Ready for take off: Helicopters in the offshore wind industry

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At first sight perhaps conventional shipping would appear to be the most obvious means of getting out to and supporting wind farm installations. A helicopter being employed on such slim structures as wind turbines with long blades does not seem to be the most obvious candidate. But nevertheless an industry has grown up that is not only capable of supporting wind installations, but also has several distinct advantages over its shipping counterpart.

Offshore WIND spoke to Dennis Bernitz, Sales and Customer Relations of manufacturer Eurocopter Group, and Niels Peter Kjeldahl, Flight Operations Director of operator Uni-Fly to get their view of the industry, the development and their view of the future.

An industry that has grown up in a mere ten or twelve years has required close association between the manufacturers, the operators and the authorities to tailor machines and flying techniques to meet the unique challenges of working with wind turbines.

For more than 10 years Eurocopter has been the largest helicopter manufacturer in the world in civil and parapublic operations. Formed in 1992 the Franco-German-Spanish Eurocopter Group is part of the EADS and with more than 11,300 helicopters currently in service in 149 countries worldwide they have 43% share of the global civil and parapublic market. In addition they provide a network of service centres, training facilities, distributors and certified agents worldwide. More recently they have seen a large uptake of their craft in the offshore wind sector.

Uni-Fly A/S on the other hand have been operating helicopters since 1970 and currently operate four crafts. At this moment Uni-Fly mainly operate in the wind farms fields west of Denmark and include maintenance, staff transfers and equipment transfers. They are justifiably proud of their record of more than 20,000 hoist (winching) operations without any accidents, incidents or injuries.

The early days

In the very early days discussions on types of support vehicles was extensive and nothing was discounted. Everything from surface vessels to submarines, seabed crawling devices and even ski lift like structures were all put on the table at some point in the discussions. Eventually the helicopter specialists were consulted and from that small beginning has mushroomed the industry we see today.

Advantages over surface vessels

Clearly the main advantage of a helicopter is its all round versatility as we will see here.

Weather wise they can operate virtually free of any restriction from sea state conditions. In reality this has two benefits, on the one hand they can often operate when the sea state prevents a surface vessel from leaving harbour. But the wind itself drives the seas and therefore after a storm the wind settles quickly whilst the sea state will take many hours to settle and as this is happening there is the possibility that another storm will come through before the sea has calmed. The short “weather window”, low wind force and relatively short excursion time, allows the helicopter to operate when the surface vessel would still be trapped in port.

This scenario happens most frequently during the autumn and winter when the wind farms are at their most productive. It is ironic considering that the ideal conditions for a surface vessel to operate are precisely the conditions when the wind turbine has the least potential generating capacity.

At personnel level there is also the consideration that, when travelling on surface craft there is a potential for seasickness, especially on the smaller craft often used for crew transfers. Moreover the victim of seasickness will often require a period of recovery time before being able to function properly and conduct the task for which they have been sent out. Whilst airsickness is not unheard of it is much less frequent.

A further demonstration of the helicopters versatility is that it can routinely travel at 130 to 150 knots subject to the type of machine whereas a surface vessel will operate at about 25 to 35 knots (1 knot is 1.852km/h ). This difference between 47km/h and 223km/h not only provides a much smaller transfer time, but also makes the helicopter the ideal rescue vehicle based on response time alone without considering its increased operational conditions ability. Mr Kjeldahl estimates that Uni-Fly response time is in the region of 20 minutes to any Danish wind turbine location and a guaranteed less than 30 minutes with a medic onboard. Furthermore to capitalize on this potential their personnel are dual trained for both routine operations and rescue operations.

Another consideration is that when a boat gets to its location a transfer from turbine to a pitching vessel is challenging enough without having an injured or ill person to transfer in emergency situations. In comparison a hoist transfer is very many times safer regardless of whether the rescue is a semi-mobile casualty or a stretcher. Moreover medical support in the form of a medic can be dropped in just as easily and of course it is always possible that the incident has happened at the top of the tower, which is where the majority of the equipment is situated. Mr. Bernitz tells of an engineer who suffered a head injury which made it impossible to get the patient down the tower and so a helicopter was the only possibility.

The benefits do not end there either, the flexibility of operation means the helicopter can operate in cooperation with surface vessels. Here they can be used to lift personnel or equipment from a large installation vessel which could be used a base or ‘hub’ quickly and efficiently to a range of turbines without the large vessel having to travel to each one.

OW 11 compleet.jpg 26 1Returning to routine operations it is usual for teams of two or three to be transferred to turbine for maintenance  and servicing work. This is mainly for safety reasons; often at least one will be electrical engineer and the other a mechanical engineer. In terms of a transportation vehicle a helicopter has the option to carry materials internally or slung under the craft. Helicopters are certified to carry sling loads of up to 4750kg (EC225). Depending on the distance to the site of operation, prevailing wind, and configuration of the helicopter, sling loads in the region of 1300kg to 1600kg for the larger aircrafts, and about 700kg for small twin engined helicopters have been operationally tested. Manufacturers and operators state that hoisting or winching operations can be conducted in gale force speeds, even as high as 50kts to 70kts (93 – 130km/h).

Passenger numbers vary of course with the size of the helicopter but five or six for smaller craft and about ten for larger craft are reasonable. At the far end of the scale an EC225 will carry 19 passengers or a sling load of 4750kg.

Adapting to wind farm operations Even though the industry is relatively new there is a wealth of experience already available. Only small changes are needed where necessary to adapt this experience to wind turbine purposes. Both the oil and gas industry and the rescue services, maritime and on shore, provide valuable experience.

Adapting to wind farm operations

Even so the early days were a steep learning curve according to Mr Kjeldahl, and both the industry and the authorities are still developing procedures and standards specific to these operations. At the same time there is need to harmonize these standards between countries at international level.

The Joint Aviation Requirements (JAR-OPS) covered many aspects of the operations from certification of operators to maintenance routines, crew training, operating conditions, operating procedures, logged hours and many other areas of operation. Since 16 July 2008, JAR-OPs has been superseded by EU-OPS which applies to all aircraft operated by European Community Member States’ operators.

There are still variations in national regulations, however. Currently the United Kingdom and Denmark share the same performance criteria for hoisting operations, but Germany has a different set of standards. Equipment requirements also vary slightly, but these requirements are relatively straightforward to address.

Clearly the offshore wind turbine rotor must not be rotating during helicopter operations, but they should also be in one of two positions either a Y position or with one blade horizontal in the opposite direction to the approach of the helicopter.

The future

At present the vast majority of operations are conducted using hoisting techniques, but as turbines get larger there is increased potential to install helipads, which by design have to be relatively heavy. In fact at this moment the Scottish government approved an offshore test site for a new 6MW wind turbine. The turbine, to be located 1,5 km off the coast of Methil in Fife, is described as ‘an innovative two bladed turbine’. Such a design allows the bladed to be ‘parked’ horizontally removing another hazard for helicopter approach. Eurocopter estimate that by 2030 there will be some 400 helicopters operating in the North Sea area alone and about 1,000 helicopters world wide. Further to this, Uni-Fly anticipate the light twin engine machines being the main tool for the next five years with the larger machines taking over after that.

Another possible area of development is that of Automatic Identification Systems (AIS). This is being discussed as part of the European Union initiative to investigate and develop an e-Navigation standard. The possibilities of platforms to act as ‘staging posts’, not unlike the hub vessels mentioned above have been also discussed. This is aimed that cutting down access and transfer times even further.

It certainly looks like this industry will ‘take off’.

Tom Oomkens & Andrew Rudgley

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