Ulstein Design & Solutions has signed a contract with Tersan Shipyard for two methanol-fuelled Ulstein SX216 Construction Service Operating Vessel (CSOV) designs. The vessels will be constructed for the Netherlands-based Acta Marine and will be number 3 and 4 with the novel Twin X-Stern solution in the Acta fleet.

Shipowner Acta Marine has already signed a long-term contract for a twelve-year basis with RWE for the two vessels to support North Sea wind farms (the TK and Sofia projects). The vessels are expected to begin operation from the Port of Grimsby in early 2025 and 2026.

Also read: Construction of Acta Marine’s new methanol-powered CSOV kicks off

Twin X-Stern

The Twin X-Stern vessels have two sterns and two main propeller units at each end. Placing either end towards the weather results in excellent operability without limitation on vessel speed. The solution leads to improved fuel efficiency whilst reducing motions, which is important for technicians who need quality rest to perform safe operations.

The Twin X-Stern offers larger flexibility regarding the choice of propeller type, a bi-symmetric hull shape and propulsion setup with fewer propulsion units is possible.

Also read: VIDEO: Ulstein launches U-Stern for monopile installation on DP

Green methanol

The hybrid power solution in these vessels, with green methanol intended as the main energy source, has dual-fuel engines supported by a battery package. Combining the fuel-efficient Twin X-Stern and the dual-fuel methanol/diesel power generators will help reduce the emissions in offshore wind farm operations.

Acta Marine wants to achieve a seventy per cent reduction in net CO2 emissions. ‘Therefore, we worked with Acta Marine to evaluate the best possible fuel alternatives,’ says Rolf-Petter Almli from Ulstein Design & Solutions. ‘Methanol’s energy density and storage are favourable, it is an accessible energy source, and dual-fuel engines that can handle both methanol and diesel are available in the market. As soon as methanol had been chosen as an alternative energy source, Ulstein Design & Solutions started to adapt the design, implementing the methanol bunkering, tank and system layouts on a conceptual level.’

Also read: Acta Marine goes for methanol for new construction service operating vessels

Ulstein SX216 CSOV design

The offshore wind service vessel designs from Ulstein have been developed to effectively support the commissioning, operation and maintenance of offshore wind farms.

The SX216 vessel has a length of 89.9 metres, a beam of 19.2 metres and accommodates up to 135 POB. It has a walk-to-work (W2W) motion-compensated gangway for safe personnel transfer to the turbines, a 3D-motion-compensated crane for cargo transfer, and it can carry a daughter craft for in-farm transfers.