WO1992008849A1

WO1992008849A1 - Floatable structures

Info

Publication number: WO1992008849A1
Application number: PCT/GB1991/001975
Authority: WO
Inventors: John Richard Yorke Gleadowe
Original assignee: Seacore Limited
Priority date: 1990-11-13
Filing date: 1991-11-11
Publication date: 1992-05-29
Also published as: AU8871091A; GB9024667D0

Abstract

A floatable structure (10, 12) such as a jack-up barge has a plurality of legs (14) upon which the structure may be supported and raised. Each leg is pivotable between an upright operative position and a recumbent storage position and means such as hydraulic rams (22) are provided for producing pivoting of said legs between said positions. Each leg may be carried by a jacking collar (16) with respect to which the leg is jackable to extend the leg when in the operative position, each jacking collar being pivotable by said rams to carry the respective leg between said operative and storage positions.

Description

FLORTABLE STRUCTURES

The present invention relates to floatable structures having a plurality of legs upon which the structure may be supported and raised, e.g. jack-up barges and rigs.

Floatable structures of the kind described above are used in offshore drilling and offshore production. They typically comprise a hull structure providing the necessary buoyancy for floating and a plurality of legs, e.g. 3, 4, or 5 legs, upon which the hull structure can be jacked-up clear of the water when at the required location. To move the floatable structure, the hull structure is jacked-down the legs until it is floating and the legs are then jacked- up to their maximum extent. The legs are heavy structures and the weight and air resistance of that portion of the legs extending above the hull structure limits the controllability and seaworthiness of the floatable structure. Any portion of the legs remaining in the water substantially increases the resistance of the floatable structure to movement through the water and again decreases the controllability and seaworthiness of the floatable structure.

Russian Patent Specification No. 791842 discloses a jack-up rig in which the lower part of the legs, below the jacking mechanism and below the level of the surface of the water, are hinged such that a lower portion of each leg can be brought from an upright operative position to a horizontal position below the water surface. Whilst this arrangement substantially decreases the draught of the rig when floating, it does not reduce the problems caused by the upper part of the legs extending high into the air above the surface of the water and neither does it decrease the length of leg immersed in the water. The resistance to movement of the rig in the direction in which the hinged legs extend may be decreased but the susceptibility to the rig to respond to water currents running transverse to its direction of movement will remain substantial as any such cross-currents will act on the whole length of the underwater part of the hinged legs.

Furthermore, the hinging of the legs greatly increases the length of the rig and will be liable to substantially decrease its steerability. This latter drawback of the arrangement described in the Russian specification will be even more severe if such a system is adapted for use on a self-propelled structure, such as a barge. The present invention provides a floatable structure having a plurality of legs upon which the structure may be supported and raised, wherein each leg is pivotable between an upright operative position and a recumbent storage position and comprising means for producing pivoting of said legs between said positions.

Preferably, when in the storage position the legs are substantially horizontal and preferably, when in the operative position, the legs are at least substantially vertical. Each leg may be carried by a mounting means with respect to which the leg is jackable to extend the leg when in the operative position, said mounting means each being pivotable by said pivoting means to carry the respective leg between said operative and storage positions. One or more hydraulic rams may be connected between the mounting means and a body portion of the floating structure for producing said pivoting movement. Other forms of means for producing said pivoting movement may be used, such as winches and chains or cables. The floatable structure may be a jack-up drilling barge and it may be self-propelled. Alternatively however, the floatable structure may be a rig and/or may be moveable only by towing.

The invention will be further described with reference to the illustrative embodiment shown in the accompanying drawings in which:- Figure 1 is a perspective view of a barge according to the invention with its legs in the operative position and its hull raised above the water;

Figure 2 is a perspective view of the barge of Figure 1 with its legs in the storage position and its hull floating in the water;

Figure 3 is a side elevation view of a pivotable leg mounting collar member as used in a second embodiment according to the invention. Figure 1 shows a drilling barge having a hull 10 supporting a deck 12 at each corner of which is a jackable leg 14 carried by a pivoting jacking collar 16 acting as a mounting means for the leg. Each jacking collar 16 is pivotable about a horizontal axis at a pivot pin 18 passing through a pair of plates 20 extending parallel to one another from one face of the collar 16. A pair of hydraulic rams 22 are provided as means for producing pivoting for each leg and are connected between the hull 10 and an upper portion of the respective jacking collar 16. When in the operative vertical position illustrated in Figure 1, each leg is jackable with respect to the respective jacking collar 16 by a known rack and pinion jacking mechanism schematically illustrated by the jacking gear boxes 24 shown by each collar 16. When the legs 14 have been raised such that the collars 16 are approximately midway along the length of their respective legs 14, actuation of the hydraulic rams 22 causes pivoting of the jacking collars 16 and the legs 14 about the horizontal axis defined by the pivot pins 18 to bring the legs 14 into the horizontal side by side arrangement illustrated in Figure 2. The legs 14 are then completely clear of the water but neither extend high above the deck of the barge nor greatly extend the length of the barge.

A somewhat modified and preferred pivot mechanism for the legs is illustrated in Figure 3. Pivot pin 18 is carried by a pair of mutually parallel deck mounted support plates 26 and the plates 20 attached to the jacking collar 16 are reduced in size compared to the arrangement shown in Figures 1 and 2 so that the horizontal pivoting axis is raised. A locking pin mechanism schematically illustrated at 28 is provided acting between the plates 20 and 26 for locking the jacking collar in the operative vertical position.

Whilst the invention has been described with reference to the embodiments illustrated in the accompanying drawings, many modifications and variations thereof are possible within the scope of the invention.

Claims

1. A floatable structure (10, 12) having a plurality of legs (14) upon which the structure may be supported and raised, characterised in that each leg is pivotable between an upright operative position and a recumbent storage position and comprising means (22) for producing pivoting of said legs between said positions.

2. A floatable structure as claimed in Claim 1, wherein each leg (14) is carried by a mounting means (16) with respect to which the leg is jackable to extend the leg when in the operative position, said mounting means each being pivotable to carry the respective leg between said operative and storage positions.

3. A floatable structure as claimed in Claim 2, wherein one or more hydraulic rams (22) are connected between said mounting means (16) and a body portion (10) of the floatable structure for producing said pivoting movement.

4. A floatable structure as claimed in any preceding claim, which is a jack-up barge.