By Jason Deign on Jun 2, 2014

The tidal industry could significantly reduce installation and operations and maintenance costs by working with smaller vessels, a study has found.

The research, led by the European Marine Energy Centre (EMEC) in Orkney with funding from the Scottish Government, shows that smaller boats can do many of the tasks currently contracted out to large, expensive ships with dynamic positioning capabilities.

One finding was that tidal developers could save between 70% and 80% of installation costs by using a gantry barge and other local vessels instead of a dynamically positioned offshore construction ship of the kind frequently used until now.

“The study was looking to see what the local fleet could do,” says Neil Kermode, EMEC’s managing director. “The principle was that we have seen two distinct philosophies emerge in the operations and maintenance on sites.

“There have been people who have sought to do things with comparatively small vessels. And then we’ve seen other companies using much bigger vessels, often North Sea or heavy lift derivatives coming in from all over the world.”

While the larger vessels are clearly capable of handling the challenging conditions found in high tidal streams, they are also costly. “The industry knows that it can’t rely exclusively on those long-term because, quite simply, they will be far too expensive,” says Kermode.

As well as costing up to hundreds of thousands of pounds a day to hire, such vessels are often tied up in carrying out other duties for high-value sectors such oil and gas, which means their availability to work on tidal projects can be a problem.

Multi-cat vessels

Not all tidal developers use them, however. Scotrenewables Tidal Power of Orkney, for example, uses a small multi-cat vessel for all of its work. The EMEC study, carried out in association with Orkney consultancy Aquatera, looked to see if others could follow suit.

One part of the research involved seeing whether locally available vessels could use moorings to stay on station in the same way as a dynamically positioned ship.

In the event, experimenters found the moored vessels were stable enough to lower a dummy turbine onto an A4 sheet-sized target on the seabed. “We found it can be done, it did work, and is safe,” Kermode says. “It unlocks a lot of things.”

“Because these assets are relatively cheap, you can actually keep them in the area waiting for the right moment.”

Ian Baylis, managing director of Seacat Services, a marine energy support firm, agrees that being able to rely on a wider, less costly range of vessels is good news for the tidal industry, because it means a vessel is more likely to be available when needed.

“With the wind farm stuff you are out there all the time,” he says. “With tidal, the turbine is plunked into the sea and then not seen for quite a while. The only times you will need a vessel is for planned routine maintenance or to pull it out because something is not working.”

Apart from the cost of hiring a large ship in itself, tidal developers need to bear in mind that vessel availability can affect project costs by extending the time it takes to be able to carry out repairs and bring damaged turbines back online.

Guaranteed access

“They will need to have guaranteed access to vessels for a given amount of time,” Baylis points out. “We have seen this with met masts in the wind industry, where a vessel could be made available in 72 hours.”

Dee Nunn, wave and tidal development manager, at RenewableUK, adds that a transition to vessels that are not so sought-after by the oil and gas industry could shave up to two-thirds of daily chartering costs.

Similarly, she says: “A lot of the developers are moving towards floating their devices out to site so they are not having to use big lifting vessels.”

The Orkney Vessel Trials project was launched by Scottish Energy Minister Fergus Ewing with a GBP£1.1m funding package last year, and took place over winter with 20 Orkney-based organisations and more than 120 people carrying out over 60 vessel operations.

It involved six performance trials covering workboat positioning and dynamic loading, gantry barge positioning and device deployment, clump weight friction, remote-operated vehicle operations, responses to man-overboard situations and dynamics of buoy submergence.

Not all of the findings were related to cost. Regarding man-overboard situations, for example, the research found that a dummy thrown into a high tidal stream would disappear from sight within seven minutes, well under the time it might take to pick them up.

As a result, EMEC is now proposing that all personnel should wear personal indicator beacons so the location of a person in the sea will show up on the navigation equipment of all the boats in the area.