Note: Descriptions are shown in the official language in which they were submitted.
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SHIP AND METHOD FOR CONVEYING AND SETTING UP OFFSHORE
STRUCTURES
This application claims priority based on European Patent Application 10 012
695.2
entitled "Ship and Method for Conveying and Setting Up Offshore Structures"
filed
October 1, 2010, which is herein incorporated by reference.
The invention relates to a ship and a method for conveying and setting up
offshore
structures. The ship and the method are especially intended for conveying and
setting up
offshore wind turbines.
Operating wind turbines on the sea promises a high energy yield due to high
average
wind speed. Consequently, more offshore wind turbines should be set up. In the
North
Sea, several large areas have been designated for setting up wind turbines.
These are
generally located outside of the 12-mile zone. The depth of water is 10 meters
to a few
multiples of 10. It frequently ranges from 40 to 50 in.
When setting up the offshore wind farm Alpha-Ventus, wind turbines were set up
using
the Thialf platform by the Dutch company Heerema. This is a very large piece
of
equipment that is typically used to set up oil platforms. The piece of
equipment remains
at the setup site for long periods. However, it only takes one to two days to
set up an
offshore wind turbine, and then the platform needs to be towed to another
setup site. It is
too time-consuming and expensive to use this piece of equipment to set up wind
turbines.
WO 2004/087494 A2 describes a ship for transporting multiple complete wind
turbines
which are aligned vertically. The ship has means for transporting the wind
turbines from
a hold to an unloading position. In addition, the ship has winches with at
least three lines
with fasteners to fasten to at least three lifting points on the foundation of
the wind
turbine. The lines are arranged at the unloading position such that their
sections running
to the lifting points on the foundation are horizontally spaced from each
other. The ship
has arms projecting at the stern on which the winches are placed. By means of
the lines
guided through the winches, the wind turbines can be lowered with their
foundations.
The wind turbines are transported from their position in the hold on rails to
the unloading
position. A disadvantage with this special ship is that the wind turbines need
to be
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transported ready assembled on their foundation so that the cargo projects
high above the
ship. The stability of the ship is increasingly impaired as the height or
respectively
number of wind turbines positioned on the ship increases. This limits the
transportation
capacity and possible uses of the ship.
WO 2007/091042 Al describes a method and a system for transporting offshore
structures as well as wind turbines. These have a support frame into which the
wind
turbine can be inserted on land in an upright position. The support frame is
used to lift
the wind turbine onto a transport ship on which it is held in an upright
arrangement. The
transport ship has pivoting crane arms from which the transport frame is
suspended. The
wind turbine is transferred from a dock to the transport ship by swinging the
crane arms.
At the setup site, the wind turbine is placed on a prepared foundation by
swinging the
crane arms in the opposite direction. The foundation has a frame that
interacts with the
support frame. The support frame is equipped with a plurality of legs having
hydraulically controlled feet. The frame on a foundation has a corresponding
number of
support structures on which the feet finally rest. The feet are movable along
a vertical
axis depending on a hydraulic control and form a damping arrangement for
installing the
wind turbine on the foundation. The ship is only suitable for transporting the
mast of a
single wind turbine. The foundations need to be set separately. After
installation, the
transport ship must be sailed to a harbor to pick up another wind turbine.
This is
problematic when numerous wind turbines need to be set up as is the case with
wind
farms.
With the familiar transport ships, setting up offshore structures is strongly
hindered by
the influence of the swell, current and wind.
Against this background, the invention is based on the object of providing a
ship and a
method for conveying and setting up offshore structures that can be used
independent of
the swell and weather conditions, and by means of which a large number of
offshore
structures can be conveyed and set up within a specific time.
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This object is achieved by a ship unit having the features of claim 1.
Advantageous
embodiments of the ship are cited in the dependent claims.
The ship according to the invention for conveying and setting up offshore
structures has:
= a hull with a U-shaped cross-section having an open stern and projections of
the
side walls extending at the rear beyond the rear edge of the floor,
= jack-up leg systems with jack-up legs integrated in the hull that are
movable in a
vertical direction with their bottom ends in positions below the ship's
bottom, and
= a crane that can be moved on the top edge of at least one side wall.
The U-shaped cross-section of the hull is particularly advantageous for the
strength of
the ship. The ship is therefore particularly suitable for conveying heavy
offshore
structures. An additional advantage for the hydrodynamics of the ship and the
connection
of the two structures is that the jack-up leg systems can be integrated in the
side walls.
When setting up offshore structures, the ship can be fixed to the ocean floor
by lowering
the jack-up legs. The ship is thereby held in a stable reference position that
is
independent of the swell and influences of the current and wind. This is
advantageous for
setting up wind turbines because the masts must be aligned precisely vertical.
In
addition, the U-cross section has the advantage that the top edges of the side
walls can be
used as a base for the movable crane. Consequently, the crane can move above
the
offshore structures with which the ship is loaded. The ship preferably has a
loading deck
on the top side of the floor to provide a high hold over which the crane can
move. By
means of the movable crane, offshore structures stored on the loading deck can
be picked
up and transported to the projections. Between the projections, the offshore
structures
can be lowered and placed on the ocean floor since the hull does not have a
loading deck
or respectively floor there. A plurality of offshore structures placed in a
row in the
longitudinal direction of the hull can be brought to the setup site in a
single trip and set
up sequentially. The ship is therefore particularly economical to use. The
crane can
transport the offshore structures vertically aligned because the load lifting
system of the
crane can grasp the offshore structures at a high attachment point. In
particular, the ship
can transport and assemble masts and vertically aligned foundations of wind
turbines.
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The wind turbine does not have to be transported and set down as a unit with
the mast
mounted on the foundation. The cargo therefore does not extend as high from
the hull of
the ship as is the case in WO 2004/087494 A2; consequently, the ship has more
options
for use.
The crane can preferably move along a rail system arranged on the top edge of
at least
one side wall.
According to one embodiment, the crane has a crane bridge that is supported on
both
side walls. The loads are thereby optimally transferred into the hull of the
ship. The
invention includes embodiments in which the crane is movably arranged on the
top edge
of only one side wall. In addition, the invention includes embodiments in
which cranes
that are separate from each other can move on the top edge of both side walls.
According to another embodiment, the crane is a portal crane that bears the
crane bridge
on supports movable on the top edges of the side walls. With the portal crane,
the crane
bridge is arranged particularly tall so that the ship can be used to convey
and set up
particularly tall offshore structures. According to another embodiment, the
crane is a
gantry screen. The crane bridge of the gantry crane can be directly supported
and moved
on the top edges of the side walls. According to another embodiment, the crane
bridge of
the gantry crane is movable on rails that are supported by supports on the top
edges of
the side walls. With this ship, the crane bridge is arranged particularly tall
so that it can
convey and to set up particularly tall offshore structures.
According to one embodiment, the side walls are cut out at the bottom in the
area of the
projections so that the bottom edge of the overhangs is arranged above the
water line of
the hull while sailing. The stern of the ship is therefore designed like a
bracket so that the
ship can sail with the hull above a pier, and a transfer site for the offshore
structures is
arranged between the projections. Offshore structures placed on the transfer
site can be
picked up with the assistance of the crane arranged on the ship and set down
on the ship.
The ship can therefore pick up offshore structures in a harbor without using
harbor
cranes. Cargo in a harbor can therefore be picked up without using the jack-up
legs. The
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ship is preferably fixed to the floor of the harbor when loading by lowering
the jack-up
legs.
According to one embodiment, the ship is a semi-submersible with ballast tanks
integrated in the hull and pumps to fill the ballast tanks with ballast water
and/or pump
out the ballast water from the ballast tanks. The ship can be sailed with
empty ballast
tanks to the setup site. At the setup site, the ballast tanks can be flooded
so that the ship
is immersed lower and more stably in the water. In this embodiment, the
position of the
ship is additionally stabilized by the ballast. When designed as a semi-
submersible, the
ship can also be used for other transportation purposes in which cargo has to
be loaded
and/or unloaded through the stern. For example, the ship can be used to
transport
pontoons or other floating cargo that can be floated into and out of the open
stern.
The ship preferably has at least three jack-up leg systems for fixation in a
stable position.
According to one embodiment, the ship has three jack-up leg systems, wherein
one jack-
up leg system is integrated at the midaxis in the front of the hull, and the
two other jack-
up leg systems are integrated in the rear of the hull in the two side walls.
According to another embodiment, the ship has four jack-up leg systems wherein
two
jack-up leg systems are integrated in the sidewalls in the front of the hull
opposite each
other, and the two other jack-up leg systems are integrated in the rear of the
hull opposite
each other in sidewalls. In this embodiment, the dimensions of the jack-up leg
systems
do not have to be as generous as is the case with the embodiment with three
jack-up leg
systems in which the front jack-up leg systems is exposed to greater loads
than the two
rear jack-up leg systems.
The bow of the ship can be designed in a conventional manner with or without a
bow
nose. According to another embodiment, the ship as a deckhouse arranged at the
front on
the hull. The deckhouse arranged at the front on the hull does not restrict
the hold.
It is to be understood that the ship has a propulsion system. This can be
designed in
various ways. According to one embodiment, the ship has a marine propeller
drive and
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front and rear maneuvering aids. The marine propeller drive in connection with
the bow
thrusters enables the ship to be precisely positioned at the setup site and in
the harbor
before it is fixed with the jack-up legs. Alternately, the ship's propulsion
system can
comprise rudder propellers by means of which the ship can be precisely
maneuvered.
According to another embodiment, the ship has a dynamic positioning system. By
means
of the dynamic positioning system, the ship can be automatically positioned at
the setup
site before it is fixed with the jack-up legs to the ocean floor.
According to another embodiment, the ship has equipment for fixing foundations
and/or
masts of vertically aligned wind turbines to the hull. In another embodiment,
the fixing
equipment comprises seats in the top side of the hull in which the foundations
and/or
masts can be inserted. The seats can have a circle of holes to fix masts on
which the mast
can be placed with a threaded ring having a complementary circle of holes. By
inserting
screw fittings into the circle of holes, the mast can be screwed to the hull.
According to
one embodiment, the seats are accessible by a gangway in the hull so that the
screw
fittings can be affixed and released if the threaded ring is arranged inside
the mast.
According to another embodiment, the hull has fastening devices for lashing
systems.
These can in particular be tension cables and/or rods with fasteners on their
ends and
clamping devices if necessary.
The ship can be equipped with offshore structures in various ways. According
to one
embodiment, the ship is either equipped homogeneously with a plurality of
foundations
or masts of wind turbines sequentially arranged in the direction of the ship's
longitudinal
axis, or heterogeneously, with alternating masts and foundations of wind
turbines. When
heterogeneously equipped, a foundation is preferably arranged next to the
stern of the
ship since this has to be set down first, and then a mast is set on the
foundation. The
position of the ship does not have to be changed. It is also quite possible
for the ship to
be heterogeneously equipped with a group of masts followed by a group of
foundations.
After the foundations are set down, the masts can be attached to the set down
foundations. At least one change of position is required to do this.
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In addition, the invention is solved by a method having the features of claim
15.
Advantageous embodiments of the method are cited in the dependent claims.
In the method according to the invention for conveying and setting up offshore
structures
on a ship according to one of the previously explained claims,
= the ship is loaded with the offshore structures,
= the loaded ship is sailed to the setup site for the offshore structures,
= the ship is fixed to the ocean floor at the setup site using jack-up legs,
= the offshore structures are lowered with the crane between the rear
projections of
the side walls at the setup site, and
= the jack-up legs are lifted from the ocean floor.
According to one embodiment, the ship is fixed to the floor of the harbor with
the jack-
up legs before being loaded, and the jack-up legs are removed from the floor
of the
harbor after loading.
According to one embodiment, the ship is immersed more deeply when it is fixed
to the
floor of the ocean by flooding the ballast tanks. The floor of the ocean is
thereby
compressed below the jack-up legs to provide a solid base.
According to another embodiment, the ship is lifted with the jack-up legs with
the hull at
least partially out of the water. This increases the load on the jack-up legs
and fixes the
ship more securely to the ground. When the hull is lifted only partially out
of the water
with the jack-up legs, the buoyancy acts on the hull. This relieves the jack-
up leg systems
so that they do not have to be as strongly dimensioned as is the case with a
ship with a
hull that can be completely lifted out of the water with the jack-up leg
systems.
According to one embodiment, the ship is positioned at the setup site for the
offshore
structures and/or at the loading site in the harbor with a dynamic positioning
system until
the jack-up legs are fixed.
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According to another embodiment, the ship is loaded with offshore structures
by moving
the rear projections of the side walls of the ship over a pier so that the
projections
encompass a transfer site for offshore structures, and the offshore structures
placed on
the transfer site can be picked up with the assistance of a crane and placed
on the hull.
According to another embodiment, the ship is loaded with wind turbines, and
the wind
turbines are placed on the transfer site.
According to another embodiment, the ship is loaded with foundations and/or
masts of
vertically aligned wind turbines, and the foundations and/or masts of the wind
turbines
are set up at the setup site.
According to another embodiment, the ship is loaded sequentially in a
longitudinal
direction with several foundations of wind turbines or several masts of wind
turbines, or
alternating masts and foundations of wind turbines, and the foundations are
set up at the
setup site, or the masts of the wind turbines are placed on foundations of
wind turbines,
or alternatingly, foundations are set up and the masts of the wind turbines
are placed on
them.
The invention is described in the following in more detail based on the
drawings of an
exemplary embodiment. The drawings show:
Fig. 1a-c a ship with three jack-up leg systems equipped with foundations and
masts of wind turbines in a side view (Fig. la), a vertical lengthwise
section (Fig. lb) and a plan view (Fig. lc);
Fig. 2a-c a ship with four jack-up leg systems equipped with foundations and
masts
of wind turbines in a side view (Fig. 2a), a vertical lengthwise section
(Fig. 2b) and a plan view (Fig. 2c);
Fig. 3a-i the ship from Fig. 2 during the trip (Fig. 3a) with lowered jack-up
legs at
the setup site (Fig. 3b), when picking up a foundation (Fig. 3c), when
lowering the foundation (Fig. 3d and e), when picking up a mast (Fig. 3f),
when transporting the mast (Fig. 3g), when positioning the mast above the
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foundation (Fig. 3h), when placing the mast on the foundation (Fig. 3i),
each in a vertical lengthwise section;
Fig. 4 a vertical lengthwise section of the ship from Fig. 2 with lowered jack-
up
legs and a hull lifted out of the water at the setup site;
Fig. 5a -j the ship from Fig. 2 when maneuvering to a transfer site for wind
turbines
on a pier (Fig. 5a), when encompassing the transfer site between the
protections (Fig. 5b), when lowering the jack-up legs into the floor of the
harbor (Fig. 5c), when picking up the mast of a wind turbine (Fig. 5d),
when lowering the mast onto the ship (Fig. 5e), when moving the portal
crane to the transfer position (Fig. 5f), when picking up a foundation (Fig.
5g), when placing the foundation on the hull (Fig. 5h), when positioning
the portal crane in trip position (Fig. 5i), when sailing from the pier with
lifted jack-up legs (Fig. 5j), each in a vertical lengthwise section;
Fig. 6a-c the ship from Fig. 2 homogeneously equipped with foundations in a
side
view (Fig. 6a), in a vertical longitudinal section (Fig. 6b) and plan view
(Fig. 6c).
Fig. 7a-c the ship from Fig. 2 homogeneously equipped with masts of wind
turbines
in a side view (Fig. 7a), in a vertical longitudinal section (Fig. 7b) and
plan view (Fig. 7c).
In the following explanation of different exemplary embodiments, corresponding
parts
are provided with the same reference signs.
According to Fig. I a ship 1.1 for conveying and setting up offshore
structures has a hull
2 having a U-shaped cross section with a floor 3 and side walls 4.1, 4.2. At
the front, the
ship has a conventional bow 5. In addition, a deckhouse 6 is arranged in the
front area on
the ship. A helicopter landing pad 7 is optionally provided.
The floor 3 and side walls 4.1, 4.2 as well as the rear wall of the deckhouse
6 delimit a
hold in the hull 2.
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The side walls 4.1, 4.2 of the hull have projections 9.1, 9.2. projecting from
the rear edge
8 of the floor 3. The projections 9.1, 9.2 each have a cutout 10.1, 10.2, the
top edge of
which is disposed above the water line 11 when the ship is sailing. The stern
12 of the
ship is therefore designed in the shape of a bracket in a side view. Between
the
projections 8.1, 8.2, the hull 2 has a large opening 13. In addition, it is
open to the rear at
the stern 12.
A propulsion system (not shown) located in the hull 2 comprises a marine
propeller drive
and front and rear maneuvering aids (such as bow thrusters) and the associated
drive
motors.
On the top side of the floor 3 is a loading deck 14.
Furthermore, jack-up leg systems 15.1, 15.2, 15.3 with jack-up legs 16.1,
16.2, 16.3 are
integrated in the hull 2. In the front part of the hull 2 directly following
the deckhouse 6,
there is a jack-up leg system 15.1 arranged centrally on the mid-axis 17. In
the rear part
of the hull 2, two opposing additional jack-up leg systems 15.2, 15.3 are
integrated in the
side walls 4.1, 4.2 .
Each jack-up leg system 15.1, 15.2, 15.3 comprises a torsion box in which the
jack-up
legs 16.1, 16.2, 16.3 are guided. At the bottom end, the jack-up legs 16.1,
16.2, 16.3 have
a stamp-shaped foot 18. The jack-up legs 16.1, 16.2, 16.3 can be moved
vertically in the
torsion boxes. To this end, drives are integrated in the jack-up leg systems
15.1, 15.2,
15.3 that for example comprise hydraulic cylinders or gears that engage with
racks. The
drives of the jack-up leg systems 15.1, 15.2, 15.3 have electric motors, for
example.
On the top edges 19.1, 19.2 of the side walls 4.1, 4.2, a portal crane 20 is
movably
arranged on rails. The portal crane 20 has two sides supports 21.1, 21.2 that
are guided
on the rails at the bottom by rollers. At the top, the supports 21.1,21.2 are
bridged by a
crane bridge 22. Hoisting gear (not shown) with load lifting means is arranged
on the
crane bridge 22.
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In addition, the portal crane 20 has drive means (not shown) for moving the
portal crane
20 along the top edges 19.1, 19.2 of the sidewalls 4.1, 4.2. The portal crane
20 can be
moved from a position shortly behind the deckhouse 6 up to the projections
9.1, 9.2 so
that loads can be lowered with the hoisting gear through the opening 13
between the
projections 9.1, 9.2.
In the example, the ship 1.1 is equipped with two complete wind turbines 23.
The wind
turbines 23 are divided into a foundation 23.1 and a mast 23.2 that bears the
generator
with the rotor 23.3. The foundation 23.1 and mast 23.2 can be vertically
assembled in a
conically designed connection area. The foundations 23.1 are designed as
tripods. Each
foot of the tripod is equipped with a nail 23.4 in a vertical guide sleeve
that can be driven
into the ocean floor. Rams are carried onboard the ship 1.1 for this purpose.
These can be
mounted on the top ends of the nails 23.4 and can be operated by means of
flexible
supply lines by a ship 1.1 power supply. This power supply can be electrical,
hydraulic
or pneumatic.
The masts 23.2 and foundations 23.1 are arranged sequentially in alternating
sequence in
the longitudinal direction of the ship 1.1, and a foundation 23.1 is
positioned at the rear.
The foundations and masts 23.2 of the windmills 23 are arranged vertically on
the load
deck 14. In this position, they can be held or respectively secured by means
of fixing
devices (not shown).
The ship 1.2 in Fig. 2 differs from the one described above in that it has
four jack-up leg
systems 15.1, 15.2, 15.3, 15.4. In this ship 1.2, there are two front,
opposing jack-up leg
systems 15.1, 15.2 integrated in the side walls 4.1, 4.2. Contrastingly, there
is no jack-up
leg system at the mid-axis 17 of the ship 1.2. Ship 1.2 has a larger hold than
ship 1.1.
According to Fig. 2, the portal crane 20 is in a position on the projections
9.1, 9.2 for
picking up and depositing cargo. Ship 1.2, like ship 1.1, is loaded with wind
turbines 23.
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Optionally, ship 1.1 or 1.2 has a tailgate (not shown) at the stern 12 that
can be closed
during the trip in order to prevent waves from entering. The tailgate is
preferably
arranged at the back end of the hold or respectively at the rear edge 8 of the
floor 3, and
preferably extends up to the top edge of the side walls 4.1, 4.2.
In Fig. 3a, the ship is shown as it arrives at the setup site where it is kept
in this position
by means of a dynamic positioning system.
According to Fig. 3b, the jack-up legs 16.1, 16.2, 16.3, 16.4 are lowered at
the setup site
so that the feet 18 penetrate the sludge line 24.1 and rest on solid ground
24.2. The ship
1.2 is only lifted slightly by the jack-up legs 16.1, 16.2, 16.3, 16.4 so that
the buoyancy
acting on the hull 2 relieves the jack-up leg systems 15.1, 15.2, 15.3, 15.4.
According to Fig. 3c, the portal crane 20 is moved over the rear foundation
23.1 so that it
can pick it up with the load lifting means (not shown). According to Fig. 3d,
the portal
crane 20 lowers the foundation 23.1 between the projections 9.1, 9.2 through
the opening
13. According to Fig. 3c, the foundation 23.1 sits on the ocean floor 24 so
that the nails
22.4 can be driven in. In this position, the connecting section of the
foundation 23.1
extends above the water line 11.
Then the portal crane 20 according to Fig. 3e moves to the rear mast 23.2 and
picks it up
with the load lifting means.
Fig. 3g and h show the ship 1.2 while the mast 23.2 is being transported to
the
foundation 23.1.
According to Fig. 3i, the mast 23.2 is joined to the foundation 23.1 at the
conical
connecting sections. Because the ship 1.2 is supported by the jack-up legs
16.1, 16.2,
16.3, 16.4, the foundation 23.1 can be be vertically aligned very precisely
and easily
joined to the mast 23.2.
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Then the jack-up legs 16.1, 16.2, 16.3, 16.4 are lifted, and the ship 1.2 is
maneuvered to
another set up site where the parts 23.1, 23.2 of the other windmill 23 are
set up.
According to another embodiment illustrated in Fig. 4, the ship 1.2 can be
lifted by
means of the jack-up legs 16.1, 16.2, 16.3, 16.4 so that the hull 2 is
disposed above the
water line 11. The advantage is that the load from the swells on the hull and
the jack-up
leg system is substantially reduced.
Fig. 5 shows the ship 1.2 when loading wind turbines 23. The stern 12 of the
ship 1.2 is
moved to a pier 25 in the harbor. This is shown in Fig. 5a. According to Fig.
5b, the ship
1.2 is maneuvered so that it encompasses a loading position 26 for wind
turbines 23
between the projections 9.1, 9.2 on which a mast 23.1 is waiting. In this
position, the
ship 1.2 is held by the dynamic positioning system. The jack-up legs 16.1,
16.2, 16.3,
16.4 are lowered so that the feet 18 penetrate the floor 27 of the harbor, and
the ship 1.2
is fixed in the loading position as shown in Fig. 5c.
Then according to Fig. 5d, the portal crane 20 is moved to the projections
9.1, 9.2 until it
overlaps with the mast 23.2. The load lifting means are fastened to the mast
23.2, and the
mast is transported by means of the portal crane 20 into the position in Fig.
5e. In this
position, it is held and secured to the hull 2 by means of suitable fixing
devices.
Then the portal crane 20 is moved to the rear as shown in in Fig. 5f. A
foundation 23.1 is
already ready between the projections. The portal crane 20 moves toward the
projections
9.1, 9.2 into the position shown in Fig. 5g. The load lifting means pick up
the foundation
23.1, and the portal crane 20 lifts it into the position in the hold shown in
Fig. 5h. In this
drawing, another mast 23.2 is already shown that is placed on the transfer
site 26. In the
above-described manner, the portal crane 20 lifts the other mast 23.2 and
another
foundation 23.1 until the ship 1.2 is completely equipped with two wind
turbines 23 as
shown in Fig. 5i. Then, according to Fig. 5j, the jack-up legs 16.1, 16.2,
16.3, 16.4 are
lifted, and the ship 1.2 is sailed to the setup site.
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Fig. 6 shows an alternative equipping of the ship 1.2 with exclusively five
foundations
23.1. This equipping can be preferable to equipping with complete wind
turbines 23
consisting of foundations 23.1 and masts 23.2 when for example it appears
advisable to
transport a load that is less tall in difficult sea and weather conditions.
With a ship 1.2
equipped in such a manner, first exclusively foundations 23.2 are placed at
various setup
sites.
Fig. 7 shows an alternative equipping of the ship 1.2 exclusively with masts
23.2. This
equipping can be preferable in good weather and favorable conditions to equip
foundations 23.1 already placed at a setup site with masts 23.2.
