Wind can propel your sailboat and charge batteries at the same time

[Gregg]

A practical and clever system that uses a submerged propeller to provide electricity when under sail and provide propulsion from batteries it charges.  It uses a servo motor to change the propeller blade pitch.
https://oceanvolt.com/solutions/systems/servoprop-sail-drive/
Video (Skip to 12:00 to see the replacement unit being installed)