VESSEL REVIEW | Donghai No 1 – Harsh environment fish harvesting platform for Chinese offshore waters

Chinese shipbuilder Ningbo Huanhai Heavy Industry recently handed over a new semi-submersible offshore fish farming platform to Zhejiang Shenlan Marine Technology. Donghai No 1 (东海1号) was built to a design by Zhuhai Gesheng Technology and will focus on harvesting yellow croaker off Zhejiang province.

Durable enough to withstand extreme offshore conditions year-round

The platform has a length of 82 metres (270 feet), a beam of 32 metres (104 feet), a height of 22 metres (72 feet), an operating draught of 13 metres (43 feet), and a harvesting capacity of 36,000 cubic metres (1.3 million cubic feet). PV panels and an energy storage system will provide the endurance necessary for the platform to operate for extended periods offshore with only minimal emissions.

The platform was designed to be capable of withstanding extreme weather and sea conditions that regularly occur in the waters off Zhejiang. Numerous ballast water tanks can be adjusted accordingly to keep the platform afloat and as level as possible, whether during harvesting operations or when it is being towed to and from various offshore areas.

Eight anchor chains each measuring 400 metres (1,300 feet) long are also fitted. The first 15 metres (49 feet) of each anchor chain is reinforced to ensure the platform is able to maintain its position even in the unlikely event of a sudden simultaneous failure of six chains.

Harvesting activities are aided by a fish monitoring system, an aquaculture environment monitoring system, a sea area care system, an automatic feeding system, and an intelligent aquaculture centralised control management system. Onboard facilities meanwhile include personnel cabins, a laboratory, a biological testing centre, offices, a conference room, a sewage treatment plant, and a seawater desalination plant.

Ensuing premium wild-quality catch in a controlled environment

Because the platform can be operated remotely from a land-based control and monitoring station, it is possible to have a limited crew complement of only four personnel on board at any given time. Underwater robots will also be available for net cleaning.

To prevent the harvesting net from being damaged due to friction, corrosion, and other external factors, the net is made of a PE double-layer mesh material with a significantly high molecular weight. This ensures that the net is significantly more durable than steel wire rope, thus minimising the risk of the net getting damaged and any harvested fish escaping.

Donghai No 1 is classed by China Classification Society. The platform will carry out aquaculture operations in the waters off Xiangshan in Ningbo City. Its projected annual output will be 900,000 fish of various species as well as yellow croaker.

The platform will be deployed in waters that are over 20 metres (66 feet) deep but not more than 50 kilometres (31 miles) from the coast. The onboard facilities will produce simulated conditions to ensure that any harvested yellow croaker will have significantly improved quality approaching that of wild yellow croaker, thus resulting in higher margins compared to fish that has been farmed closer to shore.