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An underwater offshore sea cage
Dahle, L.A.; Jorgensen, L.; Vangen, K.; Aarsnes, J.V. (1989). An underwater offshore sea cage, in: De Pauw, N. et al. (Ed.) Aquaculture: a biotechnology in progress: volume 1. pp. 1001-1007
In: De Pauw, N. et al. (Ed.) (1989). Aquaculture: a biotechnology in progress: volume 1. European Aquaculture Society: Bredene, Belgium. ISBN 90-71625-03-6. 1-592 pp., more

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Document type: Conference paper


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  • Dahle, L.A.
  • Jorgensen, L.
  • Vangen, K.
  • Aarsnes, J.V.

    Most fish will suffer when kept in waters with temperatures near O°C. They will not eat very much, and they will be more sensitive to stress and diseases. To avoid the low-temperature problems and problems arising from environmental loads in the surface region, an underwater offshore sea cage has been developed to a pre-engineering level. The project has been divided into three phases. First the biological and physiological consequences were briefly studied in order to define problems to be solved at a later stage by technical means. Secondly, a set of design criteria was established, both to meet the requirements of the fish, and to satisfy the needs of handling and operation of the sea cage. Finally a design analysis for the sea cage was performed, resulting in a proposal for a structure which should satisfy the fish as well as the fish farmer. Tests were carried out to study the behaviour of the salmon when exposed to high pressure with and without the possibility of snapping air. Rapid decompressions were also performed to study the consequences of sudden rising of the sea cage. This is essential because of the possibility of accidents or mal- operation of the sea cage .The tests stipulated that the salmon must have the possibility to snap air and consequently the sea cage must be equipped with an air chamber. Too rapid decompressions seemed to stress the fish, setting requirements on the mooring system and operation. The mooring system had to be designed for both submerged and surface operation of the sea cage. Three mooring systems were evaluated for different water depth; one tension-leg type anchoring. one spread-mooring system, and a combination of these two systems. Environmental forces and responses were calculated for all conditions. and a simple structural strength analysis was performed for the most critical conditions.

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