Drones: Unpiloted composite vehicles head out to sea

Although the term drone for the most part has been synonymous with unmanned aerial vehicle (UAV) — that is, machines built to fly — the concept is being freshly applied to craft designed with the help of advanced composite materials to operate autonomously or semi-autonomously in marine and terrestrial environments as well.

A case in point are the sailboat drones designed and built by Saildrone (Alameda, CA, US), a marine robotics company founded in 2012. The company has built a fleet of about 20 of the semi-autonomous craft. They are intended as replacements for expensive (and manned) research ships and stationary buoy systems now deployed around the globe to gather data on everything from weather to fishery populations. 

The sailboat drones are equipped with an array of instruments, including sonar and other sensors, for measuring water temperature, wave height, salinity and carbon dioxide levels. An onboard computer stores and transmits data and also steers the craft via a GPS downlink. Thirty watts of power are supplied by lithium-ion batteries, which are charged by solar panels installed in the 4.6m tall sail, manufactured in-house by Saildrone from carbon fiber composite skins, using an unspecified process. The boat’s other composite components include a carbon fiber mast, boom and tabbed tail fin — the latter, a sort of unmanned, above-water rudder, responsible for keeping the ship trim to the wind at all times. 

Saildrone fabricates parts from a variety of stock and custom tubing manufactured by a West Coast supplier. That supplier reportedly uses roll-wrapped prepreg and a toughened epoxy, supplied by Mitsubishi Chemical Carbon Fiber and Composites (Irvine, CA, US). Ordinarily, the tubes are oven-cured on a metal mandrel. 

Recently, two of the 7m-long, 0.5-MT drones completed the longest voyage to date, returning to San Francisco Bay after an 8-month, 7,000-km round trip to the equatorial Pacific. The mission’s directive, conducted in collaboration with the National Oceanic and Atmospheric Admin. (NOAA, Boulder, CO, US), was to take temperature and other measurements of the currents associated with the climate-disrupting system known in North America as El Niño. For the past 40 years, these measurements have been provided by a NOOA-maintained grid of buoys moored to the Pacific sea floor, called the Tropical Atmosphere Ocean (TAO) array. In recent years, however, the TAO array has degraded due to marine growth and destruction wreaked by fishing trawlers. It is expected that the mobile saildrones will be able to provide more readings, over a wider range, with greater accuracy than the aging buoy system.