Fish anchor diving behaviour: confirmation through field tests in the Swan River

This paper reports the results from field tests on a 1/15th scaled fish anchor. The tests were conducted at three locations in the Swan River, Perth, Australia. Two series of tests were performed from the Burswood and Maylands jetties with water depths between 1·1 and 1·9 m. The final series of tests were undertaken in deeper (2·6 m) waters from a barge. The riverbed at the Burswood jetty and barge test location consisted of clay, and that at the Maylands jetty comprised sandy silt. The tip embedment depths of the scaled fish anchor, with dry weight of 0·304 kN and impact velocity of 5·89–9·55 m/s, in soft clay were 1·17–2·40 times the anchor length. For similar impact velocities, the embedment depths in sandy silt were 30–60% shallower. By comparing the field test data in clay, the fish anchor achieved normalised embedment depths similar to those of the torpedo and OMNI-Max anchors under half or less impact velocity. Importantly, the field tests confirmed the diving behaviour of the fish anchor under loading with mudline inclination of 20° and 25°, with the second peak dictated by the capacity. The ultimate capacity was 5–7 times that of the anchor submerged weight in water.