Adrienne wanted to keep her boat as simple as possible.

She started with two floats, like everyone else, then realized that one would suffice. Once she had one float, the larger pair of rubber bands was replaced with a single smaller band, then filled the motor compartment (juice bottle) with water and set a session record with her pared down design.

Jeremy noticed that the PVC motor solution (orginally intended to be slung under the bottle) would fit inside the mouth of the bottle.

In this case, side floats were required to keep the boat from rotating. This worked (like in the first side-float design posted earlier) since the PVC weighed down the rear of the boat and kept the propeller submerged. The high angle of attack also let the bow of the boat ride up on the water and succesfully break the beam sensors on both ends of the track.

Despite all previous failed attempts to get a boat with side floats working, this guy managed it.

The critical issue is that the propeller is half out of the water. With one blade pushing on the water and one on the air, it generates a lot of off-axis thrust which (usually) turns the boat into the wall of the track. Furthermore, the half-in / half-out propeller throws a huge spray of water as it chugs down the track. It’s a real crowd pleaser.

Now that the Maker Faire is over, you’d think I’d be sick of juice bottle boats. But I keep doodling new designs…

I had really hoped to try some radical designs during the faire, but with the volume of kids we had coming through, we had to keep things pretty simple. Nonetheless, I kept trying to get one of the older kids to build the “Auger Drive” - James was the only one willing to take the risk. In this radical departure from conventional boat-building, the whole bottle is used as a propeller. The problem is that the alignment of the fins is critical to success - too much angle of attack and it starts to act like a paddlewheel that moves the boat sideways, not enough and it spins to fast and produces little forward motion.

Here’s an idea with two fins that are used like fish tails. I could tell from making the sketch that it was going to be too complicated to build at the faire.

By cutting the bottom off of the bottle and putting a fan propeller inside, it seemed possible we could make a pretty good turbo-jet. The hard part here is getting baffles in place to keep the pressurized water from leaking back around the fan.

Mounting the propeller on the cap all those times and only just now did it occur to me that we could probably make a helicopter.

One of the ways that Tinkering School stays interesting for me is that we don’t overly pre-test the ideas - that way the kids participate in the experimentation. So, it took us two sessions to get the kinks worked out of the boat formula, but once we got it working, the kids lined up to make boats.

We had to put up a sign-up sheet about halfway through the morning on Saturday. From then on we were booked up for the rest of both days.

Check out Julie’s action shots on Flickr. We’ll get some video up in the next day or so.