Tethys One — Autonomous Underwater Inspection Drone
Tethys One.
Thrive in Rough Waters.
The only underwater drone built to inspect stationary in currents up to 3.5 knots. Autonomous navigation, zero-visibility 3D mapping, hot-swap batteries and a full modular payload system — carried in by two people and surveying in ten minutes.
Inspect · Map · Measure · Recover
One drone for the water that defeats conventional ROVs
Standard inspection ROVs lose station the moment the current picks up — in rivers, tidal zones and outfall flows, coverage gets missed and surveys get abandoned. Tethys One was engineered from the ground up for exactly those conditions: it holds position and inspects autonomously in flow up to 3.5 knots, maps in zero visibility, and runs a full library of swappable payloads from a single platform.
- Stationary inspection in currents up to 3.5 knots — rivers and tidal sites included
- DVL-assisted station-keeping: position, heading, depth and distance hold
- Real-time 3D mapping where cameras see nothing, via multibeam sonar
- Hot-swap batteries — unlimited field time, no vehicle recovery to change packs
- Full modular payload system — one vehicle reconfigured per mission
Built for where inspection usually stops
Fast water, zero visibility and confined infrastructure are exactly the conditions that shut conventional inspection methods down. Tethys One was designed to remove each limit.
🌊 Strong Currents
Conventional ROVs drift off target and lose coverage in flow. Tethys One holds station and inspects stationary up to 3.5 knots.
🌫️ Zero Visibility
Turbid rivers and harbours blind cameras. Multibeam sonar builds real-time 3D where there is nothing to see.
⚠️ Diver Risk
Currents, confined spaces and contaminated water put divers at risk. The drone keeps people out of the water.
🐢 Slow Mobilisation
Vessels and dive teams are expensive to mobilise. A two-person crew deploys Tethys One in ten minutes.
Built for Where Others Are Swept Away
The engineering that lets Tethys One inspect, hold and map in the very conditions that stop conventional systems.
Holds station where the current is the mission
Tethys One is engineered specifically for rivers and tidal zones. Its omnidirectional thruster layout and station-keeping let it hold a fixed inspection position — and stay there working — in currents that disable conventional ROVs. No anchoring, no drift, no missed coverage.
- Purpose-built for rivers, tidal currents and offshore flow
- Stationary inspection — not just transit — in moving water
- Stable enough for measurement and close-up structural work
Full awareness, close to the structure
Omnidirectional movement across roll, pitch and yaw is matched by a 360° sensing envelope — DVL plus side- and front-facing sonar. Terrain following and obstacle awareness keep the vehicle a safe, programmable stand-off from the seabed and from the structure being inspected, even in tight or cluttered sites.
- 360° movement control in roll, pitch and yaw
- Terrain following with programmable stand-off distance
- Obstacle awareness from multi-directional sonar
- Confident close-range flight around complex infrastructure
See in water where there is nothing to see
Where turbidity blinds a camera, Tethys One's front-facing multibeam sonar generates real-time 3D point clouds of the structure and seabed. After the dive, the data is delivered as post-processed photogrammetric and bathymetric 3D models — defensible survey deliverables, not just video.
- Real-time multibeam 3D in zero-visibility water
- Photogrammetric & bathymetric 3D models delivered after each survey
- Centimetre-level detail for damage detection and change comparison
Reach out, grab and recover — no diver required
With the modular manipulator fitted, Tethys One does more than look. Operators can grab, lift and interact with the environment directly from the surface — intuitively enough that new pilots are productive quickly. Underwater lifting capacity is equivalent to one fully-equipped diver.
- All-electric 3-axis arm — grab, lift and recover objects
- Lift capacity equivalent to one fully-equipped diver
- Intuitive control — short learning curve for new operators
Station-Keeping That Changes the Mission
Set a waypoint, lock a distance to structure, or run a repeatable survey pattern — Tethys One flies it while the operator monitors the inspection feed.
Repeatable coverage — the same path, every survey
Tethys One fuses DVL, AHRS, altimeter and pressure data to hold position and orientation in flowing water with no manual compensation. That turns inspection into a planned, repeatable operation: comparable data on every pass, points of interest tagged live, and the pilot freed to focus on findings rather than flying.
- Depth lock — holds altitude above seabed or distance to object
- Heading hold — resists rotation in cross-currents
- Waypoint-to-waypoint autonomous survey missions
- Repeatable coverage for reliable change detection
- Live point-of-interest marking without interrupting the dive
One screen — sonar, map and telemetry together
A single ruggedised display shows the live sonar fan, a plan-path mini-map and full vehicle telemetry — so the operator commands the mission and reviews findings from one place, in daylight, at the water's edge.
Real-World Deployment
Two-person crew. Ten-minute setup. No crane, no support vessel.
At 35 kg the system is carried by hand to the water's edge — off a bridge, a quay or a riverbank — and inspecting within ten minutes, with no additional handling equipment.
One Vehicle. Every Mission.
Swap sonar, manipulators, thickness gauges, cleaning systems and detection payloads in the field. All display natively on the Tethys UI.
Reconfigure between dives, not between vehicles
Instead of a different specialist ROV for every task, Tethys One carries a library of payloads on standardised bays. Fit imaging sonar for navigation, a multibeam for mapping, a CP probe or thickness gauge for integrity, a manipulator for intervention, or a cavitation lance for cleaning — and change the configuration on site, between dives.
- Standardised top & underside payload mounting
- Sonar, navigation, measurement, manipulation, cleaning & detection
- Every payload streams live to the Tethys UI
- Custom payload integration available on request
Imaging Sonar
Navigation & Positioning
3D Mapping
Inspection & Measurement
Manipulation & Cleaning
Detection
Metal Detector
Electromagnetic detection of magnetic and non-magnetic metals. High sensitivity, unaffected by mineralised soils. Max ROV speed 1 knot with detector active. 300 m depth-rated.
Magnetometer
Detects ferromagnetic materials — iron, steel, nickel — for locating submerged ammunition and UXO. Real-time measurement display integrated with Tethys UI. 300 m depth-rated.
Need a payload not listed here? Tethys supports custom payload integration on request.
Discuss Custom Configuration →Full Tethys One Specifications
Complete technical data for the Tethys One and its payload options. Contact us for mission-specific configuration advice.
Physical & Performance ▾
| Vehicle Weight | 35 kg |
| Depth Rating | 300 m |
| Tether Length | 400 m standard (extendable on request) |
| Current Resistance | Stationary inspection up to 3.5 knots |
| Degrees of Freedom | 6-DOF omnidirectional |
| Setup Time | 10 minutes (2 operators, no additional equipment) |
Power & Battery ▾
| Runtime per Pack | 4 hours |
| Battery System | Hot-swappable — field-changeable without recovery |
| Total Field Time | Unlimited (with spare packs) |
Imaging System ▾
| Camera | Full HD — 100° tiltable |
| Front-Facing Sonar | Multibeam (standard) |
| Mapping Output | Photogrammetric and bathymetric 3D models |
| POI Marking | Real-time, live during dive |
Navigation & Sensors ▾
| Station-Keeping | DVL + AHRS fusion — depth, heading, distance hold |
| Terrain Following | DVL altitude-based — programmable stand-off |
| Obstacle Detection | Multi-directional sonar |
| Mission Capability | Waypoint-to-waypoint autonomous survey |
| DVL Bottom-Track (Nucleus 1000) | 10 cm – 50 m |
| DVL Bottom-Track (DVL 500) | 0.1 m – 175 m |
Sonar Payloads ▾
| M750d — Range | Up to 120 m · 500 m depth-rated |
| M1200d — Range | ~40 m, higher resolution · 500 m depth-rated |
| M3000d — Range | ~30 m, highest resolution · 500 m depth-rated |
| Surveyor 240-16 MBES | 240 kHz · 80° cross-track · ~50 m survey depth · 300 m rated |
Inspection & Manipulation Payloads ▾
| CP Probe Accuracy | ±5 mV (Ag/AgCl half-cell) |
| UT Probe Range | 3 – 250 mm steel |
| UT Probe Accuracy | ±0.1 mm |
| UT Probe Depth Rating | 500 m |
| Manipulator Reach | ~0.4 m |
| Manipulator Lift | 2 kg at full extension |
| Manipulator Closing Force | 600 N |
| Manipulator Accuracy | 0.1° joint positioning |
| Cleaning System Max Pressure | 300 bar (4,350 psi) |
| Cleaning System Flow | 80 LPM |
Wherever Conditions Are Too Demanding
Tethys One was built for the environments that defeat conventional inspection ROVs — fast currents, zero visibility and complex infrastructure.
Energy Infrastructure
Offshore oil & gas platforms, wind-turbine monopiles, hydropower intakes and penstocks, and nuclear cooling structures — in the currents and visibility these sites impose.
Civil & Marine Infrastructure
Bridge piles, lock and sluice gates, subsea cable routes and harbour-bed mapping — rapid deployment, no dewatering, no diver risk in flowing water.
Search & Rescue
Police, coastguard and border operations in fast rivers and tidal zones — autonomous sonar-and-video area search where diver entry is unsafe.
Maritime & Shipping
Hull inspection at berth, propeller and rudder assessment, mooring-chain surveys and port infrastructure — without drydocking or a dive team.
Surveillance & Demining
UXO and ordnance survey with the magnetometer payload, security inspection of submerged assets, and ferromagnetic detection for cleared-route confirmation.
Marine Science
Habitat mapping, bathymetric survey in turbid estuaries, sampling in currents too strong for conventional platforms, and film in challenging conditions.
Local Expertise.
Full Lifecycle Support.
SepcoTech A/S is an authorised Tethys Robotics distributor. We handle the full purchase process — from system configuration and quotation through delivery, commissioning and ongoing support.
- Authorised distributor — full manufacturer warranty coverage
- Shipping from Roskilde, Denmark — fast dispatch, no import delays
- Crew training and mission planning support included
- Live water demonstration available before purchase
Request a Quote for Tethys One
Tell us about your inspection challenge and we'll prepare a tailored configuration and quotation — or answer any technical questions about the system.
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