The U.S. company Saildrone has been producing sail-powered unmanned surface vehicles for years now. The USN has used these surface drones in the Middle East, Caribbean and Eastern Pacific. The Explorer model in use so far is 23 feet long and has a height of 16 feet. As can be seen in the photo the sail is more akin to an aircraft wing than the canvas sails of old. The speed is just 3 knots, but the endurance is up to a year. Solar arrays power onboard systems. Many of the missions are environmental in nature but onboard cameras provide some military function.
Saildrone has also designed larger sail-powered USVs.
https://www.saildrone.com/missions