This is my own design for a "sailboat" capable of traveling directly upwind. A fun toy to let go on the lake and see where it ends up :)
The wind drives the air propeller which drives the water propeller via a rubber band. A set of small rollers sits inside the mast to direct the rubber band and keep it from rubbing. The rubber band serves double duty by also holding the water prop in place.
The boat is kept pointing upwind by a weather-vain tiller which is connected to the rudder by a second rubber band. As the wind direction changes, the tiller is blown to the side, causing the rudder to turn and steer the boat back into the wind.
All parts are 100% 3D printable, with the exception of 2 rubber bands. All STL files are orientated correct to be printed, just drop in and print. All parts can be fit on a standard 200mm x 200mm build plate at the same time, if you dare!
Don't forget to print 2 of the Mast Rollers. And note that the thicker side goes towards the front.