Blowing in the wind: floating for maximum buoyancy

Twin Boom floats supporting cables


Twin Boom floats supporting cables

By André van der Mout,
Managing Director at Oil Control Systems

“How can electricity be brought to the mainland safely, undamaged and quickly?”

It’s a question many offshore companies have asked with the increasing focus on wind energy as a sustainable source of energy. It’s one of the world’s fastest growing sustainable energy sources; a trend expected to continue in the forthcoming years.

This trend has resulted in declining technology costs and fewer security issues, but also the need to really tackle environmental problems. Quicker, easier and cheaper: that’s the challenge Oil Control Systems had to face in order to bring electricity to the mainland.

Trending: wind energy as a challenge
All onshore and offshore windmills across the world combined now add up to nearly 500,000 MW of wind power capacity. This type of sustainable energy currently has a remarkable market share: approximately 4% of the global electricity market is covered by more than 300,000 wind turbines.

Open locations, such as seas and lakes, are ideal for wind energy. The air doesn’t get slowed down here; winds are stronger, more frequent and more consistent. While the sea is the ideal place to harvest wind energy, it is also a force of nature which makes it difficult to work safely. A calm sea is essential to build and maintain.

Transporting electricity by sea
Sea wind farms or individual wind turbines are often located 20 kilometres or more from the shore. Cable-laying ships usually take care of the landing of pipes and cables, where the cables run from the rear of the ship to the land. The draught of these ships is too shallow in most places for the cables to reach all the way to the land. The closer to the shore, the more shallow the seabed, resulting in ships easily getting stuck.

You can imagine an unfamiliar seabed with limited visibility doesn’t inspire a great deal of confidence. The seabed holds many secrets. It’s difficult to determine what lies below sea level. Pipes and cables are usually made from solid and durable material which are quite resilient. However, it isn’t a good idea to drag these pipes or cables across the seabed to the shore. Wear or damage will quickly occur, resulting in increasing costs.

Good visibility of cables is important to avoid them suffering damage. An underwater camera offers a solution, but has proven to be expensive in practice. Another solution is the use of underwater robots. These robots with caterpillar tracks transport cables while driving across the sandy seabed. Once arrived on shore, the cable is further dragged across land. Underwater robots can only drive on flat sandy soil, they’re therefore not suitable for all locations.

“Making electricity float can be a real challenge, but it does offer scope for new techniques.”

Oil Control Systems decided to deploy a new technique to make electricity float: Twin Boom floats. Their knowledge of the offshore market, years of experience with offshore techniques and a broad network of many quality products have led to a technique which can guide electricity across the sea to the mainland.

How air can provide maximum thrust
Cables must reach the mainland safely, quickly and undamaged. Not a job which can be done with just any technique. A strong and airtight product is needed in order to generate maximum thrust and subsequently boost the wind energy industry. Durable reinforced PVC turned out to be the solution, partly because of its special three-layer welding joint.

 Connecting floats to a power cable


Earlier techniques proved that cables, hoses and pipes will move quickly if they’re not fastened securely. Cables disappear below sea level and will easily get stuck in the propellers of other ships. The new floating technique takes this into account. Cables are kept in place by putting floats underneath them. Keeping them afloat will ensure they remain visible. Add the bright red and yellow colours into the equation and nobody will overlook them anymore.

Powerful natural elements
A floating and visible technique would appear to be complete. However, this certainly isn’t everything which needs to be taken into consideration. Wind, currents and waves complicate working at sea. The floats had to be designed in such a way that they would lessen these powerful side effects.

We therefore opted for a strong and airtight product, which consists of a middle groove with two floats. One air-filled float would be ineffective in such situations and much harder to manoeuvre. Any possible problems can quickly be tackled through the use of multiple small floats. This technique has been designed in such a way that it has a buoyancy of 80 kg to 600 kg.

A look behind the scenes at the Burbo Bank Extension project
The Burbo Bank Extension offshore wind farm is located 8 km off the British coast in Liverpool Bay. The wind farm consists of 32 wind turbines with a length of 195 metres, each supplying 8 MW of power. Together they generate enough energy to supply 230,000 households with electricity.

A tidal area measuring more than 350 metres meant safety was a top priority. Jan de Nul deployed a DP2 ship for the cable installation. Oil Control Systems’ new technique was used to safely land the cables. A total of 758 floats have been used to guide cables to the mainland. The empty floats were hoisted on deck, inflated and mounted around the cables. They subsequently went into the water via a chute.

Time was an important factor throughout this project. Delays cost time and time costs money, also at sea. The entire operation was completed in 18 hours, partly as a result of the float technique. The floats were removed by divers, deflated and compactly stored after completion of the project. Ready to be used for the next project.

Blowing in the wind – floating in the future
Wind energy is a mature source of emission-free electricity. The use of wind turbines will continue to grow in the forthcoming years. New challenges will undoubtedly arise along with this growth. Oil Control Systems is responding to the need to cut costs in the sustainable energy sector, making sure the development of energy is given every possible opportunity.

The Industry Contribution is a new section in which the offshore wind industry companies share their project endeavors or analyses. This article was produced by Oil Control Systems and does not necessarily reflect the view of No member of the editorial team took part in creation of this article. Please contact us at [email protected] for inquiries.