Project Ideas:

1.  Build a boat that you can ride in.  Start out by designing and testing small boats using sticks and a plastic sheeting skin.  Scale up the final design for human capacity.  Contest judging may be based on low drag or stability.  [These could be made simply, from sticks gathered in the woods and plastic sheeting. Construction outside.]

2.  Putt-Putt boat race.  Make candle/steam-powered boats.  [Boats could be judged on distance or speed, with a multiple round, tournament-style competition http://www.youtube.com/watch?v=RvlM-_glZ_g  http://www.youtube.com/watch?v=a_5FVQbeC6g  ]

3.  Projectile Hang Time Contest.  Design a projectile to achieve maximum time aloft when launched from a large-barreled, pressure-powered gun.  Launch pressure and nozzle opening will be consistent.  Projectile masses and sizes may vary; parachutes are allowed.

4.  Vortex launcher battle.  Create vortex launchers that will knock down a cup at a maximum distance with maximum precision and accuracy.  Intra-class battle; knock over the other class's cups. http://www.youtube.com/watch?v=-VL0M0jmu7k

5.  Naval warfare.  Putt putt boat contestants could also build water guns and attempt to sink their opponents boats.  The boat that makes it the farthest wins.  There could be a mass start where block 1 battles block 2.  A best 3 out of 5 competition would reward sturdy boats.