Hobby Underwater Drones

Matching depth rating to real water

Water pressure rises quickly as you descend. NOAA's National Ocean Service puts the increase at one atmosphere for every 10.06 metres (33 feet) of depth, and the Woods Hole Oceanographic Institution notes that at 10 metres the pressure is already double that at the surface. Seals, housings and connectors on a drone are built for a rated depth, so read that figure against the places you actually plan to dive. A lake, marina or reef visited on holiday may be far shallower than a drone's limit, which gives you headroom. If you hope to explore offshore wrecks or flooded quarries, check the rating and whether the maker's warranty covers dives near it.

Tether length and handling on the surface

The cable is what links the drone to your screen, and it shapes your day more than any other feature. Longer is not always better. In current or wind the tether adds drag that the thrusters must fight, and a long loose cable is easier to snag on moorings, weed or rocks. Think about how far you will really travel from the boat or shore, then add some slack. Check whether the drone comes with a reel, how the tether connects to the controller or a floating relay, and how easily a damaged length can be replaced. Practise paying out and recovering the tether on land before your first dive.

Cameras and lights for murky water

Light fades fast underwater. According to NOAA's National Ocean Service, sunlight may travel about 1,000 metres into the ocean under the right conditions, but there is rarely significant light beyond 200 metres. Coastal and lake water carrying plankton and sediment usually dims far sooner, so the lights on a drone can matter more than its headline video resolution. Ask the maker for footage shot in green, cloudy water rather than clear tropical seas. Check whether the lights can be dimmed to cut glare from particles, whether the camera tilts, and whether the drone records onboard as well as on your phone, in case the live feed drops.

Buoyancy, trim and care after a dive

Engineers aim to make underwater vehicles neutrally buoyant, the Woods Hole Oceanographic Institution explains, so they can hover without spending energy correcting their position. Sea water is denser than fresh water, so a drone trimmed for a lake may sit differently in the sea; check whether yours has adjustable weights or floats. After a dive in salt water, rinse the drone, connectors and tether in fresh water, let everything dry before storage and inspect the propellers for fishing line or weed. Compare the published depth ratings, tether options and spare parts of any model you shortlist, such as the Chasing Dory or a Blueye vehicle, before you travel with it.

Sources and further reading

• How does pressure change with ocean depth? — NOAA National Ocean Service.
  Short explainer on how water pressure builds with every metre of depth, in atmospheres.
• How far does light travel in the ocean? — NOAA National Ocean Service.
  How deep sunlight reaches in the sea and where the sunlit, twilight and dark zones begin.
• Why is pressure different in the ocean? — Woods Hole Oceanographic Institution.
  Explains pressure at depth and why vehicles are built strong and close to neutrally buoyant.

Common questions

Is an underwater drone worth it for snorkelling or fishing trips?

It can be, if you enjoy filming or exploring places you cannot reach on a single breath. Expect to spend time learning to handle the tether and the drone in current, and remember that murky water limits what any camera can show.

Where am I allowed to fly a hobby underwater drone?

Rules vary by place. Harbours, marinas, nature reserves and dive sites may restrict drones, and private lakes need the owner's agreement. Keep clear of swimmers, divers and wildlife, and ask the local harbour office or site manager before launching.