Effect of Fin Shape on the Penetration and Pullout of Torpedo Anchors in Marine Clays-Paper

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The study investigates how fin width and length affect the penetration, soil response, and pullout capacity of torpedo anchors in soft marine clay. Six equal-mass, laboratory-scale anchors were dropped into transparent synthetic clay at approximately 5 m/s. High-speed imaging and digital image correlation (DIC) were used to track soil movements during installation and extraction.<br /><br />Fins reduced penetration depth: the finless anchor reached 3.0 times its length, compared with 2.1–2.8 times its length for finned anchors. Longer and wider fins generally produced shallower penetration and larger zones of soil displacement. DIC showed that soil near the anchor nose and fins was most affected; movements around the nose were primarily downward, while soil behind it could move upward.<br /><br />Pullout capacity depended on embedment and interaction with the surrounding soil. The finless anchor had a peak capacity of 7.9 N, or about 2.3 times its dry weight. Increasing fin length raised capacity by 33% for fins 0.325 times the anchor length and 54% for fins 0.65 times the length. Among the tested widths, the 0.25-diameter fins produced the highest capacity, 18.7 N—more than twice the finless anchor’s capacity. Wider fins did not improve capacity, in part because they reduced embedment.<br /><br />Overall, fins trade some penetration depth for greater holding capacity. The best-performing tested configuration combined fins 0.25 times the shaft diameter wide and 0.7 times the anchor length long. The findings demonstrate the value of fin geometry in anchor design, though they are based on laboratory-scale tests.

Keywords

torpedo anchors

fin geometry

soft marine clay

penetration depth

pullout capacity

soil displacement

digital image correlation

laboratory-scale tests

anchor design

embedment