Here's a video of it in action!
https://youtu.be/EtTMcURcMaU

A boat that you can use to propel itself using a balloon.
The entry on the top of the boat fits a standard balloon but should be ziptied for best use

You can also scale the model down to fit on your printer, but then you will almost definitely need to ziptie the balloon on.

Once the balloon is on and snug, you can blow through the hole in the back to fill it up.

Once put in the water, it will move itself forward.

If you have anything that can be used to add weight (like BBs) I recommend gluing those in the back of the model's hull--before the deck of the boat has started to print. This will make sure more of the back hole is underwater when it is propelling.