U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060APPENDIX EBOOM MOORINGE-1 INTRODUCTIONTo form an effective barrier to oil movement, containment booms must be held stationary, exceptwhen towed or employed in the free-drift containment mode. To prevent movement, deployedbooms must be secured at each end and usually at several locations along their length. Booms aresecured to the seabed by clumps and ordinary drag embedment anchors and to convenientlylocated piers, dolphins or other structures by assorted fittings. The relative merits of differenttypes of anchors in different seafloors is discussed in Appendix G of the U.S. Navy Ship SalvageManual, Volume 1, S0300-A6-MAN-010. The ESSM system maintains 500-pound STATOanchors for boom mooring. STATO, LWT, Danforth, stockless, mushroom or other type anchorsof various sizes may be available from the ESSM system and other Navy, Coast Guard, other governmentagency or commercial sources. The size, type and number of anchors or other attachmentsrequired to restrain a given length of boom depends on the current and wind forces actingon the boom, the configuration desired and on the seafloor composition when anchors or clumpsare used.E-2 MOORING BOOMS WITH ANCHORSMooring leg tension at the anchor should be nearly parallel to the seafloor. Upward forces willtend to break most anchor types out of the seafloor, allowing them to drag. Mooring leg lengths offive times the water depth are usually sufficient to ensure tension parallel the seafloor when nonbuoyantmaterials, such as wire rope, chain, nylon or manila are used. When buoyant lines, suchas polypropylene or polyethylene are used, a short length of chain should be attached between theanchor and the mooring rope to ensure the mooring leg lies parallel to the seafloor at the anchor.Chain should also be used in conjunction with nonbuoyant fiber line mooring ropes on rock, shingleor coral seafloors to prevent chafing.It is important that the mooring leg provide horizontal restraint to the boom, without vertical tensionthat will tend to submerge the boom and allow oil to escape. A buoy installed in the mooringleg 10 to 12 feet from the boom, as shown in Figure E-1, can help prevent vertical tension on theboom. Mooring legs along the length of a boom should be attached by two leg bridles to avoidcausing the boom to layover in strong current or wind. The restraint of a single point attachmentforms a rotating couple with the current drag, as shown in Figure E-2, if not attached precisely atthe center of lateral resistance.E-1