Hands-on Activity Clay Boats

Quick Look

Grade Level: 7 (6-8)

Time Required: 1 hour

Expendable Cost/Group: US $0.75

Group Size: 1

Activity Dependency: None

Associated Informal Learning Activity: Clay Boats

Subject Areas: Chemistry, Measurement, Physical Science

NGSS Performance Expectations:

NGSS Three Dimensional Triangle


Students use a small quantity of modeling clay to make boats that float in a tub of water. The object is to build boats that hold as much weight as possible without sinking. In the process of designing and testing their prototype creations, students discover some of the basic principles of boat design, gain first-hand experience with concepts such as buoyancy and density, and experience the steps of the engineering design process.
This engineering curriculum aligns to Next Generation Science Standards (NGSS).

A photo of whitewater rafting on a river in Oregon.
Students quickly find that when they mold clay into shapes resembling this inflatable raft, the clay floats much better than if it is molded into shapes resembling more typical boat hulls.
Copyright © U.S. Bureau of Land Management http://www.or.blm.gov/roseburg/images/Recreation/rafting2.jpg

Engineering Connection

Density is an important property in many materials engineering applications. Building clay boats to hold as much weight as possible is a classic engineering design problem.

Learning Objectives

After this activity, students will be able to:

  • Describe a means to make a material that is denser than water (modeling clay) float.
  • Describe the steps of the engineering design process used to create a dense but floatable object.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS Performance Expectation

MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved. (Grades 6 - 8)

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This activity focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Alignment agreement:

Models of all kinds are important for testing solutions.

Alignment agreement:

The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

Alignment agreement:

  • Students will develop an understanding of the attributes of design. (Grades K - 12) More Details

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  • Students will develop an understanding of engineering design. (Grades K - 12) More Details

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  • Evaluate designs based on criteria, constraints, and standards. (Grades 3 - 5) More Details

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  • Design involves a set of steps, which can be performed in different sequences and repeated as needed. (Grades 6 - 8) More Details

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  • There is no perfect design. (Grades 6 - 8) More Details

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  • Apply the technology and engineering design process. (Grades 6 - 8) More Details

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  • Understand the structure, classifications and physical properties of matter. (Grade 6) More Details

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Materials List

  • non-hardening modeling clay, 1/2 stick (~2 ounces or 50-60 grams) per student, plus some extra in case any get too wet to mold
  • tub of water, at least 6 inches deep, per four or five students
  • 100+ large washers to use as weight for boat testing, such as 1.5-inch fender washers; available at hardware stores
  • paper towels (dozens)
  • roll waxed paper
  • masking or transparent tape

Worksheets and Attachments

Visit [www.teachengineering.org/activities/view/duk_float_mary_act] to print or download.


Very little introduction is required for this fun activity. In fact, this activity makes a good introduction for the associated lesson. However, if students did not already complete the Determining Densities activity portion of the Floaters and Sinkers lesson, introduce this activity by showing the class a half-stick of modeling clay and asking if they think it will float or sink in a beaker of water.

After students make their predictions, drop the clay stick into a beaker of water to demonstrate that the clay sinks. Then write on the board, "Engineering desgn challenge 1: Create an object out of clay that floats." (Then continue with the activity, as described in the Procedures section.)


With the Students: Challenge 1 (5-10 minutes)

  1. Have each student tape a sheet of waxed paper (~18" long) on the surface of his or her work station. This makes cleanup much easier, since wet clay gets very messy.
  2. If you have not already done so, write on the board, "Engineering design challenge 1: Create an object out of clay that floats." Note that the wording specifies the creation of an object as opposed to a boat. In fact, students who attempt to mold their clay into the shapes of familiar boat hulls will quickly realize that these shapes are less than ideal – at least for clay.
  3. Give each student a half stick of modeling clay, and place several tubs of water throughout the classroom. Let students know they can test their objects as often as they like, but advise them to pat the clay dry after testing and before shaping it into a new design.

With the Students: Challenge 2 (15-20 minutes)

  1. As students successfully complete Part 1, challenge them with a new goal. Write on the board, "Engineering design challenge 2: Design an object out of clay that can carry the largest load of washers possible." Show students the washers that will be used to make up the load.
  2. As students work, encourage them to continue making improvements every time their boats sink. Students may become competitive and want to declare a winner, and it is quite possible that a tie for the number of washers supported will occur. Should this happen, use a balance to determine the actual mass of the washers held, since slight variations exist in the masses of individual washers.


buoyancy: The ability to float in a liquid (or rise in a gas).

density: Mass per unit volume of a substance at a given pressure and temperature.


Design Process Reflection: Ask students to each write a paragraph describing in their own words the steps of the engineering design process that they followed as they created something new and unique—a clay object that floats in water.

Making Sense: Have students reflect on the science concepts they explored and/or the science and engineering skills they used by completing the Making Sense Assessment.

Investigating Questions

Lead a class discussion by asking questions referring to experiences students had while designing their floating clay objects. Example questions:

  • What did you notice while building your boats?
  • Why did you make the changes you made?
  • What boat designs seemed to work best? What is it about these designs that made them successful?
  • What boat designs did not seem to work well? What is it about these designs that made them less successful or unsuccessful?
  • How did your boat design change throughout the activity?
  • What steps of the engineering design process did you use as you solved these design challenges? (Understand the problem > brainstorm different designs > select the best design > make a plan > build a prototype > test the prototype > improve the design until it meets the problem objectives to your satisfaction. If students require some guidance in answering this question, point out that each design they tested reflected a design idea for how the clay might be made to float; each test produced data, either the boat sank or floated; the results from the test provided new information that they used to make improvements and modify the design, which was tested again, etc.)

Troubleshooting Tips

If students do not dry their clay adequately between tests of "seaworthiness," the clay may become too wet to work with. Have some extra clay on hand to give to students if their original portions becomes unworkable.

Activity Extensions

Expect students to have a number of observations about the shapes of successful boats, and express some curiosity about "real" boats and their design features. Assign students conduct library and Internet research to find out about boat designs and how they affect performance. Information on this subject is also covered in the Lesson Background & Concepts for Teachers section of the associated lesson.


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More Curriculum Like This

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What Floats Your Boat?

Students use modeling clay, a material that is denser than water and thus ordinarily sinks in water, to discover the principle of buoyancy. They begin by designing and building boats out of clay that will float in water, and then refine their designs so that their boats will carry as great a load (m...

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© 2013 by Regents of the University of Colorado; original © 2004 Duke University


Mary R. Hebrank , project writer and consultant

Supporting Program

Engineering K-PhD Program, Pratt School of Engineering, Duke University


This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

This activity was originally published, in slightly modified form, by Duke University's Center for Inquiry Based Learning (CIBL). Please visit http://ciblearning.org/ for information about CIBL and other resources for K-12 science and math teachers.

Last modified: December 5, 2020

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