54 longer than the second-gen, but the latter is much more productive: in eight to 10 hours [survey condition dependent], it covers about 108% more seafloor area while running the same mission,” Chiau notes. “It is significantly faster to launch and easier to operate. Its efficiency unlocks more ways to optimise data quality and rate-of-acquisition coverage. “That makes the newer version much cheaper to run on a per-hour or perdataset basis, and as an added measure to ease operating costs, we’ve gone through FAA and DoT clearances, allowing our lithium batteries to be flown to survey locations, enabling rapid response.” Flying high and low Bedrock’s AUV consists of two halves, which are designed to fit together via self-aligning connectors and mechanical latches, thereby minimising mission equipment requirements. This tool-free approach also prevents a range of minor hazards, such as a loose screw or a screwdriver rolling off a ship deck during assembly and delaying a survey by hours – a setback that Chiau has experienced in past projects. The front half is referred to as the payload section. Currently, two different hot-swappable front halves exist, each with a varying survey sensor arrangement. The first is the “high fly” configuration, designed for bathymetry over a wide area. This integrates a Norbit OEM MBES-42 multibeam sonar, which scans at 400 kHz with a 130° swath and 512 beams, a Blueprint Subsea Starfish 454 side-scan sonar and an Ocean Floor Geophysics’ Self-Compensating Magnetometer. The second is the “low fly” payload section, intended to complement the “high fly” AUV to fulfil geophysical surveys very close to the seafloor, which uses the same magnetometer, along with the Norbit SBP-42 sub-bottom profiler and Blueprint Subsea’s Starfish 992 side-scan sonar. Within both payload section designs is a dry enclosure, which tightly houses the AUV’s main computers, the navigation (inertial, GNSS and aiding DVL) systems, a communications module and a wet section that arranges the sonars. Within the survey sonars, those include a forward-looking sonar (FLS) for perception, constant altitude terrainfollowing and obstacle avoidance. The rear half is the propulsion section. This contains a battery, designed and built in-house to the optimal form factor, as well as two shrouded electric thrusters, their two respective ESCs and four servo-actuated rudder fins in an X-configuration. Replacement of these electrical components does require an Allen key, as they are secured into the AUV’s back half via six bolts with O-ring seals, but such maintenance would not form nominal daily operations. “But we do pride ourselves at removing opportunities for human error, so there’s no cabling between the two halves. Try to fit two halves of an AUV together with a cable in there, and it will dangle or snag or shear on something. With the design we’ve chosen, the two halves can be mated while blindfolded,” Chiau notes. “Every mistake all of us at Bedrock have experienced or learned about in the past on AUVs, field operations, system design, we pooled together and put a hard ‘no’ against having any of them in this system. We want to look out for the field ops teams, for whom normal things become five times harder purely because they’re at sea, so we design-out the issues, rather than relying on procedure or memory.” Despite the different designs and componentry in either half, the AUV’s centre of buoyancy is roughly at the joint between them, such that it remains level when submerged or surfaced. It is also slightly positively buoyant as a safety default: if one or multiple systems should fail, the vehicle will float up to the surface where it can be retrieved. Navigation The benchmark defining Bedrock’s navigation requirement was a set of very tight horizontal and vertical survey path tolerances (especially challenging in shallower water of less than 40 m), which customers in the offshore construction space expect of surveyors. If such parties are to trust that an enormous, expensive monopile or pylon should be safely installed at a given location, they must completely trust that the AUV knows exactly wherever it is in the water column at every moment of the survey, relative to the areas it scans. “Most survey regulations on those are written for ships, which have constant GNSS corrections; there are few, if any, such rules for AUVs, especially here in the US, which is why it has been so hard for AUVs to break into constructiongrade or equivalent offshore surveys in addition to the industry being risk averse,” Chiau explains. “If we could hit those navigation accuracy tolerances, a huge market would open up to us, especially as the US has an initiative to hit 30 GW of clean August/September 2024 | Uncrewed Systems Technology Bedrock was the first company to dive using an Exail Phins 9 Compact, the SWaP-optimised FOG INS being critical to precise navigation on a limited internal volume budget (Image courtesy of Exail)
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