Wave Gliders [1] have been doing that for years.
The tiny Wave Gliders are quite useful. They're small, smaller than a surfboard. They're considered "marine debris" for vessel safety purposes. Electronics is so small today that they carry compute power, GPS, cameras, and Iridium for communications, plus other small oceanographic instruments as desired. They're tough enough to survive hurricanes. The control center has AIS info and steers them away from vessel traffic. Propulsion is mostly passive, using wave action to propel the glider forward. They're slow, but make steady progress.
It's a quiet, useful and profitable technology.