The winds of opportunity: optimising propulsion for next-generation windfarm vessels

The winds of opportunity: optimising propulsion for next-generation windfarm vessels

5 min read

16 Mar 2021

Text

Amanda Thurman

Ian Hamilton

Photo

Wärtsilä Corporation

5 min read

16 Mar 2021

Text:

Amanda Thurman Ian Hamilton

Photo:

Wärtsilä Corporation

With the predicted increase in the number of windfarms globally there will be a need for Wind Turbine Installation Vessels (WTIVs) that can handle larger turbines and are capable of operating further from shore in some of the world’s most demanding sea conditions. These WTIVs will need a propulsion system that is configured specifically for the vessel and its operating profile to deliver high-performance dynamic positioning (DP) and main propulsion. In this webinar, prominent industry experts explain how this can be achieved.

Market landscape and outlook

Jon Nation, GM Marketing Propulsion, Wärtsilä, hosted the event and opened by introducing Vincent Bast, Product Sales Manager, Thrusters & PCS, Wärtsilä, who shared his insights into the current market landscape and what we can expect to see in the future.

“The offshore wind market is moving faster than predicted, with a clear move towards decarbonisation and green energy, and a push for green investment.”

- Vincent Bast, Product Sales Manager, Thrusters & PCS, Wärtsilä

“The offshore wind market is moving faster than predicted, with a clear move towards decarbonisation and green energy, and a push for green investment”, explained Bast, sharing the impressive statistic that total installed wind power globally is likely to grow from 29 GW in 2020 to 235 GW in 2030 (source: Global Wind Energy Council) and possibly even higher. “The sector has risen above oil and gas for the first time, with capital expenditure at USD 51bn versus oil and gas at USD 41bn“, he added.

Multiple vessel types will be needed to support these offshore windfarm operations, with varying operating profiles and key capabilities. There is currently a particular need for WTIVs to cope with the market growth. ”Larger and heavier turbines mean larger and more complex installation vessels are needed, and as the turbines are further from shore the operating conditions are extremely challenging. Accurate DP performance is essential to keep vessels safely in position”.

Insights from an owner/operators

As an owner and operator, Jan Gabriel, Head of Construction and Conversion at DEME, shared some valuable insights into thruster applications in offshore windfarm construction vessels. ”Offshore operations require thrusters for sailing and dynamic positioning, making azimuth thrusters a great solution,” Gabriel explained. ”Because water depth in marshalling ports is limited, thrusters that are under the bottom of the ship may need to be retractable, and as the sailing speed of these vessels is typically less than 14 knots, ducted propellers are advised.”

Gabriel also talked about the advantages of having an 8° tilted propeller shaft and nozzle to achieve high thrust with limited power, explaining how the tilt reduces the interference between the thruster wake and the flat-bottomed hull, increasing the bollard pull by up to 23% and reducing fuel consumption.

“There is a need to split main propulsion power over two, three, or even four thrusters because of draft and redundancy constraints.”

- Jan Gabriel, Head of Construction and Conversion, DEME

Next Gabriel discussed the arrangement of stern thrusters on a wind turbine vessel. ”There is a need to split main propulsion power over two, three, or even four thrusters because of draft and redundancy constraints,” he pointed out. ”This requires careful positioning of thrusters, avoiding excessive forbidden zones when in DP and avoiding ventilation when the vessel is rolling and pitching.”

Finally Gabriel shared how to extend dry-docking intervals. Classification societies mandate thruster inspections every five years, but this can be extended to seven-and-a half years using a few key measures such as painting and cathodic protection, the OFS3 propeller shaft seal and the Wärtsilä Propulsion Condition Monitoring Service (PCMS).

Early involvement is the key to success

Next, Norbert Bulten, Product Performance Manager at Wärtsilä, shared how early involvement with customers in the design phase – combined with Wärtsilä’s extensive in-house skills – is key to achieving optimum results. He began by explaining the basics of station keeping and how it is crucial for WTIV operation, pointing out that WTIVs will stay in position providing the environmental forces are counteracted by the force of the thrusters. Bulten then addressed the other necessary consideration for WTIV thrusters: transit operation to reach the windfarm location. “We need to find the balance between azimuth thrusters for transit that can also perform well for dynamic positioning“, he said. “Wärtsilä offers a mix of propulsion products to address these operational requirements: main stern thrusters, retractable bow thrusters and tunnel thrusters.“

“Winds and waves come from every direction, so to keep position during operation, 360° DP capability is required.”

- Norbert Bulten, Product Performance Manager, Propellers & Gearboxes, Wärtsilä

Propulsion performance is down to individual thruster performance, thruster interaction losses and multiple thruster cooperation, Bulten explained. “We have developed a modern DP capability calculation method that considers the performance of an azimuth thruster over its 360° circumference to reduce interaction losses. Winds and waves come from every direction, so to keep position during operation, 360° DP capability is required. We use Thrust Allocation Logic (TAL) to determine thruster loading and thruster azimuth angle, balancing environmental forces and thrust. Using Wärtsilä’s OPTI-DP tool ensures everything is fully considered, enabling a fully optimised WTIV solution. 

Wärtsilä thruster solutions

Arnoud Dinslage, Product Manager Thrusters, Wärtsilä, was up next discussing Wärtsilä’s thruster solutions. First he ran through the different thruster types and how they can help with DP, station keeping and manoeuvring. Looking more closely at Wärtsilä’s retractable thruster portfolio, Dinslage talked about the high thrust performance, thanks to the WTN-type nozzle, the optimised design of the propeller gearbox and the reduced interaction losses due to the 8° tilted shaft.

WTIVs come in two distinct types, and jack-up vessels have different requirements and operating profiles to floaters: floaters are continuously in DP operation, whereas jack-up vessels only require DP when they are lifting or lowering their legs. Despite these differences, safe and reliable DP is essential for both vessel types, and fully understanding thruster configuration requires more than just knowing the number of thrusters and the required power. With support from our experts, thruster selection and positioning can be optimised in the beginning of the vessel design, potentially reducing thruster dimensions, weight and power requirements. This doesn’t just impact the thruster scope: the positive effect could be transferred up to the vessel power balance due to the lower propulsion power requirements, or to the vessel deck load due to the lower weight of the propulsion equipment. It could also increase the vessel’s DP capabilities.

“This is a full lifecycle approach. Reliability, safety and maintenance considerations are designed into Wärtsilä thrusters.”

- Arnoud Dinslage, Product Manager, Thrusters, Wärtsilä

Dinslage concluded by pointing out that this is a full-lifecycle approach. Reliability, safety and maintenance considerations are designed into Wärtsilä thrusters, complemented by advanced integration capabilities and optimised configuration support in the design phase of the vessel. After delivery the support continues. Utilising Wärtsilä’s PCMS, thruster maintenance can move from static calendar-based to dynamic condition-based maintenance, helping improve vessel availability, reliability and profitability while reducing risks and maintenance costs.

An Americas perspective

Mark Keneford, General Manager, New Build and Projects, Americas, Wärtsilä, shared his perspectives from the North American market: In North America we have a team of people with an awful lot of experience in complex projects, including a significant focus on the windfarm industry. To develop our systems and solutions, we start working with ship owners, operators, designers and even shipyards very early in the process, analysing vessel operating profiles and requirements. This helps us to put together a data-driven, tailored trade-off study to configure the best solution for the specific vessel. After this we make a deep-dive propulsion study, looking at fuel consumption, emissions, capability for alternative fuels in the future, hybridisation, electrification and other factors. We end up with an integrated solution that best meets the requirements of the vessel. 

Keneford then echoed Dinslage by saying that support continues throughout the vessel lifecycle, sharing details of how that lifecycle support is carried out in the Americas and the many aspects it covers. He concluded by inviting viewers to get in touch with his team at any time to discuss the support they can offer.