Technical Field:
[0001] The present invention relates to a turret assembly for mooring a storage and production
vessel to a seabed and for transferring fluids from a subsea flowline to the vessel,
wherein the turret assembly comprises notably a geostationary inner turret unit displaying
at least one through-going channel extending axially along a longitudinal center axis
of the inner turret unit. The present invention also relates to a vessel comprising
said turret and a method for installing said turret onto such a vessel.
Background and prior art:
[0002] The function of a turret is to moor a weathervaning vessel to a seabed without creating
excessive forces on the mooring lines. This is achieved by use of a swivel and bearings
that keeps the turret geostationary during vessel rotations. Turrets on storage or
production vessels must also provide space for pipelines extending along an axial
center of the turret. The swivel enables the transfer of fluid flows. communication
signals, hydraulics and any power between the geostationary turret and the weathervaning
vessel.
[0003] Turrets for ensuring safe mooring of weathervaning vessels have been known for decades.
As an example, patent publication
GB1189758A discloses a conventional turret extending between the deck and the keel of a vessel.
The turret is kept geostationary by a deck positioned rotatable table. A more recent
example of a turret is disclosed in patent publication
WO 98/56650 where a relatively small sized turret is located near the keel level of the vessel.
In contrast to the turret disclosed in
GB1189758A the rotatable chain table is attached below the vessel. In this way the chain table
can adequately take up bending moments exerted by e.g. the mooring chains. The arrangement
also enables easy removal of the lower part of the turret wall from the vessel in
order to transform the vessel back to a transport tanker.
[0004] EP 1886914 A1 discloses a vessel with a mooring system comprising a turret anchored to the seabed
and a turret casing being part of the vessel, wherein the turret and turret casing
are interconnected by a connecting element comprising a bearing arrangement. The connecting
element has a first end connected to the turret casing and an opposite second end
connected to the turret. The connection between the connecting element and the vessel
has a symmetric arrangement of the fixing means.
[0005] Other examples of conventional turrets are patent publication
US 5782197 A disclosing a turret device for anchoring a vessel to the seabed and to transport
fluids through pipes, patent publication
WO 93/24733 A1 disclosing a system for use in offshore petroleum production comprising a submerged
buoy and patent publication
EP 2778041 A1 disclosing an assembly for transferring fluids between a vessel and a turret structure
mounted on the vessel. However, none of these publications describes a turret support
structure rotationally surrounding the entire inner turret unit.
[0006] Furthermore, common for all conventional turrets is that they have a construction
where the forces from the turret to the vessel are transferred via radial and axial
bearings capable of handling horizontal and vertical forces. The bearings situated
at the lower part of the turret experience typically the largest radial loads, but
some horizontal loads may also be transferred to the upper radial layer in order to
balance any bending moments from the mooring line forces. Axial forces from the mooring
lines and the weight for the turret construction must be carried by axial bearings
(or any other arrangements capable of both transferring forces and to rotate). A turret
of conventional design typically has a bearing integrated into the vessel structure
with a diameter equal to the largest diameter of the turret construction.
[0007] Pipes for fluid flow, signal, etc., as well as mooring lines, must be placed within
these bearings. An example of such a design is disclosed in
WO 2015/063262.
[0008] The challenges with these conventional turret constructions are numerous. When bearings
are integrated into the vessels structure, deformations caused by the external loads
on the vessel are transmitted to the bearings, setting higher demands on bearing tolerances,
flexibility, etc. Such vessel deformations are particularly challenging for axial
bearings transmitting high loads over a large bearing diameter. The mean forces within
the axial bearings are high while the dynamic loads are weaker. In order to accommodate
horizontal forces, conventional turret constructions also comprises upper and lower
radial bearings, where the main part of the horizontal forces are absorbed at the
lower radial bearing. The upper radial bearing is normally situated at the same level/area
as the axial bearing. The horizontal forces normally undergo large dynamic variations
relative to the mean forces. Hence, the forces that generate moments responsible for
limiting the rotation of the turret construction are therefore mainly due to frictional
forces within the axial bearing. This rotational moment is proportional to the size
of the force, the friction coefficient and the bearing diameter. If sliding bearings
are used the moments set up by mooring lines may not be sufficient for turning the
turret. Active rotation of the turret may then be required, i.e. by turret rotating
motors.
[0009] Another disadvantage with the above described prior art is that the turret will be
affected by any deformation force or external force acting on the hull of the vessel,
resulting in greater demands for bearing size and tolerances.
[0010] In addition, none of the above mentioned prior art discloses a solution where a complete
turret assembly, i.e. a turret construction comprising all components necessary to
establish a satisfactory mooring of a storage or production vessel, may be installed
onto the vessel while being in dock.
[0011] Thus, there is an object of the invention is to provide a turret assembly for mooring
a production vessel to a seabed and for transferring fluids from a subsea flowline
to the vessel, which mitigate at least some of the above mentioned short-comings.
[0012] A particular object of the invention is to provide a turret assembly that is not
significantly affected by any deformation of the vessel hull.
[0013] A second particular object of the invention is to provide a turret assembly that
may accept less severe requirements for tolerance, flexibility, etc., than conventional
turret assemblies.
[0014] A third particular object of the invention it to enable turret rotation at low friction
moments.
[0015] A fourth particular object of the invention is to provide a turret assembly that
has a size and a shape that allows mounting of the turret assembly when the vessel
in question is in dock.
Summary of the invention:
[0016] The present invention is set forth and characterized in the independent claims, while
the dependent claims describe other characteristics and embodiments of the invention.
[0017] In particular, the present invention relates to a turret assembly suitable for mooring
a production vessel to a seabed and suitable for transferring fluids from a subsea
flowline to the vessel. The turret assembly comprises a geostationary inner turret
unit displaying at least one through-going channel extending axially along a longitudinal
axis of the inner turret unit, a turret supporting structure rotationally surrounding
the inner turret unit and a bearing arrangement situated between the inner turret
unit and the turret supporting structure allowing the inner turret unit to rotate
relative to the turret supporting structure and to transfer forces from the inner
turret unit to the turret supporting structure.
[0018] The turret supporting structure furthermore comprises fixing means configured to
fix the turret supporting structure to a hull structure of the vessel in such a way
that, in use, any deformation force acting on a hull of the vessel has insignificant
impact on the turret assembly. Said fixation should preferably be a rigid fixation.
[0019] The bearing arrangement between the geostationary inner turret unit and the turret
supporting structure permits the vessel to pivot around the inner turret in response
to changes in wind, waves, and currents without disturbing any seabed extending equipment
being guided through the through-going channels, for example risers, cables, umbilicals,
etc. The inventive turret assembly may optionally be equipped with auxiliary equipment's
such as bending limiters for ensuring an operation effective guiding of the seabed
extending equipment through the turret assembly from the vessel to the seabed at operation
site.
[0020] The bearing arrangement preferably comprises at least one sliding bearing.
[0021] The rotational axis of the turret supporting structure is concurrent with the longitudinal
center axis of the geostationary inner turret unit.
[0022] Hereinafter, the term 'insignificant impact' signifies an impact that has no operational
influence on the above stated objects of the invention.
[0023] In one advantageous embodiment an exterior contact surface of the turret supporting
structure is designed such that, when installed in a vertical extending shaft of a
vessel, both horizontal and vertical forces are transferred between the hull of the
vessel and the turret supporting structure. An example of such a designed may be a
wedge-shaped contact surface.
[0024] In another advantageous embodiment the fixing means is, relative to the longitudinal
center axis of the inner turret unit, located at or above the level of the upper bearing.
[0025] In another advantageous embodiment of the invention, the fixing means is arranged
asymmetric relative to a longitudinal (vertical) center plane of the inner turret
unit. For example, the fixing means may be fixed at the exterior of the turret supporting
structure at one side of the longitudinal center plane running through the longitudinal
axis and directed perpendicular to a direction of motion of the vessel during use
and/or at one side of the longitudinal center plane running through the longitudinal
axis and directed parallel to the direction of motion of the vessel during use.
[0026] In another advantageous embodiment of the invention, the bearings arrangements comprising
an upper bearing situated at an upper part of the turret supporting structure, and
a lower bearing situated at a lower part of the turret supporting structure having
a larger diameter than the diameter of the upper bearing. The lower bearing(s) has/have
a diameter that allows chain cables to pass at the inside of the bearing surface(s),
for example the diameter of at conventional turret assembly. Since the movements of
the vessel causes large variations of the horizontal load that accumulates in the
lower radial bearing(s), the frictional forces in this / these bearing(s) do not have
large impact on the turret rotation relative to the vessel. Typically, the rotation
takes place when the horizontal loads are small.
[0027] The upper bearing has a diameter that should accommodate guide tubes 14 for seabed
extending equipment 16, but not including mooring equipment 8,11 such as chain cables
8. Preferably, the diameter of the upper bearing may be less than 75 % of the diameter
of the lower bearing, more preferably less than 70 %, even more preferably less than
65 %, even more preferably less than 60 %, for example 50%. Even smaller diameters
of the upper bearings compared to the lower bearing are foreseeable.
[0028] The upper part of the turret supporting structure is herein defined as the part constituting
less than 20 % of the total longitudinal length of the structure measured from the
structure's top, for example approximately the vertical extension of the transverse
beam at the structure's upper end. The lower part is defined as the part constituting
less than 40 % of the total longitudinal length of the structure measured from the
structure's base, for example from the base up to the start of the narrowing of the
diameter of the inner turret unit. Any other parts of the turret supporting structure
may be defined as the structure's mid part.
[0029] In another advantageous embodiment of the invention, the exterior contact surfaces
of the turret supporting structure are, relative to the longitudinal center axis,
located within the lower part, at or above the lower bearings.
[0030] In another advantageous embodiment of the invention, the upper bearing comprises
an axial upper bearing accommodating loads predominantly parallel to the longitudinal
center axis of the turret assembly and a radial upper bearing accommodating loads
predominantly perpendicular to the longitudinal center axis of the turret assembly.
[0031] In another advantageous embodiment of the invention, the lower bearing comprises
a radial lower bearing accommodating loads predominantly perpendicular to the longitudinal
center axis of the turret assembly.
[0032] In another advantageous embodiment of the invention the turret assembly comprises
at least one chain cable extending at least partly between the inner turret unit and
the turret supporting structure, wherein the end of the at least one chain cable is
fixed at a position situated between the upper bearings and the lower bearing. Preferably,
the end of the at least one chain cable is guided through at least one anchor winch,
where said at least one anchor winch is fixed to the inner turret unit below the upper
bearing. Further, the end may be fixed to a respective chain locker of the inner turret
unit.
[0033] In another advantageous embodiment of the invention the turret assembly further comprises
at least one pivotable fairlead for guiding and control of the chain cable. Preferably,
the at least one pivotable fairlead is fixed at a position located below the lower
bearing of the inner turret unit in order to ensure that the chain cable may be pulled
in/out and may rotate during operation at varying loads and load directions. The fairleads
are further designed such that the total radial diameter set up by the at least one
fairlead and the inner turret unit is changeable between a radial diameter being larger
than the inner diameter of the base of the turret supporting structure and a radial
diameter being smaller than the inner diameter of the base of the turret supporting
structure. In this way the turret assembly (including the fairleads) may be arranged
fully into the vessel's shaft during transport and be expanded during mooring.
[0034] Conventional fairleads may be used for the inventive turret assembly. Instead of
conventional fairleads one may use alternative solutions such as fairlead arrangements
for locking chains at the outside of the fairlead, or where the fairlead has been
replaced with a rotating arm having integrated chain stoppers. The two latter alternatives
may be particularly useful for the chain cables since they will experience a significantly
reduces out-of-plane bending, and at the same time avoid being situated in the splash
zone where there are higher requirements in respect of corrosion rate.
[0035] The invention also concerns a production vessel suitable for producing hydrocarbons
from an offshore reservoir. The production vessel comprises a hull displaying at least
one well or shaft extending vertically within the hull. The well is open in at least
at its lower end. The vessel further comprises a turret assembly in accordance with
any one of features mentioned above which is adapted to, and mounted within, the well.
[0036] The invention also concerns a method suitable for mooring a vessel to a seabed. The
method comprises the steps of prefabricating, while in dock, a turret assembly comprising
a geostationary inner turret unit displaying at least one through-going channel extending
mainly parallel to a longitudinal center axis of the inner turret unit and a turret
supporting structure rotationally surrounding the inner turret unit, transferring
the prefabricated turret assembly into a well or shaft located within the vessel such
that a base of the inner turret unit is situated in a transport position at or above
a keel or base of the vessel, moving the vessel to an offshore mooring site, vertically
lowering the prefabricated turret assembly to a mooring position where the base of
the inner turret unit is located below the keel of the vessel and locking the prefabricated
turret assembly into the mooring position.
[0037] In one advantageous embodiment of the invention the method further comprises the
step of unlocking the prefabricated turret assembly from its mooring position, vertically
raising the prefabricated turret assembly from its mooring position to the transport
position prior to moving the vessel from the offshore mooring site.
[0038] In another advantageous embodiment of the invention the step of prefabricating includes
mounting a plurality of fairleads at or near the base of the inner turret unit, the
plurality of fairleads being pivotably mounted near the base enabling pivoting of
the fairleads towards the exterior wall of inner turret unit. The term 'near the base"
is defined as the part constituting less than 20 % of the total longitudinal length
of the inner turret unit measured from the base and in relation to the lowest part
of each fairleads. For example, the lowest part of each fairlead may be flush with
the base of the inner turret unit.
[0039] In another advantageous embodiment of the invention, the prefabricated turret assembly
mentioned in the method is in accordance with any of the features mentioned above.
[0040] The above mentioned turret assembly has thus a configuration that reduces the effect
of deformations in the vessel hull, as well as reducing the required rotational moment
in order to rotate the relevant part of the turret assembly.
[0041] The term "geostationary" is made in reference to a weathervaning vessel.
[0042] The term fairlead is in the following referred to a device for guiding a chain line,
rope or cable around an object, out of the way and/or to hinder lateral movements.
The prior art fairlead may be a separate piece of hardware or simply a hole into a
structure. The fairlead constituting part of the inventive turret assembly is a separate
piece of hardware that may rotate during operation.
[0043] The terms "upper part" and "lower part" of the turret assembly is referred the upper
(deck) and lower (keel) parts of a vessel.
[0044] In the following description, numerous specific details are introduced to provide
a thorough understanding of embodiments of the claimed turret assembly, vessel and
method. One skilled in the relevant art, however, will recognize that these embodiments
can be practiced without one or more of the specific details, or with other components,
systems, etc. In other instances, well-known structures or operations are not shown,
or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.
Brief description of the drawings:
[0045]
- Fig. 1
- shows a perspective view of the turret assembly according to the present invention,
- Fig. 2
- shows a turret supporting structure according to the present invention, where fig.
2 (a) shows a cross sectional side view and fig. 2 (b) shows a cross sectional view
along section marked C-C in fig. 2 (a),
- Fig. 3
- shows a longitudinal cross section view of the geostationary inner turret unit according
to the present invention,
- Fig. 4
- shows a top view of the turret supporting structure and fixing means according to
the present invention,
- Fig. 5
- shows the turret assembly according with the invention in a transport position within
a vertical extending shaft of a vessel,
- Fig. 6
- shows the turret assembly of fig. 5, seen from below,
- Fig. 7
- shows the turret assembly in an operable position,
- Fig. 8
- shows the turret assembly of fig. 7 seen from below, and
- Fig. 9
- shows a perspective view of the turret assembly according to the invention in the
operable position.
Detailed description of the invention
[0046] Various objects, features, aspects and advantages of the inventive subject-matter
will become more apparent from the following detailed description of preferred embodiments,
along with the accompanying figures in which equal numerals represent equal or similar
components.
[0047] Figure 1 shows an embodiment of a turret 1 for mooring a production vessel to a seabed
(not shown). The turret 1 comprises a geostationary unit 5 comprising guide tubes
14 which extends in the direction of the unit's 5 (and thus turret's) center axis
15. The plurality of guide tubes 14 are configured to guide risers, umbilical's or
cables 16 through the axial length of the turret 1 (see figure 9). By connecting the
geostationary unit 5 of the turret 1 rotationally to the vessel 100, the vessel 100
may pivot around the geostationary unit 5 in response to changes in wind, waves, and
currents without disturbing either the risers 16 or the mooring lines 8,11. The inventive
turret 1 further comprises a weathervaning unit 6 that rotationally surrounds the
axial circumference of the geostationary unit 5 and which is fixed to the geostationary
unit 5 and to its surrounding hull / vessel structure 110 by bearings 2,2',3 and by
fixing devices 7a,7b, respectively. As better illustrated in figure 4, the positions
of these fixing devices 7a,7b are arranged asymmetrically around the central axis
15 of the turret 1. More specifically, the four fixing devices 7a,7b in figure 4 rigidly
connects the weathervaning unit 6 to its surrounding hull 110 at one radial side of
the center axis 15 only, for example at one side of the center axis 15 in the longitudinal
direction of the vessel 100. The reason for this particular arrangement is that any
distortion / deformation of the hull 110 will not be transmitted to the weathervaning
unit 6, but instead cause a displacement of the weathervaning unit 6 in direction
away from the fixing devices 7a,7b that avoids destructive built-up of stresses within
the turret 1. I.e., any hull distortions have insignificant impact on the operation
of the turret 1.
[0048] Below the guide tubes 14 there may be installed auxiliary equipment such as bending
limiters. Such equipment may be mounted prior to setting up the vessel at the production
field.
[0049] As seen in figure 1 the turret 1 comprises a small diameter upper bearing 2,2' situated
at an upper part of the weathervaning unit 6, and a large diameter lower bearing 3
(i.e. larger than the upper bearings 2,2') situated at a lower part of the weathervaning
unit 6. The upper bearing 2,2' may comprise both an axial upper bearing 2 and a radial
upper bearing 2', while the lower bearing 3 may comprise a radial lower bearing 3
only.
[0050] Figure 7 also shows a plurality of chain cables 8 being connected to respective anchor
winches 10. The anchor winches 10 are fixed to the geostationary unit 5 below the
upper bearings 2,2'. Each of the chain cables 8 are guided through respective chain
stoppers 9 situated on the geostationary unit 5, in figure 1 seen supported on a projecting
block 18 below the upper bearings 2,2'. The chain cables 8 are pulled in by the dedicated
anchor winches 10. This arrangement renders pull-in of mooring lines 8,11 possible
without forcing the vessel 100 to keep a fixed heading during the operation. In an
alternative embodiment, the anchor winches 10 may be arranged on a deck 108, for example
at the same level as the upper bearing(s) 2,2', or arranged on or above the main deck
108 of the vessel 100. Anchor winches 10 may be installed for every group of anchor
lines 8,11 and/or for each of the anchor lines 8,11. If only one anchor winch 10 for
each anchor line 8,11 group is used, a chain cable 8 will after pull-in be locked
into position by the chain stopper 9 and the chain cable 8 is cut of. The end of the
chain 8 situated above the chain stopper 9 may advantageously be suspended in a chain
hang-off padeye placed on the geostationary unit 5. By use of one anchor winch 10
per anchor line 8,11 it is no longer necessary to cut the chain cable 8.
[0051] The turret 1 further comprises a plurality of fairleads 13 into which the chain cables
8 are guided. The pivotable fairleads 13 are fixed to the lower end of the geostationary
unit 5 below the lower bearing 3 such that the fairlead's outermost radial position
(that is, in the outermost position in the direction perpendicular to the center axis
15) may be switched between positions outside and inside the weathervaning unit 6.
The latter positions of the fairleads 13, pivoted to have outermost radial positions
laying within the smallest cavity diameter of the weathervaning unit 6, are useful
when the turret 1 is to be lifted into the vessel 100, either in parts or in it's
entirely, for example during transport from docking to production site.
[0052] Figures 2 (a) and (b) show cross section views of the weathervaning unit 6 viewed
from the side (a) and at section C-C (b), respectively. Three fixing devices 7a,7b
are shown, arranged to form the mentioned asymmetric configuration.
[0053] In both figures 1 and 3 a plurality of guide tubes 14 are seen extending through
the geostationary unit 5 with an angle from the center axis 15 slightly larger than
zero, for example between 1-10°. The tubes 14 are configured to contain various equipment
16 intended to be guided down to the seabed during operation, for example risers,
umbilical's or cables (see figure 9). Due to the bearings 2,2',3 between the geostationary
unit 5 and the weathervaning unit 6, the vessel 100 is allowed to pivot around the
geostationary unit 5 in response to changes in wind, waves, and currents without disturbing
above mentioned equipment 16 or the mooring lines 8,11.
[0054] Figures 5 and 6 shows an embodiment where the turret 1 is arranged in a transport
position inside a dedicated vertical extending shaft 4 within a hull 110 of a docked
production vessel 100 comprising a vessel deck 108, a keel 102, derrick 104 with winches
and a winch locker, an access trunk 107 (to access mid part of the turret 1 from the
deck 108) and thrusters 103. The vessel 100 is situated on supporting blocks 101 on
the docking base 105. A water line of the vessel 100 is indicated with reference 109.
As in figures 1 and 3 a plurality of fairleads 13 are shown pivotably fixed to the
lower end 6' of the turret 1. Since the turret 1 in figures 5 and 6 is in its vertically
retracted position (transport position) the fairleads have been pivoted to one side,
thereby reducing the total diameter sufficiently to fit into the relevant diameter
of the shaft 4. Figures 5 and 6 shows a particular fairlead configuration at a vertically
retracted position seen from the side and from below, respectively. The vertical displacement
of the turret 1 is achieved by use of the derrick 104. Also shown in figure 6 are
six through-going channels 14 for guiding seabed extending equipment 16 such as risers,
umbilical's or cables (se figure 9).
[0055] Figure 7-9 shows the turret 1 arranged inside the dedicated shaft 4 of a production
vessel 100 submerged in water 109, and where the turret 1 is in an operational position,
i.e. vertically lowered by the derrick 104 to a level where the fairleads 13 may be
pivoted to such a degree that their diameter exceeds the outer diameter of the shaft's
4 lowest part. In this operational position any seabed extending equipment 16 may
be guided through the plurality of guide tubes 14 and any seabed extending mooring
lines 8,11 may be arranged as seen for conventional turrets. In figure 8, a total
of six guide tubes and a total of 12 mooring lines are illustrated as an example.
Each mooring lines 8,11 are in the embodiment of figure 8 composed of a chain cable
8 extending from the anchor winch to a position below its respective fairlead 13 and
an anchor line 11 (for example made of polyester) extending from the submerged end
of the chain cable 8 to the seabed. Figure 9 shows in perspective the turret 1 in
its operational position within the vessel 100 and with a swivel arrangement 20 enabling
the introduction of fluid into some or all of the seabed extending equipment 16 during
vessel rotation / weathervaning.
[0056] As described earlier, the axial and radial bearings 2,2' are transferring forces
from the geostationary unit 5 to the weathervaning unit 6 (and vice versa). Furthermore,
fixing devices 7a,7b situated between the weathervaning unit 6 and the vessel structure
/ hull 110 are transferring the forces on to the vessel structure 110. The fixing
devices 7a,7b preferably set up a rigid fixing, creating a "single" moveable unit.
In a particular configuration the lower part 6' of the weathervaning unit 6 has contact
faces that are configured such that both horizontal and vertical forces may be transferred
to the vessel structure 110. Further, the fastening point at the upper part 6" of
the weathervaning unit 6 is configured such that the deformation of the vessel structure
110 is not transferred to the turret 1. This means that any deformation force acting
on the vessel structure 110 has insignificant impact on the turret 1. This feature
is herein achieved by fastening only one side of the upper part 6" of the weathervaning
unit 6 to the vessel structure 110. Normally the fastening of the weathervaning unit
6 should be arranged to the side of the turret 1 having a component dominantly in
the vessel's 100 direction of motion. However, if the vessel 100 experiences transverse
deformations it may be beneficial to fasten the weathervaning unit 6 with a component
dominantly in the vessel's 100 transverse direction.
[0057] In order to lower the requirements of tolerances and to minimize the moments needed
to rotate the turret 1, the diameter of the upper axial bearing(s) 2 is significantly
reduced compared to a conventional turret. This diameter reduction is achieved by
letting only seabed extending equipment 16 such as risers and/or umbilicals pass inside
the upper axial bearing(s) 2. In this way the diameters of both the upper axial bearing(s)
2 and the upper radial bearing(s) 2' will be reduced, thereby lowering the friction
moments. This again will significantly simplify the demands for bearing tolerances
etc.
[0058] The bearing surface(s) of the upper axial bearing(s) 2 and the upper radial bearing(s)
2' may be locked to the weathervaning unit 6, for example at or near its rim. Since
the fixing(s) is/are only on one side (in the longitudinal and/or transverse direction)
the deformations from the vessel 100 will not be transferred to the bearing surfaces.
This ensures that the bearings 2,2',3 will have an optimum contact face being at least
close to independent of outer strains.
[0059] As a consequence of the method of lifting / lowering the turret 1 (figure 5 and 7),
the main (or even the entire) mounting procedure may take place when the vessel 100
is still in dock. By suspending part or the entire turret 1 in a position where the
lower part of the turret 1 are located in line with, or above, the keel 102, conventional
docking is possible where the vessel 100 is supported on supporting blocks 101 having
a conventional height. When the vessel 100 is out of the dock, for example over a
hydrocarbon producing area, at least part of the turret 1 may be lowered and locked
into the operational / mooring position. In an equivalent way the at least part of
the turret 1 may be lifted up to a transport position prior to further transport and/or
docking.
[0060] In the preceding description, various aspects of the assembly, the vessel and the
method according to the invention have been described with reference to the illustrative
embodiment. For purposes of explanation, specific numbers, systems and configurations
were set forth in order to provide a thorough understanding of the invention and its
workings. However, this description is not intended to be construed in a limiting
sense. Various modifications and variations of the illustrative embodiment, as well
as other embodiments of the system, which are apparent to persons skilled in the art
to which the disclosed subject matter pertains, are deemed to lie within the scope
of the present invention.
List of reference numerals / letters:
1 |
Turret assembly / turret |
2 |
Upper axial bearing |
2' |
Upper radial bearing |
3 |
Lower radial bearing |
4 |
Turret receiving space / vertically extending shaft / well |
5 |
Geostationary inner turret unit / Geostationary unit |
5' |
Base of inner turret unit |
5" |
Top of inner turret unit |
6 |
Turret supporting structure / weathervaning unit |
6' |
Lower part of the outer turret unit |
6" |
Upper part of the outer turret unit |
7a |
First fixing means (for fixing of outer turret unit to vessel traverse of vessel's
direction of motion), fixing device |
7b |
Second fixing (for fixing of outer turret unit to vessel along vessel's direction
of motion), fixing device |
8 |
Chain cable |
9 |
Chain stopper |
10 |
Anchor winch |
11 |
Anchor line / mooring line |
13 |
Fairlead |
14 |
Through-going channels / guide tube |
15 |
Center axis of turret assembly / turret |
16 |
Equipment (risers, umbilical, cables, etc.), seabed extending equipment |
18 |
Projecting block |
20 |
Swivel arrangement |
100 |
Turret assembly vessel |
101 |
Supporting block |
102 |
Keel / vessel base |
103 |
Thruster (as part of a dynamic positioning system of the vessel) |
104 |
Lifting device / derrick |
105 |
Docking base |
106 |
Vessel anchor |
107 |
Access trunk (to access mid part of turret 1 from vessel deck 108) |
108 |
Vessel main deck |
109 |
Water / water line |
110 |
Vessel hull / vessel structure |
1. A turret assembly (1) for mooring a production vessel (100) to a seabed (105) and
for transferring fluids from a subsea flowline to the vessel (100), wherein the turret
assembly (1) comprises:
- a geostationary inner turret unit (5) displaying at least one through-going channel
(14) extending axially along a longitudinal center axis (15) of the inner turret unit
(5),
- a turret supporting structure (6) rotationally surrounding the inner turret unit
(5), the rotational axis of the turret supporting structure (6) being equal with the
longitudinal center axis (15) of the geostationary inner turret unit (5), the turret
supporting structure (6) comprising fixing means (7a,7b) configured to fix the turret
supporting structure (6) to a hull structure of the vessel (100), the fixing means
(7a,7b) being arranged asymmetric around the longitudinal center axis (15) of the
inner turret unit (5), and fixed onto the exterior of the turret supporting structure
(6) either;
- at one side of a center plane running through the longitudinal center axis (15)
and directed perpendicular to a direction of motion of the vessel (100) during use,
or
- at one side of a center plane running through the longitudinal center axis (15)
and directed parallel to the direction of motion of the vessel (100) during use, or
- a combination thereof,
so that, in use, any deformation force acting on a hull (110) of the vessel (100)
has insignificant impact on the turret assembly (1), and
- a bearing arrangement (2,2',3) situated between the geostationary inner turret unit
(5) and the turret supporting structure (6) allowing the inner turret unit (5) to
rotate relative to the turret supporting structure (6) and to transfer forces from
the geostationary inner turret unit (5) to the turret supporting structure (6).
2. The turret assembly (1) in accordance with claim 1, wherein an exterior contact surface
of the turret supporting structure (6) is designed such that, when installed in a
vertical extending shaft (4) of a vessel (100), both horizontal and vertical forces
are transferred between the hull (110) of the vessel (100) and the turret supporting
structure (6).
3. The turret assembly (1) in accordance with claim 1 or 2, wherein the fixing means
(7a,7b) is, relative to the longitudinal center axis (15), located at or above the
level of the upper bearing (2,2').
4. The turret assembly (1) in accordance with any one of the preceding claims, wherein
the bearings arrangements (2,2',3) comprising;
- an upper bearing (2,2') situated at an upper part (6") of the turret supporting
structure (6) and
- a lower bearing (3) situated at a lower part (6") of the turret supporting structure
(6) having an diameter being larger than the diameter of the upper bearings (2,2').
5. The turret assembly (1) in accordance with claim 4, wherein the diameter of the upper
bearing (2,2') is less than 75 % of the diameter of the lower bearing.
6. The turret assembly (1) in accordance with any one of claims 4 or 5, wherein the upper
bearing (2,2') comprises
- an axial upper bearing (2) accommodating loads predominantly parallel to the longitudinal
center axis of the turret assembly (1) and
- a radial upper bearing (2') accommodating loads predominantly perpendicular to the
longitudinal center axis of the turret assembly (1).
7. The turret assembly (1) in accordance with any one of claims 4 to 6, wherein the lower
bearing (3) comprises a radial lower bearing (3) accommodating loads predominantly
perpendicular to the longitudinal center axis of the turret assembly (1).
8. The turret assembly (1) in accordance with any one of the claims 4-7, wherein the
turret assembly (1) comprises at least one chain cable (8) extending at least partly
between the inner turret unit (5) and the turret supporting structure (6), wherein
the end of the at least one chain cable (8) is fixed at a position between the upper
bearings (2,2') and the lower bearing (3).
9. The turret assembly (1) in accordance with claim 8, wherein the end of the at least
one chain cable (8) is guided through at least one anchor winch (10), the at least
one anchor winch (10) being fixed to the inner turret unit (5) below the upper bearing
(2,2').
10. The turret assembly (1) in accordance with claim 8 or 9, wherein the end of the at
least one chain cable (8) is fixed in a chain locker (17) of the inner turret unit
(5) via at least one anchor winch (10).
11. The turret assembly (1) in accordance with any one of claim 8 to 10, wherein the turret
assembly (1) further comprises at least one pivotable fairlead (13) for guiding and
control of the chain cable (8).
12. The turret assembly (1) in accordance with claim 11, wherein the at least one pivotable
fairlead (13) is fixed below the lower bearing (3) on the lower end of the inner turret
unit (5) and designed such that the total radial diameter set up by the at least one
fairlead (13) and the inner turret unit (5) may change between a radial diameter being
larger than the base diameter of the turret supporting structure (6) and a radial
diameter being smaller than the base diameter of the turret supporting structure (6).
13. A production vessel (100) for producing hydrocarbons from an offshore reservoir, the
production vessel (100) comprising a hull (110) displaying at least one well (4) extending
vertically within said hull (110) and having an lower open end, wherein the vessel
(100) further comprises a turret assembly (1) in accordance with any one of claims
1-12 mounted within the well (4).
14. A method for mooring a vessel (100) to a seabed, wherein the method comprises the
steps of:
- prefabricating, while in dock, a turret assembly (1) according to any one of claims
1-12,
- transferring the prefabricated turret assembly (1) into a well (4) located within
the vessel (100) such that a base (5') of the inner turret unit (5) is situated in
a transport position at or above a keel (102) of the vessel (100),
- moving the vessel (100) to an offshore mooring site,
- vertically lowering the prefabricated turret assembly (1) to a mooring position
where the base (5') of the inner turret unit (5) is located below the keel (102) of
the vessel (100), and
- locking the prefabricated turret assembly (1) into the mooring position.
15. The method in accordance with claim 14, wherein the method further comprises the step
of:
- unlocking the prefabricated turret assembly (1) from its mooring position,
- vertically raising the prefabricated turret assembly (1) from its mooring position
to the transport position prior to moving the vessel (100) from the offshore mooring
site.
16. The method in accordance with claim 14 or 15, wherein the step of prefabricating includes
mounting a plurality of fairleads (13) near the base (5') of the inner turret unit
(5), the plurality of fairleads (13) being pivotably mounted near the base (5') enabling
pivoting of the fairleads (13) towards the exterior wall of inner turret unit (5).
17. The method in accordance with any one of claims 14 to 16, wherein the prefabricated
turret assembly (1) is in accordance with any one of claims 1 to 12.
1. Drehzylinderanordnung (1) zum Verankern eines Produktionsschiffes (100) an einem Meeresboden
(105) und zum Übertragen von Fluiden von einer Unterwasserströmungsleitung zu dem
Schiff (100), wobei die Drehzylinderanordnung (1) Folgendes umfasst;
- eine geostationäre innere Drehzylindereinheit (5), die mindestens einen durchgehenden
Kanal (14) aufweist, der sich axial entlang einer Längsmittelachse (15) der inneren
Drehzylindereinheit (5) erstreckt,
- eine Drehzylinderstützstruktur (6), die die innere Drehzylindereinheit (5) drehbar
umgibt, wobei die Drehachse der Drehzylinderstützstruktur (6) der Längsmittelachse
(15) der geostationären inneren Drehzylindereinheit (5) entspricht, wobei die Drehzylinderstützstruktur
(6) Befestigungsmittel (7a, 7b) umfasst, die dazu ausgelegt sind, die Drehzylinderstützstruktur
(6) an einer Rumpfstruktur des Schiffes (100) zu befestigen, wobei die Befestigungsmittel
(7a, 7b) asymmetrisch um die Längsmittelachse (15) der inneren Drehzylindereinheit
(5) angeordnet sind und folgendermaßen an der Außenseite der Drehzylinderstützstruktur
(6) befestigt sind;
- entweder auf einer Seite einer Mittelebene, die durch die Längsmittelachse (15)
verläuft und während der Verwendung senkrecht zu einer Bewegungsrichtung des Schiffes
(100) gerichtet ist, oder
- auf einer Seite einer Mittelebene, die durch die Längsmittelachse (15) verläuft
und während der Verwendung parallel zur Bewegungsrichtung des Schiffes (100) gerichtet
ist, oder
- eine Kombination davon,
derart dass bei der Verwendung jede Verformungskraft, die auf einen Rumpf (110) des
Schiffes (100) wirkt, einen unbedeutenden Einfluss auf die Drehzylinderanordnung (1)
hat, und
- eine Lageranordnung (2, 2', 3), die zwischen der geostationären inneren Drehzylindereinheit
(5) und der Drehzylinderstützstruktur (6) angeordnet ist und es der inneren Drehzylindereinheit
(5) ermöglicht, sich relativ zur Drehzylinderstützstruktur (6) zu drehen und Kräfte
von der geostationären inneren Drehzylindereinheit (5) auf die Drehzylinderstützstruktur
(6) zu übertragen.
2. Drehzylinderanordnung (1) nach Anspruch 1,
wobei eine äußere Kontaktfläche der Drehzylinderstützstruktur (6) derart ausgebildet
ist, dass sowohl horizontale als auch vertikale Kräfte zwischen dem Rumpf (110) des
Schiffes (100) und der Drehzylinderstützstruktur (6) übertragen werden, wenn diese
in einen sich vertikal erstreckenden Schacht (4) eines Schiffes (100) eingebaut ist.
3. Drehzylinderanordnung (1) nach Anspruch 1 oder 2, wobei sich die Befestigungsmittel
(7a, 7b) in Bezug auf die Längsmittelachse (15) auf oder über dem Niveau des oberen
Lagers (2, 2') befinden.
4. Drehzylinderanordnung (1) nach einem der vorstehenden Ansprüche, wobei die Lageranordnungen
(2, 2', 3) Folgendes umfassen;
- ein oberes Lager (2, 2'), das sich an einem oberen Teil (6") der Drehzylinderstützstruktur
(6) befindet, und
- ein unteres Lager (3), das sich an einem unteren Teil (6") der Drehzylinderstützstruktur
(6) befindet und einen Durchmesser aufweist, der größer ist als der Durchmesser der
oberen Lager (2, 2').
5. Drehzylinderanordnung (1) nach Anspruch 4,
wobei der Durchmesser des oberen Lagers (2, 2') weniger als 75 % des Durchmessers
des unteren Lagers beträgt.
6. Drehzylinderanordnung (1) nach einem der Ansprüche 4 oder 5,
wobei das obere Lager (2, 2') Folgendes umfasst:
- ein axiales oberes Lager (2), das Lasten aufnimmt, die überwiegend parallel zur
Längsmittelachse der Drehzylinderanordnung (1) verlaufen, und
- ein radiales oberes Lager (2'), das Lasten aufnimmt, die überwiegend senkrecht zur
Längsmittelachse der Drehzylinderanordnung (1) verlaufen.
7. Drehzylinderanordnung (1) nach einem der Ansprüche 4 bis 6,
wobei das untere Lager (3) ein radiales unteres Lager (3) umfasst, das Lasten aufnimmt,
die überwiegend senkrecht zur Längsmittelachse der Drehzylinderanordnung (1) verlaufen.
8. Drehzylinderanordnung (1) nach einem der Ansprüche 4-7, wobei die Drehzylinderanordnung
(1) mindestens eine Ankerkette (8) umfasst, das sich mindestens teilweise zwischen
der inneren Drehzylindereinheit (5) und der Drehzylinderstützstruktur (6) erstreckt,
wobei das Ende der mindestens einen Ankerkette (8) an einer Position zwischen den
oberen Lagern (2, 2') und dem unteren Lager (3) befestigt ist.
9. Drehzylinderanordnung (1) nach Anspruch 8,
wobei das Ende der mindestens einen Ankerkette (8) durch mindestens eine Ankerwinde
(10) geführt ist, wobei die mindestens eine Ankerwinde (10) an der inneren Drehzylindereinheit
(5) unterhalb des oberen Lagers (2, 2') befestigt ist.
10. Drehzylinderanordnung (1) nach Anspruch 8 oder 9,
wobei das Ende der mindestens einen Ankerkette (8) über mindestens eine Ankerwinde
(10) in einem Kettenkasten (17) der inneren Drehzylindereinheit (5) befestigt ist.
11. Drehzylinderanordnung (1) nach einem der Ansprüche 8 bis 10,
wobei die Drehzylinderanordnung (1) ferner mindestens eine schwenkbare Klüse (13)
zum Führen und Steuern der Ankerkette (8) umfasst.
12. Drehzylinderanordnung (1) nach Anspruch 11,
wobei die mindestens eine schwenkbare Klüse (13) unterhalb des unteren Lagers (3)
am unteren Ende der inneren Drehzylindereinheit (5) befestigt und derart ausgebildet
ist, dass der radiale Gesamtdurchmesser, der von der mindestens einen Klüse (13) und
der inneren Drehzylindereinheit (5) hergestellt wird, zwischen einem radialen Durchmesser,
der größer als der Basisdurchmesser der Drehzylinderstützstruktur (6) ist, und einem
radialen Durchmesser, der kleiner als der Basisdurchmesser der Drehzylinderstützstruktur
(6) ist, wechseln kann.
13. Produktionsschiff (100) zum Produzieren von Kohlenwasserstoffen aus einer Offshore-Lagerstätte,
wobei das Produktionsschiff (100) einen Rumpf (110) umfasst, der mindestens einen
Schacht (4) aufweist, der sich vertikal innerhalb des Rumpfes (110) erstreckt und
ein unteres offenes Ende aufweist,
wobei das Schiff (100) ferner eine Drehzylinderanordnung (1) nach einem der Ansprüche
1-12 umfasst, die innerhalb des Schachtes (4) montiert ist.
14. Verfahren zum Verankern eines Schiffes (100) an einem Meeresboden,
wobei das Verfahren folgende Schritte umfasst:
- Vorfertigen einer Drehzylinderanordnung (1) nach einem der Ansprüche 1-12, während
es im Dock liegt,
- Überführen der vorgefertigten Drehzylinderanordnung (1) in einen Schacht (4), der
innerhalb des Schiffes (100) angeordnet ist, derart dass sich eine Basis (5') der
inneren Drehzylindereinheit (5) in einer Transportposition an oder über einem Kiel
(102) des Schiffes (100) befindet,
- Bewegen des Schiffes (100) zu einem Offshore-Ankerplatz,
- vertikales Absenken der vorgefertigten Drehzylinderanordnung (1) in eine Verankerungsposition,
in der die Basis (5') der inneren Drehzylindereinheit (5) unterhalb des Kiels (102)
des Schiffes (100) angeordnet ist, und
- Verriegeln der vorgefertigten Drehzylinderanordnung (1) in der Verankerungsposition.
15. Verfahren nach Anspruch 14,
wobei das Verfahren ferner folgenden Schritt aufweist:
- Entriegeln der vorgefertigten Drehzylinderanordnung (1) aus ihrer Verankerungsposition,
- vertikales Anheben der vorgefertigten Drehzylinderanordnung (1) aus ihrer Verankerungsposition
in die Transportposition, bevor das Schiff (100) von dem Offshore-Ankerplatz bewegt
wird.
16. Verfahren nach Anspruch 14 oder 15,
wobei der Schritt des Vorfertigens das Montieren einer Vielzahl von Klüsen (13) in
der Nähe der Basis (5') der inneren Drehzylindereinheit (5) beinhaltet, wobei die
Vielzahl von Klüsen (13) in der Nähe der Basis (5') schwenkbar montiert ist, was das
Schwenken der Klüsen (13) in Richtung der Außenwand der inneren Drehzylindereinheit
(5) ermöglicht.
17. Verfahren nach einem der Ansprüche 14 bis 16,
wobei die vorgefertigte Drehzylinderanordnung (1) einem der Ansprüche 1 bis 12 entspricht.
1. Assemblage de tourelle (1) pour l'amarrage d'un navire de production (100) à un fond
marin (105) et pour le transfert de fluides d'une conduite sous-marine jusqu'au navire
(100), dans lequel l'assemblage de tourelle (1) comprend :
- une unité de tourelle intérieure géostationnaire (5) présentant au moins un canal
traversant (14) s'étendant axialement le long d'un axe central longitudinal (15) de
l'unité de tourelle intérieure (5),
- une structure de soutien de tourelle (6) entourant, de manière à pouvoir tourner,
l'unité de tourelle intérieure (5), l'axe de rotation de la structure de soutien de
tourelle (6) étant identique à l'axe central longitudinal (15) de l'unité de tourelle
intérieure géostationnaire (5), la structure de soutien de tourelle (6) comprenant
des moyens de fixation (7a, 7b) configurés pour fixer la structure de soutien de tourelle
(6) à une structure de coque du navire (100), les moyens de fixation (7a, 7b) étant
agencés asymétriques autour de l'axe central longitudinal (15) de l'unité de tourelle
intérieure (5), et fixés sur l'extérieur de la structure de soutien de tourelle (6)
soit :
- à un côté d'un plan central traversant l'axe central longitudinal (15) et dirigé
perpendiculairement à un sens de mouvement du navire (100) en utilisation, ou
- à un côté d'un plan central traversant l'axe central longitudinal (15) et dirigé
parallèlement au sens de mouvement du navire (100) en utilisation, soit
- une combinaison des deux,
de sorte que, en utilisation, toute force de déformation agissant sur une coque (110)
du navire (100) ait un impact insignifiant sur l'assemblage de tourelle (1), et
- un agencement de paliers (2, 2', 3) situé entre l'unité de tourelle intérieure géostationnaire
(5) et la structure de soutien de tourelle (6) permettant à l'unité de tourelle intérieure
(5) de tourner par rapport à la structure de soutien de tourelle (6) et de transférer
des forces de l'unité de tourelle intérieure géostationnaire (5) à la structure de
soutien de tourelle (6).
2. Assemblage de tourelle (1) selon la revendication 1, dans lequel
une surface de contact extérieure de la structure de soutien de tourelle (6) est conçue
de sorte que, lorsqu'elle est installée dans un arbre d'extension verticale (4) d'un
navire (100), des forces horizontales et verticales soient transférées entre la coque
(110) du navire (100) et la structure de soutien de tourelle (6).
3. Assemblage de tourelle (1) selon la revendication 1 ou 2, dans lequel les moyens de
fixation (7a, 7b) sont, par rapport à l'axe central longitudinal (15), situés au niveau
ou au-dessus du palier supérieur (2, 2').
4. Assemblage de tourelle (1) selon l'une quelconque des revendications précédentes,
dans lequel
les agencements de paliers (2, 2', 3) comprennent :
- un palier supérieur (2, 2') situé à une partie supérieure (6") de la structure de
soutien de tourelle (6) et
- un palier inférieur (3) situé à une partie inférieure (6") de la structure de soutien
de tourelle (6) ayant un diamètre plus grand que le diamètre des paliers supérieurs
(2, 2').
5. Assemblage de tourelle (1) selon la revendication 4, dans lequel
le diamètre du palier supérieur (2, 2') est inférieur à 75 % du diamètre du palier
inférieur.
6. Assemblage de tourelle (1) selon la revendication 4 ou 5, dans lequel
le palier supérieur (2, 2') comprend :
- un palier supérieur axial (2) recevant des charges principalement parallèles à l'axe
central longitudinal de l'assemblage de tourelle (1) et
- un palier supérieur radial (2') recevant des charges principalement perpendiculaires
à l'axe central longitudinal de l'assemblage de tourelle (1).
7. Assemblage de tourelle (1) selon l'une quelconque des revendications 4 à 6, dans lequel
le palier inférieur (3) comprend un palier inférieur radial (3) recevant des charges
principalement perpendiculaires à l'axe central longitudinal de l'assemblage de tourelle
(1).
8. Assemblage de tourelle (1) selon l'une quelconque des revendications 4 à 7, dans lequel
l'assemblage de tourelle (1) comprend au moins un câble de chaîne (8) s'étendant au
moins partiellement entre l'unité de tourelle intérieure (5) et la structure de soutien
de tourelle (6), dans lequel l'extrémité de l'au moins un câble de chaîne (8) est
fixée à une position entre les paliers supérieurs (2, 2') et le palier inférieur (3).
9. Assemblage de tourelle (1) selon la revendication 8, dans lequel
l'extrémité de l'au moins un câble de chaîne (8) est guidée à travers au moins un
guindeau (10), l'au moins un guindeau (10) étant fixé à l'unité de tourelle intérieure
(5) au-dessous du palier supérieur (2, 2').
10. Assemblage de tourelle (1) selon la revendication 8 ou 9, dans lequel
l'extrémité de l'au moins un câble de chaîne (8) est fixée à un puits à chaîne (17)
de l'unité de tourelle intérieure (5) via au moins un guindeau (10).
11. Assemblage de tourelle (1) selon l'une quelconque des revendications 8 à 10, dans
lequel
l'assemblage de tourelle (1) comprend en outre au moins un chaumard pouvant pivoter
(13) pour le guidage et la commande du câble de chaîne (8).
12. Assemblage de tourelle (1) selon la revendication 11, dans lequel
l'au moins un chaumard pouvant pivoter (13) est fixé au-dessous du palier inférieur
(3) à l'extrémité inférieure de l'unité de tourelle intérieure (5) et est conçu de
sorte que le diamètre radial total constitué par l'au moins un chaumard (13) et l'unité
de tourelle intérieure (5) puisse changer entre un diamètre radial qui est supérieur
au diamètre de base de la structure de soutien de tourelle (6) et un diamètre radial
qui est inférieur au diamètre de base de la structure de soutien de tourelle (6).
13. Navire de production (100) pour la production d'hydrocarbures depuis une zone d'exploitation
en mer, le navire de production (100) comprenant une coque (110) présentant au moins
un puits (4) s'étendant verticalement à l'intérieur de ladite coque (110) et ayant
une extrémité ouverte inférieure, dans lequel
le navire (100) comprend en outre un assemblage de tourelle (1) selon l'une quelconque
des revendications 1 à 12 monté à l'intérieur du puits (4).
14. Procédé d'amarrage d'un navire (100) à un fond marin, dans lequel le procédé comprend
les étapes suivantes :
- la préfabrication, à quai, d'un assemblage de tourelle (1) selon l'une quelconque
des revendications 1 à 12,
- le transfert de l'assemblage de tourelle (1) préfabriqué dans un puits (4) situé
à l'intérieur du navire (100) de sorte qu'une base (5') de l'unité de tourelle intérieure
(5) soit située à une position de transport au niveau ou au-dessus d'une quille (102)
du navire (100),
- le déplacement du navire (100) jusqu'à un site d'amarrage en mer,
- l'abaissement vertical de l'assemblage de tourelle (1) préfabriqué à une position
d'amarrage à laquelle la base (5') de l'unité de tourelle intérieure (5) est située
au-dessous de la quille (102) du navire (100), et
- le verrouillage de l'assemblage de tourelle (1) préfabriqué à la position d'amarrage.
15. Procédé selon la revendication 14, dans lequel le procédé comprend en outre les étapes
suivantes :
- le déverrouillage de l'assemblage de tourelle (1) préfabriqué de sa position d'amarrage,
- le levage vertical de l'assemblage de tourelle (1) préfabriqué de sa position d'amarrage
à la position de transport avant le déplacement du navire (100) depuis le site d'amarrage
en mer.
16. Procédé selon la revendication 14 ou 15, dans lequel l'étape de la préfabrication
inclut le montage d'une pluralité de chaumards (13) à proximité de la base (5') de
l'unité de tourelle intérieure (5), la pluralité de chaumards (13) étant montés de
manière à pouvoir pivoter à proximité de la base (5') permettant le pivotement des
chaumards (13) vers la paroi extérieure de l'unité de tourelle intérieure (5).
17. Procédé selon l'une quelconque des revendications 14 à 16, dans lequel l'assemblage
de tourelle (1) préfabriqué est selon l'une quelconque des revendications 1 à 12.