Hard to go only with a sail, this attempt in the US was not so successful
About 15 years ago an Italian team built a yacht to cross Mauritania desert to bring some boxes to preserve ancient and precious manuscripts in Chinguetti. One of the main trouble in towns was crossing electric and telephone lines but maybe with a gaff sail you'll stay a bit lower.
Some time ago I was talking to an engineer I met by chance at a sustainable mobility event. This lad (he designed the green runner
http://www.green-runner.it/, a lighter version of the Segway) did some sums and told me that yes, an electrosailing hybrid is achievable running at a good average speed, more likely the best way is a brushless motor (the same of electric bikes, I guess in English is called torque-motor) inside the front wheel (in a 3 wheeler). Sailing however will be essential to recharge batteries.
Ciao - Enrico