THE way we study oceans could be transformed by a high-tech "surfboard" that generates its own power from sunlight and water waves. The device is capable of navigating at sea for months at a time and recently completed a 4000-kilometre trip from Hawaii to San Diego, California.
Gathering data on the oceans has always been difficult: survey ships are costly to deploy and buoys take data only at single sites. So engineers at Liquid Robotics, a company based in Kamuela, Hawaii, decided to build an autonomous vehicle that would be cheaper and more flexible than either of these options. They knew that winged robot "gliders" had been patrolling the ocean depths for a decade. These craft have a bladder which can be inflated or deflated to make them rise or sink. Tilting their wings appropriately allows this vertical movement to be converted into forward thrust.
But how to create a self-powered surface vehicle? Liquid Robotics's answer is Wave Glider, a surfboard-like float attached by a cable to a set of wings several metres underwater. "The glider is propelled entirely by wave power," says Justin Manley, the company's science director. When a wave lifts the board, it pulls on the wings and tilts them from the horizontal, generating forward thrust. A trough lets the wings tilt the other way, also producing forward thrust (see diagram) . The craft's top speed is about 2.25 knots (1.2 metres per second).
The float has solar panels that recharge its onboard batteries and provide up to 10 watts of power for communications, GPS and other sensors. The craft's course, which is independent of the direction of the waves, is set by a radio-controlled rudder. "You simply log in from your laptop and tell it where to go. And since we have the luxury of GPS all the time, navigation can be very accurate," says Manley.
Wave Glider could have several applications beyond simply measuring the state of the ocean along its route. It could act as a communications relay for robotic submarines so they would never need to surface, and it is so quiet that it is ideal for passive sonar systems, which detect underwater sounds. It could also help track marine animals which have been fitted with radio tags.
Another possibility is that the craft could serve as a replacement for monitoring buoys. The US National Oceanic and Atmospheric Administration (NOAA) has a global network of moored buoys that relay data from sensors measuring pressure on the ocean floor, looking for telltale signs of a tsunami.
The trouble is that the buoys often lose their moorings, and must be replaced by ship. "We can put a Wave Glider on an aircraft and deploy it using a locally hired fishing boat almost anywhere in the world in under 48 hours," says Manley. By moving in small circles Wave Glider can stay in one spot, emulating a buoy.
Eddie Bernard, director of the NOAA's Pacific Marine Environmental Laboratory in Seattle, is evaluating the Wave Glider and other robotic vehicles, which he says are revolutionising data collection.
"Chartering an oceanographic vessel costs $20,000 a day," he says. "So we need a way to get more data more cheaply and we need as many options for getting it as possible."
