Sea1 starts building second of four offshore energy support vessels

December 16, 2025, by Nadja Skopljak

Norwegian offshore services provider Sea1 Offshore has cut the first steel for the second of four offshore energy support vessels (OESVs) it has on order with a shipyard in China.

Sea1 Offshore placed the order for the first two OESVs with Chinese shipyard Cosco Shipping in November 2024, with the contract for the construction of two additional vessels following this March.

The Norwegian company reported today, December 16, that the steel cutting for Sea1 Citrine had been completed, exactly three months after a steel-cutting ceremony on September 16 marked the start of construction of the first vessel, named Sea1 Diamond.

Furthermore, according to Sea1 Offshore’s social media, the keel laying ceremony for Sea1 Diamond took place some two weeks ago, during which two accommodation blocks (2D2P and 2D2S), each weighing over 50 tons, were formally joined.

The first bottom block erection on the skidway was planned for December 15, marking the transition into the next phase of construction, where progress will accelerate.

Based on the ST-245 design, the OESVs will be 120 meters long, with a cargo deck of 1,400 square meters, and each will be equipped with a 250-ton deck crane and a remotely operated vehicle (ROV) hangar and a moonpool.

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. They will provide accommodation for up to 120 personnel.

Kongsberg Maritime will deliver comprehensive equipment packages for the OESVs.