Description:FIELD OF INVENTION
[0001] The present invention relates to a method for installation of offshore wind turbine fully assembled on double hull floatable mounting structure for transporting and installing a wind turbine using hydraulic cylinders on preinstalled jacket structure, periodical maintenance, and eventual decommissioning.
BACKGROUND OF INVENTION
[0002] Wind energy is an energy source that is renewable, pollution free and of large reserves. In view of climate change due to global warming there is increasing focus on wind energy to minimize the discharge of greenhouse gases from use of fossil fuels.
[0003] Offshore wind power or offshore wind energy is the generation of
electricity through wind farms in bodies of water, usually at sea. There are higher wind speeds offshore than on land, so offshore farms generate more electricity per amount of capacity installed. For example: a turbine in a 15-mph wind can generate twice as much energy as a turbine in a 12-mph wind. Faster wind speeds offshore mean much more energy can be generated, and offshore wind farms are also less controversial than those on land, as they have less impact on people and the landscape.
[0004] In recent years, the offshore wind industry has grown at an extremely fast rate due to the higher wind speeds on the ocean. However, the assembly and installation of offshore wind turbines has proven to be difficult and expensive due to the nature of the water and weather conditions. The different types of foundations range from steel monopiles, tripods and jacket structure in addition to gravity based concrete structures that are also used.
[0005] Currently, the most common technique adopted for construction of offshore wind turbine is to install the offshore wind turbine components one by one:
 Installation of the foundation structure
 Installation of Transition Piece
 Installation of Turbine Tower
 Installation of Nacelle
 Installation of Blades
[0006] The most common means of offshore installation of the wind turbine is by using custom built offshore wind farm installation vessels. These are often jackup-vessels that are self-propelled with self-elevating mechanism. Jack-up-vessels have retractable legs that are raised during transit. Once the vessel reaches the installation location, the legs are extended downwards and is then supported by the seabed allowing the vessel to raise itself above the sea surface. Since the vessel is not in contact with the sea surface, it is not impacted by the waves and
provides a stable platform for offshore installation.
[0007] Offshore wind farm installation vessels are expensive to charter typically costing between 100000$/day to 200000$/day. In view of the increasing adoption of offshore wind power worldwide, the availability of these vessels is also in question. The high charter costs and scarcity of these specialized vessels act as a bottleneck to the adoption of offshore wind energy as a sustainable and costeffective means of transition to green energy.
[0008] So, it is necessary to solve the problem of high installation costs and availability of specialized vessels to make offshore wind energy accessible for more countries around the world.
[0009] Some of the cited prior arts are listed below:
Non-patent literature discusses about Offshore Wind Turbine Foundations:
Leveling and Fixation with Hydraulic Cylinders
Offshore wind turbine foundations are built in various configurations, with one of the commonest being the monopile-transition piece foundation, (MP/TP).
MP/ TP Offshore Wind Turbine Foundations:
These steel foundations are used in relatively shallow water (for depths up to 40m). They are one of the simplest types of foundation and round section steel piles, with a diameter of between 3.5 and 4.5 meters. Depending upon the type of ground, the monopile is driven some 10 to 20 meters into the seabed – which provides a secure base for mounting the transition piece and the tower sections.
An important advantage of this type of foundation is that extensive preparation of the seabed is not necessary. Heavy-duty piling equipment is needed, and this foundation type is not ideal in locations with many large boulders in the seabed.
Leveling the Transition Piece:
When you consider the height of these wind turbines and the forces they need to withstand, you can appreciate how important it is to make sure the transition piece is perfectly level. As well as providing stability and structural integrity, this will ensure the turbine generates maximum yield. The transition piece is fitted over the top of the monopile.
The leveling process is done using six to twelve pre-installed hydraulic cylinders attached inside the transition piece. Using hydraulic cylinders makes it possible to position the transition piece to a precise position - even if the monopile is not completely level. The hydraulic leveling system makes use of aluminum spring return cylinders. There are many variants available, and these can be provided with the required capacity and stroke to comply with the design of the application. The system will be supplied complete with fully compatible hoses and HPU’s.
Fixation of the Transition Piece:
Before the TP’s leave the manufacturing yard, six pre-installed horizontal positioned hydraulic cylinders are mounted at the lower part of the TP for fixation during installation and grouting. The equipment connected to each cylinder usually contains six twin hose-sets, including a hose cutter for each cylinder. The fixation cylinders are required to remain pressurized during the grouting process by a manifold.

These cylinders are operated subsea and plungers need to be retracted after the hydraulic system is depressurized. Retracting the plunger is ensured by activating the hose cutter and a reinforced return spring – eliminating the risk of point load and contact corrosion with the MP.
A hydraulic leveling system contains steel spring return cylinders for subsea use, each with a capacity and stroke that complies with your design of the application. The system can be supplied complete with hoses and HPU’s.
Offshore Wind Turbine Foundation: Summary of the Leveling Process
1. Before the transition pieces leave the manufacturing yard, the hydraulic cylinders are set up within the transition piece.
2. The equipment connected to each of the cylinders is predefined between the design engineers of the T&I Contractor in cooperation with the TP Manufacturer and the wind supporting team.
3. Leveling takes place by activating the cylinders. All cylinders are required to remain pressurized during the grouting process by using a ball valve and holding the pressure.
4. Once the transition piece is confirmed a level it is permanently fixed to the monopile by filling the annulus between the monopile and transition piece with high strength grout.
5. The fixation cylinders are operated subsea, and the plunger on each needs to be retracted after the hydraulic system is depressurized to avoid steel to steel contact
6. Retracting the plunger is ensured by activating the hose cutter and a
reinforced return spring. This eliminates the risk of point load and contact corrosion with the monopile.
7. Environmental considerations that are considered include the type of oil. For example, some specific project requirements may state the equipment is pre-filled with the water glycol or bio-degradable oil.
Preventing Subsea Oil Spills:
The quantity of oil used in a small number of hydraulic cylinders may seem small when compared to oil spills from offshore oil and gas operations. But even a small amount can cause harm to wildlife and marine ecosystems. An alternative system besides cutting the hoses subsea and to avoid any leakage from transition piece fixation can be achieved using a Remote Hose disconnector.
The Remote Hose Disconnector RHDC is tested, witnessed, and certified by Lloyds till 100 meters subsea and can be reused.
The advantages of this system are:
 No oil spill in the sea during disconnection
 No need to use a hose cutting tool
 No waste of materials
 Repeatable use
Another Non-Patent Literature discusses about the installation phase is a critical stage during the lifecycle of an offshore wind turbine. This paper presents a state-of-the-art review of the technical aspects of offshore wind turbine installation. An overview is first presented introducing the classification of offshore wind
turbines, installation vessels, rules and regulations, and numerical modeling tools.
Then, various installation methods and concepts for bottom-fixed and floating
wind turbines are critically discussed, following the order of wind turbine
foundations and components. Applications and challenges of the methods are
identified. Finally, future developments in four technical areas are envisioned.
This review aims to guide research and development activities on offshore wind
turbine installation.
WO2022028661A1 explains about a tool for aligning tubular structures of a wind turbine comprises: a support part for attaching the tool to an end region of a first tubular structure. So, as to extend axially outward there from; and a guide part connected to the support part by a bias part and adapted to engage an interior wall of a second tubular structure wherein the bias part is arranged to urge the guide part to exert a radial force on said interior wall when the second tubular structure is moved axially toward the first tubular structure, thereby to guide the second
tubular structure into axial alignment with the first tubular structure.
OBJECT OF INVENTION
[0010] The main object of the invention is to provide a method for installation of an offshore wind turbine, in which four reusable hydraulic cylinders of maximum stroke length of 15 m are installed on a dedicated casing permanently attached to the jacket foundation structure for effectively installing a fully pre-assembled offshore wind turbine on to the jacket foundation structure without any impact.
[0011] Yet another object of the present invention is to provide a method for installation of offshore wind turbine without the need for an expensive specialized windfarm installation vessel.
SUMMARY OF INVENTION
[0012] The present invention relates to a method of installation of an offshore wind turbine fully pre-assembled at port and placed on double hull floatable mounting structure for transporting to offshore windfarm site where the wind turbine is installed using reusable hydraulic cylinders on pre-installed jacket structure without any damage to Jacket structure, and present invention also relates to removing the wind turbine for periodical maintenance, and eventual decommissioning.
[0013] In the present invention the wind turbine that is ready to operate state is pre-installed on a floating barge using onshore crane on port side along with seafastening grillage to steadily hold the wind turbine assembly, and then the floating barge is towed to offshore using a tug, and then the floating vessel is connected to pre-installed mooring spread using supporting vessel and then the floating vessel is positioned to the correct to dock with the pre-installed Jacket structure using mooring winches installed on the floating barge by means of winch pull-in and pay-out.
[0014] Thereafter by extending the hydraulic cylinders installed in dedicated casings of Jacket structure along with the shock absorber and guide frame assembly to take full load of wind turbine then by lowering the hydraulic cylinders to position the fully assembled wind turbine on the jacket foundation then fix the transition piece with the pre-installed Jacket foundation structure to complete the installation process. Then over a period of time using the reverse process of towing floating barge and anchoring using mooring spread the wind turbine is removed from Jacket structure for periodical maintenance/decommissioning.
DETAILED DESCRIPTION OF INVENTION
[0015] The present invention relates to a method for installation of an offshore wind turbine fully assembled on double hull floating vessel for transporting and installing a wind turbine on a pre-installed Jacket foundation structure having a dedicated casing for reusable hydraulic cylinders.
[0016] The Detailed step by step method of installation of an offshore wind turbine on a pre-installed Jacket foundation structure using reusable hydraulic cylinders is as follows.
[0017] At first the mooring pattern is laid in advance of the arrival of the floating vessel (6) carrying the fully assembled wind turbine (22) to hold and to align the floating vessel on to jacket foundation structure. The pre-installation of the mooring spread (21) is completed by means of an Anchor Handling Tug Supply Vessel (AHTS) (18) especially used for laying anchors on the seafloor. The mooring pattern consists of a delta flipper anchor (1), anchor chain (2) and steel rope (3) used to connect the anchor chain to the winch, which is installed on the installation vessel deck and necessary buoys (4) that are connected to ends of steel
rope and the anchor, helps in recovering fore steel rope and anchor.

[0018] The pre-assembly of the wind turbine components is carried out along the quay side of a port closest to the windfarm site using an onshore crane and is assembled on a double hull floating barge structure. The parts of pre-assembled wind turbine is assembled one by one in the following order:
At first the long vertical turbine tower (9) along with the transition piece (12), which is the interface between the pre-installed jacket structure and the turbine tower is placed, the transition piece is fitted with the TP Temporary Guide Attachment (26) which is used for ease of transport of the fully assembled wind turbine and TP Temporary Guide Attachment (26) is also used to mate with the guide frame assembly (16) during offshore installation. Then pod shaped nacelle (10) is placed on the tower to hold the generator and long slender turbine blades (11) are connected to the ends of the nacelle using a crane in a ready to operate
state on to a floating double hull vessel.
[0019] The floating barge (6) fitted with a transport sea-fastening grillage (8) is a restraining structure/mechanism that is designed specifically to withstand all loads (static load of the wind turbine, vessel acceleration loads & wind loads) due to vessel motion during the sea transport of the fully assembled wind turbine (22) to hold the wind turbine assembly in position on the vessel deck.
[0020] The Jacket foundation structure is installed on a dedicated location prior to the arrival of fully assembled wind turbine assembly along with the hydraulic cylinders, Shock absorber assembly (15) just above the hydraulic cylinders that reduces the impact load and guide frame assembly (16) placed on top of the Shock absorber assembly to ensure the unhindered mating of jacket and the turbine transition piece during installation procedure. The Jacket foundation structure of
the present invention has a dedicated casing to hold the reusable hydraulic cylinders during installation made as an integral part of the Jacket structure to sustain the load of the wind turbine load so as to not cause damage to the Jacket structure. The use of a permanent casing structure in the jacket together with reusable hydraulic cylinders is the pitch concept of the invention.
[0021] The installation of the hydraulic cylinder (13), shock absorber assembly (15) and guide frame (16) assembly are completed using a supporting crane vessel (24). A supporting crane vessel (24) is a cheap and simple solution to complete pre-installation activities prior to the arrival of the floating barge (6) carrying the fully assembled wind turbine. A cheap land-based crawler crane (25) is installed on the supporting crane vessel (24) to lift and install the hydraulic cylinder (13), shock absorber assembly (15) and guide frame assembly (16) on the jacket. Once the wind turbine installation is complete, the same supporting crane vessel (24) is used to remove the hydraulic cylinder, shock absorber assembly and guide frame assembly from the jacket and it is stored on the deck of the supporting crane vessel (24).
[0022] The double hull floating barge (6) fitted with transport grillage for stability of fully assembled wind turbine (22) is towed to the offshore installation site by means of a tug (19) which helps in towing a vessel from one location to another location.
[0023] After the floating barge arrives on site, still being connected to the tug (19), a support vessel (20) which assists the installation barge during installation process, picks up the four winch lines one after the other from the floating barge (6) and connects to the pre-laid mooring pattern (21). The four winches (5) onboard the floating barge deck are used to wind up or wind out the wire rope, and adjust tensions on all the mooring lines. After the mooring lines are tensioned, the tug (19) disconnects from the vessel and then the floating vessel is positioned by means of the mooring winches (5). The aft winches (5) pay-out and the fore
winches (5) pull-in to move the vessel forward to the exact location to position the floating barge and the wind turbine above the pre-installed jacket structure.
[0024] Once, the floating barge is in position using pre-installed mooring spread, the four hydraulic cylinders (13) are extended upwards from the jacket to take over the load of the fully assembled wind turbine (22). The guide structure (16) will enable easy guidance of the transition piece structure (12) fitted with the TP Temporary Guide Attachment (26). The shock absorbing assembly (15) will absorb any sudden contact loads during the lifting of the hydraulic cylinders (13). Once the full weight of the wind turbine is taken by the hydraulic cylinder (13), then the hydraulic cylinders are lowered and the fully assembled wind turbine is
positioned and fixed to the jacket foundation structure (6), and by removing the guide structure (16), shock absorbing assembly (15) and the four hydraulic cylinders using the supporting crane vessel (24) completes the installation method of offshore wind turbine.
[0025] Within a period of time for periodical maintenance or eventual
decommissioning, the reverse method in which the floating barge (6) is towed by means of tug (19), the hydraulic cylinders (13) are re-installed on the jacket structure (17), then the hydraulic cylinders (13) are then extended till the it takes over the weight of the wind turbine (22). The wind turbine (22) is then lowered in place on the floating barge (6) and the wind turbine is transported to shore location for maintenance/decommissioning.
[0026] The offshore wind turbine installation using reusable hydraulic cylinders is a one-step installation and disassembly for the complete installation of offshore wind turbine, such that the offshore operation eliminates the need for large offshore cranes fitted on specialized offshore windfarm installation vessels, it is readily operable for large offshore wind turbine, the operation can be easily performed with high ratio of success, and the cost of installation is greatly reduced than the existing technique.
[0027] The floating installation barge (6) can optionally be redesigned to
accommodate two fully assembled wind turbines on its deck such that this enables the installation of two wind turbine sets in a single voyage. While the wind turbine assembly is being installed on one jacket structure, the supporting crane vessel will complete the pre-installation activities on the adjoining jacket foundation structure such that two wind turbine sets can be installed in quick succession.
[0028] Advantages of the invention are:
 Low construction noise.
 Low installation cost.
 Faster completion of offshore wind turbine installation.
 Small area of seabed disturbance.
 Less probability of pollutant leakage during offshore operation.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIGURE 1 shows a schematic view of a single mooring spread unit (21) installed using AHTS (18) of an offshore wind turbine installation using reusable hydraulic cylinders.
[0030] FIGURE 2 Shows a schematic view of a four-point mooring spread system (21) of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 1 and 2 explains the pre-installation of mooring spread (21) consisting of Delta Flipper anchor (1) of required holding capacity, chain (2), steel rope (3) of sufficient breaking strength and pick-up buoy (4). The mooring spread is preinstalled on the required location with the help of Anchor Handling Tug Supply Vessel (AHTS) (18) and the number of number mooring lines and configuration are estimated as per motion study based on site weather conditions.
[0031] FIGURE 3 shows a schematic view of pre-assembled wind turbine unit (22) of an offshore wind turbine.
[0032] FIGURE 4 shows a rendered view of wind turbine unit (22) assembled on the floating vessel (6) using onshore crane (23) of an offshore wind turbine
Figure 3 and 4, shows the assembling of the transition piece (12). The transition piece is fitted with the TP Temporary Guide Attachment (26) which is used for ease of transport of the fully assembled wind turbine and TP Temporary Guide Attachment (26) is also used to mate with the guide frame assembly (16) during offshore installation, turbine tower (9), nacelle (10) and turbine blades (11) with the assistance of onshore crane (23) at a port in the proximity of the offshore windfarm site. This method enables to limit the use of offshore cranes fitted on specialized offshore windfarm installation vessels, thereby considerably reducing
overall cost involved in the installation process in comparison with existing techniques. And, relative to the offshore hoisting equipment, the onshore hoisting equipment are more simple, low-rent, and convenient to maintain and have high availability and reliability.
[0033] FIGURE 5 shows a schematic view of installation barge being towed to site for an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 5 Shows the transportation of the fully pre-assembled wind turbine (22), loaded on to a floating barge (6) and is towed to site by a tug (19). The installation barge (6) is to be preferably catamaran hull type, thereby providing better stability for transportation and offshore installation.
[0034] FIGURE 6 shows a rendered view of installation vessel (6) with deck equipment of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 6 shows the barge is equipped with mooring winches (5) as per the mooring line configuration, wind turbine sea fastening (8), and A-Frame hoist structure (7) that can be used if required for any adjustments to the hydraulic cylinder (13) during the offshore installation process A-Frame hoist structure (7) is for redundancy. The primary responsibility for installation and removal of the reusable hydraulic cylinders remains with the supporting crane vessel (24).
[0035] FIGURE 7 Shows a schematic view of exploded view of jacket structure (17) and the hydraulic cylinders (13) of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 7 shows four heavy duty hydraulic cylinders (13) with a maximum stroke length of 15 m, piston diameter of approximately 600 mm installed on the permanent casing structure (14) present in the jacket foundation structure.
[0036] FIGURE 8 Shows a schematic view of jacket structure (17) with
hydraulic cylinders (13), shock absorbing assembly (15) and guide frame assembly (16) of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 8 shows the installation of shock absorbing assembly (15) to reduce the dampen the impact loads, and the guide frame assembly (16) on top of the jacket structure (17) for aligning the transition piece to the jacket structure (17) for effectively unloading the wind turbine (22) on to the jacket structure prior to commencing of the turbine installation process onsite.
[0037] FIGURE 9 Shows a schematic view of installation vessel (6) onsite of an offshore wind turbine installation using reusable hydraulic cylinders.
[0038] FIGURE 10 Shows a schematic view of support vessel (20) taking mooring line from the installation vessel (6) of an offshore wind turbine installation using reusable hydraulic cylinders.
[0039] FIGURE 11 Shows a schematic view of support vessel (20) connecting mooring line to the mooring spread system (21) of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 9, 10 and 11 shows that on reaching the installation barge on site, a support vessel (20) positioned onsite picks-up the pre-laid mooring line (21) and connects it to the installation barge (6) mooring winches (5) and then the winches (5) onboard tension the mooring lines, after this the tug (19) disconnects. Then the vessel is positioned by means of the mooring winches (5).
[0040] FIGURE 12 shows a schematic view of side view of installation vessel (6) connected to mooring spread system (21) of an offshore wind turbine installation using reusable hydraulic cylinders.
[0041] FIGURE 13 shows a schematic view of top view of installation vessel (6) connected to mooring spread system (21) of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 12 and 13 shows that the aft winches (5) pay-out and the fore winches (5) pull-in to move the vessel forward to direct the floating barge to selected location suitable for docking with Jacket foundation structure, Same process is applied in reverse to move the vessel after wards for removing wind turbine, and to move the vessel towards PORT & STARBBOARD side.
[0042] FIGURE 14 shows schematic view of unloading stages of wind turbine assembly (22) onsite of an offshore wind turbine installation using reusable hydraulic cylinders.
Figure 14 shows that the four hydraulic cylinders (13) are extended upwards and takes over the load of the fully assembled wind turbine. The guide structure (16) will enable easy guidance of the transition piece structure (12) fitted with the TP Temporary Guide Attachment (26) on to the jacket foundation structure (17). The shock absorbing assembly (15) will absorb any sudden contact loads during the
lifting operation. Once the full weight of the wind turbine is taken by the
hydraulic cylinder (13), the cylinder is lowered and the fully assembled wind turbine (22) is fixed to the jacket foundation structure (17), completing the installation process. After completing the installation, the guide frame (16), the shock absorbing assembly (15) and the hydraulic cylinders (13) can be retrieved with the help of the supporting crane vessel (). Thus, the same unit can be used for installation of multiple wind turbines assemblies, and for periodical maintenance or eventual decommissioning, the reverse method can be applied whereby the hydraulic cylinders (13) are re-installed on the jacket structure (17).
The hydraulic cylinders (13) are then extended till the it takes over the weight of the wind turbine (22). The wind turbine (22) is then lowered in place on the floating barge (6) for transport to shore location for
maintenance/decommissioning.
[0043] Figure 15 and Figure 16 shows a rendered image of a floating installation barge redesigned to accommodate two fully assembled wind turbines on its deck such that this enables the installation of two wind turbine sets in a single voyage. While the wind turbine assembly is being installed on one jacket structure, the supporting crane vessel will complete the pre-installation activities on the adjoining jacket foundation structure such that two wind turbine sets can be installed in quick succession.
[0044] Figure 17 shows a zoomed in view of the shock absorbing assembly (15) guide frame assembly (16) on top of the jacket structure (17) for aligning the transition piece to the jacket structure (17) for effectively unloading the wind turbine (22) on to the jacket structure prior to commencing of the turbine installation process onsite.
[0045] Figure 18 shows a rendered view of the supporting crane vessel (24) crawler crane (25) and on the deck of the supporting crane vessel multiple sets of the shock absorbing assembly (15) guide frame assembly (16) and hydraulic cylinders (13) can be seen.
REFERENCE NUMERALS
1. Delta Flipper Anchor
2. Steel Anchor chain
3. Steel Rope
4. Buoys
5. Mooring Winches
6. Floating Installation Barge (Floating vessel)
7. A-frame Hoist structure
8. Wind Turbine Sea-fastening Grillage
9. Vertical Turbine Tower
10. Pod shaped Nacelle
11. Turbine Blades
12. Transition Piece
13. Hydraulic cylinders
14. Dedicated Casing
15. Shock Absorber Assembly
16. Guide Frame Assembly
17. Jacket Foundation Structure
18. Anchor Handling Tug Supply Vessel
19. Tug
20. Supporting Vessel
21. Mooring Spread
22. Pre-assembled Wind Turbine
23. Onshore Gantry Crane
24. Supporting Crane Vessel
25. Crawler Crane
26. TP Temporary guide attachment , Claims:1. A method for installation of offshore wind turbine using reusable hydraulic cylinders comprising of:
a. pre-installing jacket foundation structure (17) with permanently attached dedicated casings (14) for hydraulic cylinders (13), Shock Absorber Assembly (15) and Guide Frame Assembly (16);
b. pre-installing mooring spread (21) to facilitate connection to the mooring winches (5) located on installation barge;
c. pre-assembling ready-to-operate wind turbine on a floating barge (6) at port side and towing the barge offshore;
d. positioning the floating barge carrying fully assembled wind turbine above pre-installed jacket structure using the pre-installed mooring lines;
e. positioning the floating barge and wind turbine above the hydraulic
cylinders (13) placed in dedicated casing (14), shock absorbing and guide assembly on to Jacket foundation structure;
wherein by lowering the hydraulic cylinders and bolting up the pre-assembled wind turbine to pre-installed Jacket foundation structure, thus completing the installation.
2. The method as claimed in claim 1, wherein the hydraulic cylinders used are heavy duty hydraulic cylinders with a maximum stroke length of 15m, piston diameter of approximately 600 mm installed on permanent casing structure in the Jacket foundation structure for effectively unloading the wind turbine on to the Jacket structure to reduce the dampen impact load to the Jacket structure.
3. The method as claimed in claim 1b, wherein the mooring spread (21) is preinstalled on required location using anchor handling tug supply vessel (18), consisting of delta flipper anchor (1), steel anchor chain (2), steel rope (3) of sufficient breaking strength and a pick-up buoy.
4. The method as claimed in claim 1c, wherein the floating barge to load the wind turbine is preferably a catamaran double hull type barge with sea-fastening grillage (8) for stability of wind turbine components: Transition piece (12), Turbine Tower (9), Nacelle (10), Turbine blades (11) assembled one by one respectively using onshore crane (23) at the quay side.
5. The method as claimed in claim 1c, wherein the floating barge is towed offshore using by a tug (19) and then the onsite supporting vessel (20) connects the floating installation barge to pre-installed mooring spread using steel rope (3) from onboard mooring winches (5). Once the mooring lines are tensioned, then disconnects the tug to move the floating barge to prescribed position using aft winches pay-out and the fore winches pull-in to move the vessel forward.
6. The method as claimed in claim 1e, wherein the docking process is achieved by extending the four hydraulic cylinders upwards from the jacket to take over the load of the fully assembled wind turbine, the guide structure guides the transition piece structure fitted with the TP Temporary Guide Attachment (26) and the shock absorbing assembly absorbs any sudden contact loads during the lifting of the hydraulic cylinders. Once the full weight of the wind turbine is taken by the hydraulic cylinder, then the hydraulic cylinders are lowered and the fully
assembled wind turbine is fixed to the jacket foundation structure, then by removing the guide structure, shock absorbing assembly and the four hydraulic cylinders using an A-frame hoist (7) completes the installation method of offshore wind turbine.
7. The method as claimed in claim 1, wherein the uninstallation of the offshore installed wind turbine is done by detaching from the Jacket structure using a reverse method in which the floating barge is towed by tug, then the hydraulic cylinders are re-installed on the jacket structure and then the hydraulic cylinders are extended till the it takes over the weight of the wind turbine. Then the wind turbine is lowered to place on the floating barge and winding out steel rope from the mooring spread for transport of wind turbine to shore location for maintenance/ decommissioning.