Under Ice with the NUI hybrid ROV

Andrew Bowen, Woods Hole Oceanographic Inst., Woods Hole, MA, United States, Michael Jakuba, Woods Hole Oceanographic Inst., Woods Hole, United States and Christopher R German, WHOI, Woods Hole, MA, United States
Overlying ice makes operating conventionally tethered ROVs on the sea floor challenging. Sea ice moves and ice breakers typically cannot hold station with equipment over the side. Glacial ice is too thick to break and conventional tethers apply only to vehicles deployable through boreholes and therefore limited in size and capability. The NUI vehicle is a hybrid ROV intended to provide open-water ROV-like capability beneath ice. The vehicle utilizes a unique hair-thin (250 um) unjacketed fiber optic micro-tether that allows the vehicle to achieve horizontal standoff distances from a support ship of several kilometers, essentially decoupling the motion of the vehicle from the motion of the ship.

NUI is capable of operating both autonomously and, with the addition the micro-tether, as an ROV. We operated NUI in both modes during the expeditions to the Arctic in 2014 and 2016. Upgrades to the vehicle performed in preparation for fieldwork in Sept/Oct 2019 have increased its depth rating to 5000 m and enable in situ conversion between low-drag survey configuration and an expanded-workspace intervention configuration.

We discuss the design and operation of NUI’s unarmored micro-tether, the hybrid control methodology that enables operating the vehicle directly or semi-autonomously and handles forced transitions between modes in case of tether loss, the use of acoustics for communication and navigation, and the recent upgrades. We report field results and lessons-learned.