Guide for Building and Classing Floating Offshore Wind Turbines July 2020 GUIDE FOR BUILDING AND CLASSING FLOATING OFFSHORE WIND TURBINES JULY 2020 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 © 2020 American Bureau of Shipping. All rights reserved. ABS Plaza 1701 City Plaza Drive Spring, TX 77389 USA Foreword (1 July 2020) This Guide provides criteria for the design, construction, installation and survey of permanently sited Floating Offshore Wind Turbines. It addresses three principal areas: the floating substructure, the stationkeeping system, and onboard machinery, equipment and systems including applicable marine systems and associated equipment and machinery, safety systems and associated equipment, and lifesaving appliances and machinery. The criteria applicable to bottom-founded offshore wind turbine substructures and foundations are provided in the ABS Guide for Building and Classing Bottom-Founded Offshore Wind Turbines (BOWT Guide). Requirements for ancillary offshore wind farm installations such as meteorological measuring towers, accommodation units, and transformer platforms are not addressed in this Guide. For the requirements for bottom-founded ancillary offshore wind farm installations, refer to the ABS Rules for Building and Classing Offshore Installations. The requirements applicable to floating ancillary offshore wind farm installations are provided in the ABS Rules for Building and Classing Mobile Offshore Units and the ABS Rules for Building and Classing Floating Production Installations. This revision incorporates the following changes: ● “Installations” or “Installation” as in context “Floating Offshore Wind Turbine Installations” or “Floating Offshore Wind Turbine Installation” deleted. ● 1-1/7.1 – Additional requirements for optional class notation “RNA” for the Rotor-Nacelle Assembly (RNA) and the tower added. ● 1-1/7.3 – A new mandatory class notation for “Strength Criteria for Site-specific Conditions (S)” added. ● 1-1/7.5 – New mandatory class notations for “Design Fatigue Life” added. ● 1-1/7.7 – New Subsection added to offer applicable notations listed in the ABS MOU Rules and the ABS FPI Rules upon agreement from ABS. ● 1-1/11.5 – Required design plans for the concrete floating substructure added. ● 1-1/15 – Information for wind turbine control systems and power cable system in information memorandum added. ● 1-1/19.1 – Abbreviation for “NPD” added. ● 1-1/19.2 – References for new revisions of ABS Guides and Rules, API and IEC standards, and ACI and ASTM standards for concrete structures added. ● 3-1/23 – A new Subsection for “Consideration for Identical Floating Substructure Design” added. ● 4-2/3 and 4-2/11.1– Requirements are aligned with API RP 2MET for storm wind models. ● 4-2/11 – Requirements aligned with IEC 61400-3-2 for extreme wind models. ● 4-3/1 – Requirements aligned with the IEC 61400-3-2 for consideration of swell conditions. ● 5-2/3 – Design Load Cases (DLCs) modified to incorporate the recent updates in the IEC 61400-3-1 and IEC TS 61400-3-2. ● 5-2/Table 1 – New design load cases (new DLC 2.5, DLC 2.6, DLC 9.1, 9.2, 9.3, DLC 10.1, 10.2 and DLC 10.3) added to incorporate the recent updates in the IEC 61400-3-1 and IEC TS 61400-3-2. ● 5-2/3.5 – A load case added where the tendon is designed to be subject to planned replacement. ● 6-1/7 – Additional design load cases DLC 10.1, DLC 10.2 and DLC 10.3 added for air gap analysis. ● 6-1/7 – Reference made to the ABS Guidance Notes on Air Gap and Wave Impact Analysis for Semi- Submersibles. ABS GUIDE FOR BUILDING AND CLASSING FLOATING OFFSHORE WIND TURBINES • 2020 ii ● Section 7-3 – Detailed requirements added for concrete floating substructure. ● 7-2/7.5 – The LRFD design referred to the ABS Guide for Load and Resistance Factor Design (LRFD) Criteria for Offshore Structures. ● 8-1/9 – New Subsection added to provide guidance on “Redundant Mooring System”. ● 8-5/11 – Added new Subsection is to provide guidance on “Dynamically Embedded Plate Anchor”. ● Section 8-6 – Reference is made to ABS FPI Rules for “Field Test”. ● 9-2/5.1.1 – DLC 4.1 and DLC 4.3 for normal shutdown, and DLC 5.1 for emergency stop added as design load cases to be considered in intact stability calculation. ● 9-2/5.3 – DLC 9.3 for power production and DLC 10.3 for parked condition added as required design load cases for damage stability calculation. ● 10-1/1 – Title of the Subsection changed to “General” to introduce the design requirements in Chapter 10 for machinery, equipment and systems. ● 10-1/11 – New Subsection on “Identification Marks” for Floating Offshore Wind Turbines added. ● 11-1/1 – Added survey requirements to denote when the turbine and tower are within the scope of classification. ● 11-1/5.1 – Modified requirements for installation and hook-up surveys for the RNA, tower, and power cable system. ● 11-2/1 – Added survey requirements to denote when the turbine and tower are within the scope of classification. ● 11-2/3 – A new Subsection and requirements for “In-Service Inspection Program (ISIP)” added. Referred Section for risk-based inspection in the Guide added. ● 11-2/5.5 – A new Subsection “Underwater Inspection in Lieu of Drydocking Survey (UWILD)” added. ● 11-2/17 – A new Subsection “Inspection for Concrete Structures” added. ● 11-2/19 – This Subsection replaced with new title and content in “Preparations for Safe Execution of Surveys”. ● Appendix A1 – A new Appendix added to provide guidance on wind spectra and coherence functions. ● Appendix A2 – A new Appendix added to provide guidance on tropical cyclone wind speed profile, standard deviation, turbulence intensity and gust factor. ● Various other changes are made to clarify the requirements. This Guide becomes effective on the first day of the month of publication. Users are advised to check periodically on the ABS website www.eagle.org to verify that this version of this Guide is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to [email protected] . ABS GUIDE FOR BUILDING AND CLASSING FLOATING OFFSHORE WIND TURBINES • 2020 iii GUIDE FOR BUILDING AND CLASSING FLOATING OFFSHORE WIND TURBINES CONTENTS CHAPTER 1 Conditions of Classification............................................................... 1 Section 1 Scope and Conditions of Classification............................. 3 CHAPTER 2 Materials and Welding....................................................................... 24 Section 1 General............................................................................25 CHAPTER 3 General Design Requirements..........................................................26 Section 1 Design Considerations.....................................................27 CHAPTER 4 Environmental Conditions................................................................ 32 Section 1 Overview..........................................................................34 Section 2 Wind.................................................................................36 Section 3 Waves..............................................................................45 Section 4 Currents........................................................................... 48 Section 5 Tides, Storm Surges, and Water Levels.......................... 50 Section 6 Other Conditions..............................................................52 CHAPTER 5 Loads.................................................................................................. 55 Section 1 Overview..........................................................................57 Section 2 Design Load Conditions...................................................59 Section 3 Determination of Environmental Loads............................72 CHAPTER 6 Global Performance Analysis........................................................... 78 Section 1 General Requirements.....................................................79 Section 2 Analysis Methodologies................................................... 83 CHAPTER 7 Design of Floating Substructures.................................................... 85 Section 1 General Requirements.....................................................88 Section 2 Steel Structures............................................................... 90 Section 3 Concrete Structures.........................................................99 ABS GUIDE FOR BUILDING AND CLASSING FLOATING OFFSHORE WIND TURBINES • 2020 iv CHAPTER 8 Design of Stationkeeping Systems................................................ 111 Section 1 General ......................................................................... 113 Section 2 Design Conditions..........................................................116 Section 3 Steel Mooring and Tendon Systems.............................. 118 Section 4 Synthetic Fiber Ropes................................................... 122 Section 5 Anchor Holding Power .................................................. 124 Section 6 Field Test....................................................................... 129 CHAPTER 9 Stability and Watertight/Weathertight Integrity.............................130 Section 1 General..........................................................................131 Section 2 Stability ......................................................................... 132 Section 3 Watertight/Weathertight Integrity................................... 141 CHAPTER 10 Machinery, Equipment and Systems..............................................142