Sea1 Offshore’s first of four 120-meter-long offshore energy support vessels (OESVs) being built in China has been fitted with an offshore crane and helicopter deck, with delivery expected in January.
Norwegian offshore services provider Sea1 Offshore placed the order for the first two OESVs with Cosco Shipping in November 2024, revealing at the time that negotiations were ongoing for the delivery of more vessels. The contract for the construction of two additional vessels was announced in March 2025.
The construction of the first vessel, named Sea1 Diamond, began in September 2025, with the second, named Sea1 Citrine, following in December.
Sea1 Diamond, launched at the yard in July, is currently undergoing outfitting and commissioning at the COSCO Nantong Shipyard, with the offshore crane and helicopter deck installed, as Sea1 Offshore reported on November 3.
According to the Norwegian firm, the 250 T Huisman crane is designed for subsea lifting operations down to 3,000 meters, while the helicopter deck is dimensioned for Sikorsky S-92.
The vessel is expected to be delivered in January 2027. Sea1 Offshore also reported that the OESV is still uncommitted and open for clients after delivery.
Based on the ST-245 design, the OESVs will have a cargo deck of 1,400 square meters, and each will be equipped with a 250-ton deck crane, two remotely operated vehicle (ROV) hangars, and a moonpool. They will provide accommodation for up to 120 personnel.
The vessels will be methanol-ready, with generators that can operate on 100% biofuel, and will be capable of serving both the oil & gas sector and the renewable energy market. Kongsberg Maritime will deliver comprehensive equipment packages.
