A Case Study of an Offshore SeaStation Sea Farm

Ocean Spar engineers have been testing the SeaStation (R) cage since 1994. Recently, larger offshore sea farming ventures have been employing the SeaStation submersible cages for growing fish at ocean sites. Of particular interest is the case study of a larger system of SeaStation cages installed and operated off Keahole Point, Kona, Hawaii. The offshore site is subject to ocean-gyre currents of 1 m/s and 50-year storm waves with significant wave heights of 9 m. The venture had six cages installed and arranged in a 2 x 3 moored array kept at a minimum submergence of 10 m. The individual cages have unique buoyancy control for raising the cage out of the water, so one half of the volume is exposed to air for cleaning and drying. This tactic also increases the efficiency of crop harvest with minimum effort by the farm operators and minimum stress to the fish. As SeaStation cages were added to fill the six cage array, the last two cages were designed with an additional feature allowing the cage to flip while submerged. The flip operation exchanged the top and the bottom of the cage, so the entire cage could be cleaned by exposure to the sun and wind. With the increasing number of cages, the grid system dynamics changed, and higher than expected currents foiled some of the operational strategies that were developed using the individual cages. This article documents the features, events, and innovative remedies that made this sea farming effort unique and worthy of note.