Sea1 Diamond has received a 250-tonne crane and a helideck at COSCO Nantong Shipyard in China, according to Offshore Energy. The vessel is undergoing outfitting and commissioning, with delivery expected in January 2027.

The report cites a 3 November update from Sea1 Offshore, which said the vessel remained uncommitted and available to clients after delivery.

The Huisman crane is designed to carry out subsea lifts at water depths reaching 3,000 metres. The helicopter landing deck is sized for a Sikorsky S-92.

Sea1 Diamond is the first of four offshore energy support vessels being built for the Norwegian owner. Construction began in September 2025, and the vessel was launched in July 2026. Work on the second ship, Sea1 Citrine, started in December 2025.

Based on the ST-245 design, the 120-metre vessels will each offer 1,400 square metres of cargo deck space and accommodation for 120 people. A moonpool and two ROV hangars form part of their subsea facilities. The ships are intended to undertake work in both offshore oil and gas and renewable energy.

The series is specified as methanol-ready, and its generators will be capable of using 100% biofuel. Kongsberg Maritime will provide equipment packages for the four vessels.

Sea1 Offshore ordered the initial pair from COSCO Shipping in November 2024. An additional two vessels were ordered in March 2025.