A Review of Bolted Connections for the Assembly of Floating Offshore Wind Turbine Foundations

Abstract

Bolted connections are being considered as an assembly method for the foundations of floating offshore wind turbines. A clear benefit of this method is the short assembly time of these foundations compared to welding. However, some concerns around corrosion, fatigue, and the ability of bolted connections to maintain preload remain. This review found that conventional ring flanges may not be suitable for the assembly of floating foundations, mainly due to the risk of bolt loosening and reduced fatigue life. However, the C1 Wedge Connection is an innovative bolted connection that has shown its ability to retain bolt preload during tests. Likewise, the Compact Flange Connection has shown its ability to retain preload without requiring maintenance during operational stages and furthermore, has a long and successful track record in offshore oil and gas applications. This review revealed several research gaps related to the use of bolted connections for the assembly of floating wind turbine foundations. These include: a lack of research on the effects of bolt loosening; dynamic loads and shear forces on bolted connections and their effect on fatigue life; structural health monitoring methods of bolted connections; and the health and safety of technicians in confined spaces with difficult accessibility. The Compact Flange Connection is perhaps the best suited bolted connection for the assembly of floating foundations. However, more research, and crucially, successful offshore demonstrations will be essential to increase confidence in the suitability of bolted connections for the floating offshore wind industry.

Keywords

Bolted connections / Floating offshore wind / Assembly time

Acknowledgments

The authors would like to acknowledge David Keane, Michael Oyinlola, and Mario Marinero, all in ESB, for their comments on the draft article.

Author Contributions

A.M.: Investigation, Data Curation, Writing—Original Draft Preparation. N.B.: Investigation, Data Curation, Visualisation, Writing—Review & Editing. A.O.: Conceptualization, Investigation, Data Curation, Writing—Review & Editing, Supervision, Project Administration, Funding Acquisition.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Funding

This research received no external funding.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Offshorewind-biz. TotalEnergies’ Floating Offshore Wind Project to Power UK Oil & Gas Platform. Available online: https://www.offshorewind.biz/2024/08/29/totalenergies-floating-offshore-wind-project-to-power-uk-oil-gas-platform/#:-:text=France%E2%80%99s%20TotalEnergies%20plans%20to%20launch%20a%20floating%20offshore,220%20kilometres%20off%20the%20eastern%20coast%20of accessed on 22 October 2025).

[2] Ocergy. OCG Wind Sustainable Offshore Solutions. Available online: https://www.ocergy.com/ocg-wind accessed on 22 October 2025).

[3] Principle Power. The WindFloat. Available online: https://www.principlepower.com/windfloat accessed on 22 October 2025).

[4] Wu X, Hu Y, Li Y, Yang J, Duan L, Wang T, et al. Foundations of offshore wind turbines: A review. Renew. Sustain. Energy Rev. 2019, 104, 379-393. doi:10.1016/j.rser.2019.01.012.

[5] Edwards EC, Holcombe A, Brown S, Ransley E, Hann M, Greaves D. Evolution of floating offshore wind platforms: A review of at-sea devices. Renew. Sustain. Energy Rev. 2023, 183, 113416. doi:10.1016/j.rser.2023.113416.

[6] Mehmanparast A, Lotfian S, Vipin PS. A Review of Challenges and Opportunities Associated with Bolted Flange Connections in the Offshore Wind Industry. Metals 2020, 10, 732. doi:10.3390/met10060732.

[7] Lochan S, Mehmanparast A, Wintle J. A review of fatigue performance of bolted connections in offshore wind turbines. Procedia Struct. Integr. 2019, 17, 276-283. doi:10.1016/j.prostr.2019.08.037.

[8] Nordlock. What Is Preload and Why Is It Important? Available online: https://www.nord-lock.com/learnings/bolting-tips/2025/what-is-preload-and-why-is-it-important/ accessed on 22 October 2025).

[9] DNV-ST-0126; Support Structures for Wind Turbines. Det Norske Veritas: Høvik, Norway, 2021.

[10] Braithwaite J, Goenaga IG, Tafazzolimoghaddam B, Mehmanparast A. Sensitivity analysis of friction and creep deformation effects on preload relaxation in offshore wind turbine bolted connections. Appl. Ocean Res. 2020, 101, 102225. doi:10.1016/j.apor.2020.102225.

[11] Braithwaite J, Mehmanparast A. Analysis of Tightening Sequence Effects on Preload Behaviour of Offshore Wind Turbine M72 Bolted Connections. Energies 2019, 12, 4406. doi:10.3390/en12234406.

[12] Karlsen Ø, Lemu HG. Comparative study on loosening of anti-loosening bolt and standard bolt system. Eng. Fail. Anal. 2022, 140, 106590. doi:10.1016/j.engfailanal.2022.106590.

[13] Ziegler L, Gonzalez E, Rubert T, Smolka U, Melero JJ. Lifetime extension of onshore wind turbines: A review covering Germany, Spain, Denmark, and the UK. Renew. Sustain. Energy Rev. 2018, 82, 1261-1271. doi:10.1016/j.rser.2017.09.100.

[14] Annoni A, Johnston C, Mehmanparast A. Fatigue life analysis of threaded connections in offshore wind turbines. Appl. Ocean Res. 2024, 153, 104287. doi:10.1016/j.apor.2024.104287.

[15] Ji X, Zou T, Bai X, Niu X, Tao L. Fatigue assessment of flange connections in offshore wind turbines under the initial flatness divergence. Front. Energy Res. 2023, 11, 1127957. doi:10.3389/fenrg.2023.1127957.

[16] Liu M, Geng R, Wang J, Li Y, Long K, Ding W, et al. The Investigation of Various Flange Gaps on Wind Turbine Tower Bolt Fatigue Using Finite-Element Method. Appl. Sci. 2024, 14, 3670. doi:10.3390/app14093670.

[17] Zou T, Niu X, Ji X, Li M, Tao L. The impact of initial imperfections on the fatigue assessment of tower flange connections in floating wind turbines: A review. Front. Mar. Sci. 2022, 9, 1063120. doi:10.3389/fmars.2022.1063120.

[18] Madsen C, Kragh-Poulsen J, Thage K, Andreassen M. Analytical and numerical investigation of bolted steel ring flange connection for offshore wind monopile foundations. IOP Conf. Ser. Mater. Sci. Eng. 2017, 276, 012034. doi:10.1088/1757-899X/276/1/012034.

[19] C1 Connections. The C1 Wedge Connection. Available online: https://c1connections.com/ accessed on 23 October 2025).

[20] Creusen KEY, Misios G, Winkes JS, Veljkovic M. Introducing the C 1 Wedge Connection. Steel Constr. 2021, 15, 13-25. doi:10.1002/stco.202100039.

[21] Cheng L, Yang F, Winkes JS, Veljkovic M. The C1 wedge connection in towers for wind turbine structures, tensile behaviour of a segment test. Eng. Struct. 2023, 282, 115799. doi:10.1016/j.engstruct.2023.115799.

[22] Cheng L, Yang F, Seidel M, Veljkovic M. FE-assisted investigation for mechanical behaviour of connections in offshore wind turbine towers. Eng. Struct. 2023, 285, 116039. doi:10.1016/j.engstruct.2023.116039.

[23] Lassesen S, Eriksen T, Teller F. NORSOK L-005—Compact Flanged Connections (CFC):The New Flange Standard. In Proceedings of the ASME Pressure Vessels and Piping Conference, Vancouver, BC, Canada, 4-8 August 2002; PVP 2002-1097, pp. 189-195. doi:10.1115/PVP2002-1097.

[24] Lutkiewicz P, Robertson D, Lee S. Subsea Flanges, Comparison Between Conventional API 6A Type 6BX Flange and SPO Compact Flange Designs. In Proceedings of the ASME Pressure Vessels and Piping Conference, Minneapolis, MN, USA, 19-24 July 2020; PVP 2020-21372, V005T05A003. doi:10.1115/PVP2020-21372.

[25] Croccolo D, De Agostinis M, Fini S, Mele M, Olmi G, Scapecchi C, et al. Failure of Threaded Connections: A Literature Review. Machines 2023, 11, 212. doi:10.3390/machines11020212.

[26] Javadi Y, Mills B, MacLeod C, Lines D, Abad F, Lotfian S, et al. Phased Array Ultrasonic Method for Robotic Preload Measurement in Offshore Wind Turbine Bolted Connections. Sensors 2024, 24, 1421. doi:10.3390/s24051421.

[27] He X, She T. A New Identification Method for Bolt Looseness in Wind Turbine Towers. Shock Vib. 2019, 2019, 6056181. doi:10.1155/2019/6056181.

[28] Haute CV, Pire T. Maintenance intervals for MP-TP bolted connections—A case study. Results Eng. 2020, 5, 100064. doi:10.1016/j.rineng.2019.100064.

[29] Fernando S. Tension Control Bolts—Explained. Hobson Engineering Company Pty. Ltd. Available online: https://cdn.hobson.com.au/documents/article-tension-control-bolts-explained.pdf accessed on 23 October 2025).

[30] Valdez R, Palacios E, Tutivén C, Vidal Y. Bolt-loosening detection in offshore wind turbines’ jacket-type supports. Struct. Health Monit. 2024, 24, 2941-2957. doi:10.1177/14759217241268522.

[31] Adedipe O, Brennan F, Kolios A. Review of corrosion fatigue in offshore structures: Present status and challenges in the offshore wind sector. Renew. Sustain. Energy Rev. 2016, 61, 141-154. doi:10.1016/j.rser.2016.02.017.

[32] Wang T, Liang G, Liu Y. Mechanical performance analysis of bolt connections for wind turbine towers after corrosion. Structures 2025, 71, 108202. doi:10.1016/j.istruc.2025.108202.

[33] Schaumann P, Eichstädt R. Fatigue Assessment of High-Strength Bolts with Very Large Diameters in Substructures. In Proceedings of the International Ocean and Polar Engineering Conference, Kona, HI, USA, 21-26 June 2015; pp. 1-6.

[34] Zhang J, Heng J, Dong Y, Baniotopoulos C, Yang Q. Coupling multi-physics models to corrosion fatigue prognosis of high-strength bolts in floating offshore wind turbine towers. Eng. Struct. 2024, 301, 117309. doi:10.1016/j.engstruct.2023.117309.

[35] Gaidai O, Yakimov V, Wang F, Zhang F, Balakrishna R. Floating wind turbines structural details fatigue life assessment. Sci. Rep. 2023, 13, 16312. doi:10.1038/s41598-023-43554-4.

[36] Fatemi A, Yang L. Cumulative fatigue damage and life prediction theories: A survey of the state of the art for homogeneous materials. Int. J. Fatigue 1998, 20, 9-34. doi:10.1016/S0142-1123(97)00081-9.

[37] DNV-RP-C203; Fatigue Design of Offshore Steel Structures. Det Norske Veritas: Høvik, Norway, 2024.

[38] Eccles B. Fatigue Failure of Bolts. Available online: https://www.boltscience.com/pages/fatigue-failure-of-bolts.pdf accessed on 30 November 2025).

[39] Schaumann P, Böhm M, Schürmann K. Improvements in the fatigue design of support structures for offshore wind turbines. Steel Constr. 2021, 14, 74-82. doi:10.1002/stco.202000060.

[40] Liu J, Ma Y, Chen J, Ji C, Su D. Research on Fatigue Assessment of the Flange Bolts Connection of Wind Turbine Based on Finite Element Analysis. In Proceedings of the 2016 2nd Workshop on Advanced Research and Technology in Industry Applications (WARTIA), Dalian, China, 14-15 May 2016; pp. 435-440. doi:10.2991/wartia-16.2016.87.

[41] Gao S, Liu J, Wang X, Zhao C, Wu F. Fatigue Damage Evaluation of High-strength Bolt for Tower of Wind Turbine. Eur. J. Comput. Mech. 2025, 33, 583-606. doi:10.13052/ejcm2642-2085.3363.

[42] Kikuchi Y, Ishihara T. Fatigue prediction of wind turbine tower considering the effect of high-tension bolt failure. Eng. Fail. Anal. 2025, 174, 109494. doi:10.1016/j.engfailanal.2025.109494.

[43] Johnston C, Doré M. Comparison of the Fatigue Performance of Galvanised M72 Bolts with Design Standard Recommendations. In Proceedings of the International Conference on Ocean, Offshore, and Arctic Engineering, Virtual, Online, 21-30 June 2021; OMAE 2021-62758, V003T03A006. doi:10.1115/OMAE2021-62758.

[44] Eichstädt R. Fatigue Assessment of Large-Size Bolting Assemblies for Wind Turbine Support Structures. Ph.D. Thesis, Gottfried Wilhelm Leibniz Universität, Hannover, Germany, 2019. doi:10.15488/5157.

[45] Rincón-Casado A, Juliá JM, García-Vallejo D, Domínguez J. Experimental estimation of the residual fatigue life of in-service wind turbine bolts. Eng. Fail. Anal. 2022, 141, 106658. doi:10.1016/j.engfailanal.2022.106658.

[46] ISO 898-1:2013; Mechanical Properties of Fasteners Made of Carbon Steel and Alloy Steel. International Organization for Standardization: Geneva, Switzerland, 2013.

[47] ISO 12944-5:2019; Paints and Varnishes—Corrosion Protection of Steel Structures by Protective Paint Systems. International Organization for Standardization: Geneva, Switzerland, 2019.

[48] ISO 12473:2017; General Principles of Cathodic Protection in Seawater. International Organization for Standardization: Geneva, Switzerland, 2017.

[49] ISO 16047:2005; Fasteners—Torque/Clamp Force Testing. International Organization for Standardization: Geneva, Switzerland, 2005.

[50] ISO 19902:2020; Petroleum and Natural Gas Industries—Fixed Steel Offshore Structures. International Organization for Standardization: Geneva, Switzerland, 2020.

[51] VDI 2230; Systematic Calculation of Highly Stressed Bolted Joints. Verein Deutscher Ingenieure: Düsseldorf, Germany, 2015.

[52] BS 7608:2014; Guide to Fatigue Design and Assessment of Steel Products. British Standard Institution: London, UK, 2014.

[53] EN 1993-1-9:2025;Eurocode 3: Design of Steel Structures—Part 1-9: Fatigue. European Committee for Standardization (CEN): Brussels, Belgium, 2025.

[54] EN 1090-2:2018+A1:2024; Execution of Steel Structures and Aluminium Structures—Part 2: Technical Requirements for Steel Structures. European Committee for Standardization (CEN): Brussels, Belgium, 2024.

[55] ASME PCC-1-2013; Guidelines for Pressure Boundary Bolted Flange Joint Assembly (BFJA). The American Society of Mechanical Engineers: New York, NY, USA, 2013.

[56] IEC 61400-3-2; Wind Energy Generation Systems—Part 3-2: Design Requirements for Floating Offshore Wind Turbines. International Electrotechnical Commission: Geneva, Switzerland, 2025.

[57] DNV-ST-0119; Floating Wind Turbine Structures. Det Norske Veritas: Høvik, Norway, 2021.

[58] American Bureau of Shipping. Guide for Building and Classing—Floating Offshore Wind Turbines; American Bureau of Shipping: Spring, TX, USA, 2025.

[59] LR-RP-003; Recommended Practice for Floating Offshore Wind Turbine Support Structures. Lloyd’s Register: London, UK, 2024.

[60] LR-RU-003; Rules for the Classification of Offshore Units. Lloyd’s Register: London, UK, 2024.

[61] NR572; Classification and Certification of Floating Offshore Wind Turbines. Bureau Veritas: Paris, France, 2024.

[62] NR445; Rules for the Classification of Offshore Units. Bureau Veritas: Paris, France, 2025.

[63] Jukes P. Fabrication Welding Processes. In Encyclopedia of Maritime and Offshore Engineering; Carlton J, Jukes P, Choo YS, Eds.; Wiley: Hoboken, NJ, USA, 2018; pp. 1-9. doi:10.1002/9781118476406.emoe148.

[64] Turan E, Koçal T, Ünlügençoğlu K. Welding Technologies in Shipbuilding Industry. Online J. Sci. Technol. 2011, 1, 24-30.

[65] Mvola B, Kah P. Effects of shielding gas control: Welded joint properties in GMAW process optimization. Int. J. Adv. Manuf. Technol. 2017, 88, 2369-2387. doi:10.1007/s00170-016-8936-2.

[66] Gidiagba JO, Olalere BI, Fawole AA, Egbokhaebho BA, Ehiobu NN, Okparaeke JI. Review of Advanced Welding and Testing for Safety in Offshore Oil and Gas. Mater. Corros. Eng. Manag. 2023, 4, 37-43. doi:10.26480/macem.02.2023.37.43.

[67] Plessis JD. Welding of Offshore Structures. Available online: https://www.spesmet.co.za/wp-content/uploads/2016/09/Welding-of-Offshore-structure-2012.pdf accessed on 25 November 2025).

[68] Afriansyah A, Arifin A. Dissimilar metal welding using Shielded Metal Arc Welding: A Review. Technol. Rep. Kansai Univ. 2020, 62, 1935-1948.

[69] Zavvar E, Rosa-Santos P, Ghafoori E, Taveira-Pinto F. Analysis of tubular joints in marine structures: A comprehensive review. Mar. Struct. 2025, 99, 103702. doi:10.1016/j.marstruc.2024.103702.

[70] Hyundai Welding. Welding Solution for the Offshore Industry. Available online: https://hyundaipns.com/data/file/download/brochures/Hyundai_Welding_Offshore_Brochure_2024_eng.pdf accessed on 25 November 2025).

[71] Gyasi EA. Welding Processes of Metals for Offshore Environment:Underwater Welding; Lappeenranta-Lahti Univ. Technol. LUT: Lappeenranta, Finland, 2019; ISBN 978-952-335-433-3.

[72] Świerczyńska A, Varbai B, Pandey C, Fydrych D. Exploring the trends in flux-cored arc welding: Scientometric analysis approach. Int. J. Adv. Manuf. Technol. 2024, 130, 87-110. doi:10.1007/s00170-023-12682-6.

[73] AWS D1.1; Structural Welding Code—Steel. American Welding Society: Doral, FL, USA, 2025.

[74] Spangineer. GMAW Weld Area. Available online: https://commons.wikimedia.org/wiki/File:GMAW_weld_area.svg accessed on 3 December 2025).

[75] Marcelochal. SMAW Area Diagram. Available online: https://commons.wikimedia.org/wiki/File:SMAW_area_diagram.svg accessed on 3 December 2025).

[76] Jones R. FCAW Diagram. Available online: https://commons.wikimedia.org/wiki/File:FCAW_diagram.svg accessed on 3 December 2025).

[77] Duk. GTAW. Available online: https://commons.wikimedia.org/wiki/File:GTAW.svg accessed on 3 December 2025).

[78] Conte R, Rodríguez Izquierdo D, Gagliardi F. Submerged arc welding process: a numerical investigation of temperatures, displacements, and residual stresses in ASTM A516-Gr70 corner joined samples. Int. J. Adv. Manuf. Technol. 2023, 127, 5437-5448. doi:10.1007/s00170-023-11908-x.

[79] Kitagawa Y, Kawasaki H. Recent development of high-strength and tough welding consumables for offshore structures. Kobe Steel Eng. Rep. 2013, 63, 16-21.

[80] Chen B-Q, Liu K, Xu S. Recent Advances in Aluminum Welding for Marine Structures. J. Mar. Sci. Eng. 2024, 12, 1539. doi:10.3390/jmse12091539.

[81] Scholl S, Schütz J, Lenhard S, Lehnert T, Staudt T, Schütz W. Development of Heavy Plates for High-Energy Welding of Monopiles for the Construction of Offshore Wind Energy Plants. In Proceedings of the 3rd International Symposium on the Recent Developments in Plate Steels, Vail, CO, USA, 2-5 June 2024. doi:10.33313/300/018.

[82] Okenyi V, Afazov S, Mansfield N, Balakrishnan J, Kyffin W, Siegkas P, et al. Submerged Arc Welding of S355G10+M Steel: Analyzing Strength, Distortion, Residual Stresses, and Fatigue for Offshore Wind Applications. Fatigue Fract. Eng. Mater. Struct. 2025, 48, 3859-3878. doi:10.1111/ffe.70010.

[83] Mathers G. Job Knowledge 97:Welding Costs. Available online: https://www.twi-global.com/technical-knowledge/job-knowledge/welding-costs-continued-097 accessed on 27 November 2025).

[84] The Welding Institute. Standard Data for Arc Welding.Available online: https://www.twi-global.com/pdfs/best-practice-guides/bpsdawv1.pdf accessed on 27 November 2025).

[85] O’Brien A. Welding Handbook. Volume 2:Welding Processes, Part 1, 9th ed.; Amer Welding Society: Miami, FL, USA, 2004; ISBN 978-0871717290.

[86] Corigliano P, Crupi V. Review of Fatigue Assessment Approaches for Welded Marine Joints and Structures. Metals 2022, 12, 1010. doi:10.3390/met12061010.

[87] Musolino J, Shi X-H, Chen B-Q. Numerical Investigation on Residual Stress and Distortion in Welded Joints of Offshore Platform Structures. J. Mar. Sci. Eng. 2025, 13, 1941. doi:10.3390/jmse13101941.

[88] DNV-OS-C401; Fabrication and Testing of Offshore Structures. Det Norske Veritas: Høvik, Norway, 2025.

[89] Poutiainen E. Design Guides for Engineering Joints in Offshore Conditions: Bolt, Weld, and Interference Joints. Master’s Thesis, Lappeenranta-Lahti University of Technology LUT, Lappeenranta, Finland, 2022. Available online: https://lutpub.lut.fi/handle/10024/164740 accessed on 23 October 2025).

[90] ISO 4042: 2018; Fasteners—Electroplated Coating Systems. International Organization for Standardization: Geneva, Switzerland, 2018. shop.standards.ie/en-ie/standards/iso-4042-2018-614129_saig_iso_iso_2624797 (accessed on 23 October 2025).

[91] Chung PP, Wang J, Durandet Y. Deposition processes and properties of coatings on steel fasteners—A review. Friction 2019, 7, 389-416. doi:10.1007/s40544-019-0304-4.

[92] Oral History Research Unit, Bournemouth University. Building the Ship. Available online: https://histru.bournemouth.ac.uk/Oral_History/Talking_About_Technology/shipbuilding/building_the_ship.htm accessed on 23 October 2025).

[93] ORE Catapult. Advanced Manufacturing of Substructure Components. Available online: https://fowcoe.co.uk/industry-insights/reports/advanced-manufacturing-of-substructure-components/ accessed on 23 October 2025).

[94] Zavvar E, Rosa-Santos P, Taveira-Pinto F, Ghafoori E. Lifetime extension of offshore support structures of wind turbines: A review. Renew. Sustain. Energy Rev. 2025, 217, 115788. doi:10.1016/j.rser.2025.115788.

[95] Rinaldi G, Thies PR, Johanning L. Current Status and Future Trends in the Operation and Maintenance of Offshore Wind Turbines: A Review. Energies 2021, 14, 2484. doi:10.3390/en14092484.

[96] Ge M, Li L, Meng H, Kai L. Offshore Wind Turbine Maintenance and Operation; Springer: Singapore, 2025; pp. 179-212. doi:10.1007/978-981-96-2175-0_6.

[97] Tp-products. Wind Power Flanges. Available online: https://tp-products.com/wind-power-flanges/ accessed on 23 October 2025).

[98] Lassesen S. The Use of Bolted Joints in Primary Load Bearing Structures. Poster Presentation PO068. In Proceedings of the Annual Wind Europe Conference, Copenhagen, Denmark, 25-27 April 2023.

[99] Gupta S, Stoddart E, Sanderson D, Morrison A. Condition Monitoring of Offshore Wind Turbines with Scour and Grout Damage in Monopile Foundations. In Proceedings of the SECED: Earthquake Risk and Engineering Towards a Resilient World, Cambridge, UK, 9-10 July 2015.

[100] Borg M, Jensen MW, Urquhart S, Andersen MT, Thomsen JB, Stiesdal H. Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation. Energies 2020, 13, 4911. doi:10.3390/en13184911.

[101] Thomsen JB, Bergua R, Jonkman J, Robertson A, Mendoza N, Brown C, et al. Modeling the TetraSpar Floating Offshore Wind Turbine Foundation as a Flexible Structure in OrcaFlex and OpenFAST. Energies 2021, 14, 7866. doi:10.3390/en14237866.

[102] Offshorewind-biz. Project to Demonstrate 15+ MW Turbine on Ocergy’s Floating Platform Kicks Off. Available online: https://www.offshorewind.biz/2025/06/23/project-to-demonstrate-15-mw-turbine-on-ocergys-floating-platform-kicks-off/ accessed on 23 October 2025).