My name is Noah and I am a 7th grade student from Massachusetts and my school project was to build a boat that can travel 30 inches with a small ball on it. You could use any type of power, but I chose rubber bands because they are much less complex and also weigh less than other propulsion systems.
Step 1: Gather Your Materials
1 - 1 liter soda bottle with cap
1 - 2 liter soda bottle with cap
1 - detergent bottle (plastic to make fins and cap to make washer)
1 small ball
multiple rubber bands
styrofoam - thin and thick
Step 2: Gather Your Tools
Hot knife or saw for cutting styrofoam
Step 3: Create the Propeller
First, tape around the 2 liter bottle as shown in the picture to create a straight line for cutting. Next cut above the tape to remove the top of the bottle. Cut up the bottle into eighths creating blades. Squish it down on a flat surface and then bend them back with your hand until it is flat. Trim each blade to an angle of your choosing, trying to make them even and trim as necessary. Twist each blade to allow them to push the air.
Step 4: Create the Body of the Boat
Mark a hole in the 1 liter soda bottle that will fit your hand and cut it out. Drill a hole in the back of the bottle toward the top with a drill bit a little bigger than your skewer.
Step 5: Create the Motor
Connect the rubber bands to the skewer with hot glue and then wind with a paper clip. Put the skewer in through the top of the bottle, leaving the rubber bands sticking out just a little. Secure them to the the bottle by screwing on the cap as seen in the photos. Put the skewer through the hole in the back of the bottle. Next create the washer by drilling a hole into the detergent cap that is slightly smaller than your skewer. Cut the edges of the cap off, creating a flat washer. At this point you need to determine the final length of the skewer and how much tension to have on the rubber bands. This will be determined by the length of your bottle and your rubber bands. Once you have determined the length, mark the skewer where it comes out of the bottle. Drill a small hole through the skewer at that point. You will now put a paper clip through the hole and wrap it around so the washer is secured and the skewer cannot move into the bottle. Next, drill a hole in the 2 liter cap that it slightly smaller than the skewer. Push the cap onto the skewer with the opening facing out to then screw on the propeller. Cut off the excess skewer and hot glue the cap to the skewer to secure them together.
Step 6: Creating the Styrofoam Base
This boat sits on two pontoons. It is important to make sure they are tall enough so the propeller does not touch the water. They should be the same size. In this example they are the length of the 1 liter bottle and the propeller sticks off the back. Cut a slight angle in the front. Cut a rectangle of Styrofoam to create the base. Hot glue (on low setting or else you will melt the Styrofoam) the pontoons to the base. To make the fins, cut the flat bottom of the detergent bottle. Cut a slit in the bottom of the pontoon to fit each of your fins and push them in.
Step 7: The Top of the Boat
The goal of this project was to be able to move a ball 30" across water. Create a small hole / divet in the top of the boat to hold the ball. Measure to find the center line of the boat to ensure stability. Hot glue the 1 liter bottle assembly to the Styrofoam base on the center line.