RE: MythBuster TV Show (Jetcat P-60SE project)
It will move in the direction the jet is pushing but slowly. Newton's law is in effect but the turbine thrust is partially cancelled out by the air hitting the sail, again Newton's law. If 100% of the energy of the air hitting the sail was converted into thrust the thing would stand still. However there will be losses so it will move in the durection the jet is pushing but more slowly.