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

S0300-A6-MAN-060The total holding power of the anchors or anchoring points securing a boom must equal or exceedthe wind and current generated drag forces acting on the boom. Current drag force can be estimatedby:Fc = 5.33A sV c2=26A s V c2English units( )Metric units( )where:F c = current drag force, lb or kgA s = area of the skirt and other submerged portions of the boom, ft 2 or m 2V2c = current velocity, ktWind force can be estimated from:F C=V5.33A ⎛ Wf------⎞⎝40⎠English units( )=V26A ⎛ Wf------ ⎞⎝40⎠Metric units( )where:F w = wind drag force, lb or kgA s = area of the boom freeboard, ft 2 or m 2V w2= wind velocity, ktIt is prudent to assume that wind and current will act in the same direction at least part of the timeand base anchor selection on the combined drag force resulting from wind and current. The dragforce formulae are based on the assumption that the boom is a rigid barrier perpendicular to thewind or current direction. In most situations, two factors cause drag forces on booms to be somewhatless than calculated:• Booms are flexible and assume curved shapes when acted on by wind and current.• Booms are usually oriented at an angle to current flow.Use of the formulae without modification provides a substantial safety factor in the selection ofanchors and mooring hardware.The total holding power of the anchors or anchoring points selected must equal or exceed thecombined wind and current drag. The number of anchoring points actually used will depend onE-3