Turbine manufacturers are doing their best to design out maintenance issues. And yet technicians and components will always need to be delivered offshore to carry out work on turbines. Vessels, therefore, are an increasingly vital element of offshore operations and maintenance (O&M).
CWind business development manager Bruce Clements says vessels’ workable sea states — the wave height at which boats can safely transfer technicians to turbine towers — will be fundamental to O&M efficiency. "If you can work in higher sea states, that’s more time you have available to carry out repairs and maintenance," says Clements. "And the longer you can operate, the more cost-effective your operation will be."
At present, most wind farms are relatively near shore. They are serviced by a mixed bag of vessels, ranging from state-of-the-art SWATHs (small waterplane area twin hull) to little more than upgraded fishing boats. They are typically leased by developers on an ad hoc basis.
Vessel operators are quite clear about the negative impact this way of doing business has on the O&M costs of offshore wind farms. Tidal Transit director Leo Hambro describes a situation where many of the vessels currently used for transferring technicians are only suitable for use at wave heights of less than 1.5 metres. This means turbines that experience faults during rough seas may be out of action for days or weeks until the weather subsides or a vessel capable of safely delivering technicians at higher sea states becomes available.
Bigger boats
"There is a shortage of the most appropriate vessels," says Hambro. "A lot of current vessels are only capable of being used on near-shore good water sites. However, now the major players are bringing in much bigger boats. This will weed out the chaff, such as ex-fishing or patrol boats. It may increase the daily cost, but it will also increase efficiencies."
Hambro thinks that the rising costs of hiring vessels could be mitigated and the number of modern, higher-performance vessels improved if wind farm owners and developers moved away from short-term vessel contracts.
"Right now the majority of developers and utilities seem to prefer short-term charters with options for project-specific roles," says Hambro. "This is no use to vessel owners as it is not bankable and they can’t get finance for new vessels. A six-month charter isn’t worth much to a bank — although it is worth more than an option."
According to Hambro, utilities must give longer-term contracts if they want to address the shortage of vessels. "If there are particular vessels they find work well, then they should lock them up. It is also more cost-effective for the utilities. I would be very happy to give both our clients better rates for longer terms, and then I could go to the bank and build my next boat," he adds.
The need to invest in high-quality vessels becomes all the more pressing in light of the huge programme of offshore wind farms planned across Europe for further-out sites that entail long boat journeys for technicians.
"Our passengers are electricians, not mariners," says Hambro. "Some may not have worked offshore before. If they are faced with a two-hour journey before eight hours of work, those first two hours are really important. The guy has to feel good to make the right decisions, rather than trying to get on to the turbine and feeling sick."
Tidal Transit has invested in three vessels so far: one working for SSE on Greater Gabbard and one for SCIRA on Sheringham Shoal, both off the East Anglian coast. The third is now being built and all aim to provide greater stability and more creature comforts for the passengers, including satellite TV and internet, games consoles and a full commercial galley.
The greater stability is provided by a hull that Hambro says eliminates the typical slam that comes with catamaran workboats in transit. The boats can operate up to 150 miles from safe haven — more than twice the current standard for most crew transfer vessels operating in the UK. They offer sleeping accommodation, and are able to transfer crew at 2-metre wave heights with ease.
The ability to stay out for several days is critical, since major turbine suppliers such as Siemens are proposing a "campaign" approach to maintenance, where large numbers of turbines are serviced at the same time.
For A2SEA chief service and logistics officer Jesper Ferløv Greth, the leaps and bounds being made in the types of vessels specifically designed to service wind farms might be one reason utilities are unwilling to sign up to long-term charters.
"It’s a pretty immature market for crew boats," says Greth. "Designs are not yet fully optimised. New vessels are able to operate in conditions that are significantly different from the vessels that are a few years old."
Greth does agree that the trend where "turbine owners are more or less buying on spot-market conditions" must improve. But he does not expect contracts that could last a project’s lifetime any time soon. "You cannot just from day one say that this is an optimum solution and that will be it for 20 years," he says. "It’s not that easy."
Greth envisages a "patchwork solution" as projects go further out, which "could be a combination of helicopters, transfer vessels and accommodation vessels".
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