Norwegian subsea construction newbuilds take shape

A steel cutting ceremony was held on 15 September for Sea1 Diamond, the first of four methanol-ready battery-hybrid offshore energy construction vessels (OECVs) ordered by Norway’s Sea1 Offshore at COSCO Nantong in China.

Built to DNV class, these large 120-m subsea construction vessels are based on Skipteknisk’s ST-245 design, with 1,400 m2 of clear deck space and accommodation for 120.

The vessels will be methanol-ready, and the generators capable of operating on 100% biofuel. Each will be equipped with a 250-tonne subsea crane and two integrated WROV hangars with side-launch capability. The high-spec designs are also prepared for the future installation of an offshore gangway, making them suitable for offshore wind operations.

“Research will assess [the] emissions reductions of the many individual measures”

When delivered in 2027, the Oslo-listed owner anticipates using the vessels for both offshore oil and gas and renewables, with an eye on commissioning and recycling work, support for the energy industry and subsea operations.

Among the key vendors for the newbuild programme is Norway’s Kongsberg Maritime, which has been contracted to supply K-Pos dynamic positioning systems, integrated control and navigation systems, battery hybrid DC electrical systems, as well as all main propulsion and thruster units.

Additionally, Kongsberg Maritime and Sea1 Offshore will collaborate on a study to accurately assess emissions reductions achieved with the Norwegian maritime technology provider’s equipment.

Kongsberg Maritime VP, sales offshore, Ottar Ristesund, said the research will “assess emission reductions of the many individual measures incorporated into the design and our deliverables. This insight may increase the awareness of the efficiency potential of operations as well as provide insight into future vessel designs.”

Kongsberg noted that the vessel’s battery-hybrid DC power and propulsion system will allow it to operate on a single engine for most of its operational time. Additionally, zero emissions operation in port and during loading operations will be possible using the vessel’s high-capacity shore connection, battery system, and energy control system.

The energy management system incorporates energy flows from the 250-t hybrid electric crane, gangways and ROV, ensuring high energy efficiency. It also captures regenerative power and balances the use of batteries with variable speed engines, whether running on diesel, biodiesel, or methanol.

Rem Offshore newbuilds

Skipsteknisk is also behind the design of Norwegian owner Rem Offshore’s two inspection, maintenance and repair (IMR) energy service construction newbuilds. These vessels, too, will use a combination of methanol and battery-hybrid propulsion to cut emissions. The first of these 117-m ST-245-IMR design ESCVs, Rem Pioneer, is ready for outfitting at Norway’s Myklebust Verft, following its launch by Vietnam’s Song Cam Shipbuilding. It will be delivered in August 2026. The Vietnamese shipyard has laid the keel for the second vessel, Rem Ocean. Rem Offshore expects Rem Ocean begin an eight-year charter agreement with DeepOcean serving Equinor when it is delivered in 2027.