Effect of fin width on torpedo anchor penetration and pullout using model tests with transparent soils

Torpedo anchors are increasingly popular for tethering of offshore structures. Using fins improves their directional stability during penetration, however, fins’ shape affects both penetration depth and pullout capacity. Experiments were carried out to investigate the effect of the width of fins on the behavior of torpedo anchors during penetration and extraction. Four torpedo models having the same weight were made, one without fins and three with four fins. A transparent soil was used to simulate soft marine clay, thus permitting visualizing torpedo soil interaction. Particle trajectories showed that soil movements in the vicinity of the torpedo were downward as the torpedo approached a given depth, and that movements reversed to upwards once the torpedo passed that depth. Measurements of soil displacements suggest that the pullout capacity of finless torpedoes depends on the friction with the shank, and for torpedoes with fins it depends mainly on the reverse end bearing.