Fun and easy to build balloon powered pontoon boat. Great STEM/STEAM activity. Kids will giggle for hours.

Supplies

Balloon
2 Empty Water Bottles
16" Copper house wire
Cork
2" piece of Straw
Rubber band (that will fit gently around 2 water bottles

Tools

Drill
Drill Bits
Pliers

Step 1: Pontoons

Connect the 2 water bottles near the base with the rubber band.

Step 2: Assemble Air Outflow Tube

Drill a hole through the cork for the straw. The hole should fit the straw snugly, mine was made with a 7/32" drill bit. Mount the cork in a vise or clamp before drilling and follow basic drilling safety. Insert the straw halfway into the cork.

If you want a slower boat you can drill a smaller hole all the way through and only drill the straw diameter halfway through the cork.

Step 3: Connect Outflow Assembly to the Pontoons

Wrap the middle of the copper wire a couple of times around the cork. Then twist the ends around the bottles near the caps. Bend the whole assembly gently so that the straw end is just near where the water level will be (see picture).

Step 4: Attach Balloon Engine

Attach the balloon. It's tricky to attach once inflated without letting air out, but it is possible. Another option is inflating the balloon through the straw without disconnecting the balloon. This works very well if you have a decent seal between the straw and cork. Last option is to use a pump if you prefer not to put something from a kiddie pool in your mouth. A simple manual bike pump with the "air mattress" style cone attachment in place of the needle or a cheap party/animal balloon pump works also.

Step 5: Launch and Play

Set the boat in the water gently and adjust the cork assembly to keep the balloon centered on top before letting go. With a full straw diameter drilled through the cork this boat lasts just over 40 seconds of run time. With a hole about half the diameter it bubbles and putters slowly for about 2 minutes.

Try not to let the balloon get wet. The wet part will keep flopping and folding in the water and stop the boat. Keep a couple dry balloons on hand.

Have fun!

Step 6: Modifications

Try different diameter holes in the cork to manage top speed and run time.

Try drilling at an angle or use a flexible "bendy" straw for steering.

Try adjusting the straw depth in the water to optimize performance.