This can be a multi meeting project or good if you have a long period of time to fill.  Also a great project while camping to fill an afternoon.

Find some information on how boats float in water and discuss with the group.

Find some information on how sailboats move using only wind power and discuss with group.

Explain to group that they are going to make a boat that will need to float and be wind (breath) propelled through water.  Provide materials to make their boat and let them choose what will be the best design and placement.  The boat should have a base of some sort, a “mast” with a paper sail.  They can decorate their boats if they like and probably should add at least something to distinguish the boats from each other.

Boats can be carved out of styrofoam, cut out of wood, built out of cardboard, or created from recycled items like juice boxes.

Two at a time put the boats in the water and at the starting sound use the straws or rolled paper to blow the boats from one side of the water to the other.

First one to the other side wins.  Keep going until there is one final winner if your group is competitive.

Talk about why the winning boat won,  what were some problems with the other boats that kept them from going as fast or straight or made them sink.