STEM Camp

[uniKorn]

Hello all!
I am helping run a STEM camp and one activity we want to do is a tinfoil boat float, if you do not know what that is, please reference this [url="http://www-tc.pbskids.org/fetch/games/activities/pdf/FETCH_FloatMyBoat.pdf"]

We are trying to put a fun twist on the activity to make it more challenging for the kids that have already done it, if you have any ideas please let me know!
As a side note, the kids we are working with are in grades 5th-8th and we want to avoid using potentially hazardous material.
Thank you!