This How can a ship carry all these taconite pellets and still float? lesson plan also includes:
Groups of two to four work together to design, construct, and experiment with a boat. Each boat must include all of the major parts of a real ship, be less than 12 inches long, and be able to carry a load up twice its own weight in calm and stormy water. They measure the water displacement of the boat and deal with the concept of safe load, so this is meant for middle school science learners. You can use this lesson when teaching them about water displacement or buoyancy.