Boat Lab
The foil boat challenge is in almost every science and engineering unit, and almost nobody keeps the numbers: real foil leaks at a crease, a splash floods the boat, and the salt water round gives three more pennies, which is inside the noise. Boat Lab holds all of that still, keeps every trial in a table, and shows the water the boat pushes aside.
Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work. mytekDev is also available from the Google Workspace Marketplace, so your school's Google admin can install it for everyone.A first lesson: One period: guess, load the first boat until it sinks, fold a better one from the same sheet, crumple the sheet into a ball, and load the best boat again in very salty water. Then compare the table.
Set up a free class Share to Google ClassroomWhat a student actually does
A clear tub of water sits on a table, with a square of kitchen foil beside it, 15 cm on a side and just under a gram. The student drags the fold lines in from the edges to choose how tall the walls are and how big the floor is, presses Fold it, and the walls rise one side at a time and the boat drops onto the water. They type a guess, then add pennies, one at a time or by tens, or tap inside the boat to put a penny exactly where they want it. Each penny sinks the boat a little lower, and a ruler on its side shows the water line climbing toward the rim.
When the water reaches the rim it pours in, the boat goes down and the pennies spill across the bottom. The table records the boat, the water, the guess, the pennies it held and how it sank: over the rim, or leaned and flooded when the pennies were bunched on one side. The student folds the same sheet another way and tries again. A low wide boat and a tall narrow one hold very different counts, and the best wall turns out to be about a sixth of the sheet.
Crumple it squeezes the same sheet into a tight ball, and it sinks at once. A measuring cylinder beside the tub catches the water each boat pushes aside: a loaded boat's water weighs exactly what the boat and its pennies weigh, and the ball's weighs less than the ball. Then the student pours salt into the tub and loads the best boat again. A dish, a canoe and two hulls fold from the same sheet; washers, gram cubes and marbles can replace the pennies; the water can be the sea, very salty, the Great Salt Lake, the Dead Sea or cooking oil; and waves can roll across the tub, where low boats suffer most. Older students can open Code and write the lab's rules themselves: how deep a boat sits, how many pennies a box holds, and the best wall for any sheet.
Sea water is only a little heavier for its size than tap water. The same boat with 80 pennies sits about half a millimeter higher in it, so the app shows the water line ten times bigger, with the old line dashed.
What they are learning while they work
Nothing here is presented as a lesson. This is what the activity is made of.
| What the student does | What it is |
|---|---|
| Watches the cylinder fill as each penny goes in | Displacement. A floating boat pushes water out of its way. The water it pushes aside weighs exactly as much as the boat and everything in it. |
| Sees the two arrows stay the same length until the last penny | Balanced and unbalanced forces. While the boat floats, its weight and the water's push up are equal. The last penny makes the weight bigger than the most push the boat can get, and it moves down. |
| Crumples the same foil into a ball and watches it sink | Why shape matters. The ball and the boat weigh the same. The boat takes up much more room below the water line, so it can push aside much more water. It is the room, not air, that holds it up. |
| Folds taller walls, then shorter ones, from the same sheet | Volume under a fixed budget. Taller walls use up foil and shrink the floor. The boat holds the most when the walls are about a sixth of the sheet, and walls a little lower lose very little. |
| Taps all the pennies into one corner | Stability. A load on one side tips the boat until that rim reaches the water first. Spread out, the whole rim reaches the water together and the boat holds far more. |
| Loads the same boat in tap water and in very salty water | Density of a liquid. Salty water is heavier for its size, so the boat pushes aside less of it to hold up the same load. Very salty water holds about a fifth more pennies; sea water only a few more. |
| Writes a guess before every trial and compares it with the count | Predict, test, redesign. The engineering design loop: a criterion (hold the most), a constraint (one sheet), fair tests that change one thing, and failure points to learn from. |
How to tell whether it landed
Ask, and let them show you. A student who has understood it can answer these without help.
- The pennies float in the boat but sink on their own. Why?
- The ball and the boat are the same foil. Why does one sink and one float?
- How much water did your boat push aside just before it sank, and how do you know without measuring it?
- Your tallest walls held fewer pennies than walls half as tall. Why?
- Why did bunching the pennies on one side sink the boat sooner?
- Why does the same boat hold more in salty water, and why only a few more in sea water?
Use it in your subject
Not a technology class? Then the app is how students show what they learned in your unit. More projects for every subject.
Elementary engineering and science
3-5-ETS1-1 to 3 most directly: a criterion, a constraint, fair tests and failure points. 3-PS2-1 for balanced and unbalanced forces, kept qualitative: at the grades 3 to 5 level the arrows have no numbers. NGSS 5-PS1-3 keeps density out of grade 5 assessment, so that level says heavier and lighter for its size and shows no density numbers.
Middle school engineering and physical science
MS-ETS1-1 to 4, and MS-ETS1-4 most of all: a model that generates data for testing and improving a design. MS-PS2-2 for the two vertical forces and the moment they become unbalanced. No NGSS middle school expectation names buoyancy; this is where the idea lives.
State density standards
Texas 5.6A, relative density with water as the reference, and 6.6D, comparing density relative to various fluids; Texas 6.7B, net force in a vertical direction from diagrams; Massachusetts 6.MS-PS1-7(MA).
High school physical science
The high school level writes the buoyant force out as rho g V in SI units, draws the boat cut across with its center of gravity, center of buoyancy and metacenter, and graphs what the sheet holds at every wall height so the top of the curve shows.
Practical notes
- AgesGrades 6 to 8 are the home ground. A grades 3 to 5 level keeps two shapes, two waters and new pennies, with no density numbers and no newtons. A high school level adds the forces worked out and the boat's steadiness.
- TimeOne period to guess, sink, redesign, crumple and try salt water. A second for the other shapes, Real foil, the puzzles and the sheet.
- EquipmentA computer or Chromebook with a modern browser. Nothing to install. A projector works well for the ball and the boat side by side. For the real thing: kitchen foil, a tub of water and a jar of pennies; the app prints a build sheet.
- CostFree. The app has no paid tier.
- PrepAbout ten minutes: load the first boat until it sinks, fold a boat with 2.5 cm walls and load it, crumple the sheet, and try very salty water, so you know the counts students will see.
- In a groupOpen Setup in the app's header: the level, which sheets, shapes, waters and cargo are on the shelves, whether the foil is ideal, real or the student's choice, whether a guess is required before the first penny, the puzzles, the sheet's questions, and an answer key to print.
For co-ops, microschools, and classrooms
Set it up once in Setup and hand the project out as the starter; the setup travels with it. Every count is exact, so two students who fold the same boat get the same number, and a class can put its best boats on one table. Real foil, when you want it, comes in a little under the ideal boat, the way real foil boats do.
Common questions
Is it free?
Yes. Boat Lab has no paid tier, and it can be tried right on this page without an account.
Does it replace building real foil boats?
No. Building them is worth doing, and the app prints a build sheet for it, with a column for what the app said. The app adds what a tub cannot: the same boat tested twice the same way, the water it pushes aside weighed, and salt water strong enough to see a difference.
How real are the numbers?
A new penny is 2.5 g and an old one (before 1982) 3.11 g. Kitchen foil is 0.016 mm thick, so a 15 cm sheet weighs 0.97 g. Tap water is 0.998 g in each cubic centimeter, sea water 1.025, and water with as much salt as will dissolve 1.197. The boat floats where the water it pushes aside weighs what it weighs, which is Archimedes' principle, and it leans by the same rule naval architects use for a box-shaped hull.
Why does my real boat hold fewer pennies than the app says?
Real foil leaks at its creases, its walls bend, pennies get dropped, and the water sloshes. In calm water the app keeps the water still, and the foil stays stiff and dry. Switch on Real foil and it adds leaks, slumping walls and pennies that do not always land where you aim. Those are our own rules: nobody has measured how much a foil boat leaks, and we found no published classroom counts to compare against.
What does it simplify?
Every shape has upright walls, so a dish is a short round pan and a canoe is a six-sided box with pointed ends. Pennies set down spread out are treated as perfectly balanced. The lean is worked out as if the whole floor stays in the water. Surface tension is worth about one penny on a 10 cm boat and is left out, and so is the water's temperature, which changes the count by less than one penny on a small sheet. Waves follow a rule of our own: a wave washes over once the rim sits less than half a wave above the still water line.
Why do the pennies sink when the boat fills with water?
Once the boat is full, only the foil and the pennies themselves push water aside, and they are heavier for their size than water. A boat of gram cubes would float awash in very salty water, because the plastic is only a little heavier for its size than tap water, so the app keeps gram cubes out of water that salty and says why.
Does it work on Chromebooks?
Yes, in the browser, with nothing to install. It is drawn on one canvas, and a 12 inch boat with 800 pennies draws only the pennies that can be seen.
Still have a question? Ask us, and a person will write back.
Where to go next
Start with Boat Lab
Trying it costs nothing and takes about five minutes. An account is what makes the work last.
Boat Lab is one of the making apps on the platform. The tub is 26 by 20 cm and filled to an overflow spout; a 12 inch sheet gets a bigger tub. Every count with ideal foil is exact, and the app's test suite checks them against counts worked by hand.
Page last reviewed November 2026.
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