Plant for the construction of large floaters, in particular for wind farms

Abstract

A plant for manufacturing a large floater (10), in particular for wind farms, comprises a starting station (110), a forming station (120), an outlet bench (140), a milling station (150) and a calendering station (160). The calendering station (160) comprises a verticalization device (164) for arranging the sheet (130) in an upright manner, and a vertical-axis calender machine (166) for bending the upright sheet (130) and forming a collar (170) for the floater (10) with vertical axis. The inner side surface of the collar corresponds to the planar face of the sheet.

Description

"PLANT FOR THE CONSTRUCTION OF LARGE FLOATERS, IN PARTICULAR FOR WIND FARMS" DESCRIPTIONField of the invention

[0001] The present invention is in the field of plants and machines for the production of large floaters; in particular, the present invention relates to an integrated system for the production of large floaters for offshore wind farms.Prior art

[0002] Wind turbines, which consist of a vertical tower, a nacelle placed on top of the tower containing the dynamo to generate electricity, and a number of rotating blades that collect the wind and drive the dynamo, are structures of enormous size. For example, a recent semisubmerged plant, in which the base is fixed to the seabed, envisages towers of a height of 100 meters above sea level, to which paddles more than 80 meters long are applied, so that the overall maximum height above sea level is about 190 meters.

[0003] Recently, for a variety of reasons, mainly environmental, plants are becoming more widespread in which turbines are placed on floaters anchored to the seabed by wire cables. Obviously, to ensure the buoyancy of such turbines, under the necessary safety conditions,the floaters must be structurally very reliable and sized to deal with even the most adverse weather conditions, such as strong winds and very rough seas.

[0004] An example of anchoring the floaters to foundation towers for floaters on the seabed is shown in document IT 2020 0001 7887 Al.

[0005] In order to reduce manufacturing costs, large steel sheets that are normally commercially available are sometimes used to make such floaters. Typically, such metal sheets have a length of 12 meters and a width of 4 meters. Each metal sheet has a substantially constant thickness, but varies from one sheet to another, from a few tens of millimeters to 100 millimeters.

[0006] There is therefore a need to manufacture these floaters in a cost-effective manner and in a sufficiently short time, notwithstanding the complexity of the construction; the layout of the plant must also be compact in order to limit land use and minimize the investment for the construction of the plant itself. Object of the invention

[0007] The object of the present invention is to provide a plant for manufacturing large-sized floaters, in particular for offshore wind turbines, from standardsized metal sheets, which may meet the aforementioned requirements. This object is achieved by a plantaccording to claim 1 . The claims dependent thereon identify additional advantageous embodiments of the invention.Brief description of the drawings

[0008] The features and advantages of the plant according to the present invention will become apparent from the following description, given by way of non-limiting example according to the figures in the accompanying drawings, wherein:- Fig. la shows a floater;- Fig. lb shows a cap of the floater in Fig. la;- Fig. lc shows a collar of the floater in Fig. la;- Fig. Id is an axial section of the floater in Fig. la;- Fig. le shows a reinforcing ring of the floater in Fig. la;- Fig. If shows a strut of the reinforcing ring in Fig. le;- Fig. 2 shows a plant for manufacturing floaters according to an embodiment of the present invention;- Fig. 3 shows a starting station, a forming station, an outlet bench, and a milling station of a plant according to an embodiment of the present invention;- Fig. 4 shows a calendering station of a plant according to an embodiment of the present invention;- Fig. 5 shows a strut application station of a plantaccording to an embodiment of the present invention;- Fig. 6 shows a tilting carriage and a welding station of a plant according to an embodiment of the present invention;- Fig. 7 shows a forming station of a floater and a welding station of a plant according to an embodiment of the present invention.Description of a preferred embodiment of the inventionThe floater

[0009] Typically, a floater structure comprises three cylindrical floaters, arranged at the vertices of an imaginary triangle, joined together, for example along the sides of the triangle, by trusses. Typically, the wind turbine, consisting of the column, the nacelle with the dynamo, and the blades, is supported by one of the floaters.

[0010] Referring to Fig. la through If, a floater 10 consists of a cylindrical side wall 12, extending along a central axis X between a lower end 14 and an upper end 16, a lower cap 18, applied to the side wall 12 at the lower end 14, and an upper cap 20, applied to the side wall 12 at the upper end 16. The side wall 12 has an outer side surface 12e and an inner side surface.

[0011] The side wall 12 of the floater 10 consists of a plurality of reinforced collars 22 which, arranged sideby side axially and welded together along the circumferential edges, form the side wall 12. Each collar 22 has an outer side surface 22e and an inner side surface 22i.

[0012] The outer side surface 12e of the side wall 12 of the floater 10 is the union of the outer side surfaces 22e of the collars 22; similarly, the inner side surface of the side wall 12 of the floater 10 is the union of the inner side surfaces 22i of the collars 22.

[0013] On the inner side surface 22i of each collar 22, axially spaced circumferential reinforcing rings 24 are welded; each reinforcing ring 24 consists of a plurality of struts 25 made up of an arched T beam, the foot 25a of which is welded to the inner side surface 22i of the collar 22.

[0014] The lower cap 18 and the upper cap 20 are prefabricated and provided to the plant according to the present invention. The cap manufacturing process is not an object of the present invention.The plant

[0015] With reference to Fig. 2 and 3, a system 100 is adapted to make a floater 10 from a plurality of metal sheets 102, a plurality of struts 25, and a prefabricated lower cap 18 and upper cap 20.

[0016] The metal sheet 102 has a length L, between a frontedge 102a and a rear edge 102b, a width W between a right side edge 102c and a left side edge 102d, an upper face 102e, and a lower face 102f.

[0017] In order to preserve the surfaces thereof, the metal sheet 102 is covered by a thin protective layer, usually painted, which forms a primer that covers, in particular, the upper face 102e and the lower face 102f.

[0018] The plant 100 comprises a starting station 110 comprising an inlet bench 112 on which a first metal sheet 102 is positioned, arranged so that the length L is arranged along a first, substantially straight feeding direction Al of the plant, and the width W is perpendicular to the first feeding direction Al. The metal sheet 102 is thus arranged on the bench 112 so as to turn the upper face 102e upwards and the lower face 102f downwards, resting on the bench. The inlet bench 112 is provided with motorized feeding means, for example a plurality of motorized rollers, adapted to move the metal sheet 102 translationally along the first feeding direction Al.

[0019] The plant 100 further comprises a forming station 120, arranged downstream of the starting station 110 along the feeding direction Al. Metal sheets 102 pass through the forming station 120 in sequence, for example a first metal sheet followed by a second metal sheet.

[0020] The forming station 120 comprises milling means for milling the front edge 102a and the rear edge 102b of each metal sheet 102.

[0021] The forming station 120 further comprises lifting means for lifting or lowering a metal sheet so that the upper face of said metal sheet is coplanar to the upper face of a preceding metal sheet, for example adapted to lift or lower the second metal sheet so that the upper face of said second metal sheet is coplanar to the upper face of the first metal sheet. In other words, the lifting means are adapted to adjust the position of the metal sheet so that the upper face of said metal sheet is on the same plane as the upper face of a preceding metal sheet.

[0022] Finally, the forming station 120 comprises first welding means for welding one metal sheet to the subsequent one, i.e., adapted to weld the rear edge 102b of the first metal sheet and the front edge 102a of the second metal sheet.

[0023] This results in a sheet 130 consisting of a sequence of welded metal sheets, coplanar at the top, i.e., having a flat upper face 130sup, since it is formed by the upper faces 102e of the metal sheets 102 made coplanar by the lifting means. Conversely, the lower face 130inf of the sheet 130 consists of the lower faces 102f of the metalsheets, which are not coplanar to each other. Thus, at the bottom, the sheet 130 will have steps due to differences in thickness between the different metal sheets, i.e., the lower face 130inf of the sheet 130 will have stepped irregularities. The sheet 130, moreover, has a total length equal to the circumferential development of the collar to be manufactured.

[0024] The plant 100 further comprises an outlet bench 140 located downstream of the forming station 120 along the first feeding direction Al, comprising a plurality of rollers on which the sheet being formed advances progressively as the subsequent metal sheets are welded.

[0025] The outlet bench 140 further comprises paint stripping means 142 adapted to strip the paint from the upper face 130sup of the sheet 130 to remove the primer, forming bands that are stripped of paint, spaced apart transversely, extending along the entire length of the sheet. In each band which has been stripped of paint, forming the collar, a respective reinforcing ring will be applied.

[0026] Advantageously, the removal of the primer along the bands in which the reinforcing rings will be applied facilitates the successful welding of the reinforcing elements, which otherwise could give rise to defects and porosity in the welding bead.

[0027] Preferably, moreover, the outlet bench 140 comprises marking means 144 adapted to mark, for example by laser, the upper face 130sup of the sheet 130; in particular, said marking is made on the bands that have been stripped of paint, preferably immediately after stripping.

[0028] Advantageously, the marking of the upper face will make the recognition of the correct position of the struts to be welded particularly efficient.

[0029] The outlet bench 140 further comprises tilting means, for example comprising an arm tilting device, adapted to tilt the sheet 130 once the painting and marking have been carried out. Following the tilting, the sheet 130 is arranged on a tilting device 146, parallel to and spaced apart from the first feeding direction A2, so that the planar face of the sheet is placed at the bottom, and the non-planar face, i.e., the face that has the steps, of the sheet is arranged at the top.

[0030] The plant 100 further comprises a milling station 150 placed alongside the outlet bench 140 and the tilting device 146, along a second feeding direction A2, parallel to and spaced apart from the first feeding direction Al.

[0031] The milling station 150 comprises a milling bench 152, comprising milling rollers and sheet locking means, for example comprising electropermanent magnets; the sheet is arranged on the milling rollers along the secondfeeding direction A2, locked in place by the operation of said locking means.

[0032] The milling station 150 further comprises a milling machine 154, for example a portal milling machine, provided with a double milling head which is translatable along said second feeding direction A2, for milling the side and front edges of the sheet 130.

[0033] Advantageously, the action of the locking means - for example, magnets - on the sheet 130 is very effective, since the face turned towards the magnets is the lower face, i.e., the planar face. Advantageously, this allows the correct positioning of the sheet to be maintained even during the milling operation of the lateral edges and front edges of the sheet, which generates elevated actions between the sheet and the milling tools.

[0034] Referring to Fig. 2 and 4, the plant 100 further comprises a calendering station 160 operating downstream of the milling station 150, along the second feeding direction A2.

[0035] The calendering station 160 comprises a calender bench 162 arranged downstream of the milling bench, which extends along the second feeding direction A2 and comprises a plurality of rollers on which the sheet 130 transits.

[0036] The calendering station 160 further comprises a verticalization device 164 adapted to operate on the sheet 130 supported by the calender bench 162 and to rotate it to make it upright, i.e., to arrange it so that it lies substantially in a plane orthogonal to the ground plane.

[0037] The calendering station 160 further comprises a calender machine 166 with vertical axis comprising a plurality of pairs of rollers 168, arranged circumferentially, and a calendering head 169. The upright sheet 130' enters the calendering head 169 and subsequently passes through the pairs of rollers 168 arranged circumferentially, thus being bent to form a circumferential wall with a vertical axis, wherein the front edge of the upright sheet 130' is finally facing the rear edge of the upright sheet 130'. The two edges are spot-welded, for example manually, thus forming a collar 170 having a collar axis Z which, at the time of formation, is vertical.

[0038] The relative position of the pairs of rollers is adjustable, so that the calender assembly may make collars of the desired diameter. For example, in the accompanying figures, a collar 170' having a minimum diameter is also shown.

[0039] Advantageously, the upright sheet 130' faces thecalender machine 166 so that the outer side surface 170e of the collar 170 is formed of the non-planar face, i.e., with steps, of the upright sheet 130', and the inner side surface 170i of the collar 170 is formed of the planar face of the upright sheet 130' formed of the union of the upper faces 102e of the sheets 102, on which the stripped areas, i.e. devoid of primer, and the markings are present. The planar face of the upright sheet 130' faces the center of the calender machine 166.

[0040] With reference to Fig. 2 and 5, the plant 100 further comprises means for moving the collar; for example, said movement means comprise an overhead crane 180a and a picker 180b, for example with a lifting beam. The picker 180b, for example by means of the overhead crane 180a, is applied to the collar 170, which is moved toward an assembly line 190 that extends along a third feeding direction A3, parallel to and spaced apart from the second feeding direction A2, on the side opposite the first feeding direction Al relative to said second feeding direction A2.

[0041] Preferably, the plant 100 comprises two or more assembly lines 190, parallel to each other.

[0042] Each assembly line 190 comprises a strut storage area 200 wherein a plurality of struts 25 is deposited, which are applied to the collar 170.

[0043] The assembly line 190 further comprises a strut application station 210. The collar 170 is transported by the movement means to the strut application station 210; at the same time, the struts 25 of the strut storage area 200 are brought to the application station 210.

[0044] The application station 210 comprises positioning means adapted to position the struts inside the collar 170, against the inner surface, to form reinforcing rings 24, and preferably automated spot-welding means suitable for spot-welding the struts to the inner surface of the collar. In one embodiment variant, the struts are manually spot-welded to the inner surface of the collar.

[0045] A pre-secured collar 170b is thus formed, made up of a circumferential side wall and a plurality of concentric reinforcing rings 24, each of which consists of a plurality of struts 25, axially spaced along the collar axis Z and spot-welded to the inner surface of the circumferential wall.

[0046] Spot-welding is defined as a process that generates a series of spot-welds, at a more or less regular distance from each other, without creating a continuous welding bead. The spot-welding between two mechanical pieces does not form a hermetic joint.

[0047] The application station and the process for applying struts to the collar assembly are illustrated in moredetail in a separate patent application in the name of the Applicant; the teachings relating to the application station and the process for applying the struts to the collar contained in such patent application are incorporated herein for reference.

[0048] With reference to Fig. 2 and 6, the assembly line 190 further comprises a plurality of tilting and self- propelled carriages 230, on which the pre-secured collar 170b is arranged with a vertical collar axis Z and then tilted so as to be arranged with horizontal collar axis Z.

[0049] Alternatively, the pre-secured collar is tilted in such a way as to assume the horizontal collar axis Z and then loaded onto the carriage.

[0050] The assembly line 190 further comprises a collar welding station 240, arranged downstream of the strut application station 210 along said third feeding direction A3. The collar welding station 240 comprises a welding arm 242 to which a carriage 230, carrying the pre-secured collar 170b with horizontal axis, approaches, so as to enter inside the pre-secured collar 170b and to weld the struts to the inner side surface, thus creating a reinforced collar 22.

[0051] Preferably, during the welding process, the presecured collar 170b is stationary and the welding arm 240moves, for example by rotation, inside said collar, carrying out the welding. Alternatively, the pre-secured collar 170b rotates on the carriage 230 about its horizontal collar axis Z, by the means of the carriage's rotational movement means, and the welding arm remains stationary inside the collar while carrying out the welding.

[0052] Advantageously, the pre-secured collar is sufficiently solid to be arranged with a horizontal axis, so as to facilitate the welding operation.

[0053] With reference to Fig. 2 and 7, the assembly line 190 further comprises a floater forming station 250, arranged downstream of said welding station 240, along the third feeding direction A3.

[0054] The floater forming station 250 comprises a movable floater welding station 260, provided with a welding arm 262 and a pair of rails 264, parallel to the third feeding direction A3. The welding station 260 operates along said rails 264.

[0055] A first carriage 230', carrying the lower cap 18 (or the upper cap 20), is arranged along the rails 264 in a predefined position; a second carriage 230'' carrying a first reinforced collar 22, approaches the first carriage 230', so that the first reinforced collar 22 is coaxial to the lower cap 18 (or the upper cap 20) and abuts withthe lower cap 18 (or with the upper cap 20). The floater welding station 260 approaches the carriages 230', 230'' and welds the lower cap 18 (or upper cap 20) to the first reinforced collar 22 along the respective circumferential edges.

[0056] Subsequently, a third carriage 230''' carrying a second reinforced collar 22 approaches the second carriage 230'' so that the second reinforced collar 22 abuts the first reinforced collar 22. The floater welding station 260 approaches the carriages 230'', 230''' and welds the first reinforced collar 22 to the second reinforced collar 22 along the respective circumferential edges.

[0057] Finally, the floater welding station 260 also welds the edges of the collar, which had only been spot-welded in the calendering station.

[0058] The process continues for subsequent reinforced collars, for example until the number of eight collars is reached.

[0059] At the end, a last carriage 230iv, carrying the upper cap 20 (or the lower cap 18), is arranged along the rails 264 and approaches the penultimate carriage, so that the last reinforced collar 22 abuts the upper cap 20 (or the lower cap 18). The floater welding station 260 approaches the last carriage 230iv and welds the uppercap 20 (or lower cap 18) to the last reinforced collar 22, along the respective circumferential edges.

[0060] The floater 10 is thus obtained, having a horizontal floater axis J which is parallel to and coincident with the third feeding direction A3, supported by an assembly of carriages which, collectively, form a transport assembly 300, movable along the rails 264.

[0061] The transport assembly 300 is operated so as to transport the floater 10 along the rails 264 outside the factory. The plant 100 further comprises a Self-Propelled Modular Transporter (SPMT) 400 that interacts with the transport assembly 300 so as to load the floater and free the transport assembly 300. The transporter 400 may thus be used for moving the floater, while the transport assembly 300 returns to the factory, so as to make the carriages available again for the construction of another floater.

[0062] A further object of the present invention is to provide a method for constructing a large floater 10, in particular for wind farms, by means of a plant 100 described thus far.

[0063] Furthermore, the object of the present invention is to provide a method for making a large floater, in particular for wind farms.

[0064] The method for monitoring the manufacture of a largefloater 10, in particular for wind farms, comprises the following steps in sequence:(i) horizontally arranging a metal sheet 102 having an upper face 102e and a lower face 102f;(ii) lifting or lowering the metal sheet so that the upper face of said metal sheet is coplanar to an upper face of the preceding metal sheet;(iii) welding a front edge of the metal sheet and a rear edge of the preceding metal sheet, thus obtaining a sheet 130 consisting of a sequence of welded metal sheets, having a planar upper face 130sup;(iv) turning the sheet 130 to arrange it upright;(v) calendering the upright sheet 130 to form an annular wall with vertical axis of a collar 170 of the floater 10, wherein the inner side surface of the collar corresponds to the planar face of the sheet.

[0065] In one embodiment, between step iii) and step iv) the following steps are envisaged: iiia) tilting the sheet so that the lower face is planar; iiib) locking the sheet having the lower planar face; iiic) milling the lateral edges of the sheet.

[0066] In a further embodiment, between step iii) and step iiia) the following steps are envisaged: iiiaa) stripping the paint from an area of the upper face of the sheet to eliminate a primer;iiiab) marking said area of the upper face.

[0067] According to a further embodiment, after step v) there is envisaged the step of: vi) reinforcing the collar with vertical axis by means of a plurality of struts 25 secured to the inner side surface of the collar by spot-welding, thus obtaining a pre-secured collar.

[0068] In one embodiment, after step vi) the following steps are envisaged:(vii) moving the pre-secured collar with vertical axis to arrange it with a horizontal axis; viii) welding the struts to the inner side surface of the pre-secured collar, thus obtaining a reinforced collar.

[0069] According to a further embodiment, after step viii) there is envisaged the step of: ix) welding the reinforced collar to a preceding reinforced collar 22 to obtain the floater.

[0070] Innovatively, the plant described above meets the aforesaid requirements, in that it makes possible the cost-effective manufacture of large floaters from standard-sized metal sheets. In particular, the calendering of the metal sheet takes place about a vertical axis; this, advantageously, prevents the collar, which is large in size and is formed only of the metal sheet, from collapsing.

[0071] Advantageously, the presence of lifting means in the forming station allows for a sheet to be made even using metal sheets of different thicknesses. In particular, the presence of steps on the lower face of the sheet and, consequently, on the outer side surface of the collar, does not in any way affect the manufacturing process of the floater collar.

[0072] Advantageously, moreover, the construction of the plant is relatively inexpensive, since the layout is very compact.

[0073] It is clear that a person skilled in the art may make changes to the plant described above in order to meet contingent needs, these changes all falling within the scope of protection as defined in the following claims.

Claims

CLAIMS1. A plant (100) for manufacturing a large floater (10), in particular for wind farms, comprising:- a starting station (110) comprising an inlet bench (112) adapted to support a metal sheet (102), arranged so that the length (L) is arranged along a first, substantially straight feeding direction (Al), and the width (W) is perpendicular to the first feeding direction, said metal sheet (102) having an upper face (102e) and a lower face (102f);- a forming station (120) arranged downstream of the starting station (110), comprising milling means for milling a front edge and a rear edge of the metal sheet (102), lifting means for lifting or lowering the metal sheet so that the upper face of said metal sheet is coplanar to an upper face of a preceding metal sheet, and welding means for welding the front edge of the metal sheet and the rear edge of the preceding metal sheet, thus obtaining a sheet (130) consisting of a sequence of welded metal sheets, having a planar upper face (130sup);- an outlet bench (140) placed downstream of the forming station (120), comprising tilting means adapted to tilt the sheet (130) so that the planar face of the sheet is placed at the bottom;- a milling station (150) downstream of the outlet bench(140), comprising a milling bench (152) which supports the sheet (130) having the planar face placed at the bottom, sheet locking means, and a milling machine (154); - a calendering station (160) operating downstream of the milling station (150), comprising a calender bench (162) having a plurality of rollers on which the sheet (130) transits, a verticalization device (164) adapted to operate on the sheet (130) supported by the calender bench (162) and rotate it to arrange it upright, a calender machine (166) with vertical axis, comprising a plurality of pairs of rollers (168) arranged along an imaginary circumference, and a calendering head (169), the planar face of the sheet (130) facing the center of said imaginary circumference of the calender machine (166) to bend the upright sheet (130) and form an annular wall with vertical axis of a collar (169) of the floater (10), wherein the inner side surface of the collar corresponds to the planar face of the sheet.

2. A plant (100) according to claim 1, wherein the outlet bench (140) comprises paint stripping means (142) adapted to strip the paint from the planar upper face (130sup) of the sheet (130) to eliminate a primer.

3. A plant (100) according to claim 2, wherein the outlet bench (140) comprises marking means (144) adapted to mark, for example by laser, the upper face (130sup) ofthe sheet (130).

4. A plant (100) according to any one of the preceding claims, comprising an assembly line (190), a strut application station (210) comprising positioning means adapted to position struts (25) inside the collar (170), and preferably automated spot-welding means adapted to spot-weld the struts to the inner surface of the collar, thus obtaining a pre-secured collar (170b) with vertical axis.

5. A plant (100) according to claim 4, wherein the assembly line (190) further comprises a plurality of tilting and self-propelled carriages (230) on which the pre-secured collar (170b) is arranged with vertical axis and then tilted so as to be arranged with horizontal axis.

6. A plant (100) according to claim 5, wherein the assembly line (190) further comprises a collar welding station (240) arranged downstream of the strut application station (210) to weld the struts to the inner side surface of the collar, thus obtaining a reinforced collar (22).

7. A plant (100) according to claim 6, wherein the assembly line (190) further comprises a floater forming station (250), arranged downstream of the welding station (240), comprising a movable floater welding station (260)for welding the reinforced collars (170c) to one another, a lower cap (18) and an upper cap (20), thus obtaining the floater (10).

8. A method for manufacturing a large floater (10), in particular for wind farms, by means of a plant (100) according to any one of claims 1 to 7.

9. A method for manufacturing a large floater (10), in particular for wind farms, comprising the following steps in sequence: i) horizontally arranging a metal sheet (102) having an upper face (102e) and a lower face (102f); ii) lifting or lowering the metal sheet so that the upper face of said metal sheet is coplanar to an upper face of the preceding metal sheet; iii) welding a front edge of the metal sheet and a rear edge of the preceding metal sheet, thus obtaining a sheet (130) consisting of a sequence of welded metal sheets, having a planar upper face (130sup); iv) turning the sheet (130) to arrange it upright; v) calendering the upright sheet (130) to form an annular wall with vertical axis of a collar (170) of the floater (10), wherein the inner side surface of the collar corresponds to the planar face of the sheet.

10. A method according to claim 9, wherein between step iii) and step iv), there is envisaged the step ofiiia) tilting the sheet so that the lower face is planar; iiib) locking the sheet having the planar lower face; iiic) milling the lateral edges of the sheet.

11. A method according to claim 10, wherein between step iii) and step iiia), there is envisaged the step of iiiaa) stripping the paint from an area of the upper face of the sheet to remove a primer; iiiab) marking said area of the upper face.

12. A method according to any one of claims 9 to 11, wherein following step v), there is envisaged the step of vi) reinforcing the collar with vertical axis by means of a plurality of struts (25) secured to the inner side surface of the collar by spot-welding, thus obtaining a pre-secured collar.

13. A method according to claim 12, wherein following step vi), there is envisaged the step of vii) moving the pre-secured collar with vertical axis to arrange it with horizontal axis; viii) welding the struts to the inner side surface of the pre-secured collar, thus obtaining a reinforced collar.

14. A method according to claim 13, wherein following step viii), there is envisaged the step of ix) welding the reinforced collar to a preceding reinforced collar to obtain the floater.

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