Note: Closed for being off-topic (whoops!), see here for the re-post on the Engineering site.
If ships at sea can tack in a zigzaggy pattern by converting backwards force from the wind (using the sail) into sideways force, then that sideways force into forward force by bracing against the (stationary) via the rudder...
source: another stackexchange question
...couldn't the same principle be true with the roles of the wind and water reversed --- as in a river with stationary air above it? Are there any rivers with the right conditions to make this happen? If the air won't work, could zigzagging cables stretched across the river do it?
