Pop-Pop Steamboat
1-2 hours
Ages 11+
What Will You Make?
Build a toy steamer that runs only on heat and the water it’s floating in.
When you picture a steam engine, you likely imagine a giant cast-iron contraption festooned with knobs, valves, gauges, linkages, and wheels. This steam-powered toy boat has no moving parts and needs only a flame and the surrounding water to zip around and make its distinctively happy sound.
My interest in pop-pop boats began when I saw Hayao Miyazaki’s stunning children’s movie, Ponyo. In it, Ponyo and her friend Sosuke sail a scaled-up version of Sosuke’s pop-pop boat around a flooded city. The boat requires only a candle and some water to run.
Once commonplace, these toys have given way to battery-powered plastic. But the pop-pop boat’s underlying principle is compellingly simple and provides the home tinker with endless room for futzing and improvement.
What Will You Learn?
Campers will explore the engineering concepts associated with how steam engines work as well as science concepts of buoyancy and motion. This project also provides the opportunity to use a variety of tools to shape metal including a hammer, tinsnips, a tube cutter, a machinist’s scribe, pliers, and a propane torch.
Build Your Steamboat
Dismantle the mint tin.
Using a small, flathead screwdriver, gently pry the hinges of the Altoids Smalls tin apart and lift away the lid. Save it.
Carefully flatten the stamped hinges of the bottom half by tapping them with a small hammer. If your hammer is too big to fit, you can squeeze in a small brass drift or 3/8″ bolt, and then tap this with your hammer to flatten the hinges.
Prepare the boiler halves.
Circumscribe a line 3/32″ from the top edge of the tin’s bottom half. Scribe a second line 3/16″ below this, 9/32″ from the top edge of the tin.
Cut along the top line with tinsnips, removing the rolled bead from the tin. Notch the corners of the tin, cutting 90° V’s to the remaining scribed line. As tidily as you can, fold the tabs along the remaining line so that they all point inward toward the center of the tin. Lineman’s pliers work well for this.
File down the folded corners.
File down the folded corners of the bottom half of the tin until you can press the lid all the way back on.
Take the lid off, flip the bottom over, and scribe a line 9/32″ from one end, parallel to the barcode. Scribe 2 more lines perpendicular to the barcode, 3/8″ in from the hinge and clasp edges of the tin.
Make punch marks at the 2 intersections with a @&&*& punch, and drill 1/8″ holes at each. Sand away the varnish and paint from the area around these 2 holes.
Attach the jet tubes.
Anneal (soften) the copper tube so that you can bend it without kinking it. Copper anneals differently than steel or glass: heat it with a propane torch until you see its surface color change, and then quench it in cold water.
WARNING: Copper conducts heat quite quickly, so use pliers or some other device (not your hand) to hold the tube while you heat it.
Use a small tubing cutter or jeweler’s saw to cut two 6″ sections of tubing. (Don’t use wire cutters, which crush before they cut.) Make sure all ends remain open.
Attach the tubes.
Gently bend the tubes into identical J shapes starting 2½” from one end and curving slightly past 90°. Sand the tips of the curved ends.
Apply flux to the sanded area around the holes in the tin bottom and to the sanded tube ends. Poke the fluxed end of each tube into the tin bottom, just far enough to rest easily in its hole, then solder the tubes in place.
Try to keep the tubes parallel. It’s easy to “sweat” these into position with a propane torch, but if you aren’t confident in your torch skills, you can epoxy the tubes in later rather than soldering (before you cement the lid down!). Make sure the tubes are clear of solder before you go on.
Cut the diaphragm opening.
On top of the Altoids lid, scribe lines 3/16″ in from each edge to describe a “window.” Drill a hole in the center large enough to admit the tip of your tinsnips, then cut out the window. Gently hammer the edges flat and sand off any sharp spots. Sand the varnish off the inside of the lid.
Make the boiler.
Cut the top and bottom off the aluminum soda can, make a vertical cut, and lay the skin of the can out flat on your bench.
Place the Altoids lid rim-down on this aluminum sheet. Scribe around the lid onto the sheet, then cut along the lines with tinsnips to create a leaf of aluminum.
Gradually trim down the edges of the leaf until you can just tuck it into the lid of the tin without it wrinkling. Once you’ve fitted the leaf, pop it out again, taking care not to crease or tear it. Cut or file away any “needles” or other sharp features on the leaf.
Seal the boiler.
Lay out dollops of J-B Weld epoxy and hardener on a disposable surface.
Sand both sides of the aluminum leaf about 3/16″ in from the edges, all the way around, to take off paint and the oxide layer that clings to the aluminum. Quickly, before oxides can re-form, mix the J-B Weld together with a stick and apply it to the inside of the lid. Lay the aluminum sheet inside the lid.
Smear the J-B Weld over the flat flanges you folded into the tin bottom, paying special attention to the gaps in the corners. Press the bottom and the lid together, sandwiching the aluminum between them. Apply J-B Weld all the way around the gap between the lid and bottom, and smear some into the hinge holes in the side of the lid.
If the aluminum leaf looks sunken or gapped around the edges, blow into the copper tubes to push it up — if you have to do this, you’ll push out some of the wet J-B Weld, so look for fresh air gaps. Using a clean, disposable rag, wipe any excess J-B Weld off the surface of the aluminum. Allow the J-B Weld to cure overnight.
Pressure-test the boiler.
Immerse the boiler, put both tubes into your mouth, and blow. If you see bubbles, you have a leak. Patch it with more J-B Weld.
When the J-B Weld is dry, test the diaphragm again: put both tubes in your mouth and suck and blow — the diaphragm should pop down and up. If it’s too tight, loosen it a little by pressing firmly on its center with your thumb.
Fit the motor to your boat.
For a boat, you can use anything small and light that floats and doesn’t catch fire. For simplicity I used a 16oz ham can, but you can make as awesome a boat as you like. You can also fit a rudder to the stern.
Measure the outside distance between the 2 tubes where they bend, subtract 1″, and drill 2 holes to this measurement in the bottom of the boat, equidistant from the center. Your punch will help get these holes started.
Depending on the shape of your boat, fitting the motor in may take a little re-bending of the tubes. Be careful of hard spots in the tubes and be ready to re-anneal them.
You can solder the tubes into your boat to seal them, but it’s easier to just use plumber’s putty or modeling clay, which you can remove to make repairs or adjustments.
Use it.
To make your boat go, you must first prime the engine with water.
Turn the boat over and pour water into one of the tubes until it dribbles out the other tube. You don’t need to fill the boiler completely: just make sure you can hear water sloshing around inside. Hold a finger over the ends of the tubes and lower the boat into the water without letting any water pour out.
Light candles or a spirit (alcohol) lamp, and place them under the boiler. In about a minute, you’ll hear the water boiling into steam.
First, a few bubbles will come out, then the boat will start puttering along in the water, and as the reaction becomes more vigorous, the diaphragm will start its obnoxious song. If the motor stops, blow out the fire, or the heat may damage the seal of the boiler.
WARNING: If you blow down one of the boiler tubes, very hot water can come out the other tube, shooting you in the face with scalding water. Don’t do this — it will hurt.
What Is Happening Here?
Pedigree and Principles
First patented in 1891, pop-pop boats use a candle or other flame to heat water in a small boiler connected to one or more pipes. The pipes run down and back into the water behind the boat; when the water in the boiler turns to steam, it pushes jets of water backward out of the pipes, propelling the boat forward.
The moving water’s momentum makes the steam “piston” overshoot its equilibrium, so the steam quickly cools, contracts, and condenses back into water. This draws cool water back up through the pipes and into the boiler, where the cycle starts again. Because the water sucking back into the tube is incoherent, coming in from all directions, rather than in a directed jet, this intake cycle doesn’t pull the boat backward. (By analogy, you can easily use a straw to blow a small ball of wadded-up paper across a table, but you can’t suck it up the straw unless you’re right on top of it.)
You can think of a pop-pop boat as a reciprocating, steam-driven water hammer, an engine with pistons made of water, or an external combustion pulsejet (see MAKE Volume 05, page 102, and Jam Jar Jet).
A later design (patented in 1916) added a “sound producer” to the boiler, a slightly convex sheet-metal diaphragm that flexes with the expanding and contracting steam. The resulting rattle makes the motor sound more mechanically complex than it actually is, and gives the pop-pop boat its name.
Traditionally these boilers are built with a thin brass diaphragm crimped and soldered into place. Thin-enough brass stock can be hard to find, so I’ve come up with a design that uses castoff packaging instead: an Altoid Smalls tin boiler with an aluminum can diaphragm. Since aluminum can’t easily be soldered, I’ve substituted J-B Weld epoxy, which is up to the task: its maximum operating temperature of 500°F exceeds the melting point of most soft solders, and its tensile strength is comparable.
Ponyo notwithstanding, this type of engine does not scale up to life-sized boats (nor, for that matter, are there sea wizards or magic talking fish). Nonetheless, there’s an undeniable pleasure in a home-built toy that scoots around on its own and has no use for batteries — except, perhaps, as ballast.
What' Next?
Running on Spirits
Using candles for any length of time will coat the bottom of your boiler with soot and leave a greasy black ring in your bathtub or sink. To avoid this, use a spirit lamp. You can make a simple one by drilling a hole in the metal lid of a very small glass or metal container, threading through a lantern wick, then filling the container with denatured alcohol.
I’ve also made spirit lamps out of copper pipe caps and copper tubing. Cut a 1¼” pipe cap short enough to fit under the boiler with room for the flame, then sweat-solder it onto a sheet metal bottom. Drill holes in the cap and solder in 2 lengths of ¼” tubing: a very short one on top (the wick holder) and a longer one in the side (the filling tube and handle), bent upwards.
With candles, this engine needs more than a single small flame to get moving. Use 2 or 3 birthday candles or a tea light with more than one wick.
See how MAKE Labs engineering intern Daniel Spangler made a Copper Pipe Alcohol Lamp for the Pop-Pop Steamboat.
This project first appeared in MAKE Volume 28, page 70. The author is William Abernathy.
Materials
Parts
- Solder and flux, lead-free solder is best (1)
- Spirit lamp, (alcohol burner) or small candles (1) such as tea lights or birthday candles
- J-B Weld epoxy, high-temperature (1)
- Copper tube, thin-wall, 1/8' OD, 1' length (1) from hobby or hardware stores. Do not use 1/8' malleable copper coil.
- Aluminum soda can (1)
- Floating vessel, small (1) such as a toy boat or a 16oz ham can
- mint tin, Altoids Smalls (1)
Tools
- Anvil or other flat surface to pound on
- Drill
- File
- Hammer If your hammer’s too big to work inside the Altoids tin, a brass drift is handy to tap on. MacGyver could make do with light whacks to a 3/8" bolt.
- Machinist's scribe
- Marking gauge aka “jenny” or “hermaphrodite” calipers
- Pliers Lineman’s pliers are best for this project.
- Plumber's putty
- Prick punch
- Propane torch
- Sandpaper
- Screwdriver
- Small tubing cutter Ordinary hacksaw blades are too coarse for the thin-wall tubing. I used a jeweler’s saw. Micro-Mark’s mini tubing cutter also looks right for the job.
- Step bit
- Tinsnips
Maker Camp Project Standards
Based on NGSS (Next Generation Science Standards)
CCSS (Common Core State Standards)
The Common Core is a set of high-quality academic standards in mathematics and English language arts/literacy (ELA).Measurement & Data
- Grades K-2
- CCSS.MATH.CONTENT.K.MD.A.1 Describe measurable attributes of objects, such as length or weight. Describe several measurable attributes of a single object.
- CCSS.MATH.CONTENT.1.MD.A.1 Order three objects by length; compare the lengths of two objects indirectly by using a third object.
- CCSS.MATH.CONTENT.1.MD.A.2 Express the length of an object as a whole number of length units, by laying multiple copies of a shorter object (the length unit) end to end; understand that the length measurement of an object is the number of same-size length units that span it with no gaps or overlaps.
- CCSS.MATH.CONTENT.2.MD.A.1 Measure the length of an object by selecting and using appropriate tools such as rulers, yardsticks, meter sticks, and measuring tapes.
- CCSS.MATH.CONTENT.2.MD.A.2 Measure the length of an object twice, using length units of different lengths for the two measurements; describe how the two measurements relate to the size of the unit chosen.
- CCSS.MATH.CONTENT.2.MD.A.3 Estimate lengths using units of inches, feet, centimeters, and meters.
- CCSS.MATH.CONTENT.2.MD.A.4 Measure to determine how much longer one object is than another, expressing the length difference in terms of a standard length unit.
- Grades 3-5
- CCSS.MATH.CONTENT.3.MD.B.3 Draw a scaled picture graph and a scaled bar graph to represent a data set with several categories. Solve one- and two-step "how many more" and "how many less" problems using information presented in scaled bar graphs.
- CCSS.MATH.CONTENT.4.MD.A.1 Know relative sizes of measurement units within one system of units including km, m, cm; kg, g; lb, oz.; l, ml; hr, min, sec. Within a single system of measurement, express measurements in a larger unit in terms of a smaller unit.
- CCSS.MATH.CONTENT.4.MD.C.5 Recognize angles as geometric shapes that are formed wherever two rays share a common endpoint, and understand concepts of angle measurement.
- CCSS.MATH.CONTENT.5.MD.A.1 Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.
- CCSS.MATH.CONTENT.5.MD.C.3 Recognize volume as an attribute of solid figures and understand concepts of volume measurement.
Ratios & Proportional Relationships
- Middle School
- CCSS.MATH.CONTENT.6.RP.A.1 Understand the concept of a ratio and use ratio language to describe a ratio relationship between two quantities.
- CCSS.MATH.CONTENT.6.RP.A.3 Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
- CCSS.MATH.CONTENT.7.RP.A.1 Compute unit rates associated with ratios of fractions, including ratios of lengths, areas and other quantities measured in like or different units.
- CCSS.MATH.CONTENT.7.RP.A.2 Recognize and represent proportional relationships between quantities.
CCSS (Common Core State Standards)
The Common Core is a set of high-quality academic standards in mathematics and English language arts/literacy (ELA).English Language Arts Standards » Science & Technical Subjects
- Middle School
-
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- CCSS.ELA-LITERACY.RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
- CCSS.ELA-LITERACY.RST.6-8.3 Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.
- CCSS.ELA-LITERACY.RST.6-8.4 Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 6-8 texts and topics.
- CCSS.ELA-LITERACY.RST.6-8.5 Analyze the structure an author uses to organize a text, including how the major sections contribute to the whole and to an understanding of the topic.
- CCSS.ELA-LITERACY.RST.6-8.6 Analyze the author's purpose in providing an explanation, describing a procedure, or discussing an experiment in a text.
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- High School
-
- CCSS.ELA-LITERACY.RST.9-10.1 Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
- CCSS.ELA-LITERACY.RST.9-10.3 Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
- CCSS.ELA-LITERACY.RST.9-10.4 Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 9-10 texts and topics.
- CCSS.ELA-LITERACY.RST.9-10.5 Analyze the structure of the relationships among concepts in a text, including relationships among key terms (e.g., force, friction, reaction force, energy).
- CCSS.ELA-LITERACY.RST.9-10.6 Analyze the author's purpose in providing an explanation, describing a procedure, or discussing an experiment in a text, defining the question the author seeks to address.
- CCSS.ELA-LITERACY.RST.11-12.1 Cite specific textual evidence to support analysis of science and technical texts, attending to important distinctions the author makes and to any gaps or inconsistencies in the account.
- CCSS.ELA-LITERACY.RST.11-12.3 Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.
- CCSS.ELA-LITERACY.RST.11-12.4 Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11-12 texts and topics.
- CCSS.ELA-LITERACY.RST.11-12.5 Analyze how the text structures information or ideas into categories or hierarchies, demonstrating understanding of the information or ideas.
- CCSS.ELA-LITERACY.RST.11-12.6 Analyze the author's purpose in providing an explanation, describing a procedure, or discussing an experiment in a text, identifying important issues that remain unresolved.
NGSS MS.Engineering Design
The Next Generation Science Standards (NGSS) are K–12 science content standards.- MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
- MS-ETS1-2. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.
- MS-ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.
- 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.
NGSS HS.Engineering Design
The Next Generation Science Standards (NGSS) are K–12 science content standards.- HS-ETS1-1. Analyze a major global challenge to specify qualitative and quantitative criteria and constraints for solutions that account for societal needs and wants.
- HS-ETS1-2. Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.
- HS-ETS1-3. Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
- HS-ETS1-4. Use a computer simulation to model the impact of proposed solutions to a complex real-world problem with numerous criteria and constraints on interactions within and between systems relevant to the problem.
