“The CDC Heron is the only vessel in the world that can provide a fully functional working platform, at any given height, enabling installation and maintenance activities regardless of environmental conditions on a wind turbine tower,” highlights...

By Heba Hashem

In the next few years, many of the warranties for Round One of wind farms and the early Round Two will be coming to an end in the UK. As warranties approach expiry, any inherent financial risk will rest with the owners, making good Operation and Maintenance (O&M) planning critical.

“Wind farm operators are going to have a shock when their five-year warranty, or in some cases longer, ends,” says John Davies, managing director of Celtic Design Consultants, the developers of multi-purpose offshore servicing vessel CDC Heron.

“During this warranty period,” he says, “the ‘maintenance’ contract is more akin to a service contract, and will perform condition-based maintenance only”.

“Reliability of machinery at the end of the five years on servicing alone, while performing condition-based maintenance, means that when the warranty and service period ends, there is a high likelihood of the next stage quickly becoming very expensive,” Davies tells Wind Energy Update.

Because the minimum has been carried out over the warranty period, major and expensive components will start to break down and need replacement – the kind of parts that cannot be changed out from the “bump and jump” boats, since they are service and not maintenance boats.

Maintenance routes

Offshore wind operators typically have four vessel options to maintain their plants: using the current influx of construction vessels; service vessels; helicopter transfers; or mothership type of vessels. Each, however, comes with a set of technical and financial drawbacks.

Construction vessels, besides being extremely expensive, are frequently restricted by weather as they have to use cranes, which are highly susceptible to wind conditions, jack-ups to wind, marine floating units to wind and sea conditions.

Helicopter transfers, which Davies describes as a “James Bond” solution are another highly expensive and high-risk method of approaching an offshore turbine.

“This is not a realistic nor cost-effective method of maintenance in this environment. And as helicopters cannot land at a turbine, they must make two journeys for each turbine”.

Service vessels

Meanwhile, catamaran and trimaran vessels were acceptable when wind farms were being constructed within short distances of 30-45 minutes from the shore. But with projects moving further away from land and the journey time becoming 2-3 hours each way, the costs of non-productivity and fuel consumption come to question.

Moreover, weather conditions can change dramatically in a journey time of one hour, thus a service vessel may reach halfway or almost to the field and have to run back to the shore. To top it all, such vessels are limited in the equipment and spare parts that they can move to the field, since everything has to be man-handled.

“One has to look very closely at what is meant by support vessels. The use of large numbers of all types of vessels from crew transfer to installation vessels is not economical.

“A case point was the London Array – just imagine the cost of fuel for these vessels, before you even begin to think about the cost impact of non-productive personnel time. This methodology will not be sustainable for Round 3 mid and far shore locations,” explains Davies.

At current levels, a 1GW farm with 200 turbines rated at 5MW is estimated to require around 3,000 maintenance visits per year, according to the LEANWIND report. The four-year long EU FP7-funded project started on December 1, 2013 with the objective of providing cost reductions across the offshore wind farm lifecycle and supply chain.

Mothership vessel

Although the mothership concept is heading in the right direction, the fact that it is a ship that either will be moored or under Dynamic Positioning means that many of the operations will continue to be subject to weather.

“Experience has shown that this type of vessel can only load and unload vessels in sea conditions with relatively low significant wave heights,” highlights Davies.

Moreover, when a mothership vessel is rolling, heaving and pitching, helicopter operations will be out of the question. No matter how good the design is, there will be always be risk of damage to the smaller service vessels, and consequently injury to personnel, particularly in the undocking and docking operations.

In addition, such vessels are only a safe haven for maintenance vessels; they cannot carry out any major turbine maintenance or replacements, or blade inspections.

“Uncertainty remains over the detailed functionality of the mothership and the safe and reliable transfer of personnel from crew boat to the mothership,” states the LEANWIND report.

CDC Heron

Wind farm operators are currently in desperate need of lower-cost vessels with faster transfer speeds, large deck areas, are fuel efficient, and have a comfortable ride as seasickness is a major contributor to lost time. As a result, technological innovations in the transfer of personnel from vessel to turbine are continuously seeking to improve accessibility. One of these innovations is the CDC Heron.

Uniquely equipped with a multi-functional secondary platform that operates and elevates independently of the main hull – a concept that has been patented – the vessel’s secondary deck elevates to allow work to be carried out on a wind turbine, hub, blades and nacelle.

“The CDC Heron is the only vessel in the world that can provide a fully functional working platform, at any given height, enabling installation and maintenance activities regardless of environmental conditions on a wind turbine tower,” highlights Davies.

His team of three have developed and patented this cutting-edge vessel based on more than 90 years of collective experience in the construction and O&M of vessels for the offshore oil and gas industry.

The vessel not only provides ‘walk-to-work’ access for any height of turbine, in water depths of up to 65 metres, but its secondary platform extends to both sides of the tower. “When the vessel’s secondary deck extends beyond the tower, it has a hydraulically powered deck, which, when lowered enables protected hands-on access all around the tower,” explains Davies.

A critical aspect of CDC Heron is its capacity for a warehouse of spares, both turbines and blades, allowing replacement parts to be kept on board and repairs to be carried out on the spot. “Think of the downtime and loss of generated energy that can be saved.”

Massive cost reductions

But what really makes the difference here is the vessel’s cost reduction proposition of 25 to 30 percent on operational costs – without taking into consideration the reduction in lost revenues by the quick return to service of a turbine.

In contrast, current construction vessels have to be chartered on spot market and therefore are prohibitively expensive for maintenance activities.

At the same time, the industry has been declaring it is trying to cut costs. Last month, Ole Nielsen, director of offshore project execution at Vattenfall, told Wind Energy Update that massive cost reductions were needed on all levels in offshore wind, and that vessels had to contribute to that.

And while there is a sufficient number of installation vessels in the market – with some even leaving renewables and returning to oil and gas – only 110 service vessels with wind experience are available and demand is expected to exceed supply by 2017.

According to the Danish Shipowners’ Association, by 2022, approximately 426 vessels will be required to deliver maintenance crews to site.

“It will be interesting to see how the economics and profitability between the current installation vessels and service vessels are in a few years from now, when there are even more installation vessels in the market, while the number of turbines being installed drops,” notes Davies.

‘The offshore wind industry needs to be focusing on all aspects of the future today,” cautions Davies.