This doesn't seem right to me, in my experience a 3 - 4 ton sailboat is around 9m long, which has a sail in the 20 - 40 m^2 range.

A 5 - 8 square meter sail is really teenie tiny.

Robotic boat, a large tank, some power-to-storable tech, a power generating turbine beneath the waterline and a huge kite. Just send it out on the oceans, to cruise aimlessly wherever the satellite uplink suggests favorable weather and have it head home when the algorithms assumes that remaining tank capacity might get filled up on the way back. Most attractive post-fossil future ever.

Unfortunately, unattended power-to-anything is very much a far away dream, despite all delusions of being able to do it large scale on Mars. All other technology is basically ready to go, and the "lateral lift" of a fast-moving boat is a perfectly adequate substitute for mooring when it comes to tapping wind on the high seas.