VESSEL REVIEW | OOS Madelief – Mussel farm demonstrator to be deployed in Dutch North Sea

Dutch offshore engineering company OOS International recently took delivery of a new semi-submersible facility designed for the harvesting of mussels in offshore waters.

Built by NAVTEK Naval Technologies of Turkey, OOS Madelief (“Daisy”) will be anchored in the North Sea, particularly in the waters near the Borssele III wind farm off the western Dutch province of Zeeland. OOS said that the design work that went into the semi-submersible mussel farm (SMF) had considered variables such as water depth, tidal currents, and environmental impact.

OOS, via its OOS SMF division, will operate the test SMF in response to declining mussel production and to further promote mussel farming as a sustainable aquaculture practice due to its low CO2 emissions. The initiative also seeks to install multiple similar farms off the coast of Zeeland.

Facilitating an alternative to mussel farming in sheltered areas

In collaboration with the Dutch shellfish sector and mussel farmers, OOS SMF developed the SMF concept, which is suitable for growing mussels based on hanging culture at open seas. The design philosophy of the SMF is based on the floater/column design of the semi-submersible offshore construction and accommodation vessels OOS Serooskerke and OOS Walcheren, enabling the SMF to be operated safely even in harsh environments.

The SMF has a length of 72 metres (240 feet), a beam of 36 metres (120 feet), and 72 mussel lines. As the farm can be submerged to varying depths, it is possible for mussels to be farmed in deeper waters than in those of the Eastern Scheldt estuary and the Wadden Sea. This ensures that the mussels are farmed under more stable conditions, as they are not exposed to bad weather or high waves.

The mussels farmed in this manner will also be of better quality, as OOS said the sheltered waters of the Eastern Scheldt and the Wadden Sea are somewhat lacking in the necessary nutrients.

Precursor to a larger, more capable mussel farm

Development of the SMF also included testing of a scale model under various current, wave, and wind conditions in a large basin. The goal was to investigate the behaviour of the system, even in wave heights of up to 13 metres (43 feet).

Five backbones with mussel lines will be attached to OOS Madelief for the cultivation of mussels offshore (so-called suspended cultivation). Over a period of approximately two to 2.5 years, both the growth of mussels and the behaviour of the system will be monitored.

After the testing period, the data obtained from the scale model test and the real-time test will lead to the final design of a slightly larger SMF named OOS Cees Leenaars, the construction of which is scheduled to commence as early as 2026.