Load Reduction and Anchor Sharing for Floating Wind Farms
Honeymooring is a grid solution for sustainable planning of floating wind farms. It is cost-effective, environmentally friendly, and enables coexistence with other ocean users. This article describes the technical principles and components of the system and reflects on the developments needed to industrialise it.
By Kasper Sandal, Engineering Specialist, Semar, Norway
The idea of Honeymooring emerged from realising that a large tension-moored buoy is an effective measure to reduce maximum forces in the mooring system for a floating unit. This is achieved by modifying the mooring system’s resulting restoring curve, making it less steep. The fundamental innovation in Honeymooring is that such a tension-moored buoy can be shared by three attached floating units, separated by 120 degrees when seen from above, without increasing the buoy dimensions or maximum anchor loads. Honeymooring is a patented solution developed by Semar. Semar is a Norwegian company providing engineering services, including design, analysis, planning and execution of marine operations.
The Main Principles of Honeymooring
The artistic impression in Figure 1 gives an overview of the main components in the Honeymooring system: anchors, shared mooring buoys, and vertical and horizontal mooring lines.
The principle in Honeymooring is to share tension-moored buoys between up to three floating wind turbines (FWTs). The buoys provide geometric stiffness to the mooring system in a way which may be thought of as analogous to an ‘inverse’ catenary mooring system, as shown in Figure 2. Since not all horizontal lines connected to a buoy will be tensioned at the same time, a buoy is used alternately by the FWTs connected to it. The maximum mooring force on the buoy and on the anchor connected to it will thus never exceed that of a buoy that is not shared. This makes Honeymooring the only load reduction device that can be shared between multiple FWTs.
The Development of Honeymooring
Niklas Norman invented the main principles of Honeymooring during the 2010s and was given resources to develop it by Semar during a period of low activity in the oil and gas industry in 2016. The results were promising, and Innovation Norway, Equinor and TotalEnergies supported a pre-study that was finished in 2021. The same year, an independent benchmark in the FIRM Research Project confirmed the cost reduction potential, and a 3-year research project with partners Equinor, TotalEnergies, Norcable and SINTEF was initiated. Jump to 2025, and the research project has both developed the concept as well as the analysis methodologies. A comparison of the early and recent versions of Honeymooring with and without loads applied to the floaters is shown in Figure 3.
The Cluster Hypothesis
What if wind farm layouts prioritised the sharing of more of the ocean area? In a recent study, we investigated whether small clusters of wind turbines with low internal spacing could compete with a homogeneous layout in terms of power production. The result is shown in Figure 4, where a clustered layout can free up 75% of the wind farm area with almost no loss in energy production. In this experiment we used a turbine spacing of only four rotor diameters. This is very small, and further research is needed to evaluate this hypothesis.
Reference Designs
To facilitate transparent comparison of Honeymooring with other mooring solutions, we have developed two reference mooring designs that are to be published in the proceedings from the EERA DeepWind 2025 conference. The designs consider a cluster of six 15MW wind turbines with 4D spacing, at a water depth of 188 metres. The depth and metocean conditions are taken for an International Energy Agency reference site offshore Ulsan, Korea. The first design is a 3-line system consisting of 10 anchors and with a design tension close to 1,200ton. The other design is a 6-line system consisting of 22 anchors and with a design tension close to 800ton. The reference designs are shown in Figure 5.
Analysis Development
Standard practice for the design of mooring systems for FWTs is to consider one FWT at a time in the analysis. With the Honeymooring concept, the FWTs are mechanically coupled, which means that all connected units should be considered in the same analysis. This requires analysis simplifications or that analysis tools are extended. On the one hand, most analysis tools can handle multiple turbines and floaters, but the computational cost becomes large when turbulent wind fields need to become so large that they cover multiple turbines. Inclusion of wake effects may also become important, and currently FAST.Farm may be the only software offering these features. On the other hand, if fatigue is not driving the design, operating cases may not be very important for the mooring design. Our current practice is to use a conservative drag disc modelling of the turbines. To investigate special topics such as yaw behaviour, we switch one of the drag discs with a full turbine model. We welcome discussion with industry, academics and regulatory bodies on how to approach these analyses.
Honeymooring Way Forward
Through extensive analysis work within Semar and with partners, we have developed a comprehensive understanding of the global behaviour of the Honeymooring system. The focus now lies in developing cost-effective and safe components and installation methods. The components will be tested in realistic conditions offshore to facilitate certification. We also continue to offer engineering studies to see how Honeymooring can be used for specific projects.
Summary
Honeymooring is a grid solution for sustainable planning of floating wind parks. It minimises cost and environmental impact while maximising area utilisation. Key benefits are:
- Reduced cost vs traditional mooring solutions
- Reduced peak loads and fatigue loads compared with traditional mooring
- Simplified interface with FWT both contractually and technically
- Pre-installation and mechanical completion allowed
- Pre-tension of polyester lines before arrival of FWT allowed
- Integrated mooring and power cable solutions may be allowed
- Tighter arrangement of FWTs in clusters allowed
- Reduced seabed footprint vs traditional mooring solutions
- Fishing activities within the wind park allowed
- No seabed damage from mooring lines or chains
- Less schedule risk with pre-installation and testing of mooring.
Biography of the Author
Kasper Sandal is an engineer with a passion for offshore wind. He holds a PhD from DTU Wind Energy and has worked in multiple disciplines and roles related to offshore wind.
