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Great power demands intelligent control

Stuart Thornton, business development and tendering manager at Offshore Heavy Transport AS, tells us about the company's vision for the next generation of offshore wind foundations.

The offshore wind industry needs bigger vessels with larger crane capacities – of this, there is no doubt. However, a step-change is also required in the level of sophistication in control systems needed to safely handle and install the next generation of offshore wind foundations.

In this article, I explain how OHT's approach to the challenges of control stands out in the marketplace.


A new philosophy is born

Our underlying philosophy has set our design trajectory and defined our development pathway in a way that differs from other vessel operators.

Under the guidance and strategic thinking of CEO Torgeir E Ramstad, OHT identified the requirement for a new, more advanced solution for the transport and installation of future offshore wind foundations. The solution would not only have to transport and safely install structures in excess of 2,000 tonnes, but would also need to be capable of installing a high number of foundations on a single deployment.

Speed and operability were also key priorities. A solution had to be found that would allow the vessel to install in challenging sea conditions whilst in DP mode – so as to avoid the use of slow and expensive mooring operations.

The offshore wind market was growing around the world, increases in economies of scale were a driver in bringing down the Levelized Cost of Energy (LCoE), and the jack-up fleet that had long served the sector were fast approaching their limits. OHT not only had to think big, they also had to think smart.

OHT would have to make a brave but calculated step as a new player into an already established offshore wind market. With a long history of operating large semi-submersible vessels, a deep understanding of how to handle and transport ultra-heavy cargoes, and a senior management team with a great understanding of both offshore wind foundations and installation vessels, OHT were well positioned to take this step.

From day one, the mission was not to simply build a really big boat, and put a really big crane on it. The design process started by making the mission equipment and control philosophy the heart of the complete system. Essentially, we conceptually designed the tools and operation methodology first, and then integrated this technology into a new class of Ulstein designed floating installation vessel – Alfa Lift was conceived.


Intelligence from space

The challenges identified by the initial development stages were complex:

  1. Transport and install as many as 10 next generation XXL foundations at a time.
  2. Install from a floating vessel in DP mode, in seas of up to 2.5m Hs.
  3. Site the foundations with pinpoint accuracy, and, in the case of Monopiles (MP), achieve a level of verticality no more than 0.25 degrees off true vertical.
  4. Install Transition Pieces (TP) and all secondary steel in the same operation.
  5. Achieve a level of efficiency of one complete foundation (including TP and secondary steel) installed every 24 hours for the duration of the project, all time inclusive.

The solution, therefore, needed to be safe, fast, efficient, and based on conveyor-belt principles. Every piece of equipment in the system had to communicate with every other piece of equipment and react quickly to inputs from the vessel motions, the environment, the seabed, and the foundations themselves.

The DP system needed to be very powerful and quick to respond. The mission equipment, comprising of the motion-compensated gripper, upending tool, and deck transportation system all needed to be sophisticated, strong, and sensitive to the smallest inputs. The 3,000-tonne main crane needed to be fast, accurate, and extremely robust. And the state-of-the-art control system (the brains behind the brawn) needed to be the most advanced of its kind.

In fact, the complex algorithms used to ensure that monopiles remain under total control during all stages of the upending process, and then completely vertical throughout the lowering, self-penetration and piling phase found their origins in the principles used to land the SpaceX Falcon 9 first stage booster rockets vertically on a floating drone vessel off the coast of Florida.

It is true to say that to affix the next generation of massive wind turbines to the ground, we looked to the stars.


Excellence and diligence in the pursuit of the most elegant solution

It should not be underestimated just how dynamic the challenges are. We have made finding the right solution to these challenges the central mission of our design and development process. Building a vessel is nothing new to OHT. Delivering a robust and workable installation solution is the challenge that we have risen to meet.

To do this, we have gathered the best engineers and problem solvers, and forged strong relationships with renowned, world-class sub-contractors. We have specified only the highest quality components and software, ensuring the control system really is up to the task. The challenges faced by all future foundation installers are the same, and OHT remain unerring in the pursuit of the safest, most efficient, truly elegant solutions. We believe that this makes us unique in the market.

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