...Deploy a Single Point Mooring (SPM) System

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Single Point Mooring

Mooring aquaculture cages in sheltered-water environments has almost entirely used multiple mooring anchors creating an array that holds the cages in a fixed position. Open-ocean aquaculture ventures experience decreased user conflicts, improved water quality, and a lack of established practices-all of which gives researchers considerable opportunities for innovation compared standard sheltered-water operations. Although intricate mooring designs are not necessary in the open ocean, challenges exist owing to the high-energy nature of open-ocean exposure and the need for cost-competitive approaches that offer commercially-viable alternatives to sheltered-water mooring systems. The Gulf of Mexico Offshore Aquaculture Consortium has developed a single-point mooring (SPM) system to moor its offshore aquaculture cage 40 km off the coast of Mississippi in 25 m of water (Illustration 1). The demonstrated and anticipated advantages of using an SPM include decreased cost, predictable mooring loads and cage movement, and reduced environmental impact.

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Single Point Mooring Block	Block Deployment	Buoy Deployment

The initial SPM configuration used a 12,000 kg concrete mooring block (Figure 2 and Photo 3) and chain tension members supported by a surface float (Photo 4). The cage was connected to the SPM using bridles running horizontally from the submerged cage rim and intersecting the SPM chain in a pear link connection. The overall length of chain provided a watch circle radius of approximately 70 m.

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Cage Recovery

The cage broke free from this SPM configuration during severe winter frontal movement just 50 days following its deployment and was missing for a period of 40 days, after which it was relocated and safely towed to shore for examination and to await redeployment (Photo 5). Inspection of the intact SPM and the recovered cage determined that the failure was due to the two cage bridle shackles colliding with each other and other components within the pear link, freeing the shackle pin keeper, and allowing the pin to drop out.

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Spectra Buoy Line	Primary Rigging Plate	Primary Bridles

Based on this experience, a specially designed triangle plate has been incorporated into the SPM system, replacing the pear link, which will properly capture the primary tension members leading from the anchor, float, and cage (Figures 6, 7 and 8).

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Redundant Rigging Plate	Redundant SPM Arial

The current mooring system also has a "redundant-SPM" configuration consisting of a redundant set of longer bridles positioned 2 meters below the primary bridles to serve as a back-up should the primary bridles fail during heavy storms (Figures 9 and 10). Both sets of bridles utilize individual triangle plates.