Simple Cardboard Boat
Find an empty milk carton or similar container. Rinse out thoroughly.
Use a hobby knife to carefully cut around the carton.
Cut a small notch in the back of the boat, this will provide space for the rudder to project out from the back of the boat.
There is a lot of experimenting to be had in the rudder department.
These two examples demonstrate how to create a simple and straightforward rudder, and a more complex, bio-inspired cardboard & tape rudder to power your boat.
Comparing different types of rudders can be lots of fun, experiment with these two types or come up with your own versions to see what makes your boat go fastest!
Straighten out a paper clip.
Bend it in half, then introduce two small 90° bends at the tips.
Stick the ends of the paper clip into the servo arm, press arm onto servo horn.
Cut a flap out of scrap milk carton and hot glue this to the paper clip.
Cut three square pieces of cardboard.
Lay these out on the piece of tape, leaving a small gap (~1/8", ~3mm) between them.
Place another piece of tape over the top and press together.
Test out your rudder to see how it moves!