Analysis of Holding Force Limit and Provision against Dragging Anchor

Abstract

Analyses of the equilibrium conditions of an anchor and a cable of a ship at anchoring are presented. Three conditions are considered: (1) a part of the cable lies on the seafloor; (2) no part of the cable lies on the seafloor and rises from the seafloor with a zero gradient of the slope; and (3) a nonzero gradient of the slope. In the third condition, a coefficient is introduced to represent the effects of the vertical component of the cable tension on the holding force of an anchor while considering the decrease in the apparent anchor weight. Formulas of the holding force limit in each condition are presented by analyzing the parameters representing the three cable conditions. Numerical examples demonstrate the effects of extended cable length, water depth, soil properties of the seafloor, and the coefficient of upward cable tension on the holding force limit and parameters characterizing the three cable conditions. Measuring the safety of anchoring in terms of the extended cable length and the current cable conditions associated with the risk allowance for dragging anchors is discussed.