Unschooling Snapshots: boat building
The kids spent one day last week at the pond building styrofoam boats and floating them on the pond. What did they learn? Engineering, design, planning, how and why things float, balast, how sails work, how to use tools safely etc. etc. etc.
I highly approve of this project! ;~) LOL Lots of info on Wikipedia about different types of sails, too.