Oshen, the UK maritime sensing and data company, has successfully demonstrated the ability of its sail-powered robots to deliver rapid seabed mapping, in a new trial with the US Navy. Its 1m long, self-sailing vessel - known as a C-Star - overcame challenging sea conditions to image key underwater features as part of a programme to accelerate the development of autonomous technologies and their integration into mainstream US naval operations.

The two-week trial took place in the waters off Cat Island, Mississippi and marked the latest phase in an on-going collaboration between the US Navy’s Commander, Naval Meteorology and Oceanography Command (CNMOC) and Oshen.

C-Star PD1 navigated stronger than forecast currents to complete multiple bathymetric transects across the Cat Island Channel and ferry lane, using a single-beam echosounder suspended from its keel to capture hydrographic features such as a sloped seabed and dredged channel. Tidal curves were successfully recreated from station-keeping depth data, one of CNMOC's key requirements, while speed and manoeuvre control capabilities were also tested: waypoint vs. heading control, and ability to sail slow, zig-zag patterns, with a view to search-and-rescue applications.

"Surveying littoral and shallow-water zones is critical to our operational readiness, but it presents unique environmental challenges," said Dr. Stacy Johnson, Lead Scientist at the Naval Oceanographic Office (NAVO). "The modular physical and power architectures of Oshen’s platforms allow us to seamlessly integrate Navy-selected sensors, like the single-beam sonar we are using for this test. It gives us an unprecedented ability to sense and map these restrictive coastal environments safely and effectively."

The ability to quickly deliver hydrographic surveys could benefit to coastal communities impacted by major storms. Typhoons and hurricanes shift sand, move wrecks and alter the depths of channels. This can render ports inoperable just when they are needed most: ships delivering disaster relief, fuel and food will be reluctant to head into affected areas for fear of running aground or hitting sunken debris. New charts highlighting changes to local underwater topography are urgently required.

Seabed mapping normally requires specialist hydrographic survey vessels. Because these are scarce, expensive and slow to mobilise, weeks or months can pass between a storm hitting and an area being deemed safe for navigation. Oshen's low-cost, self-sailing robot boats can close the gap: fitted with the same single-beam echo sounder used in the US Navy trial, they can quickly scan changes to the seabed to depths of c.80m (262 feet), sufficient for the majority of the world's port areas.

Powered by the sun and wind, C-Stars can stay at sea for months on end with little or no support. Self-organising constellations of C-Stars could therefore be kept on stand-by in priority areas such as the Philippines, the Caribbean or the Bay of Bengal, ready to provide rapid reconnaissance when needed. At other times they could gather met-ocean data for weather forecasting or conduct ecological surveys.

There are also other, non-emergency applications for the mapping capability. While most shallow, heavily-trafficked waters of the world are well charted, significant areas were last surveyed using lead lines in the era of Shackleton and Scott. The effects of seafloor dynamics and climate change mean charts for these regions may be decades out of date, potentially putting ships, crew and infrastructure at risk.

With traditional hydrographic survey vessels costing upwards of £20,000 per day to charter, low-income nations may lack the resources to do regular, full-scale surveys. Oshen’s robotic sailboats provide an affordable alternative. Small and one-person portable, individual C-Stars could be permanently stationed at key ports or channels, delivering a basic, but valuable, year-round underwater monitoring capability for less than half the cost of hiring a regular survey boat for a day.

Gordon Jones, Defence and Oceanography Lead at Oshen, said: "After a major storm, the question authorities have to ask is, 'Is this port or inlet safe to enter?' For the most effective crisis response they need an answer in hours, not weeks. C-Stars can deliver that. They are not meant to replace dedicated hydrographic surveys, but fill that critical gap between the storm passing and the survey ship arriving. They have proven their ability in the open ocean, surviving Category 5 hurricanes. Now C-Stars are demonstrating their versatility and value in shallow, inshore waters too.”