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33 Mayflower Autonomous Ship | Dossier vibration can shake connections and joints loose, and high winds can rip antennas from masts and cause USVs to roll or drift off course. “Some people think we must have benefited from all the great advances in autonomous cars over the past 10 years, but cars are constrained to operate in very prepared and known environments that have been optimised for them,” Phaneuf says. “Most of the modern world has been built around automotive transport and the rules regarding their speed, movement and use. None of that translates to USVs: on the open ocean, ships can move in any direction, come at us from anywhere, and our ‘roads’ are constantly moving and changing beneath us.” With these challenges in mind, sensors are installed to ensure as complete an informational picture as possible so that the Mayflower can localise itself and hence calculate its next heading with high accuracy and integrity. As mentioned, Veripos provided the GNSS systems, which consist of two of its high-end LD8 receivers, as well as four marine antennas (for dual antenna inputs to provide heading information feeds for each receiver) positioned about a metre above the solar deck. The iXblue AHRS and Silicon Sensing IMUs serve to aid navigation accuracy between GNSS updates while providing safety-critical data on pitch, roll and heave (which are vital for autonomously navigating waves to prevent any associated damage or capsizing). “We also have six camera systems installed on the mast, for 360 º awareness around the ship as well as helping to verify that we are where we’re supposed to be, and a fathometer for measuring the water depth when in littoral zones,” Scott says. Thompson adds, “In terms of sensor quality, we don’t need 4K cameras or anything crazy for identifying buoys, rigs or other points of reference to gauge position; standard HD cameras tend to be good enough. “The main thing is whether the camera can dynamically adjust for varying light levels. If not, your models can be rendered useless in the face of overexposure to sunlight, floodlights or other light sources, and computer vision can’t really overcome that by itself. “It’s also important that we have cameras with maritime-grade ruggedness. We’re using a number of 1080p industrial bullet cameras at the moment, which work great for what we need. “We run a stacking-layering approach to building a comprehensive digital world environment using all those input sensors. We don’t have to do much filtering, thanks to the high quality of the sensors we’re using, and we’re not trying to achieve GNSS-denied navigation or anything heavy duty like that since this is a proof-of-concept research vehicle.” The GNSS data streams interface with embedded nautical charts, which can be viewed on electronic chart displays by the operators and clients. For the past 2 years the Mayflower team has also worked closely with the United Unmanned Systems Technology | February/March 2022 In the spring this year, the Mayflower will re-attempt its autonomous Atlantic crossing, to be followed by surveys along the US east coast on behalf of partners and clients