Note: Descriptions are shown in the official language in which they were submitted.
`
~2~
The present invention relates generally to s-tructures for supporting
offshore platforms above the surface of the water and more particularly to a
structure that includes a leg having an overall cross-sectional area that is
greatest adjacent the seabed and decreases moving upwardly along such leg from
the seabed to a region above the seabed and is substantially constant moving
from such region to the platform. While the invention has application in many
types of offshore platform configurations, it is particularly useful in connec-
tion wi~h mobile, jackup type offshore platforms.
Rigs for performing various operations at sea, often referred to as
"offshore rigs", generally include a superstruc~ure or platform supported above
the surface of the water by a support structure extending between the super-
structure and the seabed.
In the prior art, support structures have commonly included a plural-
ity of legs extending either vertically or at an angle between ~he platform and
the seabed. The legs of the prior art ordinarily have a substantially uniform
cross-sectional area along their entire length. For examples of such prior
art legs, see, e.g., United States Patent No. 3,466,878, issued to Esquillan
et al on September 16, 1969, (cylindrical or tubular legs) and United States
Patent No. 3,183,676, issued to LeTourneau on May 18, 1965, ~lattice-type legs).
The legs may engage the seabed by means of spud caissons ~see, e.g., LeTourneau,
supra), or by means of piles driven into the seabed (see, e.g., Esquillan,
supra), or by means of a flat surface, referred to as a "mat", interconnecting
the lowermost ends of the legs and resting directly on the seabed (see, e.g.,
United States Patent No. 3,699,688, issued to Estes on October 24, 1979). The
legs may be interconnected by a truss network as shown in United States Patent
No. 3,093,972, issued to Ward on June 18, 1963. The legs of the prior art
sometimes do not have a uniform cross-sectional area along their entire length.
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342
For examples of sucll prior art legs, see, e.g., United States Patent 4,045,968,
issued to Gerwick, Jr. on September 6~ 1977. For examples of other non-uni-
form cross-section structures which might be placed in the water, see, e.g.,
United States Patent 3,201,945, issued to Sutton on August 24, 1965 and draw-
ings of Offshore Equipment Development Co. bearing the date of July 12, 1976.
Pilings may also be used, see, e.g., United States Patent 2,592,448, issued to
McMenimen on April 8, 1952, and United States Patent 3,466,878, issued to
N. Esquillan et al on September 16, 1966. While applicant is unsure that a
model exhibited ~or view in Houston at the offices of Brown ~7 Root, Inc. to
customers of Brown ~7 Root, Inc. and others is prior art, applicant also wishes
to point out the existence of this.
Generally speaking, the support structure,~including the number,
arrangement and actual configuration of the legs must be established so that
the structure is capable of supporting several thousand tons of weight above
the surface of the water with a high degree of overall stability as well as
withstanding the often tremendous forces of winds, waves, currents and tides.
As the length of the legs of the support structure increases, however, the
potential of a leg of the support structure to fail due to the forces of wind,
waves and/or currents increases. In order to lessen this potential for failure,
there has been a tendency in the prior art to increase the structural strength
of longer length legs by increasing the cross-sectional area of such legs uni-
formly along their entire length or to add frame-type bracing extending their
entire length (see, United States Patent No. 3,007,316, issued to Higgins, Jr.
on November 7, 1961). It is known in the prior art, however, that the force
per unit length arising from wave motion acting on a submerged cylindrical
pile can be approximated as:
f - 1/2 ~ CDDU ¦U¦ + ~ CM ~ D ~ U
- 2 - t
where f = force per unit length
= density of the fluid
U = velocity perpendicular to the pile due to`wave motion
U = acceleration perpendicular to the pile due to wave motion
t
D = pile diameter
CM= inertial coefficient
CD= drag coefficient
In accordance with the foregoing, it can be seen that the force per unit
length generated by a particular wave increases as the cross-sectional area
of the pile increases. Thus, as the cross-sectional area of a leg of a sup-
port structure is increased for the purpose of withstanding the forces of
waves, the effective force generated by a particular wave also increases.
Similarly, additional bracing along the entire length of the leg adds to the
total cross-sectional area of the leg, including the region along the leg
where the velocity and acceleration of the fluid in a wave is the greatest,
whereby the force generated by the wave at that region is increased. As a
result, the prior art techniques of increasing the structural strength of the
legs uniformly along their entire length is highly inefficient.
The present invention is a highly efficient structure for use in
supporting an offshore platform above the surface of the water. The structure
of the invention includes a leg whose cross-sectional area is largest in the
region where the tendency to fail due to the forces of wind, current, waves
and tides is the greatest and is smallest in the region where the velocity and
accelcration of the water due to wave action is the grea~est. In this regard,
it has been found that, for support structures in deep water, the region where
the leg of a support structure is mos~ likely to fail due to the forces of
wind, current, waves and tides is the greatest is the region of the leg adjacent
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the seabed. This is due to the fact that most of these forces act at or near
the surface of the water whereby the greatest moment generated by such forces
is at the seabed. Furthermore, it is known in the prior art that the veloci-
ty and acceleration of the water due to the action of a wave is greatest at
the crest of the wave and decreases rapidly moving from the crest toward the
seabed. As a result, for a cylindrical pile having a uniform cross-section,
the force per unit length impressed against a pile by a wave decreases sub-
stantially exponentially moving from the crest of the wave to the seabed.
According to one aspect of the invention there is provided a struc-
ture for supporting a jack-up platform above the surface of a body of water,
the structure comprising:
a leg having a first end and a second end, said leg having a first
portion of variable cross-sectional area extending from said first end to a
point intermediate said first end and said second end and a second portion of
substantially constant cross-sectional area extending from said intermediate
point to said second end, the cross-sectional area of said first portion being
greatest at said first end and decreasing moving from said first end to said
intermediate point, the cross-sectional area of said second portion being no
greater than the cross-sectional area of said first portion at said interme-
diate point.
For a further understanding of the nature and objects of the presentinventionJ reference should be had to the following detailed description,
taken in conjunction with the accompanying drawings, in which like parts are
given like reference numerals and wherein:
Figure 1 is an elevation of a jack-up rig, including one embodiment
of the support structure of the invention, in position to be transported to
or from the operations site;
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Figure 2 is an elevation of the jack-up rig of Figure 1 in its
jacked-up position at an operations site;
Figure 2A is a plan view of the jack-up rig of Figure l;
Figures 3 and 4 are a plan view and a partial elevation, respective-
ly, of a leg of one embodiment of the support structure of tha invention;
Figures 5 and 6 are a plan view and a partial elevation, respective-
ly, of a leg of an alternative embodiment of the support structure of the
invention;
Figures 7 and 8 are a plan view and a partial elevation, respective-
ly, of a leg of an alternative embodiment of the support structure of the
invention;
Figures 9 and 10 are a plan view and a partial elevation, respective-
ly, of a leg of an alternative embodiment of the support structure of the
invention;
Figures 11 and 12 are a plan view and a partial elevation, respective-
ly, of a leg of an alternative embodiment of the support structure of the
invention;
Figures 13 and 14 are a plan view and a partial elevation, respec-
tively, of a leg of an alternative embodiment of the support structure of the
invention;
Figures 15 - 28 are cross-sectional views of various alternative
configurations of the leg cords of the legs shown in Figures 3-14 showing how
a rack and truss work, if any, can be attached thereto;
Figures 29 and 30 are a partial elevation and a partial cross-sec-
tional view, respectively, of an alternative configuration of the leg cords
of the legs shown in Figures 3-14;
Figures 31 and 32 are a partial elevation and a partial cross-sec-
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tional view, respectively, of an alternative configuration of the leg cordsof the legs shown in Figures 3-14;
Figures 33-35 are partial elevations, from two angles7 and a partial
cross-sectional view, respectively, of an alternative configuration of the
leg cords of the legs shown in Figures 3-14; and
Figures 36-38 are partial elevations, from two angles, and a partial
cross-sectional view, respectively, of an alternative configuration of the leg
cords of the legs shown in Figures 3-14;
Figure 39 is an elevation of a jack-up rig in its jacked-up position
at an operating site which utilizes piling through a leg chord that extends
to the surface of the water;
Figure 40 is an elevation of a jack-up rig in its jacked-up position
at an operating site which utilizes piling through a portion of a leg chord
at a cant which is steeper than the rest of the leg chord;
Figure 41 is a cross-sectional view of the portion of a leg chord
taken along section lines 41-41 of Figure 40;
Figure 42 is a cross-sectional view of an alternate configuration of
the portion of the leg chord shown in Figure 41; and
Figure 43 is a partial elevation of a jack-up rig in its jacked-up
position at an operating site with a portion of a leg chord in a vertical plane
and a portion of the rest of the leg chord at a cant.
The support structure of the preferred embodiment of the invention
has particular utility and provides great benefits when used as part of a
mobile jack-up rig to be used in deep water, such as, for example, water
greater than 40Q feet in depth. Such rigs, in turn, may be used for deep water
drilling, crane support or workover wherein mobile buoyant or nonbuoyant open-
work jack-up platforms are used in tender-assisted or in a self-contained
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manner. It should be realized, however, that the support structure of the
invention could be used to support and/or suspend any of a variety of appara-
tus above a water surface in depths that may vary from a few feet to deep
water.
Referring to Figure 1, mobile jack-up rig 11 is shown in its trans-
portable position. Rig 11 includes a platform or superstructure 13 and a
support structure that includes legs 15, 16, 17 and mat 19. Although the sup-
port structure is shown in elevation as including three legs, any number of
legs can be used depending on the design of the platform, the nature of the
use of the platform, the environmental and other physical conditions of the
operations site and/or the desires of the user.
Mat 19 is substantially flat and made of a heavy material. The par-
ticular size and configuration of mat 19 may vary widely in accordance with
numerous considerations including the number, orientation and configuration
of the legs of the support structure.
Legs 15~ 16, 17 are substantially identical, each leg having a por-
tion 21 whose cross-section decreases rom its lowermost portion to its upper-
most portion, such decrease resulting from a diminution of the lateral ex-
pense of the leg substantially around the entire boundary of the leg measured
from any member of the leg (herein referred to as a "variable cross-section
portion~). Variable cross-section portion 21 extends from mat 19 to point 23
spaced above mat 19 and substantially constant cross-section portion 25 ex-
tending above point 23. The particular configuration of legs 15, 16, 17 may
vary widely in accordance with the foregoing description. Numerous exemplary
embodiments will be described infra with reference to Figures 3 through 43.
It will be noted, however, that for all embodiments the cross-sectional area
of variable cross-section portion 21 ~the cross-sectional area at some point
iiZ3~;2
along the length of a leg is defined herein as the total area bounded by a
line lying in a plane perpendicular to the axis of such leg at such point and
completely surrounding all components of the leg) is greatest at the lowermost
point of the leg and decreases moving upwardly away from such lowermost point
toward point 23.
Each of legs 15, 16, 17 is movably attached to platform 13 by a
jacking means shown in Figure 2A as a rack-and-pinion type jack that includes
pinion drive apparatus and leg guide 29 secured to platform 13 and racks 33
secured along the lengths of the leg. Pinion drive apparatus may include
electric motors, hydraulic motors or other prime mover. Although rack-and-
pinion type jacking means is preferred, any type of jacking means, such as,
for example, chain jacks and friction jacks, may be used. The jacking means
should be such that mat 19 can be variably positioned between (1~ a raised
position wherein mat 19 is located just beneath platform 13 ~see Figure 1),
and ~2) a lowered position wherein mat 19 is spaced a substantial distance,
for example, 400 feet, beneath platform 13 ~See Figure 2). The actual dis-
tance beneath platform 13 that mat 29 can be positioned will, of course, de-
pend on the length of legs 15, 16, 17. After the appropriate distance has
been reached between platform 13 and mat 29, legs 15, 16, 17 may be welded or
otherwise attached to platform 13 ~such as at 358,359 of Figure 39).
Platform 13 should be sufficiently buoyant or should be connected to
appropriate floating apparatus such that rig 11 will float on the surface of
the water when mat 19 is in the raised position ~see Figure 1). In this way,
when mat 19 is in the raised position, rig 11 can be towed to the operations
site At the operations site, mat 19 is lowered to seabed 39 ~see Figure 2).
Once mat 19 is resting on seabed 39, jacking is continued so as to raise plat-
form 13 above the surface of the water. In this position, the desired opera-
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tions of the rig can begin.
Preferably, the length of the variable cross-section portion 21 of
legs 15, 16, 17 should be approximately equal to the average depth of the
water so that point 23 will ordinarily be proximate or below the surface of
the water. In this regard, it will be appreciated that a particular jack-up
rig will be used at numerous operation sites and that the average depth of
the water will vary from one site to another. Therefore, it is unlikely that
point 23 will always be at the surface of the water.
Figures 3-14 show various embodiments of the support structure of
the invention, the leg of all such embodiments including one or more leg cords
which may be vertical or inclined. Figures 15-37 show various configurations
of the leg cords that can be used in the embodiments of Figures 3-14. Because
the particular attachment of a rack or other jacking means component to a leg
will depend largely on the configuration of the leg cord or cords, such rack
or other jacking means will be described only will reference to Figures 15-37,
although it will be understood that where the support structure is used as
part of a jack-up rig, the legs of the support structure will have some type
of jacking means connected thereto or incorporated therewith.
Referring to the embodiment of Figures 3 and 4, variable cross-sec-
tion portion 21 includes (1) constant cross-section leg cord 41 secured -to
mat 19 at point ~3 and extending substantially vertically therefrom; ~2) cons-
tant cross-section leg cord 45 secured to mat 19 at pOillt 47 spaced away from
point 43, extending upwardly from mat 19 and toward cord 41 and secured to
cord 41 proximate point 23, i.e., the uppermost point of portion 21; (3) cons-
tant cross-section leg cord 49 secured to mat 19 at point 51 spaced from both
points 43 and 47 and extending upwardly from mat 19 and toward cord 41 and
secured to cord 41 proximate point 23; and (4) reinforcement truss network 53
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extending among cords 41, 45, 49. In accordance with the foregoing, it can be
seen that portion 21 of the embodiment of Figures 3 and 4 has a generally
pyramidical configuration with point 23 at the peak of the pyramid and points
43, 47, 51 at the base of the pyramid. Constant cross-section portion 25 of
the embodiment of Figures 3 and 4 includes an extension of cord 41, referenced
in Figure 4 as 41A.
The embodiment of Figures 5 and 6 is similar to that of Figures 3
and 4 except that the leg further includes piles, such as that shown at 57
driven through leg cords 45, 49 and mat 19 into seabed 39. Leg cords 45, 49
of the embodiment of Figures 5 and 6 will ordinarily have a tubular configura-
tion (see, e.g., the configurations of Figures 15-17 described infra) so that
piles can be driven therethrough. Using such piles, rig 11 can be used as a
battered leg fixed platform similar to fixed platforms already in use. Unlike
a fixed platform, a rig 11 using the leg of Figures 7 and 8 can be recovered
and reused.
Referring to the embodiment of Figures 7 and 8, variable cross-sec-
tion portion 21 includes truncated cone 61 having base 63 secured to platform
19. Preferably, one side of cone 61 is substantially vertical. Cone 61 may
be made of steel plate reinforced by internal stiffening members (shown in
Figure 8 as dashed lines 64). Cone 61 has a substantially circular opening at
point 23. Constant cross-section portion 25 includes tubular member 65 having
a diameter substantially equal to that of ~he circular opening of cone 61 at
point 23. Member 65 is secured to cone 61 at point 23 and extends substan-
tially vertically therefrom. It will be appreciated that the embodiment of
Figures 7 and 8 includes only a single leg cord whose cross-section varies
below point 23 and is constant above point 23. The embodiment of Figures 7
and 8 may further include piles 66 driven ~hrough member 65, cone 61 and mat
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19 into seabed 39.
The embodiments of Figures 9 through 1~ differ from those described
with reference to Figures 1 through 8 in that the support structure in which
such embodiments are used includes a spud can 101 at the base of each leg
rather than a mat 19. Spud cans, also called spud caissons, are well known
in the art of offshore rigs and any configuration of spud can or caisson can
be used in such embodiments.
Thus, the embodiment of Figures 9 and 10 is similar to that of
Figures 5 and 6 except that spud can 101 is substituted for mat 19. The like
parts of the embodiment of Figures 9 and 10 and the embodiment of Figures 5
and 6 are given the same reference numbers. Similarly, the embodiment of
Figures 11 and 12 is similar to that of Figures 7 and 8 except that spud can
101 is substituted for mat 19. The like parts of the embodiment of Figures
7 and 8 and the embodiment of Figures 11 and 12 are given the same reference
numbers.
Referring to the embodiment of Figures 13 and 14, variable cross-
section portion 21 includes (1) parallel leg cords 81, 83, 85 secured to spud
can 101 and extending substantially vertically therefrom, leg cords 81, 83,
85 being arranged in a generally triangular pattern and connected together by
truss network 87; (2) leg cord 89 secured to spud can 101 at a point spaced
away from cords gl, 83,85 and extending from spud can 101 upwardly and general-
ly toward cords 81, 83, g5 in a plane common to cord 83 and secured to cords
81, 85 proximate point 23 by truss members 91, 93, respectively; and (3) truss
network 95 extending among cords 81, 85 and 89. Constant cross-section portion
25 includes extensions of cords 81, 83, 85,shown as cords 95, 97, 99, connected
together by truss network lOl. If the leg cords of the embodiment of Figures
13 and 14 have a tubular configuration, such embodiment may further include
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~L152~3~2
piles, shown as dashed lines 103, extending through such cords and spud can
101 into seabed 39.
As indicated supra, Figures 15-36 show various configurations of leg
cords that can be used in the embodiments of the support structure of the in-
vention shown in Figures 3-14. A cross-sectional view of each such configura-
tion is shown together with a portion of a truss network (indicated by refer-
ence number 111) which may be attached thereto ~such as for leg cords ~1, 43,
47 of Figures 3-6, 9 and 10, and leg cords 81, 83, 85 and 89 of Figures 13 and
14). It will be noted~ however, that for some embodiments, such as the single
cord embodiment of Figures 7, 8, 11 and 12, no truss network will be included.
Also, in showing and describing such configurations, reference l~ill be made to
jacking means or a component thereof. It will be understood however, that not
all leg cords will include or otherwise be part of jacking means. For example,
leg cords 43 and 47 of Figures 3-6, 9 and 10 and leg cord 89 of Figures 13 and
14 ordinarily will not include or otherwise be part of jacking means. Further-
more, where one of the leg cord configurations of Figures 15-36 is used as the
leg cord of the embodiment of Figures 7, 8, 11 and 12, it will be understood
that the dimensions of such cord over portion 21 will increase moving from
point 23 to either mat 19 or spud can 101 as the case may be. As a final
preliminary note to the description of the configurations of Figures 15-37, it
will be understood that, excepting the configuration of Figure 16, all of such
configurations have been used in leg cords of the prior art.
Each of ths configurations of Figures 15-28 includes a principal
member 121 with one or more racks of a rack-and-pinion jacking means attached
thereto. Such racks are identified generically by reference number 133. De-
pending on the embodiment, rack 133 may have a single pinion-engaging edge
(such a rack is specially identified as rack 133A with the pinion-engaging
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edge identified as edge 201 and the opposite edge identified as edge 203) or
may have two pinion-engaging edges (such a rack is specially identified as
rack 133B with the pinion-engaging edges identified as edges 205).
In accordance with the foregoing, Figure 15 shows member 121 as
including cylindrical tubular beam 211. A rack 133A is secured to the outside
surface of beam 211 with edge 201 facing radially away from beam 211. Rack
133A of the Figure 15 embodiment extends axially along beam 211. Beams of
truss network 111 are connected to the outer surface of beam 211 and extend
generally away from rack 133A. Figure 16 S}IOWS a leg cord configuration si-
milar to that of Figure 15 except that two additional racks 133A are secured
to beam 211, such additional racks being azimuthally spaced to either side of
the first rack 133A by, for example, 90 degrees. Figure 17 shows a leg cord
configuration similar to that of Figure 16 with only the additional racks 133A
shown as diametrically opposed to one another. The first rack 133A shown in
the Figure 16 configuration is deleted.
Figures 18-20 show principal member 121 as including cylindrical
tube 213. The Figure 18 configuration includes a rack 133B extending across
a diameter of tube 213 with beams of truss network 111, attached to and ex-
tending from tube 213 on one side of rack 133B. Edges 205 of rack 133B both
are disposed outside of and face away from the outer surface of tube 213. The
Figure 19 leg cord configuration is similar to that of Figure 18 except ~hat
rack 133B of Figure 19 extends through a non-diametrical cord of tube 213 and
is spaced farther from the-beams of truss network 111 than is rack 133B of
Figure 18. The Figure 20 configuration includes a rack 133A extending radially
through the wall of tube 213 such that edge 201 of rack 133A faces outwardly
from the outer surface of tube 213 and edge 203 of rack 133A is inside tube
213 and faces toward the center of tube 213. Member 121 of the Figure 20 con-
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figuration further includes reinforcement plates 215, 217 extending between
edge 203 of rack 133A and the inner surface of tube 213.
Figures 21 and 22 show principal member 121 as including tube 219
having notch 221 of V-shaped cross section extending along the entire length
of tube 219. The configuration of Figure 21 includes a rack 133A extending
radially through tube 219 at the innermost point of notch 221~ Edge 201 of
rack 133A is recessed inside of notch 221 so that no part of rack 133A extends
beyond the outer surface of tube 219. Edge 203 of rack 133A is inside tube
219 proximate the center of tube 219. Member 121 of the Figure 21 configura-
tion further includes plates 223, 225 extending from edge 203 of rack 133A tO
the inner surface of tube 219. The beams of truss network 111 extend from
tube 219 generally away from notch 221. The Figure 22 leg cord configuration
is similar to that of Figure 21 except that plates 223, 225 are deleted and
rack 133A extends completely through tube 219 and is attached at edge 203 to
the inner surface of tube 219.
In the leg cord configurations of Figures 23 and 26, principal member
121 includes flat steel beam 231 of rectangular cross-section. In the Figure
23 configuration, beam 231 perpendicularly abuts a rack 133B at the center of
such rack 133B such that edges 205 face away from either side of beam 231.
The beams of network 111 are connected to opposite sides of beam 231 and ex-
tend generally away from rack 133B. In the Figure 24 configuration, a rack
133A perpendicularly abuts beam 231 at the center of one side of beam 231 such
that edge 201 of such rack 133A faces away from beam 231. The beams of network
111 are both connected to and extend away from the other side of beam 231.
The configuration of Figure 25 is similar to that of Figure 24 except that
member 121 of the configuration of Figure 25 further includes reinforcement
plates 241, 243 extending between either side of the rack 133A and the ends of
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beam 231. The configuration of Figure 26 is similar to that of Figure 25
except that the rack 133A of Figure 26 does not directly abut beam 231. In-
stead, edge 201 of rack 133A is spaced from beam 231. Rack 133A of Figure 26
is connected to beam 231 by means of plates 241, 2~3.
In the leg cord configurations of Figures 27 and 28, principal mem-
ber 121 includes tube 251 having a substantially square cross-section. In
the Figure 27 configuration, a rack 133A extends through a corner of tube 251
with edge 201 exposed outside of tube 251 and facing away from tube 251 gene-
rally in the directlon of an extension of a diagonal of tube 251. Edge 203
of rack 133A faces toward the center of tube 251. Member 121 oE the Figure
27 configuration further includes steel reinforcement plates 253, 255 extend-
ing between the edge 203 of rack 133A and the sides of tube 251 opposite the
corner of tube 251 through which the rack 133A extends, such sides being iden-
tified as sides 257, 259, respectively. Beams of truss network 111 are con-
nected to and extend from sides 257~ 259, respectively. In the Figure 28 con-
figuration a rack 133B extends completely through a diagonal of tube 251 such
that edges 205 of such rack 133B both are disposed outside of tube 251. Beams
of truss network 111 extend from the sides of tube 251 to one side of the rack
133B.
Each of the configurations of Figures 29-36 includes cylindrical
tubular principal member 321 with beams of truss network 111 secured to and
extending from the outer surface of member 321. The configurations differ on-
ly with respect to the jacking means related thereto. Thus, the configuration
of Figures 29 and 30 is to be used ~ith a pin-type jack and includes a plural-
ity of holes 323 extending through the wall of member 321. Such holes may be
arranged in a plurality of axial lines spaced azimuthally about member 321 as
shown in Figures 29 and 30. In the configuration of Figures 31 and 32, member
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321 has 2 smooth surface to be used with a friction-type jack such as those
manufactured by DeLong or Varco. In the embodiment of Figures 33-35, parallel
steel plates 327, 329 are attached to and extend from the outer surface of
member 321 along the length o member 321. Steel plate 331 is attached between
the outer edges of plates 327, 329 so as to form a flat surface spaced away
from member 321 and extending generally axially along member 321. Steel plate
331 has holes 333 extending therethrough so as to provide a rack-type means
for a pin-type jack. Alternatively, as shown in the configuration of Figures
36-38, a series of steel boxes 335, each having an outer plate 337 with a hole
therethrough can be secured in an axially-extending line to the outer surface
of member 321.
Referring -to the embodiment of Figure 39, mobile jack-up rig 11',
which is similar to rig 11 described supra except for the type of jacks and
specific leg embodiment, is shown jacked up by chain jacks 356 on chains 340
such as a system produced by Hydronautics, Inc. Chains 340 are suitably
fastened or anchored at the upper end of leg cords 339 near platform 13' by
chain arms 354 set on the end of leg cords 339. Chains 340 extend from arms
354 through jacks 356, jacks 356 being mounted on platform 13'. Chains 340
extend from jacks 356 to the lower ends of leg cords 339 and are wrapped around
neptune hooks 352 located near the end of leg cords 339 farthest from plat-
form 13'.
Variable cross-section portion 21 is similar to that of Figures 3
and 4 except that the constant cross-section leg cords 339 and 341 include
piles 343, 358, respectively~ driven through the hollow center of leg cords
339, 341 and through a suitable opening in mat 351 into seabed 39, and leg
cords 341 extend to the surface 345 of the water. Leg cords 339, 341 of the
embodiment of Figure 39 will ordinarily have a tubular configuration (see,
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~L5~3g~Z
e.g., the configurations of Figures 15-17 described supra) so that the piles
can be driven therethrough. Using such piles, rig 11' can be used as a bat-
tered leg, fixed platform similar to fixed platforms already in use. Unlike
a fixed platform, a rig 11' using the leg of Figure 39 can be recovered and
reused.
A pile driver 350 is suspended by a crane 348 or other suitably
lifting means by a suitable cable 349 and run around a sheave 347 on crane
348 and suitably attached to a winch 346 mounted on platform 13'. Crane 348
is suitably attached to leg cord 339 or to a derrick barge not shown.
When the mat 351 is resting on the sea floor 39 and platform 13' is
jacked up in a suitable position above the surface of the sea 345, piles 342,
343 are driven through the center, hollow portions of leg cords 339, respecti-
vely by pile driver 350. The piles 342, 343 are driven to a suitable penetra-
tion into the sea floor 39 by pile driver 350. After piles 342, 343 are
driven to a suitab~e depth, the piles 342, 343 are suitably welded at 357, 360
or grouted using cement 358 to leg cords 338, 341. After platform 338 is
welded or otherwise suitably attached to leg cords 338, 341, wells 344 can be
drilled Wells 344 may be located outside of the perimeter of platform 13'
as shown in Figure 39 if rig 11' is a production rig. Also leg cords 338,
341 may be used to support the conductors of wells 344.
Referring to the embodiment of Figure 40, mobile jack-up rig ll",
which is similar to rig ll' described supra except for the specific leg embo-
diment and illustration of the pile driving equipment, is shown jacked-up by
chain jacks 364 on chains 340.
Variable cross-section portion 21 is similar to that of Figures 3
and 4. Leg 365 includes leg cords 366, 369, with leg 366 braced by leg cord
369. Leg cord 369 connects to leg cord 366 by welding or other suitable tech-
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' ,
~S~3~2
nique at 375 which is near the surface of the water 345 at the maximum design
water depth of leg 365. As in the other embodiments, leg cords 369 are suit-
ably attached to leg cord 366 by brace members 372 and 373. Leg cord 370 sup-
ports leg cord 369 of the embodlment of Figure 40 and will ordinarily have a
tubular configuration (see, e.g., the configurations of Figures 15-17 described
supra) so that piles can be driven through pile guide 370. Leg cord 369 con-
nects to and is supported by pile guide 370 at a suitable point 376 by welding
or other suitable technique below the surface of the water 365 but above the
seafloor 39. The cant of pile guide 370 is steeper than the cant of leg cord
369. Piles 371 are driven through the hollow center of pile guide 370 and a
suitable opening in mat 368 into seabed 39 by means of a subsea hammer, or by
means of a ch~n jack or reverse osmosis system of coating the pile with metal-
lic paint and electrically charging the paint to lower friction) or by other
suitable means. After the pile 371 is driven to a suitable depth, the pile
is grouted with a suitable grout 381 to hold the pile 371 to the pile guide
370.
Referring to Figure 42, a cluster of pile guides 372, 373 and 374
are suitably attached to a brace leg cord 369' by members 378, 379 and 380 and
connected by suitable welding or other connection to leg cord 369'. Piles
375, 376 and 377 are driven through pile guides 374~ 373, and 372 respectively
into the seabed 39 to a suitable dep~h.
A leg embodiment similar to the leg embodiment of Figure 40 is shown
in Figure 43. However, a constant cross-section leg portion 21 supports the
variable cross-section leg portion 21, which is similar to that of Figures 3
and 4. Leg cord 400 of constant cross-section leg portion 21 may be adapted
to receive pilings.
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