Hydraulic and earth engineering – Marine structure or fabrication thereof – With work deck vertically adjustable relative to floor
Reexamination Certificate
1999-03-05
2001-05-15
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
With work deck vertically adjustable relative to floor
C254S097000
Reexamination Certificate
active
06231269
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an offshore rig suitable for conducting mineral exploration and production operations, and more particularly to a self-elevating jack-up rig incorporating a releasing mechanism for a rack chock.
Jack-up rigs have been extensively used as the types of offshore working platforms especially suitable for deployment in medium water depth. Generally, this type of rig uses jackable legs for supporting a working platform, or hull at an elevated position in a selected location. When a jack-up rig is towed to a desired location, the legs extend upwardly through wells in the hull so as not to interfere with the towing. Once the rig is delivered to the selected location, the legs are lowered to the bottom of an ocean, and powerful jacks elevate the hull to an operating level above the waves.
The hull and the legs are rigidly engaged with each other through a system of rack teeth on the supporting legs and opposed, matching rack sections of rack chocks. The rack chocks are moved horizontally and vertically to allow a mating alignment with the leg chords. When the alignment is completed, the rack chock rigidly connects the hull to the legs of the rig. During operation of the rig, the legs and the hull remain locked in their unitary connection, resisting overturning moments imposed on the legs by wave forces.
When the legs and the hull are rigidly engaged, considerable pressures act on the surfaces of the meshed teeth of the leg chords and the rack chocks. In effect, the teeth become locked, and withdrawal of the rack chock from engagement with a leg chord becomes extremely difficult.
Still, under certain circumstances, such when repositioning the hull or the entire rig, the engagement between the legs and the hull must be broken. Oftentimes, conventional methods and equipment cannot generate sufficient force to release a “frozen” jack.
Heretofore, various methods have been employed for releasing of a screw jack. One of the conventional methods involves burning of the jack bearing plate or cap in order to break the rigid engagement between a leg chord and a rack chock. This method is labor-intensive, time-consuming and relatively expensive. Additionally, the cap must be replaced before the screw jack is moved laterally into an engagement with the leg teeth to reinstate the rigid engagement of the hull to the legs.
Other known techniques involve the use of a wedge-shaped device, wherein an inclined surface of the wedge facilitates release of the chock mechanism. This design is disclosed in U.S. Pat. Nos. 5,486,069 and 5,611,645 issued to John O. Breeden. Both patents disclose a fixation system that uses a toothed chord chock, which moves both horizontally and vertically. The toothed rack chock has upper and lower inclined surfaces. The fixation system includes an upper and lower wedge, which rides on upper and lower fixed inclined surfaces. The upper and lower wedges move to engage the upper and lower inclined surfaces of the rack chock and release the engagement between the leg chord and the rack chock. While such design can work satisfactory in many cases, there exists a need for a more straightforward design for releasing of a rack chock.
The present invention contemplates elimination of drawbacks associated with prior designs and provision of an improved mechanism for releasing of a rack chock from its rigid engagement with a leg chord.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a jack-up rig with a rack chock releasing mechanism.
It is another object of the present invention to provide a rack chock releasing mechanism, which prevents locking of the rack chock in relation to a leg chord.
It is a further object of the present invention to provide an improved jack-up rig assembly, wherein the danger of a frozen rack chock is eliminated.
These and other objects of the present invention are achieved through a provision of a worm gear assembly operationally connected to a frame that carries a rack chock of a jack-up rig. The worm gear assembly comprises a tooth wheel with plurality of teeth disposed about a circumference of at least a portion of the tooth wheel and a worm gear member. The teeth have inwardly concave upper surface. The tooth wheel has a hollow body mounted on a shaft that is operationally connected to the rack chock.
The worm gear member is provided with a worm thread about a middle portion thereof, the thread having a generally frustoconical configuration. The worm gear member has a central shaft connected to a drive motor, and when the thread is engaged with the teeth of the tooth wheel rotational force is transmitted from the drive motor to the tooth wheel shaft.
By causing rotation of the tooth wheel, a moving force is imparted on the rack chock to facilitate positioning of the rack in engagement with a contact surface of the leg chord and disengagement therefrom when the tooth wheel is rotated in an opposite direction.
REFERENCES:
patent: Re. 32589 (1988-02-01), Goldman et al.
patent: 3343371 (1967-09-01), Heitkamp
patent: 4662787 (1987-05-01), Tatsuguchi
patent: 4813814 (1989-03-01), Shibuta et al.
patent: 5921714 (1999-07-01), Goldman
patent: 5943919 (1999-08-01), Babinski
patent: 6030149 (2000-02-01), Foo et al.
Geiger, Sr. Paul
Shear Morris
Bagnell David
Friede & Goldman, Ltd.
Keaty Professional Law Corporation
Singh Sunil
LandOfFree
Apparatus for releasing a rack chock of a jack-up rig does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for releasing a rack chock of a jack-up rig, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for releasing a rack chock of a jack-up rig will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2562738