FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Method of building a jack-up rig
APPLICANTS
Larsen & Toubro Limited, Floating Systems Business Unit, Engineering and Construction Division, Powai Campus (W), Saki Vihar Road, Mumbai 400 072, Maharashtra, India, an Indian company
INVENTORS
Kasturirangan Narayanan, Varghese George and Pal Chirag, all of of Larsen & Toubro Limited, Floating Systems Business Unit, Engineering and Construction Division, Powai Campus (W), Saki Vihar Road, Mumbai 400 072, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a method of building a jack-up rig.
BACKGROUND OF THE INVENTION
Jack-up rigs are a type of mobile platforms or offshore structures that are mainly used for offshore drilling of oil wells. A jack-up rig essentially comprises a hull provided with legs and footings (spud cans) and equipments mounted on the hull. The most popular jack-up rig design comprises 3 legs, but there are also jack-up rigs with 4 or more legs. Jack-up rigs are generally placed in relatively shallow waters, usually less than 400 feet (120 m) of water and are designed to stand still on the sea floor, resting on the legs. The equipments mainly comprise three types namely marine equipment, mission equipment and elevation equipment (lifting mechanism). After the jack-up rig is towed to a site, the lifting mechanism allows to lower the legs into the seabed and raise the hull to provide a stable work deck capable of withstanding the environmental loads.
The hull is a watertight structure that supports or houses the equipments and accommodates personnel and their belongings and food articles, thus enabling the jack-up rig to perform its tasks. When the jack-up rig is afloat, the hull provides buoyancy and supports the weight of the legs and footings, equipments, and the other loads on the hull. The legs and footings of a jack-up rig are steel structures that support the hull when the rig is in the elevated mode and provide stability to resist lateral loads. Footings help to increase the soil bearing area thereby reducing required soil strength.

A jack-up rig operates in three main modes namely transit mode when moving from one location to another, elevated mode when raised on its legs, and jack up or down mode when the rig is between afloat and elevated modes. Each of these modes has specific precautions and requirements to be followed to ensure smooth operations of the jack-up rig. A jack-up rig can be motorised or self propelled.
Jack-up rigs are generally built on land by first building the hull and installing a part of the equipments on the hull and also installing sufficient portion of the legs on the hull that are required to jack-up the hull. The hull with the part of the equipments is lifted on the portion of the legs already built on the hull and the remaining portion of the legs is built and the remaining equipments are installed on the hull. Skid ways or slip ways are generally used to skid out the jack-up rigs into the sea. The skid ways are normally associated with submersible barge or modified dumb barge and slipways are normally associated with skid beams and multi-ton rollers or SPMTs (self propelled modular transporters) or air gas bags. Skid ways are prohibitively expensive and require high investments. Slipways are also very expensive and require relatively large area for making a gradual approach slope into the water.
Jack-up rigs are also built in dry docks (drydocks). Dry dock is a huge and massive permanent construction or structure mainly comprising a basin or vessel that can be flooded with water and drained. A typical drydock, popularly known as graving dock, is usually made of earthen berms and concrete and is closed by gates. A graving dock requires huge capital investment to build it and also high maintenance cost. Therefore, continuous use of the dry dock is necessary to

recover the initial investments made. This necessitates continuous rotation of the jobs in the dry dock which means a large and constant concentration of labour to speed up activities inside the dry dock.
Rig walking is also used to build jack-up rigs. In rig walking the nose and aft legs of the hull are lifted up and the hull is twisted and inclined to pivot the hull about the aft using sand dunes. Rig walking is quite time consuming and can possibly damage the hull due to stresses formed as a result of twisting of the hull. During rig walking, it is necessary to secure all the equipments on the hull and reinforce and strengthen all the locations of pivoting of the hull. This is quite difficult and cumbersome to carry out and is expensive and requires a large concentration of labour.
SUMMARY OF THE INVENTION
According to the invention there is provided a method of building a jack-up rig
comprising the steps of:
(i) identifying a building site having earth of the required load bearing
capacity in the proximity of a sea;
(ii) forming a plurality of spaced apart reinforced open trenches at the site
corresponding to the legs of the jack-up rig;
(iii) building the legs and spud cans of the jack-up rig at the site and lowering
the legs with spud cans in the open trenches;
(iv) building the hull of the jack-up rig at the site around the legs on stools
supported in the area between the trenches;

(v) installing equipments on the hull;
(vi) jacking up the hull on the legs and removing the stools;
(vii) dredging the site below the sea level to form a recessed area having a
mouth opening into the sea and having a size corresponding to the hull that
would submerge in the water in the recessed area with a clearance between the
bottom of the hull and bottom of the recessed area and allowing sea water to
flow into the recessed area;
(viii) lowering the hull on the legs and submerging the hull in the sea water in
the recessed area; and
(ix) floating out the jack-up rig into the sea after raising the legs.
According to an embodiment of the invention, the reinforced open trenches are formed by driving open caissons at the site and excavating the earth from within the open caissons and retaining the caissons in place in the open position thereof.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
Figs 1 to 6 of the accompanying drawings schematically illustrate the various steps of the method of building a jack-up rig according to the invention. A construction site 1 having earth of the required load bearing capacity for building a jack-up rig is identified in the proximity of a sea (not shown). Instead of sea, the construction site also can be in the proximity of a river or creek (not shown) opening into the sea. Therefore, reference to the term sea in the specification should be understood to include a river or a creek communicating

with the sea. A plurality of spaced apart reinforced open trenches 2 are formed at the construction site corresponding to the legs of the jack-up rig by driving open caissons 3 at the site and excavating the earth from within the open caissons and retaining the caissons in place in the open position thereof. The legs 4 and spud cans 5 of the jack-up rig are built at the site and are lowered in the open trenches (Fig 1). The hull 6 of the jack-up rig is built at the site around the legs on stools 7 supported in the area between the trenches (Fig 2). The equipments 8 are installed on the hull. The hull is jacked up on the legs and the stools are removed (Fig 4).
The site is dredged below the sea level to form a recessed area 9 having a mouth (not shown) opening into the sea and having a size corresponding to the hull that would submerge in the sea water in the recessed area with a clearance between the bottom of the hull and bottom of the recessed area (Fig 5). The portion of the hull that would submerge in the water in the recessed area with a clearance between the bottom of the hull and bottom of the recessed area is generally understood to be the draft in the technical field of the invention. In case the construction site selected for building the jack-up rig contains impediments such as rocks, the impediments are to be obviously removed before dredging.The hull is lowered on the legs and submerged in the sea water marked 10 in the recessed area and the jack-up rig is floated out into the sea after raising the legs (Fig 6).
According to the invention, dry docks and skid ways or slip ways and associated barges, skid beams, multi-ton rollers or SPMTs or air gas bags and rig walking, all have been eliminated thereby eliminating associated disadvantages. The method of

the invention is very simple and easy and convenient to carry out and is also less time consuming and less expensive in that according to the method the legs and spud cans of the jack-up rigs are built and lowered in the reinforced open trenches at the site. The hull is built around the legs, equipments are installed on the hull, the construction site is dredged below the sea level and the jack-up rig is floated out into the sea. In case any inclination test is required to be performed on the jack-up rig, it can be easily carried out after raising the legs of the jack-up rig submerged in the recessed area and before floating out the jack-up rig into the sea. The invention does not require any permanent structures and equipments at the site to carry out the method.
It should be understood and appreciated that the scope of the invention need not necessarily be confined to building of jack-up rigs. The invention can be advantageously used for any other floating structures. The reinforced open trenches also can be made in any other manner. Such variations of the invention are obvious to person skilled in the art and should be construed and understood to be within the scope of the invention.

We claim
1. A method of building a jack-up rig comprising the steps of:
(i) identifying a building site having earth of the required load bearing
capacity in the proximity of a sea; (ii) forming a plurality of spaced apart reinforced open trenches at the site
corresponding to the legs of the jack-up rig; (iii) building the legs and spud cans of the jack-up rig at the site and lowering the legs with spud cans in the open trenches;
(iv) building the hull of the jack-up rig at the site around the legs on stools supported in the area between the trenches; (v) installing equipments on the hull; (vi) jacking up the hull on the legs and removing the stools; (vii) dredging the site below the sea level to form a recessed area having a mouth opening into the sea and having a size corresponding to the hull that would submerge in the water in the recessed area with a clearance between the bottom of the hull and bottom of the recessed area and allowing sea water to flow into the recessed area;
(viii) lowering the hull on the legs and submerging the hull in the sea water in the recessed area; and (ix) floating out the jack-up rig into the sea after raising the legs.

2. The method as claimed in claim 1, wherein the reinforced open trenches are formed by driving open caissons at the site and excavating the earth from within the open caissons and retaining the caissons in place in the open position thereof.