...Deploy a Ballast Weight

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The ballast weight is a circular concrete block weighing approximately 3,200 kg for the OAC cage (Picture 1) and having a toggle through its middle to attach it to the bottom of the spar buoy (Picture 2). In its proper position (Figure 3), the ballast weight provides necessary weight to maintain the cage in the water column and provide stability during high seas and wind. Initial deployment of the ballast weight is performed while up righting the spar and therefore not having any netting to impede the attachment procedure (See Deploy an Offshore Aquaculture Cage). However, periodically a farm operator might have the need to exchange an existing ballast weight or deploy a new ballast weight. This might be due to the existing one breaking off during extreme storm conditions or structural changes to the cage, such as adding a new feeder system. This would have to be completed without disrupting the fish or other operations of the farm and without requiring the complete break-down of the cage. Recently, the OAC faced this situation when its ballast weight broke off the spar during severe storm conditions.

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When the OAC crew arrived on site to install a new ballast weight they found the cage sitting several feet higher in the water and noticeably listing to one side toward the single-point mooring system (Figure 4). The crew was forced to develop an innovative approach to replace the ballast weight while retaining simplicity and keeping diver safety in mind. To do this, they first tied the University of Southern Mississippi research vessel IX 508 to the cage rim and divers attached a block to the spar edge closest to the vessel (Figure 5). Next, the new ballast weight was lowered to the sea bed using the vessel's winch and U-frame (Figure 6) and divers re-entered the water to move the lowering rope to the block and secure it (Figure 7).

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Once the lowering rope was secured within the block, the vessel slowly lifted the new ballast weight using its winch (Figure 8) until the ballast weight was close to the bottom of the spar (Figure 9). In this position, divers could easily maneuver the ballast weight line in position at the bottom of the spar and insert the shackle pin for attachment (Figure 10). Following attachment, the vessel slowly let the lowering rope back out until the cage began absorbing the weight of the cage (Figure 11) and eventually stabilized in its normal position in the water column (Figure 12). Divers then entered the water for the final time to release the vessel rope and retrieve the block from the bottom of the spar. Upon completion, the cage is back to its proper position in the water column and properly upright (Figure 13).