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 installilng large offshore structures
comprises a plurality of support legs provided at opposite side portions of the hull
and movable. upward and downward, and lifting means provided at the opposite side
portions for moving the support legs upward and downward relative to the hull. Accordingly
the large offshore structure, which is built in the form of an assembly, or large
blocks thereof can be loaded onto the hull and transported to the site of installation,
where the hull is lifted along the support legs to the same level as a foundation
structure, with the support legs rested on the sea bottom in the vicinity of the foundation
structure, so that the offshore structure or blocks thereof can be transferred from
the 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 structure
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. In addition, since the support legs are rested
on the sea bottom to support the hull when the offshore structure is to be loaded
or.unleaded, the work can be carried out with safety and properly without permitting
heaving of the hull.
[0005] With the working ship of the present invention for installing large offshore structures,
a skidway is provided on the upper deck of the 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 at rest in the vicinity of 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 for installing large offshore structures
has a hull 1 which is provided at opposite side portions with a plurality of support
legs 2 which are movable upward and downward and with lifting means 3 for the support
legs. The lifting means 3, each provided for each of the support legs 2, are fixed
to a horizontal upper deck 4 of the hull 1. The support legs 2 extend vertically through
the hull 1 and the lifting means 3. By the lifting means, the hull 1 and the support
legs 2 are movable upward and downward relative to each other and can be locked to
each other at the desired position. Each of the support legs 2 is provided at its
lower end with a spud member 5 so as to contact the sea bottom over an increased area.
[0009] Provided on the upper deck 4 of the hull 1 are a skidway 6 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 structure on the skidway 6, and a control
room 7 for operating the lifting means 3, etc.
[0010] A large offshore structure constituting a plant, for example, will be installed in
the following manner with use of the working ship described above (see Fig. 3 to Fig.
6).
[0011] First, the stern end of the working ship is brought alongside the quay 8 of the factory,
the support legs 2 are rested on the sea bottom, and the level of the hull 1 is adjusted
to position the skidway 6 on the working ship flush with a skidway 9 on the quay 8.
The large offshore structure 10 built in the form of an assembly in the factory is
then transferred from the skidway 9 on the quay 8 onto the skidway 6 on the working
ship by the transfer device on the ship or by a transfer device on the quay 8 (see
Fig. 3 and Fig. 4).
[0012] The offshore structure 10 transferred to a specified position is fastened to the
hull 1 when so desired, the support legs 2 are released from the sea bottom and the
working ship is then 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 10 is rested
on the sea bottom at the site. The foundation structure 11 has an upper end projecting
above the sea level and carrying a cap truss 12.
[0014] After the working ship loaded with the offshore structure 10 has reached the site,
the ship is stopped in the vicinity of the foundation structure 11, and the position
of the ship is adjusted (see Fig. 5).
[0015] By the lifting means 3, the support legs 2 are lowered into engagement with the sea
bottom, and the hull 1 is then lifted along the support legs 2 and locked in the position
where the skidway 6 is at the same level as the cap truss 12. Subsequently a temporary
skid is provided between the hull 1 and the cap truss 12. The offshore structure 10
is transferred from the hull 1 to the; specified position on the cap truss 12 with
use of the transfer device on the working ship (see Fig. 6). Finally the offshore
structure 10 is secured to the cap truss 12 as by welding.
[0016] The structure of the hull 1, and the structure and number of the support legs 2 as
well as of the lifting means 3 are not limited to those of the foregoing 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.