Homemade Floating Boats To Hold Pennies I Need To Build A Styrofoam Boat For A School Project.?

I need to build a styrofoam boat for a school project.? - homemade floating boats to hold pennies

The boat to swim and have 5 marbles. We can use almost anything to make the boat, but it must be made at home. I fear that if the balls (on the right side of school early flotation added) are stationary can not change too much weight and capsize the boat. Suggestions? Thank you.