Aircab / energyfree airship drive

The concept of Aircab shows the usage of free energy,which is supplied through water flow.Cities who are connected by a river are able to supply each other with goods,also passengers can be transported by Aircabs.This way creates a constant connection between cities.The energyfree mechanism works through a funnel shaped sail installed under water which is moved forward by the waters flow.When the aircabs are pulled against the current,sails fold together so there is no resistance.Helium filled zeppelins are connected to the sails.Aircabs are a safe way of using zeppelins.They are permanently connected to the drivesystem so therefor cant crash