Thanks for clarifying. So is it the motion of air molecules flowing across the boat because the boat is in motion (air flowing from front to back)? It seems like that would create as much or more drag than it'd recapture. Or are the air molecules in motion from wind coming from the side?
” So is it the motion of air molecules flowing across the boat because the boat is in motion (air flowing from front to back)? “
The pressure difference around the cylinder causes a deflection in the motion of air molecule in a direction that provides forward motion.
This is new to me but a conventional sail does not impart all force in the forward direction.