By Rikki Stancich in Paris

With an aptitude for problem solving, BMT Nigel Gee has already presented two promising solutions for the offshore wind energy sector.

As part of a joint-industry team, BMT Nigel Gee led on the design of a transport and installation barge (TIB) for gravity foundations designed for Round 2 and 3 wind farms.

The TIB forms part of a low-cost innovative turbine foundation solution conceived by a team comprising engineering consultancy, Gifford, BMT Nigel Gee, and structural engineering firm, Freyssinet, under the auspices of the UK Carbon Trust’s Offshore Wind Accelerator programme.

More recently, BMT Nigel Gee teamed up with specialist marine engineer, Houlder Ltd, to develop a turbine access system designed to operate in 2 metre sea states without the need for a dynamic positioning system or a complex stabilised platform.

WindEnergyUpdate speaks to John Bonafoux about how such innovative thinking will help the UK to achieve its 2020 offshore wind targets safely and efficiently.

WindEnergyUpdate: You recently mentioned that challenging offshore conditions presented by greater distance from shore and turbine density require a rethink in vessel design. What kind of design features could be built in to address these issues?

John Bonafoux: With the current sites, the focus has been on higher speed vessels that can get crew and supplies to the turbines as quickly as possible. The current practice has been to bring the vessel hard up against the turbine foundation in order to effectively stick the bow of the vessel to the turbine and make the transfer.

However, this practice will be more limited for Round 2 sites, given that there will be an increased need to complete transfer operations  in wave heights of  2 metres and more . Also, the far shore sites will require vessels to have greater speed and better motion stability if they are to provide good  year-round operability.

Where the Round 3 wind farms are concerned, we are talking about two groups: near and far shore. The far shore wind farms will require offshore accommodation platforms or ‘flotels’. So you will need larger vessels to transfer crew and supplies to the accommodation platforms, and smaller ‘intrafield’ vessels for field coverage. 

The latter would not have such a high-speed requirement, but they would need to have good ‘sea keeping’, to be able to cope with the rougher seas.

Also one of the key challenges will be the protection of the vessel in severe offshore conditions. As such, investigation is needed into how to actually dock these vessels and whether there is the possibility of physically lifting them out of the water at the accommodation platform overnight or in foul weather

With the near shore developments, the issues would be similar to Round 2 developments, insofar as they could be serviced from port. The issue is that a larger number of turbines means that vessels will probably need to carry more than 12 passengers. However, current regulations dictate that there must be no more than 12 passengers per vessel.

WindEnergyUpdate: Health and safety is a growing concern in the offshore wind sector. How could both vessels and turbine designs be improved to meet minimum
safety standards?

John Bonafoux: Health and safety-wise, we think that this current method of pushing up against the turbine foundations presents a real danger of larger wave heights forcing the vessel to break free. We do view this as a potential health and safety hazard and one that could severely limit operability in rough sea conditions

Together with Houlder Ltd., we are developing a turbine ‘transfer access system’ that compensates for the motion between the turbine and the vessel.

There is also talk of using helicopters, but we think this is a step in the wrong direction, given that the oil and gas sector is trying to move away from heli-transfer.

WindEnergyUpdate: Given the global nature of the wind energy sector, is there a need for universal standards when it comes to offshore wind HSE and if so, which body should be responsible for setting such standards?

John Bonafoux: Health and safety is a difficult area – particularly in a young industry. It is extremely challenging to have universal standards – even in the North Sea oil and gas sector. In any case, some sort of minimum baseline for standards would be desirable. As a body, the HSE Executive would be the best organisation to complete that role.

Possibly one of the most difficult regulatory challenges will be certification of transfer vessels, as most of these currently come under the Maritime and Coastguard Agency (MCA) Workboat code, which limits the number of passengers to 12.

However, the demand for increased passenger numbers and the vessels needed for Round 2 and 3 will probably need to carry more passengers, which will present difficulties with MCA code compliance.

We understand that there have been some discussions between offshore wind companies and the MCA regarding this, but it remains to be seen as to whether the regulations are adjusted to accommodate the fact that these vessels may need to carry more than 12 passengers, or whether the vessels will be certificated under the IMO High Speed Craft (HSC) Code.

WindEnergyUpdate: Have you identified the choke points in vessel supply over coming years? Which types of vessels will be in shortest supply?

John Bonafoux: BMT is mainly looking at operations and maintenance planning and there are already some issues with long lead deliveries on vessels. The biggest issue is supply of installation vessels.

Concerns have been raised regarding Northern European shipyards’ ability to meet this demand and EWEA/CESA have already called for the European Investment Bank to support the required build-out.

But taking a longer-term view, these vessels could be built anywhere. International shipyards are showing a lot of interest – and with the current market a lot of them are hungry for work.

WindEnergyUpdate: Is there will likely be a growing demand for floating turbines,
given that they remove the need for specialist installation vessels?

John Bonafoux: We haven’t really looked at the floating turbine option in any great detail, and we’re not sure if a robust and cost effective solution is available yet.

BMT has been working on the design of gravity foundations with Gifford and Freyssinet, the installation of which is less effected by sea state than for piling operations.

To respond to this article, please write to the editor:

Rikki Stancich: rstancich@gmail.com