The new underwater glider can stay at sea at least twice as long as previous submersibles
that used battery power. It is the first autonomous underwater vehicle
to travel great distances for extended periods running on green energy,
according to the Woods Hole Oceanographic Institution (WHOI).

Scientists have invented the Prius of ocean-going submersibles - a new
"green" robotic glider that runs on energy absorbed from the heat of
the sea, rather than batteries.

Submersibles gained fame in 1985 when WHOI’s remotely-operated underwater vehicle, "Argo," discovered the wreck of the RMS Titanic near Newfoundland.

Built by the Webb Research Corporation in Falmouth, Mass., the new submersible has successfully traveled back and forth between two of the U.S. Virgin Islands,
St. Thomas and St. Croix, more than 20 times. WHOI researchers plan to
use the data gathered by the craft to study ocean currents in the area.

To power its propulsion, the submersible gathers thermal energy from
the ocean. When it moves from cooler water to warmer areas, internal
tubes of wax are heated up and expand, pushing out the gas in
surrounding tanks and increasing its pressure. The compressed gas
stores potential energy, like a squeezed spring, that can be used to
power the vehicle.

"This glider allows longer missions than previous [battery-run]
versions," said Ben Hodges, a physical oceanographer at WHOI. "It could
be out there for a year or two years. None of the old ones could go
beyond six months. And producing fewer batteries is good for the
environment."

The torpedo-shaped glider moves through the ocean by changing its buoyancy
to dive and surface, unlike motorized, propeller-driven undersea
vehicles. To rise, oil is pushed from inside the vehicle to external
bladders, thus increasing the glider’s volume without changing its
mass, making it less dense. The oil can be shifted inside to increase
the density and sink the vehicle. A vertical tail rudder allows the
glider to be steered horizontally.

Technically, the new vehicle is a hybrid, like Toyota’s Prius,
because it uses a small amount of battery power to run the onboard
instruments and to move the rudder.

Gliders of this type are perfect for long-term, long-distance journeys that humans can’t make, Hodges said.

"They can be very helpful in getting measurements that would be too
expensive to get otherwise - any kind of study that requires long-term
measurements from multiple locations," Hodges told LiveScience. "If you had to be there in a ship, it would cost millions of dollars."

Via Live Science