Installation of Fleet Moorings at Diego Garcia, B.I.O.T.

Abstract The installation of fleet moorings when using propellant embedment anchors is presented. Specifically, the installation of eleven fleet moorings-at the Diego Garcia coral atoll in the Indian Ocean is discussed, since this represents the largest use of propellant embedment anchors to date. The moorings themselves are original in their design and are described in terms of component size. seventeen mooring buoys and 88 legs of chain wereinstalled to produce these eleven moorings. Installation equipment and installation procedures are presented, explaining the anchor-first, buoy-last construction method. Background associated with prediction of anchor performance is used to assist in understanding performance and data produced by the actual use of propellant embedment anchors for this project. The 88 successful propellant embedment anchors installed provided designed holding capacities of 100,000 Ibs each (28 anchors) and 150,0001bs each (60 anchors) at a cost of only $10K - $15K for expendable materials per anchor using a total package for each anchor shot that had a deck load of less-than 15,000 Ibs. Each anchor was load tested vertically to its full design load. The data associated with the load tests and the eight anchors which pulled out during load testing is presented along with required solutions to pullout problems. The Fleet Mooring Project demonstrated the mobility and positive utility of propellant embedment anchors for a coralline seafloor similar to that found at Diego Garcia. Supporting data is presented, including results of load tests of some other 100,000 Ib propellant embedment anchors which held over 200,000 Ibs of vertical force after five years in the seafloor at Uiego Garcia. Introduction On 31 March, 1980, the Chesapeake Division, Naval Facilities Engineering Command, was tasked toprovide engineering and construction support for the design, procurement and installation of eleven fleet moorings in the lagoon at Diego Garcia, British Indian Ocean Territories. Diego Garcia is a coral atoll found in the Chagos Archipelago chain of islands in the middle of the Indian Ocean approximately 70 below the equator. These moorings were urgently required by the Commander-in-Chief, Pacific Fleet, and installation was completed 17 March, 1981. Due to the extremely rapid response required, maximum use was made of existing Navy inventories of chain and other mooring materials stockpiled on both coasts of the United States as well as at various overseas locations. Mooring designs and installation procedures were tailored to make use of these on-hand materials as well as anchoring methods previously shown to be satisfactory for the coralline seafloor found at Diego Garcia. The propellant embedment anchor (PEA) developed by the Naval Civil Engineering Laboratory was selected for use with these moorings due to its proven success on three previous buoy installation projects in the Diego Garcia lagoon. Traditional drag weight anchors were not determined to be the best choice for long term anchoring of moorings in the lagoon's coralline seafloor. The eleven moorings as designed by the Chesapeake Division's Ocean Engineering and Construction Project Office (FPO-1) required the use of seventeen mooring buoys and 88 legs of chain.