hand. Ballast chambers 96 are selectively and
independently ballasted and deballasted whereby the vessel may be
partially submerged with the platform 20 remaining substantially
level throughout the partial submergence of the vessel and the
stability of the vessel in both roll and pitch may be corrected
during partial submergence and retention of the vessel at the
column stabilized, high draft, drilling depth. To this end, a
plurality of conduits 98 extend from a centrally located pump room
P in each of the hulls in opposite longitudinal directions to the
several ballast compartments 96, there being, in the preferred
form, four ballast compartments in each of the aft and forward
portions of each hull. A pair of conduits 100 extend aft from pump
room P and terminate in a pair of compartments 102 which may be
employed as supplemental ballast compartments or as compartments
containing drilling water. While not a part of the ballasting
system per se, a pair of bilge water conduits 104 extend fore and
aft from pump room P into the bilges of the hulls and are in
communication with the ballast pumps in a manner to be
described.
The pump room is provided with a sea suction inlet indicated at 106
and an overboard discharge indicated at 108 controlled by suitable
power operated gate valves 110 and 112, respectively, the hull
sides being indicated by the dashed lines in FIG. 9. A pair of
pumps 114 and 116 are provided to suction sea water through inlet
106, past valve 110, through pumps 114 and 116 via conduits 118 and
120 respectively, past check valves 122 and 124, respectively, and
into a conduit 126 communicating with main ballast conduit 128.
Opposite ends of .Iadd.a.Iaddend.main conduit 128 communicate with
fore and aft ballast conduits 98 through suitable power operated
valves 130, ballast conduits 98 being arranged in parallel at
opposite ends of main conduit 128. With valves 110, 122, 124, and
130 open, the four ballast compartments at the fore and aft
portions of each hull may be ballasted with sea water at an equal
rate to maintain the platform substantially level when the vessel
is being partially submerged to a high draft column stabilized
drilling level or position.
To refloat the vessel with the hulls 12 having freeboard, valve 110
is closed and valves 112, 130, and 132 are opened. Pumps 114 and
116 operate to pump water in the same direction as before and
accordingly suction main conduit 128 through conduit 134, thereby
suctioning ballast conduits 98 and withdrawing ballast water
therefrom for discharge through conduit 126, open valve 112 and
outlet 108. It is thus readily seen that by selective operation of
valves 110, 112, and 130, and 132, selected compartments of
compartments 96 may be ballasted and deballasted as desired to
affect the attitude of the vessel about heel and trim axes, and to
assist in the drilling operation. Moreover, this can be
accomplished when the vessel is in any operating condition, i.e.,
low draft floating with the hulls having freeboard, high draft
column stabilized floating during drilling operations or any
intermediate position during submerging or refloating
operations.
Conduit 192 connects the port and starboard pumprooms and
communicates with ballast conduit 128. By activating the
appropriate valves, including valve 190 in conduit 192, ballast can
be transferred from one hull to the other. In the event that one
pumproom becomes flooded due to extreme damage, the ballasting
system can be controlled by opening valve 190 and controlling the
ballast system with the pumps in the other hull.
The ballast drilling water conduits 100 are also connected in
parallel to the aft end of main conduit 128 through suitable valves
138 similar to valves 130. Thus, the ballast drilling compartments
102 can be ballasted, deballasted, and selectively ballasted and
deballasted similarly as compartments 96 by selected operation of
valves 138 and the aforementioned valves 110, 112, and 132.
A fresh water intake or filling conduit 140, communicating with the
machinery deck via uptake conduit 142, and a fresh water suction
conduit 144, communicating with the ship's service fresh water pump
146, each communicate with a fresh water compartment 148 located
aft of the pump room on the inboard side of the hull. A conduit 149
communicates between fresh water pump 146 and the machinery deck
via uptake conduit 150. A pair of fuel oil suction conduits 152
communicate with fuel oil tank 154 located forward of the pump room
on the inboard side of the hull and provides fuel oil to the
machinery deck via an uptake conduit 156 by means of fuel pump 158.
Drill water is pumped from the aft drilling water compartment 162
and the ballast/drilling compartments 102 via conduits 164 and 100,
166, respectively, into a main drill water conduit 167 by a pump
168 which delivers the drill water via suitable valve 170 to the
machinery deck via an uptake conduit 172. A drill water conduit 174
communicates with the forward drilling water compartment 176 and
provides drill water to the machinery deck via pump 168 and conduit
172. Suitable valves 178 are provided in conduits 164 and 166 and
these together with valve 176 in conduit 174 are selectively
operable to fill and suction compartments 102, 162 and 176, whereby
drill water may be transferred to and from the drilling rig and may
be employed for the purposes of ballasting and deballasting the
vessel.
It is a significant feature of the present invention that vessel 10
can be towed between drilling sites at speeds on the order of 10-12
knots providing the present vessel with a mobility heretofore
unavailable in prior semisubmersible type platforms. To this end,
hulls 12 have bow, stern and midbody designs and have a
displacement when deballasted to support the entire weight of the
vessel in a low draft floating condition with the hulls 12 having
freeboard. In this low draft floating condition, it will be noted
that the mast 46 is pivoted to extend horizontally as seen in FIG.
1, thereby lowering the overall center of gravity of the vessel,
wind resistance, and excessive dynamic loading on the mast 46.
Thus, when floating with the twin hulls having freeboard, vessel 10
has the greater righting stability and decreased roll angles
characteristic of a catamaran type vessel. It will be seen that the
support structure for platform 20 including truss formations 22 and
stabilizing columns 24, are disposed above the waterline and
accordingly do not present a frontal area to the water to offer
resistance to passage therethrough. In the low draft floating
condition, only twin hulls 12 displace water and the hydrodynamic
characteristics of the hulls, particularly their substantially
streamline shape as well as the absence of support structure in
contact with the water, minimizes their resistance to passage
through the water and permit the towing of the vessel at
significantly higher speeds than theretofore possible with prior
semisubmersible platforms.
When vessel 10 reaches the drilling site, the anchors (not shown)
and anchor lines 80 are deployed to maintain the vessel directly
over the drilling site. Hulls 12 are then ballasted preferably by
simultaneously ballasting fore and aft compartments 96 thereby
maintaining the vessel level, to submerge the hulls below the water
line with the vessel being submerged to the extent that columns 24
are partially submerged for approximately half their effective
height h, thereby locating the mean water line above the upper
surfaces of the hulls at a distance of approximately half the
distance between platform 20 and the upper surface of hulls 12. In
this manner, the maximum anticipated wave is prevented from acting
against hulls 12 and platform 20 and acts only in the open frame
area between the hulls and the platform; this reduces the adverse
effect of wave action on the vessel which has excellent motion
minimizing characteristics in the column stabilized high draft
floating condition. As the vessel is partially submerged, anchor
lines 80 are made taut by operation of winches 78 to maintain the
vessel over the drilling site.
At the predetermined submerged depth, valves 130 are closed and the
displacement of the submerged portions of columns 24 and the
residual displacement of the hulls are sufficient to maintain the
vessel in the floating high draft condition. It is a significant
feature hereof that the foregoing vessel has optimal stability
characteristics in the floating high draft condition. To this end,
the columns are designed to provide a sufficiently large
displacement of the submerged portions thereof and this, in
combination with the displacement of the submerged hull, provides
sufficient overall buoyancy to support the entire weight of the
vessel including the drilling rig, crew's quarters, etc., in the
floating high draft condition as well as a sufficiently large water
plane area at the aforementioned depths of submergence to provide
an adequate righting moment arm to return the vessel to a level
position. The columns are also designed to provide a sufficiently
small displacement of the submerged portions thereof to preclude
large amplitudes of the vessel displacement in heave and .Iadd.a
.Iaddend.sufficiently small water plane area to provide a longer
period of and hence a gentle roll. The columns provide a roll
sufficiently slow as to preclude tossing about of operating
personnel, equipment and machinery on platform 20 (which as seen in
FIG. 2 are at a considerable height above the roll axis RA when the
vessel is in the high draft condition) 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 96, and, if necessary, compartments
102.
Particularly, to afford motion minimizing characteristics .[.of.].
.Iadd.to .Iaddend.the vessel within the designed constraints
imposed on the vessel, such as width limitations to permit passage
through the Panama Canal, the operating parameters, for example,
the drilling rig, deck load, etc., the cross sectional area and
configuration of the columns, the weight distribution of the
vessel, and the geometry of the submerged hulls and portions of the
hulls to platform connections specifically the submerged column
portions are such as to maintain the natural period of the vessel
in the high draft condition at least as great as six seconds and
are preferably such that the natural period of the vessel in the
high draft condition lies within a range of 6 to 40 seconds.
It will be noted that the primary purpose of the present variable
draft vessel is to minimize vessel motion due to wave action,
particularly when operating in the high draft column stabilized
condition. Ideally, this is accomplished by submerging the vessel
approximately one-half the effective heights of columns 26 thus
precluding wave action against the platform as well as the hulls so
that only the exposd columns 24 and trusses 22 between the platform
and hulls are exposed to wave action. However, even when this
vessel is operating within design limits in the high draft column
stabilized condition with the motion-minimizing characteristics
afforded by the described vessel construction, there is some vessel
response to wave action, i.e., the wave action against columns 24
and the other support structure including trusses 22. Because of
this, when the period of the waves according to existent sea
conditions is close to the natural period of the vessel, there may
be amplification of vessel motion which may become so excessive as
to interfere with drilling and other operations, even though the
vessel is submerged to the usual operating condition with the mean
water line at approximately one-half the effective height h of
stabilizing columns 24. 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
within certain predetermined limits to vary the draft of the vessel
to a greater or lesser extent from the ideal column stabilized high
draft condition which locates the mean water surface one-half the
effective height h. The maximum variation of vessel draft from the
ideal draft in column-stabilized floating condition 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 in
draft in the column stabilized floating condition, i.e., by
ballasting or deballasting, from the ideal column-stabilized draft
of one-half h, is such that the distance between mean water surface
and either the underside of the platform or the topside of hulls 12
is not less than 0.75 of the existent mean wave height.
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 and the stability and motion
minimizing characteristics thus afforded the vessel are optimum for
a vessel of the foregoing construction.
To refloat the vessel, the anchor lines are loosened or the anchors
are shipped aboard the vessel and ballast compartments 96 and/or
compartments 102 are pumped to evacuate the water therein as
hereinbefore described. The combined displacement of the hulls and
the submerged columns is sufficient to raise the vessel to the low
draft floating condition illustrated in FIG. 1, the stabilizing
columns acting continuously to stabilize the vessel during
refloating operations.
In either floating condition, the stability characteristics of the
twin hull vessel afford use thereof as a tender with one or both of
cranes 84 and 86 being operable to service another drilling rig or
vessel. The vessel is self-contained in that crews quarters, the
required auxiliary equipment, and deck load, etc., is on board and
accordingly the vessel can provide these facilities to service
another drilling structure. Auxiliary equipment, crews quarters,
etc. may be located within columns 24 in addition to being located
on platform 20.
Certain basic principles are employed in the construction of the
present vessel:
(1) A pair of elongated, laterally spaced hulls 12, having bow,
stern and midbody designs and lying 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 with
the hulls having freeboard, and the hulls are compartmented for
ballasting in a predetermined volumetric relation to the
stabilizing columns 24 as noted in points (6) and (7)
hereafter.
(3a) The vessel should have at least six stabilizing columns 24,
with half of the columns being disposed on each hull on opposite
sides of the roll axis RA and a first and second pair of such
columns on opposite sides of the pitch axis PA (passing through the
center of the flotation) with the third middle pair of such columns
located adjacent or intersected by the pitch axis when a total of
six stabilizing columns are used.
(3b) 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, as illustrated, for example, in FIG. 4;
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, as illustrated for example in FIGS. 10A and 10B.
(4) to stabilize the vessel, each of columns 24 should have a
predetermined area which is constant in cross section throughout
the effective height thereof per point (6) below.
(5) The platform or main deck is supported above the upper surfaces
of the hulls a predetermined height h which is at least equal to
and preferably slightly greater than the maximum anticipated wave
height, i.e., the vertical distance between wave crest and
trough.
(6) The effective height of the stabilizing columns is equal to and
preferably slightly 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.
(7) The stabilizing columns 24 are constructed so that their lower
portions having a height equal to one-half the effective height
provide a combined displacement together with the residual
displacement of ballasted hulls 12 so as to float the vessel in a
.[.height.]. .Iadd.high .Iaddend.draft condition meeting the
requisites of point (6).
(8) When floating in the high draft condition, the stabilizing
columns provide stabilizing righting moments about the roll axis RA
and the pitch axis PA in proportion to their volumetric
displacement, cross sectional area and their respective distances
from each such axes, whereby such righting stabilizing moments are
of a magnitude to maintain the vessel within optimum limits of roll
and/or pitch inclination and period of roll and/or pitch for
drilling operations.
(9) The vessel is ballasted to a partial submergence of
approximately one-half the effective height of the stabilizing
columns to maintain the vessel in a high draft 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 above
optimum high draft condition such that the distance between the
mean water surface and either the underside of the deck of top side
of the hull is not less than 0.75 of the mean wave height.
(10) The cross sectional area and configuration of the columns, the
weight distribution of the vessel, and the geometry of the
sumberged hulls and portions of the columns are such as to maintain
the natural period of the vessel in the high draft condition at
least as great as six seconds and preferably such that the natural
period of the vessel in the high draft column stabilized condition
lies within a range of 6 to 40 seconds.
An illustrative preferred embodiment of a vessel constructed
according to the present invention has an overall length of 270
feet at hulls 12 with each hull 12 having a beam of 30 feet and
inside spacing of 30 feet from each other, providing an overall
hull beam of 90 feet. The effective height h of the stabilizing
columns 24 is 24 feet. The centroids of the columns 24 are equally
spaced 411/2 feet from the vessel's longitudinal centerline. The
pairs of outer stabilizing columns 24 are spaced about 212 feet
apart, with the central pair of columns 24 being midway between.
The length and width of the columns 24 are 34 feet and .[.23.].
.Iadd.32 .Iaddend.feet respectively with the ends being formed
cylindrical in shape providing an overall area of approximately
667.5 square feet. To provide a larger righting moment about the
roll axis RA, the bottles 24 preferably overhang 8 feet beyond the
outboard hull sides providing an overall vessel beam of 106 feet,
and, accordingly, an overall length-to-width ratio of approximately
21/2:1 is provided.
SUMMARY OF CONSTRUCTION AND OPERATION
Thus, the present invention provides a twin hull, variable draft
column stabilized drilling platform having a plurality of
connecting members including spaced upstanding stabilizing columns
24 which are fixed at their lower ends to a pair of laterally
spaced, elongated parallel hulls 12 and which support a drilling
platform 20 including crew's quarters and machinery spaces, at
their upper ends. The spaced hulls are compartmented to provide
ballast tanks 96 which are deballasted when the vessel is towed to
and from drilling sites to provide sufficient hull displacement to
support the vessel (and its drilling rig, crew's quarters and
machinery spaces) in low draft condition with the hulls having
freeboard. The hull compartments 96 provide a safety factor in the
event of a collision or otherwise rupturing certain of the
compartments. At the drilling site, the hulls' ballast tanks 96 and
tanks 102, if necessary, are ballasted to submerge the hulls
normally to a distance about one-half the effective height of
stabilizing columns 24 which is about one-half the height of the
maximum anticipated wave whereby platform 20 remains supported
above the maximum anticipated wave height. The displacement
required to support the platform/barge in the high draft floating
condition is provided by the submerged hulls and portions of the
stabilizing columns 24, the vessel in this condition being
otherwise unsupported. The present vessel is thus different from
the previously discussed prior types of self-contained fixed
platform, self-elevating barges and surface floating vessels as the
present vessel operates in two distinct conditions (1) low draft
floating with the hulls having freeboard and (2) high draft column
stabilized floating; thus, the vessel involves stability and
structural criteria differing from the abovementioned prior type
vessels or fixed platforms. The present vessel of this invention is
further distinguished from such prior type vessels in that sole
support in both conditions is provided by buoyancy whereby factors
for ground supported operation are not involved.
Moreover, the present vessel is also significantly different in
concept, construction and mode of operation from previously
described semisubmersible platforms as will now be discussed.
Mobility between and stability at the drilling sites are prime
requisites for an effective drilling vessel. The vessel of this
invention can be towed between drilling sites at speeds greatly in
excess of towing speeds for prior drilling platforms and the like,
due to use of twin hulls having sufficient displacement to locate
the stabilizing columns 24 above the waterline when the vessel is
in the floating condition and hulls having stern, bow and midbody
designs characterized by hydrodynamic and hydrostatic properties.
Contrary to the provision of interconnecting base structure at the
lower ends of polygonally located stabilizing columns as in prior
art semisubmersibles, whereby the base structure creates
significant drag when those semisubmersibles are towed on the water
surface so that towing speeds are limited to about two knots, the
streamlined parallel twin hulls 12 of the present vessel are
interconnected only above the waterline when the vessel is in the
freeboard low draft floating condition thus enabling significantly
greater towing speeds of about 10-12 knots and thereby greatly
reducing the time in transit between drilling sites. Moreover, by
utilizing twin streamlined parallel hulls 12, the overall beam of
the present vessel is significantly less than the width of prior
equilateral symmetrical polygonally shaped semisubmersible vessels,
while the present vessel can support a corresponding weight in
drilling platform, machinery, and equipment. Further, this
construction enables the present vessel to be towed through narrow
waterways such as the Suez and Panama Canals, while previous
polygonally shaped semisubmersibles could not. Additionally, the
twin hulls feature hereof provides high stability in the freeboard
low draft floating condition notwithstanding the relatively high
locus of the center of gravity of the overall vessel necessitated
by spacing the drilling platform, machinery and equipment at an
effective height above the hulls based on the anticipated sea
states in which the vessel will operate, as hereinafter more fully
discussed.
The ability of the present vessel to provide a stable floating
platform in various wave conditions without recourse to the
symmetrical equilateral polygonally shaped structures of prior
semisubmersibles heretofore thought necessary to stabilize the same
in a floating column stabilized condition, is highly significant as
it permits use of the above-described twin hull support, thus
combining in a single vessel the desirable stability
characteristics of a twin hulled low draft vessel having freeboard
and a column stabilized high draft vessel and drilling platform. To
stabilize the present vessel and its drilling platform 20 in the
floating high draft condition, wave action against the vessel must
be minimized as a cause of unfavorable motion characteristics. By
submerging the twin hulls such that the platform and upper surfaces
of the hulls are respectively spaced above and below the waterline
a distance at least equal to one-half the maximum anticipated wave
or to half the effective height of columns 24, wave action against
the larger surface area of hulls 12 or the drilling platform is
substantially eliminated, and waves act only against the relatively
small area of open support structure and framework between the
drilling platform and the hulls. The location, size and
configuration of the vessel's stabilizing columns 24 are effective:
to maintain the vessel in a buoyant high draft condition; to locate
and maintain the drilling platform 20 and hulls 12 respectively
above and below the maximum wave amplitude; to preclude large
vessel motions in heave due to large column displacement and the
inertial properties of the vessel; to provide a sufficient righting
moment when unstabilized about roll and pitch axes of a magnitude
to correct the rolling and pitching motion; and to generally
minimize the effect of the wave action against the vessel when in
the floating high draft condition.
The stabilizing columns 24 are located adjacent opposite end
portions of each hull with an additional column located on or
adjacent the transverse axis through the center of flotation to
provide moment arms about roll and pitch axes such that the
hydrodynamic forces act to establish righting moments in the high
draft condition 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 floating high draft positions of
the vessel. It may be noted at this point that the width of the
twin hulled vessel imposes a restriction on the moment of inertia
developed about the roll axis as the transverse distance of
stabilizing columns 24 along each hull from the centerline of the
vessel is limited to one-half the width of the vessel. The
stabilizing columns 24 are therefore provided with water plane
areas sufficiently large to compensate for the smaller moment arm
in the transverse direction, and a preferred form of the vessel has
the stabilizing columns located as close to the outboard sides of
the hulls as possible, and in the illustrated embodiment portions
of the columns are outboard of the hulls to further increase this
righting arm.
While the preferred form of the vessel described herein provides
three or an odd number of pairs of columns, an even number of pairs
of columns can be provided, four pairs 24 thereof being illustrated
in the embodiments of the present vessel shown in FIGS. 10A-10B. It
is seen, in this embodiment, that a like number of pairs of columns
24 are disposed on opposite sides of the transverse pitch axis PA
and in a generally symmetrical relation thereabout, the middle
pairs of columns thereof being spaced on opposite sides of the
pitch axis PA.
The effective height of the stabilizing columns from the upper
surfaces of the twin hulls to the under surface of the platform may
be equal to and preferably slightly greater than the height of the
maximum anticipated wave such that in the floating high draft
condition, the hulls remain underwater and the platform above water
for all waves. The stabilizing columns 24 also have a shape
providing a constant cross sectional area throughout their
effective height, thus presenting constant water plane areas to the
water surface. Thus, submergence and emergence of stabilizing
columns 24 due to wave action act to stabilize the vessel at a
gentle stabilizing rate. If the cross sectional area of the upper
half of stabilizing columns 24 were progressively increased in the
upward direction, a shortened and undesirable roll and pitch period
could occur with adverse effect on the drilling operation; and a
progressive decrease in the cross sectional area of the upper half
of the stabilizing columns 24 would result in large undersirable
roll and pitch angles.
The magnitude of the cross sectional areas and hence the water
plane areas and displacement of the present stabilizing columns is
determined in part by the magnitude of the displacement of the
hulls and satisfaction of other counter-vailing criteria. A
sufficiently large column or bottle displacement is provided to
afford adequate buoyancy to support the vessel in the high draft
condition with the hulls ballasted and providing a small proportion
of total displacement. Sufficient water plane areas are provided
for the columns to insure an adequate righting moment about roll
and pitch axes with the roll and pitch angles not exceeding optimum
limits. The column or bottle displacement, however, is sufficiently
small so that large vessel displacements in heave are avoided.
Additionally, the water plane areas are small enough to provide a
period of roll which provides safe and comfortable operating
conditions. The reduced water plane area also generally minimizes
the wave action against the vessel.
A crane 84 is located adjacent one side of the raised platform to
service the self-contained drilling rig. A second crane 86 is
preferably also provided on the opposite side of the vessel for
like purpose.
The twin hull stability of the present vessel is great enough to
enable the vessel to carry heavy deck loads. When employed as a
tender barge, one of the small cranes 84 or 86 will be eliminated
and a heavy duty crane (e.g., 150 ton lift capacity) would be
substituted; this crane would preferably be mounted on one of the
center columns 24 to utilize the column for structural support. In
this usage, not only does ballasting the hulls submerge the vessel
to provide a stable platform for drilling operations but also the
hull compartments 96 can be selectively ballasted to correct the
vessel heel and trim, respectively, to offset the weight of, and
variations in, loads applied to the vessel via the crane. Further,
the ballast correction can be applied to the vessel in both the
high and low draft conditions.
It will be appreciated that the foregoing described vessel may be
employed in other types of marine operations and fitted out with
suitable structure consonant with such employment. For example,
instead of mounting a drilling rig on platform 38, the column
stabilized vessel of this invention may be adapted as a heavy duty
derrick barge by mounting a heavy duty crane thereon along the
centerline of the vessel, with other portions of the vessel being
constructed similarly to corresponding portions of the vessel
herein described and illustrated, with appropriate modification as
to size. This vessel can be used as a dredge vessel by mounting and
operating standard dredging equipment taking advantage of all the
motion minimizing characteristics of the foregoing described
vessel.
It is therefore seen that the objects of the present invention are
fully accomplished in that the present vessel provides a deep water
drilling unit having rapid mobility in transit between drilling
sites as well as an exceedingly stable structure when in high draft
condition at drilling depths over a drill site. Moreover, the
vessel provides for a self-contained drilling operation or as a
tender servicing other drilling structures.
This invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof.
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