Uncrewed Systems Technology 046

53 Seaber YUCO | Digest That is how we’ve been able to use different things such as CTD sensors, multi-parameter sondes, sidescan sonars, and underwater cameras and LEDs.” Hull production Different IP ratings are given for the various components in the YUCO, for splash-proofing, water ingress, pressure resistance and others. To validate internally that the hull is capable of the depths Seaber has set as a hard target, the company has its own pressure test bench, which it uses to check that the YUCO can survive the pressure at up to 450 m depths over its lifetime (to guarantee a margin of safety for continuous operations at 300 m). The YUCO hull’s main elements are carbon composite and high-density plastics. The design engineers have avoided exposing any electronic couplings between the different materials, to prevent rusting or biofouling from algae or barnacles, but aside from that, few anti-biofouling measures have been taken, given the low risk of it when using carbon or plastics. “We work with local suppliers for most of the hull,” Simon comments. “We designed everything in-house and then advised on the appropriate thicknesses of materials, with most of our design work being carried out using SolidWorks.” No YUCO is ever in the water for more than a day (with one or two breaks as well during each day, given the endurance limits), so there is insufficient exposure to the water for biofouling to accumulate. To prevent degradation of its appearance from the action of seawater or ultraviolet radiation, some minimal coating is used for protecting the paint, and the screws for securing the hull parts are titanium and stainless steel. “As far as in-house manufacture goes, we’re now able to make up to four units a week, although we’ll ramp that up in the future,” says Simon. “We plan to keep production not just within France but local to Brittany, to stay true to our low- carbon philosophy. “The shape of the mast has also been iterated to improve the YUCO’s hydrodynamics and aerodynamics as it moves through the water or at the surface. It also serves as a handle for carrying and protecting the connector to start and charge the YUCO.” In addition to hydrodynamics, each fin has been designed with rupture points about halfway up their heights and running lengthways, so that if there is a strong shock against any of them, the top of the fin will break off. That dissipates the impact’s energy and prevents the shock running through to the hull, which could spring a leak that would threaten the internal electronics. Navigation At present, all the main applications targeted by Seaber do not require USBL acoustic aiding, and as LBL requires external elements such as buoys or seafloor pylons, this latter approach has been avoided. The sole acoustic navigation system on board is an A50 DVL from Water Linked. In addition to sensing the YUCO’s distance and speed over the seafloor, it was chosen for being, as Simon states, “The smallest and most cost-effective on the market.” Each unit measures 66 mm in diameter and is 25 mm tall, consuming 3 W to measure velocity accurate to 0.1 mm/s and altitudes of up to 50 m above the seabed. “As well as obviously improving navigational accuracy, the DVL helps us to compensate for currents and in autonomously avoiding obstacles such as boulders on the seafloor. You can program altitudes and inclines that you want the YUCO to avoid, to help it avoid bumping against things coming up from below.” The company has also avoided installing FOGs, as they could triple the YUCO’s unit price. Instead, an AHRS using an industrial-grade IMU has been developed, following experiments aimed at benchmarking the performance of every MEMS accelerometer, gyroscope and magnetometer the company could acquire (as well as every combination of the sensors it could make). The AHRS and DVL, along with a pressure sensor for depth and GNSS updates for surface positions, are integrated as Seaber’s INX (Intuitive Navigation eXperience). Proprietary algorithms for sensor fusion and processing of data for refined accuracy have also been developed. “We take just the raw data from each sensor and run it through our own maritime algorithms, because generally most INSs use algorithms aimed at surface or above-surface vehicles,” Simon explains. “Standard-issue Kalman filters and other algorithms are therefore not optimised for an AUV going underwater for many minutes at a time.” Uncrewed Systems Technology | October/November 2022 A visualisation of ocean conductivity and temperature data from a YUCO- CTD, acquired while performing a helical descent-and-ascent survey pattern