A sea-going robotic glider that uses heat energy from the sea to propel itself has been tested by American scientists.

The yellow torpedo-shaped machine has criss-crossed the 4,000m deep Virgin Island Basin between St Thomas and St Croix more than 20 times since it launched in December. The development teams from the Woods Hole Oceanographic Institution (WHOi) and Webb Research Corporation in Falmouth, Massachusettes have predicted the vessel could continue on its own for another six months.

Most gliders rely on battery-powered motors and mechanical pumps, however, this one draws its energy from the differences in temperature between warm surface waters, and the colder, deeper layers of the ocean.

Wax filled tubes inside the vessel expand when it is gliding through warmer water. This heat is used to push oil from a bladder inside the hull to one outside, changing its buoyancy.

Cooling of the wax at depth in colder waters reverses the cycle.

The machine traces a saw-tooth profile through the water column as it glides through the ocean, surfacing periodically to fix positions via GPS and to relay data back to base.

Dave Fratantoni, WHOi, explained: “We are tapping a virtually unlimited energy source for propulsion.”

The eventual aim of the project is to deploy a fleet of vehicles to study much larger flows in the North Atlantic.

Frantantoni continued: “Gliders can be put to work on tasks that humans wouldn’t want to do or cannot do because of time and cost concerns. They can work around the clock in all weather conditions.”