While we are at it lets put a fan on our sail boat to make it go faster.
http://answers.yahoo.com/question/index?qid=20080506234729AApZqDe
http://www.youtube.com/watch?v=0CrXvOKPymk
I will admit that I posted this thread as an almost trolling joke, but this i actually can speak on, I have been sailing for many years, and have been teaching sailing for 6 years now, The yahoo answers are an absolute joke, mostly cause they never once recognize a sail as a airfoil WHICH IT IS
the diagram above shows the forces at work in a sailboats movement, air passing over the sail creates lift like a wing heading in the direction of the red arrow, this force can be divided into two vectors as shown by the blue arrows labeled A and B, Force A is negated by the keel underneath the ship as shown with a green arrow. If the force of the green arrow negates the force of arrow A then only arrow B's force remains thus producing forward motion through the lift of an airfoil. If the keel did not exist all sailboats would travel in the direction of red arrow. With that said producing a greater force in direction of the wind would produce greater lift that could be easily negated by the keel in the water. But to make this work you would have to place the fan at an angle to the ship as a wind force coming directly on the bow of the ship would produce a red arrow that runs perpendicular to the ship and therefor be completely negated by the green arrow.
So if we add a fan into the equation, as shown here, we can see that the force of the air from the fan is shown in purple pushing backwards should have 2 effects, one shown in light purple is the vectors of the increase in force of the sail due to increased airflow, and once again the force perpendicular to the ship is negated, The second is the force produced by the fan pulling air like a propeller would shown in yellow, and once more we devide the force into vectors shown in light yellow, and of course the perpendicular force is eliminated by the keel. Notice how with both the light purple and light yellow arrows pointing in the direction of boats travel are not negated. and therefor indicate an increase in speed.
None of the yahoo answers mentioned this and the video supposedly "proving" the concept doesn't even use a sail, just a flat area for the wind to blow and that is not how a sail works, but it does prove that a parachute in a zero g environment could be pushed by a fan held by the user in the direction of the fan.
As for the hovercraft, now thats funny, and idk, ill have to ponder that one