Time (and costs) saved using unmanned surface vessels (USV) over conventional methods for hydrography can be dramatic — especially in autonomous mode. Numerous firms, large and small, have discovered how modest investments in such craft can completely revolutionize their hydrographic operations. One such firm is the family owned and operated Coastal Geomatics in North Carolina.
“With conventional methods, it used to take us four weeks with a three- or four-person crew to do the bathymetry for 26 canals that we do every two years for the City of Holden Beach,” Chris Stanley, owner and manager of Coastal Geomatics, said. “Now, with our Apache we do this over four days of high tide; about four to five hours per day.”
Stanley had been surveying in the local area for more than 30 years and had partnered in several local firms. In 2020, he decided to start his own firm, together with his two adult sons Alan and Ian: Coastal Geomatics was born.
“We do a lot of boundary work, and topographic surveys as there is a lot of construction going on in the area,” Alan said. “We also do flood insurance work, FEMA elevation certificates, and hydrographic work — we are on the coast.” Holden Beach is on one of North Carolina’s barrier islands, separated from the mainland by the Intercoastal Waterway. Coastal Geomatics has standing contracts to do hydro work for FEMA beach erosion annually, and the biennial canal surveys for the city.
The move to a USV for hydrographic surveys made a lot of sense, however a past bad experience with the technology prompted Stanley to be extra diligent in choosing a boat. At one firm for which the elder Stanley had worked in the past, they had acquired a USV that he said was essentially “a jet ski, with a mix of components cobbled together.” He added that they had never really gotten it to work right, and it now sits idle in a storage unit.
The Stanleys did some research on the current state of small USV, noting that some still seem like “contraptions” and decided instead to test out three models from CHC Navigation: the Apache 3, 4, and 6. They had considered the tri-hulled Apache 6 for some offshore work they sometimes do, however, they chose the Apache 4 for now. It has a dual GNSS antennas for position and heading that is tightly coupled with an IMU for uninterrupted positions, a single beam echo sounder, and a 360° camera. It has a sensor well that can accommodate most of the popular models of acoustic doppler current profilers (ADCP), though Coastal Geomatics is not presently using an ADCP. It can be run fully autonomously for missions defined in the AutoPlanner software, or remotely piloted — Coastal Geomatics needed both options. They noted how the boat is compact, easy to operate, and all components are well integrated with watertight seals.
For open water areas of their contracted surveys, they put the USV in full autonomous mode, where they say it is quite efficient. However, there are specific tasks where a remote pilot needs to take over.
The canals surveyed for the city to inform dredging operations are about 100 feet wide and each house has a floating dock. There is a 20- to 30-foot strip between the docks. The old method, Ian explained, was to put one of the crew in a small flat bottomed Jon boat, with a crew member on each side of the canal, often with a fourth using a total station. Points across the canal from bulkhead to bulkhead were taken with a long prism pole, handing the pole off to the crew member on the other side after each crossing. The dynamics of which residents’ boats might be at the docks on any given day made full autonomy for that phase of the surveys impractical.
Coastal Geomatics’ solution was to employ a peddle-powered kayak, guiding the Apache remotely. The flexibility of their new craft has enabled the firm to execute multiple types of surveys and expand their hydrographic services more efficiently.
