The design and analysis of a four-cage grid mooring for open ocean aquaculture

Abstract

In an effort to expand open ocean aquaculture operations, a submerged, four-cage grid mooring system was designed, analyzed and deployed in 52m of water at an exposed site maintained by personnel at the University of New Hampshire. Mooring system geometry, subsurface flotation and pretension requirements were specified using analytical techniques, which included standard chain catenary equations and equilibrium analysis. Mooring gear and ground tackle were sized, in part, by modeling the designed system using a finite element program. The model included representations of potential sets of mooring gear and four Sea Station™ submersible cages (totaling 7200m3 of containment volume). Numerical simulations were performed using a wave height of 9m, wave period of 8.8s and a current of 1m/s as input. Using the results of the simulations, along with practical experience, a system design load of 178kN was obtained. The design load was used to specify mooring components and the gear was deployed during the summer of 2003. The species being raised in the system include Atlantic halibut (Hippoglossus hippoglossus), Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Future work will incorporate the development of automated, high capacity feeding systems for servicing submerged cages, harvesting systems and uniquely engineered support vessels.