What’s the Best Design to Float Your Boat?

By Bertina Banks, July 2, 2009

Grade Level

  • Middle School


  • Product Design

Subject Area

  • Mathematics
  • Science
  • Technology

Lesson Time

180 minutes for classroom activities


In this lesson students will draw on their factual understanding of buoyancy and density to design a boat that will float in water while carrying a load. Students will view short videos on buoyancy and boat design. Students will work in collaborative groups to answer the following question:  Should different considerations be taken into account when designing boats based on their destination?  For example: fresh water vs. salt water?  If yes, explain and provide examples.  If no, explain and provide examples. This question will pique student interest in boat design.

National Standards


Students will:
  • connect their prior factual understanding of buoyancy and density to their boat design
  • determine the volume of water displaced by an object placed in water
  • identify that when the mass of water displaced is equal to or greater than the mass of the object, the object will float
  • design a boat that will carry cargo
  • compare various boat shapes to judge cargo-carrying capacity
  • brainstorm and design a model for a boat that floats with a load (the best boat design will carry the heaviest load)
  • present their design
  • incorporate student and teacher feedback into their design



  • computers with internet access
  • modeling clay
  • clear plastic container (the bottom part of a two liter bottle)
  • tape
  • metric ruler
  • balance
  • masses
  • aluminum foil (1 meter)
  • four craft sticks
  • four toothpicks
  • two straws
  • tape
  • glue
  • projector (for viewing movies)


Prior to this lesson it is important to remind students of what buoyancy is and what affects it. Teacher will facilitate discussion based on a video about how boat design has changed over the years.  Students will brainstorm about how their design correlates with its function. Day One: Introduction 1.  Students will watch two videos on buoyancy. 2. Teacher will introduce Web sites that serve as resources to help students to design their boats. Say, “We will watch a brief video to review the principles of buoyancy.  As you watch try to answer the following question: How can I explain what buoyancy is to my nine-year-old cousin?” Show students the video at: https://videos.howstuffworks.com/discovery/6540-mythbusters-lets-talk-buoyancy-video.htm (MythBusters: Let’s Talk Buoyancy, on buoyancy, etc., to be viewed before students design their boats.) 3. Say, “Next we will watch a video that applies the principles of buoyancy.  Pay special attention to the considerations that were made during boat design throughout history.” Show students the video at: https://newali.apple.com/ali_sites/ali/exhibits/1000813/ (Note: Teacher may use entire video or choose sections depending on the length of the class; a summary of the narration is listed below: a) Opening to 7:10--Introduction b) 7:10 to 29:24--Science teacher Dr. Barbara Hagerman takes students through a lesson on the scientific principles of buoyancy, stability, displacement, and ballast. Information on Archimedes and questions from students are also included. c) 29:24 to 50:45--The scientific principles discussed in the previous section are put into practical application as members of the Discovery Expedition discuss the purpose and design of their replica pirogues and keelboat. Video of their construction and use on the river is included along with questions from students. d) 50:45 to 1:05:07--We are joined by Ike Hastings of the American Sternwheeler Association who discusses the purpose and design of sternwheelers.  Images of construction and operation of sternwheelers are included as are questions from students. e) 1:05:07 to End—Final questions from students, information from boat builders on how they combat the prospect of a “waterlogged” boat, summary of science learned.) 4. At the close of class students will discuss what they learned about buoyancy and ship design. Day Two: Design Challenge (Note: Some of Day Two’s lesson may run over to Day Three.) 1. Say, “You are all designers. A thrifty cargo shipper is your client.  You have been asked to design a boat that will carry cargo made from very simple materials.  Here are the rules of the game:
  • You may use only the materials listed to build your boat.
  • You may omit only one item from the listed materials. All others must be included.
  • Your boat may be no larger than 50 cm in any dimension.
  • When testing the boats, the last mass added to the boat (the one that makes it sink) must be removed from the boat before totaling the mass that the boat held.
2. Place students into small groups to brainstorm design ideas (provide large chart paper). 3. Students will design and build their boat. 4. Building and testing the designs.  Say “Now you will test to see if your boat can carry cargo.” a) Mass (or weigh) your boat that you designed on a scale and record the number in your data table. b) Mass one penny and record this number in your data table. c) Estimate how many pennies can be loaded in your boat without sinking the boat. Record this amount in your data table. d) Place your boat in a large container of water. See if it floats! If not, reshape it and try again. e) Place one penny at a time into the boat until you reach a point where you add a penny and the boat sinks. (Hint: Remove the last penny and then count the remaining pennies in the boat and multiple this number by the mass of one penny. Add this number to the mass of the boat and record in your data table. See attachment.) 5. Say, “Your client the cargo shipper wants to be assured that your boat can carry a load.  Therefore you must demonstrate that your boat can carry clay as well as pennies.” a) Put a strip of tape on the outside of the container from top to bottom.  This will be where you mark the changes in water level. b) Determine the mass of one of the objects you will use to add weight to your boat. Record this mass in the data table. c) Fill the container two-thirds full of water. Make a mark on the tape strip on the outside at the water level. d) Make a ball of the modeling clay.  Determine the mass of the clay ball.  Record the mass of the clay in the data table. e) Drop it into the water.  Mark the new water level on the tape.  Use the ruler to measure the change in water level.  Record the water level change in the data table. f) Remove the clay ball.  Brainstorm with your group to design a shape from the clay that you think will float and hold the most weight.  Sketch the shape.  Reshape the clay.  Be sure to use the same amount of clay.  Put your new clay boat in the water.  Mark the water level.  Measure the change and record. g) Predict how many pieces of cargo your boat will hold.  Record your prediction in the data table. h) Test your prediction by adding cargo pieces to your boat.  Each time you add a piece mark the change in water level on the tape strip.  Measure and record the change in water level.  Add cargo pieces until the boat sinks.  Dry your clay and weights.  Return the materials. i) Graph the data you have recorded. Day Three: Present and Reflect 1. Students will present their design to the class explaining the amount of load they were or were not able to carry.  If students modified their design this should also be explained to peers and teachers. Teacher will facilitate reflection by using the following questions: a) Did some boat designs perform better than others (according to the data?) b) How is the winning boat designed? Draw a picture of it. Why do you think it could hold more pennies? c) Did how you loaded the pennies on the boat make a difference?  What is the best technique for adding pennies to a boat? d) How did your estimate and actual number of pennies compare?


The teacher will listen to and observe students as they work in small groups and individually. The teacher will evaluate the students using the analysis questions listed above for Day 3.

Enrichment Extension Activities

This lesson can be extended by students answering the following question:  How many grams of water does your boat plus pennies displace when your boat is floating at maximum load capacity? Design an experiment to find out. Or  students can complete the “floating or sinking” activity: a) Find twenty items from your environment (at home, in your classroom, or outside). b) Sort the items into two separate piles; those you think will sink and those you think will float. c) Create a spreadsheet using Excel to record your predictions. Save the spreadsheet according to your teacher’s directions. Predict which items will sink and which will float. Record your predictions. d) Get a large container of water and test each item one at a time, by placing them into the bucket/bowl of water. Place a check mark by those items that you predicted correctly. Questions and Analysis: a) What do you notice about items that float? What do they have in common?  What is different? b) What do you notice about items that sink? What do they have in common?  What is different? c) Did any items seem to both float and sink? d) Can you modify any of your collected items that sank and make them float? e) Can you modify any of your collected items that floated and make them sink? f) What conclusions can you make about what sinks and what floats from your observations so far?  

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