2nd Generation Vessels: Hype or Hallelujah? (A2SEA Story)

Often, new technology doesn’t live up to expectations – and there have been plenty of expectations around second-generation vessels such as SEA INSTALLER. Has this much-awaited vessel delivered on its promises? 

The first of A2SEA’s second-generation installation vessel designs, SEA INSTALLER incorporates innovation after innovation – all aimed at making installation faster, safer and less costly. Since reporting for work in December, 2012, she has been put to the test at Gunfleet Sands, Anholt and, most recently, at West of Duddon Sands, installing a total of more than 120 wind turbines. But has her advanced design proved its worth in the field?

Capacity as promised

To begin with, SEA INSTALLER has easily lived up to its expected capacity. By this, we mean that she has, for example, proved capable of carrying up to eight 3.6 MW turbines at a time and installing these as required. That shouldn’t surprise anyone. It’s more interesting to examine the operational side of things, assessing the vessel’s performance in terms of A2SEA’s “famous” 24/12/24/12 principles.

24/12/24/12

As a second-generation vessel, SEA INSTALLER was purpose-built to install turbines. During the design phase, the 24/12/24/12 mantra functioned as a springboard for creating innovative approaches to installation methodologies and to technologies that could support these methodologies. Like its sister vessel, SEA CHALLENGER, SEA INSTALLER was designed to bring the installation task much closer to these aims.

For those who are new to offshore wind, the row of numbers represents four distinct but interrelated objectives:

  • 4 hours to dock, load and sail
  • 12 hours to get into position, stabilise, install and leave again
  • 4 hours to commission
  • 12 m/sec maximum wind speed for lifting and installing blades

If we examine the vessel’s most recent project, West of Duddon Sands (WoDS), a joint venture between DONG Energy and Scottish Power, in relation to 24/12/24/12, we can see that definite progress has been made – at least where factors that can be controlled by A2SEA are concerned.

24 hours to dock, load and sail?

At WoDS, we were running at full capacity, carrying eight Siemens Wind Power 3.6 MW turbines at a time. And, if the loading task itself were all that mattered for the 24-hour target, SEA INSTALLER would have beaten expectations by a wide margin. Harbour restrictions, however, aren’t within her control, so while loading was a great success, the pilot-to-pilot time pulled in the other direction. Overall, however, the average result was, in fact, right on the money – sometimes a little under 24 hours, sometimes a little over. By way of comparison, loading eight turbines of this size onto one of our first-generation vessels (in terms of loading time per turbine) would likely have taken up to 24 hours!

12 hours from position to position?

Once out at the wind farm location, SEA INSTALLER’s goal was to work to a 12-hour cycle that matches tidal patterns. Twelve-hour installation had been achieved several times before, but the aim was to do this consistently. At WoDS, the vessel and its crew managed to achieve a consistent position-to-position time of between 12-15 hours, with the installation task completed in around six hours. That’s certainly something to be proud of and it proves that, if we could figure out a way to build automatic tide control into SEA INSTALLER’s design, we could achieve an even more impressive position-to-position result!

Power to the grid within 24 hours?

Commissioning a wind turbine once it has been put into place is a task that falls outside A2SEA’s scope of work. If SEA INSTALLER could claim to have any positive influence on this part of the overall installation work at WoDS, it might be because improved onboard accommodation facilities made Siemen Wind Power’s technicians feel even more rested, relaxed and ready to work at their very best. But we’ll let them be the judge on that one…

At 12 m/sec wind speed?

Proposed just a few years ago, the 12m/sec wind speed target is perceived somewhat differently today. Even with SEA INSTALLER, blades are still being lifted in not much more than 9m/sec. That’s not because it’s physically impossible, but because blade size is on the increase, and because there’s a lot of emphasis on safety for everyone on board. With these factors, no one really wants to push up against the wind speed limits. Efforts are being made however, to work with standardised blades and standard installation routines that can enable lifting at higher wind speeds once again. For now, progress on this front must be left in the hands of the turbine manufacturers.

Benchmarked excellence

A key difference is that SEA INSTALLER is purpose-built and highly fault tolerant. There’s plenty of redundancy built into the design, so she is more reliable than first-generation vessels and quite capable of continuing with installation tasks, albeit at a slower pace, even if a sub-system fails.

We’re always testing our vessels’ performance against benchmarks, and continually looking for improvements. But looking at SEA INSTALLER’s
performance, we haven’t seen any high-priority areas for improvement. All of her major systems perform as they should, and even though a number of minor subsystems have encountered difficulties, overall downtime due to technical breakdowns is much lower than we would normally expect.

So overall, we’re very happy with SEA INSTALLER. And, while first-generation vessels have cost advantages, particularly for operations and maintenance tasks, there’s no doubt that the new generation is capable of delivering on its promises.

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Source: A2SEA, September 22, 2014
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