2 liter with SRBs
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.

Project Steps

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!