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Floating Offshore Wind – First-hand experience in this new specialist sector of offshore wind

April 2020

Offshore wind is a successful, rapidly growing market globally, and is set to grow in importance exponentially in the decades to come, becoming the backbone of our clean power system.

Floating wind technology is expected to be an important part of that growth, becoming a game changer in the successful exploitation of the enormous wind potential available in deeper waters with higher wind resources. Whilst the silhouette on the horizon of these floating sites may look the same, the technology, operations and skills required to support the installation of these sites is quite different to that of fixed bottom wind, which make knowledge sharing across the industry critical, and highlights the need to appoint teams with the experience and skills to successfully execute the projects.

We spoke to one our OIMs, Dan Norris, who recounts his experience on the 2018 Kincardine Floating Offshore Wind Farm project working onboard the Global Symphony.

“Being part of a team largely based up in Aberdeen, I was excited when I first heard about the Kincardine project, right on our doorstop. Global Offshore were involved in route clearance, cable installation and trenching operations at the first turbine.”

“I was first involved in the project with the cable route clearance operations. Once these operations were complete I transferred to the Global Symphony.  Good cooperation between the local fisherman and the project team meant that the route was clear ready for the vessel to complete the cable installation and trenching operations.

Shore end pull-in operations weren’t without their challenges. Working the ROV and vessel in shallow water with strong currents and rocky seabed conditions meant careful planning and excellent communications with the shore end pull-in team were required. Careful calculations also had to be conducted to ensure the cable split pipe protection was installed at the correct location as the cable exited the HDD. Once shore end operations were completed successfully the vessel surface laid the cable towards the Kincardine offshore wind platform along the cleared route.”

Precise work to complete the cable pull-ins

“The final phase of the cable installation workscope involved cable pull-in operations at the KIN01 offshore floating platform. The main difference between our normal cable installation operations to fixed monopile wind turbines is of course pulling up to the surface of the floating wind turbine platform and installing buoyancy modules on the cable to form the cable catenery.

Over the years, the Global Symphony has been involved in numerous pull-in operations of this type, of various umbilical’s and risers, but until now working on oil & gas projects, pulling into FPSOs and Semi-Sub rigs. The experience gained from these previous operations helped us for second end pull-in operations at the offshore wind platform KIN01. We made use of dual ROV operations during the pull-in to make things easier; monitoring both the pull-in at the I-tube on the underside of the platform as well as at various locations along the catenary, simultaneously.”

Working at a floating platform creates new challenges

“Symphony’s normal cable pull-in operations involve pulling into fixed monopile wind turbines where the aperture for the pull-in is typically 1.5m altitude from the seabed. In these cases the quadrant system is used to deploy the final bight on the seabed. For Kincardine, 13 subsea buoyancy modules had to be installed to form the catenary between the seabed touchdown point at the I-Tube on the underside of the platform. Calculations on the installation locations of the buoyancy modules along the cable were essential to ensure that the correct cable catenary was formed.

This is different from the normal pull-in operations to fixed monopile wind turbines where the cable is simply deployed to the seabed and is secured in the aperture of the monopile by use of a CPS system. The catenary was supported by the use of the vessel crane whilst the messenger wire from the Kincardine platform winch pulled the cable end and pull-in head towards the I-tube. Again careful vessel positioning and control of the crane was required to maintain the correct cable catenary, with the tension on the platform messenger wire monitored at all times. Once the pull-in head was successfully engaged into the I-Tube, the platform team continued pulling on the cable to break the weak link and pulled up the correct amount of cable overpull required from termination at the platform.

As-Installed survey confirmed that the catenary, buoyancy locations and touchdown location of the cable were within tolerance and the Kincardine cable had been successfully installed.”

Sharing knowledge and skills across offshore sectors

“For Kincardine we had a very experienced offshore team; from the Shift Supervisors who control all aspects of the operations between different departments through to the ROV, survey teams and deck crew. I have worked with some of the project team who were onboard the Global Symphony for 20 years on various projects and different vessels all over the world including cable installation, ploughing, survey work, oil & gas construction, pipelay, umbilical lay and of course power cable installation in the wind farm industry.

It was also good to see some old faces also joined the vessel to be part of the successful team on the Symphony for the Kincardine project. I have been involved in the offshore industry for 22 years, and specifically focused on offshore wind for the last five of those years. Previous to this I was involved in cable lay and burial of fibre optic cables and then the offshore oil and gas construction industry. Having been involved in most of the different industries offshore for a significant amount of time, I believe the sharing of knowledge and skills is essential between the different offshore sectors.

The development of floating offshore wind platforms will undoubtedly be a big growth area as offshore wind farms are installed in areas of deeper water. Lessons learnt from installation of oil and gas semi-submersible platforms and FPSOs can be used for installation of floating offshore wind turbines.”

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Floating Offshore Wind – First-hand experience in this new specialist sector of offshore wind

Hear from one of our team who played a key role onboard during one of our floating offshore wind farm cable installation projects.

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