Engineering Boats

In this unit, students investigate what makes an object float or sink, exploring the science phenomena of properties of objects that float and sink. This page is a high-level extract of the last lesson in 2nd grade that has students applying their knowledge about the relationship between an object’s properties and its ability to float. Students take on an engineering challenge in which they use limited materials to design a boat that floats holding 50 pieces of cargo (marbles).

Science Background for Teachers:

The science background gives teachers in-depth information about the science phenomena being studied in this unit about density and boats. 

All boats have a hull, which includes the part of the boat that goes underwater as well as the part in the middle that is hollowed out where people and cargo go. There are different hull shapes, including a flat-bottom hull and a round-bottom hull.

Some shipbuilders leave room for large pockets of air in the boat’s bottom half to make it less dense. Air makes objects less dense, which helps them float. Modern boats are usually built of metal or fiberglass, but they can also be built from wood, plastic, or a variety of other materials.

In addition to a boat’s materials and shape, how the cargo is distributed also affects the boat’s ability to stay afloat. Too much mass on either end could tip the boat, causing water to spill over the side. This would change the boat’s round-bottom hull center of gravity and the amount of water it displaces, and thus the upward force of buoyancy.

Supports Grade 2

Science Lesson: Engineering Boats

In this lesson, students take on the role of engineers to design and build their own boats with limited materials that floats holding 50 pieces of cargo. They test multiple iterations of their prototype and discuss which design works best based on the evidence they gather.

Science Big Ideas

    • Engineers use what they know about what makes an object float or sink to design boats that can carry different amounts of cargo. 

Sample Unit CTA-2
Discover Complete Hands-on Screens-off Core Science Curriculum for K-8 Classrooms

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Science Essential Questions

  • How are boats different from other vehicles, including student propeller cars from the last unit?
  • Why is it important for boats to float well?
  • What can affect a boat’s ability to float?
  • What kinds of things do engineers who design boats need to think about when planning their design?
  • How does density affect a boat’s ability to float?

Common Science Misconceptions

Misconception: All big objects sink, while little objects float.
Fact: The most important factor in whether an object floats or sinks is its density. An object’s density is determined by the materials that make it up and its volume.
Misconception: The shape of a boat is unrelated to how well it can stay afloat.
Fact: A boat’s shape plays a major role in how buoyant the boat will be. Other factors that influence buoyancy include size and the materials of the boat.

Science Vocabulary

Density : a property of matter; the amount of matter packed in a certain amount of space

Float : to stay above the surface of water or another fluid such as air

sink :  to drop down in water or another fluid such as air

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Density and Shape

The shape of an object also affects how well it floats. Boats are a good example of this. Boats carry people and cargo on the water. There are many kinds of boats.

Some boats are large. Cruise ships carry thousands of people. Some boats are small. A canoe carries one or two people.


Shape of a Boat

The body of the boat is called the hull. The hull includes the part of the boat that goes underwater. It also includes the part in the middle that is hollowed out. This is where people and cargo go.

There are different hull shapes. One shape is a flat-bottom hull. Another shape is a round-bottom hull.

Even though the hull can be different shapes, all boats have a large surface that touches the water

Gravity pulls down on objects in the water. This is the weight of an object. It pushes some of the water out of the way. In response, the water pushes back.

The more of the boat that touches the water, the more water it pushes out of the way and the more the water pushes back. This helps the boat float.


Hands-on Science Activity

For the hands-on activity in this lesson, students are presented with a scenario and pick out information from it to help them define a problem that they will create a prototype to solve. Students then review the solution criteria and constraints before using the engineering design process to prototype a solution. Once students build their prototype, they test it to determine how well it solved the problem. Students use the data they gather from their first prototype solution to improve their second prototype so that it better solves the problem. They repeat this process with their third prototype. Students then evaluate their prototypes to explain which prototype best solved the engineering problem given the criteria and constraints from the scenario.

Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

  • Vocabulary Check
  • Lab Checkpoints
  • Concept Check Assessment 
  • Concept Map Assessment 
  • And More...


Science Standards

See How KnowAtom Aligns to NGSS Science Standards

Discover hands-on screens-off core science curriculum for student centered K-8 classrooms. KnowAtom supports classrooms with all hands-on materials, curriculum, and professional development to support mastery of the standards.

Download the Alignment to NGSS

Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.