Two Liter Soda Bottle Boat
30-60 min
Ages 5+
What Will You Make?
Recycle soda and water bottles to make your own paddle boat.
What Will You Learn?
This easy build uses two important scientific principles, buoyancy and stored kinetic energy, to float and drive a simple boat. The parts are all readily available around most homes, and the boat can be assembled in minutes, though a bit more time with waterproof markers can add some style to the outcome. Consider experimenting with additional components like fins for stabilization, to improve the performance.
Build the Boat
Attach the Sticks
Using the tape, attach the sticks or dowels on opposite sides of the soda bottle (empty, but with cap secured) so that they overlap the bottle by about 1/3 its length, and then extend 6″ – 8″ from the bottom.
Make the Paddle
You will cut the paddles out of the plastic lids, based on dimensions you measure with the ruler. Measure the space between the sticks. Subtract 1″ from this measurement. This will be the width (W) of your paddle pieces.
Add 1” to measurement of the spacing between the sticks and that will be the length (L) of your paddle pieces.
Cut two paddles out of your plastic lids, using the width (W) and length (L) measurements you calculated.
On each paddle, cut a slit from the mid-point on one length-measured side to the middle (two sides have the (L) dimension; cut from the L/2 point on the edge to the center point of the paddle piece).
Slide the slits of your paddle pieces together so that the middles of the pieces meet, and the two form a single + shape. Use tape to secure and strengthen the paddle.
Mount the Paddle
Slip two rubber bands over the sticks to the midpoint between the bottom of the sticks and the bottom of the soda bottle.
Mount the paddle by putting it between the loops of the rubber bands so that each side of a rubber band is on an opposite side of the axis of the paddle.
Mount the Outriggers and Launch
For stability, tape a ½ liter water bottle to the outside of each wood stick, on either side of the paddles. These will act as outriggers, and maxize the paddles’ effectiveness.
Wind the paddle counter-clockwise, turning the paddle over the top of its rotation to the right of the “top” of your boat.
Set your boat into a pool or other body of water, and let it go!
What Is Happening Here?
Buoyancy
With lots of air inside, the boat has positive buoyancy and will rise above the water to float on top. With little or no air inside, the boat has a negative buoyancy and will sink under water. Experiment with different amounts of water to adjust how your boat floats int he water.
Outriggers
Outrigger boats are various watercraft featuring one or more lateral support floats known as outriggers, which are fastened to one or both sides of the main hull. Unlike a single-hulled vessel, an outrigger or double-hull vessel generates stability as a result of the distance between its hulls rather than due to the shape of each individual hull.
Potential versus Kinetic Energy
When you wind up the paddle, the rubber band stores energy. This is potential energy, which occurs because the twisted rubber band is not in equilibrium—you have to hold it in place or it will unwind. When you let go of the paddle, the rubber bands unwind to rotate the paddle and push the boat forward. That unwinding is the conversion of potential energy to kinetic energy, which is the energy of motion. The rubber band moving the paddle and the paddle pushing on the water and the boat moving forward are all examples of kinetic energy.
What' Next?
Experimentation
Try different sizes and shapes of bottles for your boat.
Experiment with different materials as your paddle.
Add more paddles or less. Try different sizes and shapes.
Try different lengths and types of materials for your paddle mountings.
Now that you have the basic idea try designing a paddle boat in a program like Tinkercad.
This project first appeared in Make Magazine in June 2013. It was written by Ken Denmead. Ken is the Grand Nagus of GeekDad.com. He’s a husband and father from the SF Bay Area, and has written three books filled with projects for geeky parents and kids to share.
Materials:
- Rubber Bands, Large enough to span the diameter of the soda bottle, and rigid enough to wind up and provide drive. (2)
- 1/2 liter plastic soda or water bottle (2)
- Wooden Sticks (10" - 14" long), "Chop" sticks or simiar thin wooden dowels will work. (2) [optional] you can also use wooden pencils, while not as long they will work, and then wrap tape around them for a neat look.
- Plastic food lids, or other sheet plastic, The plastic lids from coffee cans or large water jug containers are perfect (2) Need enough area to cut two rectagles each with one side just smaller than the diameter of the two liter bottle, and the other side about 3/4" longer.
- Tape, Duct, or other reasonably waterproof tape (1)
- Two Liter Plastic Soda Bottle (1)
- Scissors Can use a craft knife instead
- Ruler
