Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Packaround of the Invention
Jackup barges having three legs are customarily
used in erecting temporary drilling platforms ~bcve the
ocean at offshore locations. ~n offshore drilling barge
must be positioned substantially above the level of the
water, even higher than the wave action anticipzted in 2
violent storm to enable offshore crilling. The platform
normally weighs several million pounds. Norm211y, it is
substantially large typically measuring 2S much as two
hundred feet along a side. The platform is supported on
three legs. The legs extend from the platform to a bottom
plate which enables them to rest on the mud beneath the body
of water. ~n elevating mechanism lifts the platform on the
three legs at the time of e~evation. Ty~ically, the barge
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is towed with the legs raised and the platform floating on
the water. ~t the time of erection, the legs are lowered
until they encounter the bottom, and they support the
platform as it is raised above the water.
The legs are quite sizable. On a modern rig, the
legs may be as much as four or five hundred feet tall. The
legs typically are formed of a triangular open lattice work
which is as much as fifty feet across. The triangular shape
is open and is typically formed of structural members as
large as four or five feet thick. Various and sundry types
of structural members are used in the construction of jackup
legs. Box beams, I beams, flanged plates, and tubular
members have been used all to form various and sundry jackup
legs. Jackup legs typically must have horizontal beams to
reinforce the three corner members. In addition they
normally include reinforcing members at angles extending
from corner to corner to give rigidity to the entire leg
structure. The horizontal beams and the angularly
positioned reinforcing members basically tie the three
corner members together, thereby defining a structure which
is able to support the weight of the drilling barqe.
It is necessary for the platform to include
equipment which lifts the platform on the jackup legs. Many
types of equipment have been suggested including devices
which insert pins into holes in the legs, rack and pinion
mechanisms and the like. The leg thus must necessarily be
constructed with a mechanism extending along its length for
engagement with the lifting mechanism and this typically
includes at least a set of holes or a rack. Typically, the
rack or the holes must be aligned with the mechanism on the
platform and to this end, appropriate flanged plates or
alignment members are incorporated. The rack and alignment
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members are typical devices known previously are necessary.
Constructions used in the past have further
required additional strength in that they have to be formed
with exposed racks and appropriate alignment flanges. While
these may impart vertical strength and otherwise serve as
support columns enabling the platform to be raised on the
leg, they have an unfavorably shaped profile presented to
the water. The profile of the leg in the water is very
important. Ordinarily, the leg is an open lattice work.
This enables waves to pass through the leg. Nevertheless,
the leg is not simply transparent to wave action. The
tendency of the leg to bend under wave impact is
proportional to a factor determined by the streamlining of
the leg as viewed from any direction. It is not possible to
know in advance the direction from where waves originate.
Accordingly, the three legs of a jackup barge must all be
designed to have a required resistance to bending in all
directions. That is to say, it is not possible to know in
advance the direction of the wave action and additionally to
know the precise azimuthal positioning of the drilling rig
relative to the wave action. Accordingly, the leg of the
drilling rig must all resist bending in all directions
around the compass. Further, the profile of the leg or the
streamlining as viewed in any particular direction must be
made optimum. The most optimum arrangement is a circular
frame member at each corner of the leg. This construction
presents the minimum resistance to wave action without
regard to the direction of impingement. However, it is well
nigh impossible to use a circular frame member because the
leg must incorporate a rack and appropriate guides to enable
the platform elevation equipment to operate. Some jackup
rig designs include vertical racks attached to legs made of
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circular stock. The rack presents an irregularity in shape
to the wave action and detracts from the streamlined shape
of the circular leg. ~ circular leg is difficult to use
as a guide because it does not provide an edge for
gr~sping. If the guide fits around the entire leg, the leg
must be built to rather expensive tolerances. Accordingly,
the present invention has been devised.
This device enables the use of circular stock in
the three corners of the triangular legs. This reduces the
profile of the completed legs to a minimum, thereby reducing
the bending which occurs in wave action and further
increasing the strength of the leg. This results in a
reduction of metal in the leg. In a representative leg for
a full size drilling rig, the leg might weigh as much as six
million pounds if constructed in accordance with teachings
of the prior art. Incorporating the leg construction of
this disclosure, a reduction of one million pounds or more
of metal in the leg is possible. The reduction of bending
moment reduces the design criteria in the hull itself,
thereby reducing the weight and cost of the hull. The
overturning moment is also reduced which allows closer
spacing of the legs or a smaller hull. This reduces the
cost of construction, increases the speed of towing,
increases the bending resistance, and otherwise provides a
more efficient platform design. As a consequence, the rack
for cooperation with the elevation equipment and the guides
which provides positive engagement therewith are recessed in
the circular cross section of the corner members of the leg
to thereby provide an optimum reduction in profile.
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Summary of the Invention
This invention is for use in jackup barges typically
having three legs where each leg is formed of a set of three
vertical corner members. The three vertical members are each
constructed in accordance with the teachings hereof. Each
one is formed of circular stock. Each one has on the inside
a vertical rack with teeth formed for engagement by elevation
equipment carried on the platform. A vertical slot is formed
in the circular members of a specified width and an undercut
on both sides is formed to enable a walking guide mechanism
to be inserted. The undercuts are ad~,acent to the teeth of
the rack.
More specifically the invention consists of a vertical
frame member adapted to be positioned at a corner of the leg
and further adapted to cooperate with a guide means on the
rig, the frame member comprising
an elongate structural member of circular cross section
which includes a parallel slot means on the exterior thereof,
said slot means having a width sufficient to enable insertion of
a guide means supported by a jack up rig into the slot means
and having a length at least equal to the desired length of
travel of the leg relative to the rig;
an undercut adjacent to said slot means which extends
parallel thereto for locking a guide means therein which guide
means has a neck and a wider portion supported by the neck and
wherein said undercut and said slot means are profiled to match
the profile of the guide means;
a rack of teeth supported by said structural member on
the interior of said elongate structural member and facing said
slot means, said slot means and said teeth forming a means for
receiving a drive gear inserted into the teeth for imparting
axial movement to said structural member; and
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wherein the circular cross section surrounds said rack
whlch is ~oined thereto by means positioned axially of said
structural member and joined to said rack.
Description of the Drawings
Fig. 1 is a side view of a jackup barge which is
raised on open framework legs in accordance with the
teachings with this invention;
Fig. 2 is a sectional view along the line 22 of
Fig. 1 showing a triangular leg constructed in accordance
with the teachings of the present invention cooperative with
elevation equipment carried on the platform,
Fig. 3 is a side view of the elevation equipment
including a plurality of pinions engaged with a rack
recessed within the circular leg construction of the present
invention;
Fig. 4 is a sectional view through the circular
leg construction of the present invention showing an
internal rack and adjacent undercuts by which a guide
mechanism is inserted in the leg to secure it relative to
the platform;
Fig. 5 shows an alternative embodiment to that of
Fig. 4; and
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Fig. 6 is a sectional view along the line 6-6 of
Fig. 4 showing the rack on the interior of the leg.
DescriEtion of the_Preferred Embodiment
Attention is directed to Fig. 1 of the drawings.
In Fig. 1, a jackup platform for supporting a drilling rig is
shown at 10. A floatable hull or platform 12 is included.
It floats on the water when it is being towed. When the
drilling rig 10 is located at the desired location, the legs
14 are lowered until the bottom plate 16 rests on the
bottom. The process is continued, thereby raising the
platform 12 above the water. It is typically raised 50 or
60 feet above the normal level of the water to be positioned
high above the wave action on the water. When this occurs,
the weight of the entire drilling rig is supported on the
legs. There are typically three legs arranged in the
triangle.
Each of the legs 14 are normally similar.
typical construction is an arrangement whereby the leg 14
includes three members arranged approximately equidistant
from one another to define an equilateral triangle. They
may be positioned as much as 50 feet apart. In this
invention, the leg 14 is preferably formed of circular stock
at each corner. The three corner members typically will
range as large as four or five feet in diameter. They are
joined together by various beams 18 and angle braces 20.
The number, size and location of the beams 18 or the
braces 20 is of no particular concern to this disclosure.
Rather, this disclosure is directed to the three typical
corner members which extend vertically on the leg 14. These
are the major structural supports. As the major structural
supports, they carry the weight of the drilling rig 10.
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Moreover, when constructed as taught by this disclosure,
they are able to withstand tremendous bending forces as a
result of the waves which strike the drilling rig 10.
In Fig. 2 of the drawings, a portion of the barge
12 is shown. The leg 14 extends through an opening in the
barge 12. The opening 22 is approximately triangular to
match the shape or cross section of the leg 14. The leg 14
includes several beams 20 which extend between the major
structural members located at the corners of an equilateral
triangle, the numeral 24 identifying the vertical members.
The three vertical members are all preferably identical.
That is, they are of equal strength, equal size and are all
meshed with the guide mechanism for use in the alignment of
the leg with the platform 12.
Ps shown in Fig. 2, the leg 14 is thus formed of
three major vertical frame members 24. They support the
load placed on the leg. An elevation device is indicated at
26. Preferably, one is located in each corner of the leg
to cooperate with each of the vertical members 2q. One is
shown with the top removed in Fig. 2 to disclose a shaft 28
which supports a drive gear 30. The gear 30 extends through
a slot and engages a vertical rack to lift the leg 14. This
will be described in detail hereinafter.
In Fig. 3 of the drawings, the platform 12 is
illustrated. It is typically a closed vessel to enable it
to float on the water when under tow. The bottom of the
hull incorporates a lower guide mechanism 32, and an upper
guide mechanism 39 is carried on the elevating apparatus 26.
They are similar in construction and differ in location.
Each one incorporates a tee-shaped protruding guide member
36 shown in Fig. 4. It has a somewhat narrow neck 38 and
protruding ears at 40. The ears are symmetrical and
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protrude on each side, thereby forming a locking guide which
fits within an appropriate shaped internal vertical slot of
the corner member 24. The leg member 24 is provided with a
vertical slot 42 extending vertically along its exposed
side. The sectional view of Fig. 4 shows reinforcing beams
20 connected at one side of the apparatus, and the slot is
located oppositely of them considered jointly. This exposes
the slot for easy cooperation with the guide mechanism 32
and 34. Each of the guide mechanisms 32 and 34 incorporates
the tee-shaped guide 36. It extends into the slot 42 and is
wider, thereby locking the guide 36 into position.
The member 24 is constructed of circular stock.
This is shown in Fig. 4 where a first segment a4 is welded
to a second segment 46 and a third curved segment 48 is
opposite the segment 44. These join together to
substantially define the exterior of the circular structure.
The gap which is left on the righthand side of Fig. 4 is
substantially closed by plates which are rolled into the
profile shown. The shaped plates include the one shown in
50 and the symmetrical plate 52, the two formed identically
but being mirror images of one another. They are welded at
the lefthand edges at the welds which are common for the
external segments 44, 46 and 48. In particular, they
terminate at curved exposed portions 54 and 56 which
portions are on the exterior of the circular member 24
thereby defining a portion of the circular surface and
further defining the vertical slot 42 for insertion of the
guide 36.
The shaped plates 50 and 52 are joined to the base
58 of a rack 60. The rack 60 has protruding teeth as better
shown in Fig. 6. The base 58 is a member extending the
length of the circular member 24. The base 58 is preferably
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welded to the plates 50 and 52. This anchors it in
location. It is of substantial stock to enable it to
support the load without shearing the teeth from the rack
60. The teeth 60 extend toward the slot 42. The teeth 60
are provided with lateral support on both sides by
incorporation of the shaped beads 62 and 64 on each side.
The beads are identical in profile or cross section. The
beads 62 and 64 are welded to the shaped plates 50 and 52
and are parallel to the rack 60. They abut the teeth 60 on
the rack and provide lateral support. Moreover, they define
a bearing surface which prevents the guide 36 from extending
to deeply into the slot 42. The guide 36 is thus captured
by the beads 62 and 64 and is not permitted to contact the
crown of the teeth. Clearance is shown in Fig. 4 between
the guide 36 and the teeth of the rack.
The internal construction of the circular member
provides substantial strength. The member 24 is
substantially strong as a result of the manner in which the
components are assembled. The base of the rack, for
instance, imparts additional vertical strength to the
structure. The base serves as a vertical reinforcement
member. The shaped plates 50 and 52 increase the resistance
of the member 24 against bending. They also cooperate to
define the vertical rack when assembled and the undercut
slot 42 to enable the guide 36 to hold the member at a
specified location.
Returning to Fig. 3 of the drawings, the guide
supports 32 and 34 each incorporate a guide as described
with reference to Fig. 4. When the leg 14 is in position
relative to the platform 12, the guide mechanisms 32 and 34
secure the leg at the required position. This enables the
elevating mechanism 26 to engage the leg and raise or lower
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the platform 12 relative to the leg. The elevating
mechanism preferably incorporates the drive gear 30 which
extends into the slot and engages the rack in the member 24.
Preferably, the elevating mechanism 26 includes two or three
drive gears which are spaced apart, each of which has teeth
which match the teeth on the rack 60. The drive gears 30
are driven in unison. Thus, the circular member 24 is held
at the requisite location to enable the drive gears to
engage the leg and raise or lower the leg as the case may
be.
The ]eg of the present invention thus transfers
the raising and lowering movement from the elevating
mechanisms 26 to the leg 14. This enables the platform 12
to be raised or lowered. This assures that the leg is held
in the necessary position for this operation.
Fig. 5 discloses an alternative form. The
circular member 24 is the same on the exterior but is
constructed differently on the interior. The version as
shown in Fig. 4 is formed of shaped plates. The version
shown in Fig. 5 is preferably formed of shaped plates. The
numeral 72 identifies a casting which has the base and the
teeth of the rack (optionally along both faces of the rack)
integrally formed and joined to a pair of angled plates 74
and 76. They position the castrack internally of the
circular member. Moreover, they provide strength against
bending. The casting 72 thus is fixed in position by the
reinforcing gussets 74 and 76 duplicated on both sides. It
is similar in that it includes the exposed slot 80 with the
appropriate undercuts for enabling the drive gear 3C to
engage the teeth. The slots 80 are duplicated to enable the
rack to be engaged from both sides, i.e., by a dual leg
elevation system. The dual slots are optional, not
mandatory. Each slot is able to receive a guide in it.
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The leg is aligned with the guides 36. The upper
or lower end of the leg is made clear of obstructions so
that the tee-shaped guide 36 can be inserted into the slot.
It is captured and constrained to movement only in the
vertical direction. The elevating mechanisms 26 at each
corner must run at the same rate and to this end, they are
preferably driven from a common source and are otherwise
provided with common drive rates. To this end, the drive
gears 30 are preferably identical in size and are rotated at
the same speed. A suitable motor is preferably connected to
each one to rotate it, typically by installing a motor in
the elevating equipment 26 which has an output shaft engaged
with the drive gear 30.
The difference in the embodiments of ~igs. 4 and 5
is more a difference in construction technique, the strength
of the structures being approximately the same. The two
embodiments have in common the incorporation of an
internally reinforced vertical member having the slot on the
exposed side adjacent to the internal rack and the undercut
guideway for the guide 36.
The guide 36 is tee-shaped; it will work equally
well if it has an added laterally directed plate parallel to
the skin of the leg member and on the outside of the column.
Thus the guide clamps the skin at the edge of the slot
means.
When the leg 14 is in the water, the circular
member 24 has the most streamlined shape possible, and hence,
the amount of metal required for the leg 14 is reduced to
obtain strength against a specified wave action in the leg.
This is particularly helpful in reducing the total weight of
the leg and hence the cost of fabrication. The slot 42 does
not create any particular problem with wave action. Even if
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the waves impinge directly on the slot, the slot is relatively
narrow, and for all intents and purposes, it does not materially
deviate from the streamlined shape obtained by the circular
cross section of the member 24. As a consequence, the
invention provides the most possible streamlined shape
without regard to the direction of propogation of the waves
acting against the leg 14.
The foregoing is directed to the preferred embodiment
of this invention, but the scope thereof is determined by the
claims which follow.
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