UST030

43 pressure or drag,” explains Eugen Olenew, team leader for the Poggy project. “Each fin consists of two plastic sheets. Inside each fin is an actuator, with a gearbox and a rope drive connecting throughout the internal structure to produce a tangential contour along the tail’s length,” he says. “When the Poggy is moving forwards, the tails are straight and symmetrical, but we can adjust the geometry of each one to alter the drag profile, which allows the craft to pitch and roll very accurately.” The technology is derived from previous r&d in EvoLogics’ Manta Ray UUV project. Shaped (and moving) like the creature, the Manta Ray used wings and fins for propulsion and steering respectively. The object of the project was to improve the hydrodynamics and energy efficiency of typical UUV systems, given that fish tend to move more efficiently – especially at lower speeds – than UUVs. “We omitted the wings from Poggy’s design to simplify the overall propulsion concept, but Poggy has two tail fins to the Manta Ray’s one, which helps it turn very sharply and precisely,” Olenew says. “It also uses less energy than other approaches, because it disturbs the water far less. “Also, the wings and fins are immune to the problem of clogging [from seaweed and other debris] that subsea thrusters can suffer from when close to the seabed. That is important for groundwater surveys, as we need a steady, slow glide along the seafloor. “We are preparing for our next sea trial in the next few months, in which Poggy will navigate to known points of SGDs to measure a number of geological and hydrological metrics. From correlations in the survey data, we’ll be able to identify new, perhaps easier ways of detecting and geolocating SGDs.” In another scientific endeavour, the Woods Hole Oceanographic Institution (WHOI) is continuing its Remus SharkCam project, with its customised Remus 100 AUV from Hydroid having been used to study the behaviour of basking sharks in UK waters. It is hoped that analysis of the wide-angle HD SharkCam’s video footage – and of UUVs | Insight We omitted the wings to simplify the propulsion concept, but we have two tail fins to help with turning sharply and precisely Unmanned Systems Technology | February/March 2020 The EvoLogics Poggy uses a pair of biomimetic fins to ‘swim’ and hold attitude with great precision through the water (Courtesy of EvoLogics) General Dynamics Mission Systems’ Bluefin-12 (pictured) and Bluefin-9 UUVs have had most of their subsystems upgraded (Courtesy of GDMS)