TECHNICAL FIELD
[0001] The present invention relates to a working ship for installing large offshore structures,
and more particularly to a working ship for use in transporting a large-scale offshore
structure, such as an offshore plant, to the site of installation and installing the
structure on a foundation structure which is built offshore.
BACKGROUND ART
[0002] Offshore structures, such as equipment for submarine oil fields and offshore plants,
to be installed on offshore foundation structures are large-sized and heavy, so that
it is impossible to build the structure in the form of an assembly and install the
assembly in place with use of a crane ship or the like. Accordingly it has been conventional
practice to build such a structure in the form of divided blocks of relatively small
sizes in accordance with the capacity of the crane ship, load these blocks onto a
deck barge moored alongside the quay of the factory or brought into the deck with
use of an offshore crane or gate-shaped crane in the factory, transport the blocks
to the site of installation, install the blocks on a foundation structure one after
another with use of the crane ship which structure has already been built, and thereafter
connect the blocks together by piping, wiring, etc. This method therefore has the
problem of involving large amounts of work for delivering the blocks from the factory,
installing them at the offshore site and connecting the installed blocks, being inefficient
and consequently necessitating a prolonged period of construction and an increased
cost.
[0003] The object of the present invention is to provide a working ship which is adapted
to easily transfer a large-sized offshore structure built in the form of an assembly
or large blocks thereof onto a foundation structure so that the large-sized offshore
structure can be constructed and installed in place within a greatly shortened period
of time.
DISCLOSURE OF THE INVENTION
[0004] The working ship of the present invention for installing a large offshore structure
comprises a lower hull, a plurality of guide posts extending upward from opposite
side portions of the lower hull, an upper hull supported at opposite side portions
by the guide posts and movable upward and downward, and lifting means for moving the
upper hull upward and downward along the guide posts. Accordingly the large offshore
structure, which is built in the form of an assembly, or large blocks thereof can
be loaded onto the upper hull and transported to the site of installation, where the
upper hull is lifted along the guide posts to the same level as a foundation structure,
with the working ship held in the vicinity of the foundation structure, so that the
offshore structure or blocks thereof can be transferred from the upper hull onto the
foundation structure easily without using any crane ship or the like. It is therefore
possible to build large offshore structures in the form of an assembly or as divided
in blocks of larger sizes, consequently making it possible to construct larger portions
in a factory under careful control. Thus offshore structures can be built with an
improved quality within a shortened period of time. Furthermore, the invention facilitates
installation at the offshore site and reduces the amount of piping, wiring and like
connecting work to shorten the period of installation. As a result, the invention,
which assures a shortened period of construction, provides offshore structures at
reduced costs.
[0005] With the working ship of the present invention for installing large offshore structures,
a skidway is provided on the upper deck of the upper hull for transferring the offshore
structure. The large offshore structure or large blocks thereof can therefore be loaded
and unloaded with ease.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006]
Fig. 1 is a side elevation showing a working ship of the present invention for installing
large offshore structures;
Fig. 2 is a plan view of the same;
Fig. 3 is a side elevation showing the working ship loaded with a large offshore structure;
Fig. 4 is a plan view of the same;
Fig. 5 is a side elevation showing the working ship moored to a foundation structure;
and
Fig. 6 is a side elevation showing the offshore structure being transferred onto the
foundation structure.
BEST MODE OF CARRYING OUT THE INVENTION
[0007] The present invention will be described below in greater detail with reference to
the accompanying drawings.
[0008] As shown in Fig. 1 and Fig. 2, a working ship 1 for installing large offshore structures
comprises a lower hull 2, a plurality of guide posts 3 extending upward from opposite
side portions of the lower hull 2, an upper hull 4 supported at opposite side portions
by the guide posts 3 and movable upward and downward, and lifting means (jacking-up
means) 5 for moving the upper hull 4 upward and downward along the guide posts 3.
The lower hull 2 and the upper hull 4 are each in the form of a box. The upper side
of the lower hull 2 and both upper and lower sides of the upper hull 4 are horizontal.
The lifting means 5, each provided for each of the guide posts 3, are fixed to the
upper deck 6 of the upper hull 4. The guide posts 3 each extend vertically through
the upper hull 4 and the lifting means 5. By means of the lifting means 5, the upper
hull 4 is movable upward and downward along the guide posts 3 and can be secured to
the guide posts 3 at the desired level.
[0009] Provided on the upper deck 6 of the upper hull 4 are a skidway 7 for facilitating
loading and unloading of large-sized structures, a known transfer device (not shown)
of the hydraulic or winch wire type for moving the structrue on the skidway 7, and
a control room 8 for operating the lifting means 5, etc.
[0010] A large offshore structure constituting a plant, for example, will be installed in
the following manner with use of the working ship 1 described above (see Fig. 3 to
Fig. 6).
[0011] First, the stern end of the working ship 1 is brought alongside the quay 9 of the
factory, with the upper hull 4 lowered to the upper side of the lower hull 2, and
the skidway 7 of the working ship 1 is positioned at the same level as a skidway 10
on the quay 9 by adjusting the ballast of the lower hull 2. The large offshore structure
11 built in the form of an assembly in the factory is then transferred from the skidway
10 on the quay 9 onto the skidway 7 on the working ship 1 by the transfer device on
the ship 1 or a transfer device provided on the quay 9 (see Fig. 3 and Fig. 4).
[0012] The offshore structure 11 transferred to a specified position is fastened to the
upper hull 4 when so desired, and the working ship 1 is towed by a tugboat or the
like to the site where the structure is to be installed.
[0013] A foundation structure (jacket) 12 for supporting the offshore structure is fixed
to the sea bottom at the site. The foundation structure 12 has an upper end projecting
above the surface of the sea and carrying a cap truss 13.
[0014] After the working ship 1 loaded with the offshore structure 11 has reached the site,
the ship 1 is moored to the foundation structure 12, and the position of the ship
is adjusted (see Fig. 5).
[0015] By the lifting means 5, the upper hull 4 is then lifted along the guide posts 3 and
locked in the position where the skidway 7 is at the same level as the cap truss 13.
Subsequently a temporary skid is provided between the upper hull 4 and the cap truss
13. The offshore structure 11 is transferred from the upper hull 4 to the specified
position on the cap truss 13 with use of the transfer device on the working ship 1
(see Fig. 6). Finally the offshore structure 11 is secured to the cap truss 13 as
by welding.
[0016] The construction of the lower hull 2 and the upper hull 4 and the number of the guide
posts 3 are not limited to those of the above embodiment but can be varied suitably.
INDUSTRIAL APPLICATION
[0017] The working ship according to the present invention is suited to use in transporting
a large offshore structure, such as an offshore plant, to the site of installation
and installing the structure on a foundation structure which is built offshore.
1. A working ship for installing large offshore structures comprising a lower hull
2, a plurality of guide posts 3 extending upward from opposite side portions of the
lower hull 2, an upper hull 4 supported at opposite side portions by the guide posts
3 and movable upward and downward, and lifting means 5 for moving the upper hull 4
upward and downward along the guide posts 3.
2. A working ship for installing large offshore structures as defined in claim 1 wherein
a skidway 7 is provided on the upper deck 6 of the upper hull 4 for transferring the
large offshore structure.