Optimising Anchor Design to Achieve Greater Embedment Depth and Holding Capacity-Paper

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The paper reviews methods for optimizing offshore plate anchors to achieve greater embedment depth and holding capacity. It examines three anchor types—suction embedded plate anchors (SEPLAs), OMNI-Max anchors and dynamically embedded plate anchors (DEPLAs)—using plasticity force-resultant models and an analytical model of the anchor and embedded mooring chain.<br /><br />Anchor diving depends on the relationship between anchor inclination and the chain’s loading angle at the padeye. Because a flexible chain cannot apply a moment, the anchor tends to rotate until the chain load passes through its rotation centre. Padeye position relative to this centre therefore strongly affects the anchor’s movement. Lower padeye load angles generally encourage diving, while the OMNI-Max and DEPLA have a narrower diving range than a simple plate anchor because their high sliding resistance makes them harder to move through the soil.<br /><br />Calculations identify optimal padeye offset ratios (padeye offset divided by eccentricity) of approximately 0.33–0.36 for SEPLA, 0.39–0.42 for OMNI-Max and 0.70–0.80 for DEPLA. Increasing the chain angle at the seabed makes the load more vertical and reduces ultimate embedment depth and capacity. For the assumed normally consolidated clay profile, calculated mudline capacities at optimal padeye positions decrease as the mudline chain angle rises from 0° to 30°: from 78.3 to 46.2 MN for SEPLA, 18.0 to 9.3 MN for OMNI-Max, and 3.9 to 1.2 MN for DEPLA.<br /><br />The results show that careful padeye placement can promote deeper embedment and improve anchor performance. However, capacities depend on soil conditions and chain characteristics; thicker chains can increase resistance to chain movement and limit embedment. Experimental or field validation of the analytical predictions is recommended.

Keywords

offshore plate anchors

embedment depth

holding capacity

suction embedded plate anchors

OMNI-Max anchors

dynamically embedded plate anchors

plasticity force-resultant models

padeye offset

mooring chain angle

anchor diving