Build a boat

In this activity, students design and build a boat out of aluminum foil to test how well it floats and how much weight it can carry. Through trial and error, they explore the concept of buoyancy and learn how boat shape and volume affect water displacement and stability.

Transcript

In this video, we will design and build a boat with aluminum foil to test how well it floats and how much weight it can carry. For this demonstration, you will need a small tub or container with water, pre-cut sheets of aluminum foil, and a large amount of small weights. In this case, the speaker is using paper clips, but you can also use pennies.

Let us begin our activity by testing how well a single sheet of foil floats and how much weight it can hold. For now, the speaker will not worry about shaping it into a boat. The speaker starts placing paper clips on top of the foil and watches how long it takes to sink. As you can see, it does not take very long before water starts coming in and the foil sinks.

Now, let us see if we can design a boat that stays afloat and carries more weight. The speaker begins shaping the foil into different boat designs. Bend and fold the sheets to create the shape you want. Think about the width, height, and overall form of the boat and how that might affect sinking or tipping over. Wide shapes usually float better because they displace more water, but you can also get creative. Your design does not need to look like a traditional boat. For example, the speaker is making a flatter version and bending up the edges so water does not spill in. At first, it may not look like a normal boat, but it will still do the job of floating.

After finishing your designs, it is time to test them. Gently place your boat into the tub of water. Does it float on its own? If it tips or sinks right away, reshape it until it stays afloat. Start adding weights a few at a time. Watch closely; is the boat tipping or is water starting to come in? If it is still holding, keep adding the weights until it finally sinks. Be careful where you place the weights; too many on one side can throw off the balance and cause it to sink faster.

Thanks to its shape, size, and height, this boat can hold a large number of paper clips before sinking. But let us see if the other designs can do the same. This design is much wider, but it lacks depth. It can hold many paper clips if the weight is spread evenly, but it is more likely to sink if one side is heavier since the low edges let water rush in. When the other two designs are tested, they do not stay afloat for long. Because they are smaller, it is harder to distribute the weight evenly, and they tip over more quickly.

How well a boat floats and how much weight it can carry depends on its size, shape, height, and weight distribution. All of these factors affect water displacement. The more water a boat displaces, the greater the buoyant force. In the test, flat, wider designs displaced more water and stayed afloat longer, while small, compact shapes sank more easily. Deeper designs also had a better chance of holding their load.

This demonstration shows the same principles real marine engineers consider when designing ships: buoyancy, stability, and efficiency.

For more activities and resources like this, visit the NOAA Office of Education website.

NOAA activity tutorial: Build a boat

Grade range: 6 – 12
Setting: Classroom, outreach events, or at-home activity
Estimated time: 30-45 minutes

🌊Background: What makes things float?

When you place an object in water, gravity pulls it downward, pushing some of the water out of the way. This is called displacement. The displaced water creates pressure in all directions, and because pressure increases with depth, the water below pushes up more than the water above. This difference in pressure creates an upward force called buoyancy. According to Archimedes’ Principle, the buoyant force is equal to the weight of the water displaced by the object.

Whether an object floats or sinks depends on:

Volume: Volume is the 3-dimensional space that an object takes up. More volume means more water is displaced, which increases buoyant force.
Shape: A wide or hollow shape can displace more water than a compact or dense shape.
Density: Density is mass divided by volume. If two objects are the same size, the heavier one is denser. If the object is less dense than water, it will float.

In addition to buoyancy, boat engineers must consider stability and friction when designing vessels for different purposes: speed, cargo, or exploration.

Learn more about ships in our resources below!

🧪Materials

Pre-cut sheets of aluminum foil
Tub or large container of water
Small weights: paper clips or pennies
Wooden skewers (optional; to make masts)
Paper squares (optional; to make sails)

🧭Instructions

Give students 1-2 sheets of foil to fold, shape, and construct their own boat. Encourage them to think about the boat’s width, height, and shape to maximize buoyancy and stability. Optional: Add a sail using skewers and paper squares.
Gently place the boat in the tub of water to check if it floats on its own. Adjust if necessary before adding weight.
Carefully place paper clips or pennies one at a time into the boat.

Does the boat stay afloat or start to sink?
Does the water come in?
Where is it strongest or weakest?

If the design fails, encourage students to rebuild and test again.

Optional challenges:

Whose boat can carry the most paper clips before sinking?
Use a larger tub and portable fans to see whose boat sails the fastest.

💡What is happening?

When the boat is placed in water:

Gravity pulls it down, and in doing so, pushes some water out of the way (displacement).
That displaced water pushes back with a force called buoyancy, which acts upward.
The more water the boat displaces (larger volume), the greater the upward force.
If the upward buoyant force is greater than or equal to the weight of the boat and its load, it will float.

Boat shape matters:

Flat, wide shapes displace more water, increasing buoyancy.
Dense, small shapes may not displace enough water and might sink.
Friction (drag) also matters for movement. Smooth, narrow hulls are faster.

🔍Scientific connection

This challenge demonstrates real principles of fluid dynamics, density, and engineering design.

Foil boat: a floating object
Water tub: simulates an ocean or lake environment
Weights: simulate cargo

The experiment reflects what real marine engineers consider:

Buoyancy (can it float?)
Stability (can it balance weight?)
Friction (can it move efficiently?)

Just like NOAA ships, successful boat designs must stay afloat while carrying instruments, people, or cargo.

⚠️ Safety notes

Supervise use of water to avoid spills or slipping.
Remind students not to drink or splash the experiment water.
Avoid sharp foil edges.