Draw your boat shape on the cardboard similar to the image . It should look like a little house and a door. Save the square you cut out to use as the paddle.
You will need to cut the square smaller on all sides so it will easily flip around inside the boat. Keep in mind that you will be covering them with tape, so the width will grow again!
You might need to trim a few of your paddles again after wrapping them with tape.
Cover the entire boat and paddle pieces with tape making sure to cover all edges, too. If water gets inside, they get soggy really quickly!
Put a rubber band around the boat and place the paddle piece between the rubber band. Twist it. You will need to twist away from the boat or the boat moves backwards.