Sailing mechanics use the same concept to sail against the wind, zig zagging. Not exactly the same, but the same.,(reply>), @FlyNAA I never said it wasn't changing direction, I said the analogy of a sailboat sailing against the wind by zig zagging is incorrect. Also zigzagging has two dimensions of movement not one, so the boat is not doing that from the perspective of land.<br>You are getting desperate to make a valid point and failing.,(reply>), @Gareth H If you haven't noticed, this boat also zig zags to change direction. It would have been quite silly to build this system to just go across the river once, and then never use it again, wouldn't it?,(reply>), ​@FlyNAA I am saying the analogy of a sailboat sailing against the wind by zig zagging (tacking) is incorrect. So it is no[t] using the energy of a flow to travel in the opposite direction [to that flow]. It is just a normal boat steering in waterflow. Obviously the energy required to move the boat laterally is coming from the waterflow.,(reply>), @FlyNAA The cable is literally just an anchor stopping the boat from going down stream. The water is providing the force, allowing the boat to move, with pressure against the keel, held in place by the cable.<br>The cable it self is not providing any force that translates to motion.,(reply>), @Gareth H By saying "no using the energy of a flow," are you saying this craft does not use energy, or that the energy it uses comes from somewhere other than a flow?