Before you start building...
...understand that this is not a slop-it-together project. You have to follow directions exactly and, from the feedback I get, most people need to build a second one before it works. I like this e-mail from Jordan:

Mr Slater Harrison,

My name is Jordan and I'm from Greece. I'm 14 years old and I must say that I'm not very good at physics! But, I wanted to make something like a wooden construction so I serched on youtube and I came up with your video about putt-putt boat! I thought that it was excactly what I wanted to do! Then, I saw all the videos of this boat. It looked so simple but when I started  I realized that it wasn't! My first try was a failure... well, I think it was a disaster because in the end my desk was full of epoxy!! My second try was a success! (I have one photo attached) When I saw it working I was very proud of my self!! I must say that your site is fantastic and I'm planning to build a plane next time! (I hope that I won't break anything!) ( I will inform you!)

Yours sincirelly,


Jordan has just the right attitude: keep trying!

The patterns you will need (PDF) follow. Do not shrink or expand the patterns, and check the scale. The engine boiler pattern--first needed in Step 7--is here and the foam boat pattern is here. If you decide to make a 3-D boat the pattern for the hull is here and the deck and cabin is here. A print-friendly list of materials and tools you will need is here ..........................

In this new page I am listing smart innovations that people have developed to make pop pops better/easier.

Part 1 Introduction to pop pop (aka putt putt) boats. Part 1 shows my students testing their boats and gives an overview of the steps involved in making the engine out an aluminum beverage can. I relate where I first encountered pop pops (in South Asia in the 1980's). Then on to a little history: of steam power in general and putt putt boats specifically. Next I show some commercial boats I bought. If YouTube is blocked at your school try this equivalent SchoolTube link


Part 2 continues the introduction. I start off relating my efforts to create an easy enough for my students to make, inexpensive steam engine that used common materials that could be found anywhere. Then I make my plea that people follow the directions carefully for the first engine, then experiment. If YouTube is blocked, try this equivelent SchoolTube video for Part 2

Part 3 goes through all the materials you will need, including an aluminum can for the engine, flexible plastic drinking straws for the jets, and epoxy glue to hold everything together and make a pressure-tight seal. If YouTube is blocked, try this equivalent SchoolTube video for Part 3 A print-friendly list of materials and tools is here. Note that if you would rather use an oil lamp instead of a candle, excellent oil lamp instructions are here.

Part 4 is Step 1 of the actual building instructions. Are you confused enough? Sorry! The steps are small. This Step 1 is just cutting off the top of an aluminum beverage can. If YouTube is blocked, try this equivalent SchoolTube video for Part 4 plus a little aluminum history (yes, that's Napoleon).

Part 5 is Step 2, cutting and trimming the middle part of the can so you have a sheet of aluminum to build the engine with. If YouTube is blocked, try this equivalent SchoolTube video for Part 5

Part 6 is Step 3, folding the aluminum sheet in half, with a thin sliver of the inside of the can showing so it's easier to separate in a later step. If YouTube is blocked, try this equivalent SchoolTube video for Part 6

Part 7 is Step 4, printing out the pattern to print actual size (no fitting to page or scaling) and checking the scale of the pattern to be sure. Then you tape the pattern onto the aluminum sheet. Save the other boiler pattern and that other weird-looking pattern called the bend pattern. If YouTube is blocked, try this equivalent SchoolTube video for Part 7

Part 8 is Step 5, cutting out the pattern and aluminum on the solid lines--carefully. Save one of the aluminum strips for a later step. Oops, I noticed that the pattern here doesn't have the writing--that's ok, same pattern. If YouTube is blocked, try this equivalent SchoolTube video for Part 8

Part 9 is Step 6, finding a sharp corner, lining up the dashed lines with the corner, and making clear fold lines on the dashed lines of the pattern. Your thumbs should be together, and press really hard so you see clear fold lines. If YouTube is blocked, try this equivalent SchoolTube video for Part 9

Part 10 is Step 7, taking all the pattern/tape off and accurately folding the edge flaps the rest of the way over with a credit card or something like it. Then you need to pound it (not rub it) flat. Be careful not to kink it. If YouTube is blocked, try this equivalent SchoolTube video for Part 10

Part 11 is Step 8, using a thumbnail to open up the end of the "pocket" a bit, then pinching the end of the long part of a flexible straw and pushing it in. Then the long part of another straw. Push all the way in, but not so hard them split the other end. If YouTube is blocked, try this equivalent SchoolTube video for Part 11

Part 12 is Step 9, putting one more straw in to form a curved dome top, but this time it's the short end of of a straw. Pinch it and push it in--on the side with the flaps--only to the bendy part. Then put tape donuts on the flat side without the flaps and tape it to a piece of cardboard. Gently push on the edges to make the bottom flat. If YouTube is blocked, try this equivalent SchoolTube video for Part 12

Part 13 is Step 10, is actually gluing the aluminum so it keeps its new shape. You should watch the whole step before starting because you only have 5 minutes once you mix the two parts together (less if it's hot). You should have equal parts and mix thoroughly. Dab it on the silver parts even where the silver disappears, especially the ends. It's really important to push the epoxy in between the folds of aluminum with the strip, for strength and to prevent leaks. GOOD NEW NOT IN THE VIDEO YET: STICKY EPOXY IS EASY TO GET OFF WITH VINIGAR. If YouTube is blocked, try this equivalent SchoolTube video for Part 13

Part 14 is Step 11, measuring 1 1/2" or 39mm from the end of the bendy part of the straws into the small part of the straw. Cut there and apply mixed up, thin, even layer of epoxy to the small part of the straws, but not within 1/4" or 6mm of the bendy part. Put the straws in the end of the aluminum, but only to within 1/4" or 6mm of the bendy part. If a lot of epoxy gets on the bendy part, wipe it off, both above and below. If YouTube is blocked, try this equivalent SchoolTube video for Part 14

Part 15 is Step 12, being careful when handling the engine and mixing up a tiny bit more epoxy and using it to seal off the 3 or 4 holes where the straws go into the engine. If YouTube is blocked, try this equivalent SchoolTube video for Part 15

Part 16 is Step 13, taking a tip from automotive people and using pressurized air into the straws to find leaks (bubbles in the water). Patch with epoxy and don't pressure test again until it is hard. Use hot water if you need to speed up the epoxy If YouTube is blocked, try this equivalent SchoolTube video for Part 16

Part 17 is Step 14, making a cardboard angle tool to set the angle between the aluminum boiler and the straws. You saved the pattern that printed out with the boiler pattern way back in part 7, step 4, didn't you?! If YouTube is blocked, try this equivalent SchoolTube video for Part 17

Part 18 is Step 15, pulling the straws longer and taping the angle tool to the boiler and straws. Make sure the folded-over edges are facing outward, not inward against the angle tool. If YouTube is blocked, try this equivalent SchoolTube video for Part 18

Part 19 is Step 16, using one of the cooler kind of hot glue guns to apply a thin layer of hot glue over the bendy part of the straws, so as stiffen them so they hold the correct angle. If YouTube is blocked, try this equivalent SchoolTube video for Part 19

Part 20 is Step 17, cutting down thin birthday candles into 4 pieces, then making a candle holder out of aluminum foil. It's important to push the aluminum down to the base of the candle, or the candle will go out before burning most of its wax. If YouTube is blocked, try this equivalent SchoolTube video for Part 20. Note that a sharp viewer has created some great instructions for making an oil lamp instead of the candle for heat.

Part 21 is Step 18, the step when you finally get to power test the engine! You don't need a boat to power test the engine. You must prime the straws every time you use the engine. And the first time you use the engine you should slosh some water around inside the engine so the little droplets of water can flash to steam and get your engine going. To start out put the candle flame in the middle between the front and the back of the engine. If YouTube is blocked, try this equivalent SchoolTube video for Part 21

Part 22 is Step 19, troubleshooting if your engine doesn't work. SKIP THIS SECTION IF YOUR ENGINE WORKS OK. Sometimes you only have to prime the straws with water and try it again and it works. Or maybe you need a more heat if you are using a tea candle (don't use a lighter or you'll ruin the engine). Sometimes there might be a leak even though you already tested it. Still, it's not hard to find it and seal the engine. Sometimes the cause of the trouble remains a mystery and you might just have to make another one (Yep, I know, I thoroughly hate having to do things over too). If YouTube is blocked, try this equivalent SchoolTube video for Part 22

Part 23 is Step 20, some tips when you're finished using the engine, like wiping off the carbon from the candle. Also, using heat to remove what's left of the candle and affix a new one so it doesn't keep falling out. Now is the time to decide which kind of boat to make for your engine. Instructions for the simple foam boat are in Part 24. But the instructions for the 3D milk carton boat are in Part 27, farther below. If YouTube is blocked, try this equivalent SchoolTube video for Part 23

Part 24 is Step21, making a simple flat boat out of a foam grocery tray. It's only held on with rubber bands, so you can move the engine to another boat later if you want. Funny, but it seems you actually have to put some weight to give the engine something to push against or the engine doesn't work well. If YouTube is blocked, try this equivalent SchoolTube video for Part 24

Part 25 is Step 22, making the boat go faster by restricting the straws a little at the end, just like real jet engines and rockets. Finally you can tell the control freak (me) to go soak his head, and you can break loose with experiments. If YouTube is blocked, try this equivalent SchoolTube video for Part 25


Part 26 is a congratulations and some final words. I depend on feedback to make the instructions better. And frankly, when you get the engine working it's encouraging to me to hear that as well. There is a gallery of pictures of people's pop pop boats that you can add your boat to. Also, now that you have made a boat, be aware that there is a Yahoo group of people from all over the world who experiment and talk about pop pop boats. Some people are just interested in engine development, or scaling up engines, others in making a beautiful boat for the engine, others in the history. There are nice people moderating the group, there is an enormous archive of tips and pictures, there is no money involved, and it's easy to join (if an internet dummy like me can do it, anyone can). And, we are mostly older people, but I think I can speak for the group that we would be thrilled to see the work that younger people are pursuing (and you are still welcome if you are a geezer like the rest of us). If YouTube is blocked, try this equivalent SchoolTube video for Part 26

An International E-Mail Group that Discusses Everything to do with PopPops!

It's a very relaxed, funny bunch of people from around the world. I think you have to join to see the archives, where there is some really amazing work, but it's free. The Yahoo pop pop group's home page is here

For dozens of other DIY science toys like this one go to the main page

If you want to make a giant boat, click here.

Making a 3D Boat Hull from a Milk or Juice Carton

Part 27 is making a 3D hull from a milk or juic carton. It's all in one Google video here or I had to cut it into 3 pieces for YouTube. If YouTube is blocked at your school, note the SchoolTube equivalents.
Section A
and if blocked the SchoolTube equivalent is

Section B
SchoolTube equivalent

SchoolTube equivalent

Most of the video is from a video I made for my students years ago. This hull is made from a 1/2 gallon or 2 litre milk or juice carton. That kind of cardboard is waterproof, east to cut, bend, glue and paint. The (PDF) pattern for the hull is here. Make sure that when you print it you do not have any box checked that "fits to page" or otherwise changes the scale. After it's cut, it's folded and fastened with staples and hot glue. After it's widened you can install the engine. The straws go out a hole in the bottom, so you seal and glue in the engine with hot glue.

Making a Rudder I got a wonderful tip about making a rudder for the boat from young Australians Elana (12) and Alex (10) who made putt putt boats with their grandad Les. Click here to see the PDF of the drawing of their ingenious rudder system (if for some reason your PDF reading program is not working, click here).

Here are the video instructions for making the deck and cabin for the 3 dimensional hull. Or...

Here are the SchoolTube equivalents (I had to break them into shorter segments)
Part 1
Part 2
Part 3

This too is made from a milk or juice carton. It fits on top of the hull but comes off if you need to get to the engine. The patterns for the deck/cabin assembly are here. A hot glue gun puts all the pieces together. You don't have to make the smoke stack, but the instructions for that are here if you want to.

Now that you've made an engine, hull and deck, check out the work of a true craftsman, my friend Daryl from Canada

Back to the science toymaker home page.




















The instructions below are out of date
The video instructions above are considerably more evolved. However, since I don't have video instructions for the boat made from a milk carton uploaded yet, I am leaving the instructions below (how to make the milk carton boat is about half way down).


Below you will find instructions for making a putt putt (aka pop pop) boat engine and body. If you came to this page directly from a search engine, it's a good idea to look at the introduction page first.

I go into detail about what makes the steam engine work in the explore page. But before you begin making the engine, you should at least have some idea what you're about to do. It is deceptively simple looking.

After cutting the top and bottom off an aluminum soda can, you will fold the middle part into a rectangular "pocket", creased shut on three edges and open like a pocket on the fourth edge (the blue part in the illustration at right). The top side of this flash boiler--where droplets of water are heated into steam--is arched, the bottom flat. The flat bottom flexes like a canning jar lid, which gives the boat its distinctive sound. Into the open fourth edge of the boiler you insert the ends of two flexible plastic straws (green in the picture). The whole thing will be glued and sealed airtight with quick set epoxy glue and silicone rubber caulk. Between two of the gluing steps you will have to wait about 15 minutes, and overnight for the last. During that time you can create the body of the boat from milk cartons, make a candle holder, and read ahead to the next steps.

Some of the following instructions might sound weird and finicky. I try to explain the "why" of the steps, but in the end you'll have to trust me that each detail is important. Do the first boat my way and get a boat that works. Then you can innovate and experiment.


Soda cans, 12 oz. 355 mL

A cut up soda can forms the boiler of the steam engine. The water/steam pushing in/out of the boiler bulges the aluminum several times per second. This also gives the engine its cool sound. The process is similar to when a canning jar lid is pushed to make a noise, though the sound is different.

Important: The soda can must not be dented. Have several on hand to start over when you make errors. Rinse out the sticky soda inside.

Plastic, flexible drinking straws, approximately 193mm long by 6mm diameter (7 5/8" by 1/4")

The straws become the jets from the engine.You ought to be able to get these at a grocery store where the beverages or paper cups are. You can also get them in department stores. There is a slightly thinner kind imported (usually from Thailand) and that works, too.

Quickseting or 5-minute epoxy

Epoxy is a very strong, two-part (which you mix together) adhesive actually used to glue real jet plane parts together. You will use it to seal the boiler airtight and glue the straw exhaust pipes. You can get it in any hardware store and most building centers. Important: Whatever the brand, get the kind that indicates that it sets fast: 5-minute, quickset, etc. or you will be waiting long periods between steps for it to harden. Even 5-minute epoxy only begins to thicken in five minutes. It takes at least 15 minutes to attain most of its strength. Putting the mixed epoxy in a warm place makes it set faster. Usually it comes in a double syringe which will help you dispense it evenly.

Although you cannot accidentally glue your fingers together the way you can with "super glue," epoxy is extremely messy. I try to keep it from getting on my hands in the first place (I never completely succeed). To get it off, I wipe as much off with a dry rag first, and only then try to get the last bit off with soap and water. By the way, epoxy smells like a moldy tuna fish sandwich.

100% silicone caulk/bathtub sealer

The silicone does two useful things. First, a thin layer of silicone spread over the epoxy seals hidden leaks. Even a pinhole leak can keep an engine from working, so silicone can gives you an extra layer of insurance. Because it is flexible, it maintains the seal even when bumped enough to crack epoxy. Secondly, though I mentioned that epoxy smells, high temperatures (such as those found at the boiler) really make it stink. So that same layer of silicone that seals hidden leaks also seals in the epoxy smell. Silicone also helps to make the candle holder.

You can buy silicone where you get the epoxy. If you don't need it for other things around the house, you can get a little tube of it since this project will only use a couple of dabs for each engine. If you get the 300ml cartridge pictured, find out how to use it and the dispenser. You have to cut off the tip and poke to puncture the seal at the other end of the tip. A nail stuck into the tip keeps the silicone from clogging when not in use. Don't get a mix of silicone with anything else. It has to be 100% silicone. It smells like vinegar as it cures. It cleans off like epoxy, above.


Utility knife (or any sharp-tipped knife or single-edge razor), good scissors, ball-point pen, pencil, tape, and a ruler (or at least a straightedge).

You will use the scissors to cut up the aluminum soda can. This will not harm the scissors. Although I show clear tape in the illustration, masking tape is better: stronger yet easier to remove.


juice or milk carton(s)

This is make the body of the boat. The cardboard from beverage cartons is waterproof, easy to cut and can be painted. In the U.S. a standard size is half gallon, or 1.819 liters. I think a similar size would work. You will need a second carton if you make the top of the boat.

aluminum foil and birthday candles

This is the stuff that is not actually the engine. You will only need a 4" strip of aluminum foil from which you make the candle holder. The birthday candles are available in department stores and grocery stores.

Step 1

Cut apart the soda can for the boiler.

Cut the top off where the can reaches its its full diameter, or just inside (up to 1/2" toward the middle). Although it is possible to start the cut with the sharp end of a pair of scissors, it is easier to start the cut with a utility knife, single-edge razor, or a sharp tipped knife. After cutting for an inch or two, switch to scissors because the can starts to collapse It is impossible to make this cut smooth. Don't worry, it will be easy to trim once the metal is flattened. Just don't cut your fingers on the jagged edge! Recycle the top. We will not use it in the project.

The next cut is straight to the bottom where the can starts to get smaller again.

. Once the cut reaches almost to where the can diameter again becomes smaller again--at the bottom-- make a sharp turn (left if you are right-handed) and start cutting off the bottom. If you pull the middle part of the can out of the way as you cut, it will be much easier to cut the bottom off than the top. You are also likely to be able to cut a smooth, straight line

Recycle the bottom. You will use the middle. You can go back and trim the long side where you made your first cut. If you look closely at what was the inside of the can (it will be silver color), you will see some scratch lines left over from when the can was formed. You should be able to find one that guides you to make a straight cut. Try not to make the strip any narrower than 50 mm (2") wide.

Gently sand the silver side of the aluminum with sandpaper. This helps glue to stick and make the boiler airtight.


Step 2

Start folding the aluminum "pocket."

Use care when folding the aluminum in the following steps because applying force unevenly or creasing too hard can cause cracks and leaks. Even a tiny leak can keep a steam engine from working.

Fold the aluminum strip in half so the so it is only about 103mm long (4") rather than 207mm (8") long. The print side of the can should be outside. First hold together the ends as shown.
Continuing to hold the ends together, make the fold with a ruler or similar object so that the pressure is applied evenly across the aluminum.

With the ruler still on the fold, tap the ruler with as much force as would be required to break an egg. Hitting to hard could cause it to split in step 6 .

Even though the edges do not line up perfectly, do not trim the edges ( you will see why in step 5).

On the end opposite the fold, tape the two aluminum flaps together with a piece of tape (masking tape is easier to get off). This keeps the ends locked together, not shifting around.

Step 3

Cut the aluminum on the pattern.

This is a PDF pattern for the boiler. After you click the "Print" button on your browser, but before you click "ok" to actually print it, make sure that the "scale" is set to "none". Once printed, measure the distance between the lines of the "SCALE CHECK". They should be about 102mm (4") apart. If you are not able to print out the PDF, click here and print it out. As with the PDF, measure the "scale check" and make sure the scale was not distorted. . Print it out and measure the scale checks to make sure the size was not distorted. Alternately, just draw the pattern. The dashed lines are exactly one inch apart. The solid lines that define the flaps and the edges of the pattern are an additional 1/4 inch farther on.

Rough-cut (bubble-cut) one of the patterns. The faint outline around the pattern shows approximately where to cut out, if you do not know what I mean by "rough-cut." On the non-print side of the pattern, stick on two "tape donuts" with the sticky side of the tape out. Turn the pattern over and stick it onto the aluminum.

Caution! It is very important to stick the pattern on as shown below.

Cutting accurately on the pattern might be a little easier if you eliminate the part hanging out over the ends. You can cut it with scissors if you are very careful not to cut into the aluminum. But I just rip the paper against the metal.

Carefully cut on the two solid, outside lines (NOT ON THE DASHED LINES)! You will fold on those later). Save one of the scrap strips of aluminum for use in Step 7.

Step 4

Fold on the dashed lines of the pattern.

I have to warn you that more of my students goof on this step than any other. I don't think that any one step is particularly hard, it's just that it has to be done very carefully and accurately.

You will need a table or something with a sharp (not rounded) corner. Stick a piece of tape on each end, in-between the dashed lines. Carefully align the dashed line closest to you exactly with the edge of the table. It is important to keep it lined up this way when you bend it.

With fingers on each hand placed close to the dashed line, start bending. Sorry about my dirty thumbnails in the picture--I was working in my garden. But notice that there is also some light color in my thumbnails because I am pushing as hard as I can. This is important because you need to make a clearly defined bend in the aluminum, not a rounded bend. Continue across the dashed line. Then peel the tape from the table, flip it around and tape it so the other dashed line is on the corner. Because of the springiness in the aluminum, you will only be able to bend it to about 45 degrees.

The photograph below shows an end view of what it should look like when you are done. Notice that the fold lines are straight and clearly defined. Carefully so as not to bend the aluminum where it shouldn't be bent, remove the paper pattern and all of the tape.


To completely flatten the fold, cover one edge with the ruler and pound it with your fist in two places, as shown by the green targets. Then cover the other edge and pound again in two places. As before, pound hard enough to break an egg. Now you have sort of a very flat metal pocket, folded shut on two sides and one end, and open on one end. Caution: Pound it gently and do not rub the aluminum with the ruler. That can cause cracks and curving.

Step 5

Measure and mark the straws.

Let's clarify some terminology before working with the flexible straws. Let's divide them into three parts: the long part, the bendy part and the short part.

Measure 36 mm (1 1/2 ") from the end of the bendy part into the short part and make a mark with the magic marker. Note: I have found recently that the engines work better if you make the mark at 1 1/2" (not 1" as stated in the illustration below). I have not had time to change the illustration.


Put another straw beside the first--oriented the same way-- and line up the ends exactly. Use the first mark as your guide to mark the second straw in exactly the same place.


Turn one of the straws around 180 degrees. With the straws side by side and the ends lined up, use the existing two marks to mark the same distance from the end of the big part of the straw. Each straw should now have 2 marks exactly the same distance from each end.

Insert the straws into the end of the boiler.

Although one end of the aluminum pocket is not folded shut, it is hard to get the straws into the flat boiler. The best thing I've found for opening up the end is a sharp pencil. Stick the point and the taper into the end into the end, but not more than 1/2" of the full-width pencil body should go in. Inserting the pencil far into the aluminum will dent it and ruin it.


With the tip of the pencil holding open the end, insert the long part of a bendy straw in a couple of inches. Take out the pencil and insert the long side of another straw in, too.


Step 6

Form a convex top and flat bottom in the boiler.

After lots of experimentation, I found that shaping the top and bottom of the boiler a particular way makes the best engines. To create that shape, first push the two straws together into the engine until you feel them start to bottom out, about 100 mm (4").

Make enough tape donuts to cover the bottom of the aluminum boiler (the bottom is the side that does not have the narrow fold-over flaps). Masking tape seems to be stronger for this than clear tape.

Tape the boiler onto something rigid and flat that can get glue on it. I use a piece of juice or milk carton. In the picture below the tape donuts are hidden because they are on the bottom of the engine, which is now flipped over so the flaps are on top. Notice how the top is now domed and the bottom is flat.

If the top is not domed, bottom flat and silver showing, you can shape it by taping the flaps as shown below, but tape just the edge. Do not tape over the silver part.

Step 7

Start sealing the boiler.

This step also glues the boiler so it maintains its domed shape. Before mixing up the glue, read all the way through this step and know what you are doing because the epoxy will start to harden in 5 or 10 minutes. Make sure the long parts of the straws are pushed all the way in. Work on newspaper and have dry rags at the ready.

See the "Materials" section above about how to get epoxy off your skin. Dispense small, equal amounts of the two parts of epoxy onto a piece of cardboard or something. They should come out equally, but trapped air bubbles can cause more of one to come out. With a toothpick or nail or Q-tip with cotton removed, thoroughly mix the epoxy.

Using something thin, apply a skinny bead of epoxy to the edge of the folded- over flaps. It's easy where you see the silver, but don't forget to get the whole line, even on the other end of the engine where the silver gets narrow and disappears.

Find the strip of aluminum that you saved in step 3. If you insert it in between the layers of aluminum as shown below, move it back and forth and around, you can get some of the epoxy in between the layers too. Getting the epoxy in there makes it much stronger seals up leaks that can keep the engine from working. It is easiest to get the strip of metal in between on the ends where the silver shows the most, but push the glue in all the was across--even where the silver disappears--all the way to the end.

Step 8

Cut candles and make candle holders.

It usually takes about 15 minutes for quick-setting epoxies to set, so let's get the power source ready while waiting. We cut a typical 60 mm (2 1/4") long birthday candle into 4 equal pieces. Each will be about 15 mm (9/16") long. I know that sounds short, but they have to be that short to fit under the engine in the right place. Besides, even a quarter of a candle burns 3 minutes or longer. Cut them with a razor, knife or even scissors.


Although only one out of four of the cut candles has a wick sticking up, don't throw the other three away. It's very easy to nip off the wax at the end with your front teeth, a dull knife (a sharp one might cut the wick) or finger nails. The dashed blue line in the illustration is a "hidden line" representing the wick hidden in the wax.


To make a reusable candle holder, tear off a piece of aluminum foil 5" wide and how ever long it comes out of the dispenser, usually about 12". Fold the strip in half lengthwise, then fold it in half again so it has some stiffness.

Although you can just crumple the end of the aluminum strip around the bottom of the candle to hold it upright, using a dab of silicone to make a tiny cup that holds the candle works better. Squeeze a dab of silicone about the size of a pea on an end of the strip. Put the bottom of a birthday candle in the middle of the silicone and twirl it in between thumb and forefinger once. Twirling causes the silicone to stick to the candle. But don't worry, when the silicone is cured it will not stick. It will just be the perfect shape to hold candles. Leave the candle straight upright in the silicone as it dries. If you repeat this on the other end of the strip with another dab of silicone and candle--and cut the long strip in half--you'll have two. You can use the candle holder that turns out best and have a backup.

Step 9

Glue the straws into the boiler.

As noted at the beginning of Step 5, the mark works better at 1 1/2" from the border of the bendy part into the small part of the straw. Because of that change in measurement, you will cut closer to the end than what appears in the illustration right below (green straws, ends cut off).

Going back to the boiler, when the epoxy has hardened (at least 20 minutes), pull out the straws and the opening will maintain its moon shape. Cut off both the straws where they are marked on the short part only. For now, leave the long parts of the straws full length even though they too are marked.

It's a good idea to scuff up the little end of the of the straws before gluing them into the aluminum boiler. Use sandpaper to make little scratches in the otherwise smooth plastic to give the glue something to grab onto. It could save you from having the straw come out later on. In the illustration I am twirling the straw with one hand while squeezing the end of the straw in sandpaper with the other hand. Do not sand the bendy part.

Mix up a small amount of epoxy. Then apply a thin layer of epoxy all the way around the small section of straw that you just sanded. If you put on too much epoxy, the second straw going in might clog with epoxy from the first--which would keep the engine from working. Try not to get it on the bendy part of the straw.

Push the glue end of the straw into the boiler. Repeat the step above with the other straw. The bendy parts of the straws should not be pulled so as to make the straw longer. Let them stay collapsed. Although in the illustration the long parts of the straws (to the right of the bendy part) appear short, don't be confused. The straws extend out to the right of the bendy part.


Keep the assembly flat as the epoxy sets so glue doesn't run into or out of the boiler. Laying it in plastic food wrap will avoid sticking problems. Let the epoxy cure for 15 minutes.

Step 10

Seal the engine.

Note: I have not had the time for a proper rewrite, but everything that I say to seal with the silicone in the instructions below I have been doing with epoxy instead. It's easier, faster and works well.

Although we have glued the engine with epoxy, it still has to be sealed. 100% silicone sealer is flexible so it bends a littler where the epoxy might crack. In the photograph below I have cut off the straws to show all the places on the end that need to be sealed with silicone.

Rather than applying silicone to the outside of the boiler, I have found that it is more effective to make plugs inside the boiler. Do this by pushing silicone into the holes where the straws go into the engine. Scrape off the extra and push more in. Do this 10 or 15 times. A little bit of silicone on the bendy part will not hurt, but scrape off large globs.


Use some more silicone to coat the flap area with a thin (about as thick as a coin) layer (shown as light blue in the illustration). This will seal any leaks that are likely to be there. Be sure to dab some on the corners, which is a common place for leaks to show up.

I apply the silicone directly from the dispenser. The silicone should not stick out over the edge because it will burn.

The next instructions switch to making the body of the boat while the silicone hardens, which will take several hours. Sometime after a few hours it would be a good idea to check back to the engine and see how it has sealed. If you submerge the aluminum boiler in water while blowing into the straws (seal your lips around them ends), air bubbles will indicate leaks. A glass or clear 2-liter soda bottle with the top cut off let you see exactly where the leaks are. Leaks where the straws go into the boiler are not so serious because more silicone will be applied there in a later step. However, any leaks anywhere else on the boiler will have to be sealed now. Make sure the


If you have small leaks where the straws go into the aluminum boiler, such leaks should get sealed in a later step when you use a gob of silicone to glue the engine into the boat body. On the other hand, if there is any leak elsewhere it has to be sealed or the engine won't work.

Fortunately, boiler leaks are pretty easy to fix. Look carefully where the bubbles come from. Take the engine out of the water and try to find the hole. Gently pat the area dry and apply a silicone layer about as thick as a coin. Don't re-test right away! Of course the air pressure would blow out the still-soft silicone. Give the thin layer an hour to dry.

Step 11

Cut out the boat body.

Cut off the bottom of a half-gallon milk carton and open up the top. One of the corners of the carton is the seam. In this corner there is not just a fold, but also a strip of cardboard that overlaps. It is important that you cut open the carton at that corner. Don't cut through the double layer--that would be too hard--but cut on either side of it. Open up the carton so it's flat.

Click here and print out the hull pattern. Some browsers--especially Netscape--change the scale and the size of the printed pattern. If the printout says something like, "Scaled-60%" try another browser. Also, the printout has a scale check. It says 2" line to line or 5 cm line to line. Make sure it's accurate. Check the scale by measuring either 2 inches or 5 centimeters. Or click here for a PDF. After you click the "Print" button on your browser, but before you click "ok" to actually print it, make sure that the "scale" is set to "none".

Cut a strip off each side of the pattern, as shown. This will make it easier to line up the pattern to the right place on carton. Make four tape donuts and put them in the corners of the actual pattern. The location for tape donuts is indicated by light blue circles, but note that they get stuck to the non-print side of the pattern. You can see where the pattern is from the non-print side if you hold it to the light.



There are two important things to remember about sticking the pattern onto the carton: First, line up the dashed line (red in the illustration) with a natural fold in the milk carton. This saves up from having to fold there, and keeps the number of structure-weakening folds to a minimum. The instructions on the pattern, "Line up this dashed line with a fold in the carton." point to the line. Second, be careful not get the pattern onto the spout part of the milk carton that has lots of folds. Keep the pattern in the area with the four big rectangles.


Cut out carefully along the solid outside line of the pattern. Then, there are two short solid lines that actually cut into the shape. Finally, there is a tiny rectangle in what will be the bottom of the boat that needs to be cut out. This rectangular hole will be where the two straws from the engine go through the bottom of the boat. A razor is the usual way to cut it out, although you could stab a hole with pencil and shape it with scissors.

Step 12

Form the boat hull.

The hull starts to take shape when you fold on the dashed lines. Depending on which way you fold, the print side of the carton will be outside (where it would show) or inside (where it wouldn't). Generally--unless you have a strong desire to advertise milk--the print will go inside. Although I acknowledge that you'll deal with that later, you don't have to consider it as you fold the carton because once it is bent one way it is easy to bend it the other way.

Start on the two dashed lines in the middle that form a "V". Either fold using a ruler--as shown--or you line it up with a sharp corner of a table or something as the aluminum was folded. However you bend the milk carton, bending accurately will save headaches later.

Next, fold on the two parallel dashed lines near the edge. You can do this the same as the others, but some people find it harder because one side is so narrow. You can use pliers, as shown.

After you have folded carefully on all dashed lines, remove the pattern and tape from the cardboard.

I use a combination of staples, hot (or cool melt) glue and tape to hold the boat together. You could also stitch it together I suppose, though I've not done it. Staples are the easiest, and if you get it wrong they are pretty easy to pull out. Hot glue is a little less conspicuous but harder to apply. You can re-melt hot glue to reposition something with the tip of the hot glue gun.

Start with the narrow flaps on the outside. Now is the time to think about which side of the carton--print or non-print--shows. Assuming you are not passionate about displaying your milk brand, fat content, etc., fold them so you see the non-print (white) side of the flaps, as shown. The print side is indicated by light blue. Staple the middle, then staple at least two times more on each side. The staples are dark blue in the illustration. Alternately, you can glue the flaps with hot or cool melt glue. If you glue, be sure to scuff up the surfaces that will be stuck together with sandpaper so the glue has something to hold on to.

I think you have to use staples to hold together the front of the boat--glue isn't strong enough. Hold the two front edges evenly. It's a good idea to temporarily tape them together so you don't have to deal with that as you staple. Make sure the narrow side flaps are on the inside and the white non-print side is on the outside. Staple first at the top, as shown. The staple should be about 1/8" or 3/16" (3 or 4 mm) in from the edge. Because the top staple will take so much stress, turn the stapler 180 degrees and put in another staple at the same place, but coming in from the other side of the boat. After that, put in three more staples end to end to the bottom. Remove the tape.

The back of the hull will look better if the two smaller side-flaps are inside and the large bottom flap is on the outside. The flaps can be glued or stapled. Gluing is preferable because if you do it right it water can't leak into the boat. With staples you have to go back and seal the back. If you glue them, use sandpaper to scuff up the joining surfaces and spread a thin layer of the hot glue around the small flaps.

At this point, the boat looks like a narrow triangle. To make it more like a real boat, grasp the two sides and use your thumbs to pull out the sides, as shown. This will test whether the staples holding the front together will hold.

Bend it open forcefully enough that it stays somewhat wider. Not only does that make it look more like a boat, but it also makes it possible to fit the engine in in the next step.

Step 13

Mount the engine into the boat.

Hold onto the base of the aluminum boiler with one hand and pull and lengthen the bendy part of the straw. Don't pull it so hard that the whole straw comes out, though. If it does, scuff it up with some sandpaper and glue it back in with a tiny bit of epoxy.

Note: I don't have time for a full rewrite, but thanks to a tip from Brenda Nyhof of New Zealand, I use (cool-melt, low-melt) hot glue instead of silicone. The lower temp variety of hot glue does not melt the straws (my first concern) and the heat from the engine does not melt the hot glue (my second reason for not using it in the first place). Using hot glue is easier and doesn't make the mess of silicone. Faster, too. So you might want to veer away from the directions below a bit.

Now it's going to get messy. Have some rags at the ready, as well as several pieces of tape. You will be putting on a huge glob of silicone around where the straws enter the aluminum boiler. The glob will do three things: seal the engine where the straws go in of any leaks it might have, glue the engine into the hull of the boat, and seal the hole where the straws go through the bottom. Apply lots of silicone. It should be on about 3/8" (1 centimeter) of the bottom of the aluminum boiler all the way around as well as on the bendy part of the straws all the way around. Remember back in step ___ we said that if there were leaks where the straws go into the boiler, we would get them in a later step. This is that later step, so make sure you seal them well.

Push the straws through the hole in the hull until the glob of silicone hits the bottom of the boat. IMPORTANT! As in the illustration, the narrow flaps that you folded over are on the other side, facing the front of the boat. The engine has to go in this way or it won't work.

Flip the boat over and tape one of the pieces of straw that you cut off earlier (or cut another). It will only be there temporarily as a spacer to hold the two straws away from the bottom of the boat. Place it as shown, about halfway between the hole and the back of the boat. The tape is not shown.

Put a dab of silicone against the straws, as shown with light blue in the illustration. When the straws are bent over it will be hard to get to that part if it needs more sealer to keep water from entering the bottom of the boat. The silicone there also helps glue the straws in place.

Bend the straws over against the spacer straw and tape them there. Make sure they are centered, not off to one side or the other. Put a thin layer of silicone over about an inch of the straws as come out the bottom of the boat. This will keep them positioned as they are now and seal any leaks. Make it as smooth as possible so it cuts through the water when the boat runs.

The aluminum boiler, too, is positioned temporarily with tape until the silicone hardens. It is shown in red in these illustrations. First center and straighten it. The engine in the illustration at left is neither centered nor straightened. In the most extreme case, you might have to loosen the tape holding the straws on the bottom so you can un-tilt it.

The end of the boiler should be about 52 mm ( 2") above the floor of the boat. Tape it there (the tape in the illustration is purple).

If you stapled the back flaps instead of hot gluing them, now's the time to seal them with a thin layer of silicone, or your boat will fill with water and sink. If you plan to paint the outside of the boat you should apply the silicone to the inside because paint will not stick at all to silicone. You might also have to seal the front. Again, a thin layer is best.

Well, the boat is like an accident victim in medical traction now, what with all that tape holding things in position. But give it overnight to dry and you can actually run the boat. Remove the tape when the silicone is dry.

Step 14

Wet, prime and test the boat.

Since you have made a steam engine, and steam is water in the gaseous state, it stands to reason that you are going to have to get some water into the aluminum boiler where the heat will be applied. Actually, the boiler will not be "full" of water. It only needs droplets of water coating the inside so the drops can be flashed almost instantly into steam. Unfortunately, just pouring water into one straw until it comes out the other straw will only wet the straws, not the inside of the engine. To understand why, imagine a cup turned up upside down and pushed down into water. The inside of the cup does not get wet because an air bubble is trapped inside. Similarly, an air bubble gets trapped in the aluminum boiler, preventing it from getting wet.

To wet the engine, pour water into one straw until it comes out the other straw.

Then cover both straws with a finger and shake up and down violently and tip it to different angles! That will splash some water into the boiler. Then shake out the extra water. Fortunately, you only have to wet the engine one time--or unless you haven't used it for a few weeks--because it tends to stay wet inside.

Now prime the jets. This puts water in the straws. Do not become confused about this just because it starts out the same as wetting the engine. Pour water into one straw until it comes out the other. But this time be careful NOT to tip the boat in such a way that the water would come out as you set it into the water. Ditto when you put the candle in. There is no shaking when you prime the jets.

Light the candle and place the candle holder so the flame is about halfway between the front of the engine and the back, or slightly forward of that point. Now you know why the candles are cut so short. Hook the aluminum foil of the candle holder onto the back of the boat. That will keep it from sliding around when the boat starts putting. It should start to putt within about half a minute.

Still not working? Click here.

Step 15

Cut out the boat top

You don't have to make the top of the boat, of course. It might give the candle a bit of protection from drafts, but mostly it's for looks. And practicing turning two-dimensional shapes into three-dimensional objects.

Click here and print out the pattern. Some browsers--especially Netscape--change the scale and the size of the printed pattern. If the printout says something like, "Scaled-60%" try another browser. Also, the printout has a scale check. It says 2" line to line or 5 cm line to line. Make sure it's accurate. Or click here for a PDF. After you click the "Print" button on your browser, but before you click "ok" to actually print it, make sure that the "scale" is set to "none". Rough cut (bubble cut) out the 4 parts and use tape donuts to affix them to the milk carton. I used purple circles in the illustration to suggest where to place the tape donuts so the pattern doesn't start to slide halfway though the cutting. Stick them on the non-print (white) side of the milk carton. Notice that each pattern has its own section of the milk carton to itself. No folds in the milk carton run through any of the patterns.


Cut out the deck pattern as shown. Keep the pattern on! Later on you will cut out on the solid line the rest of the inner part, but not yet. Tape it on to

Straighten out a small paper clip. It will make the back of the deck strong.

Use pliers again to shape as shown below. The long side should be about 58 mm long and centered approximately between the two shorter end sides. The length of the short sides does not matter. If yours do not seem to be as long as those in the picture, don't worry about it. When you place it on the end of the deck, as shown, the paper clip ends should split the ends of the deck.


On the print side of carton, which is also the side without the pattern, scuff up the cardboard with sandpaper where shown in the illustration so the glue will stick. Use two small pieces of tape (green in the illustration) to stick the re-shaped paper clip on the end of the cardboard, as shown.This still leaves most of the paper clip exposed. Squeeze out hot glue (red in the illustration) over the exposed part of the paper clip. Don't be stingy with the glue. Submerge the metal and make sure it won't come off. When that glue has cooled, pull off the tape and get that part of the paper clip too.

When the glue is all cool, cut out the rest of the inside part. With sandpaper scuff up the area near the edge where you just cut out. That done, peel off the pattern and tape on the other side.


Now turn your attention to the "cabin wall" part. It will curve, and that curve will be easier to shape if you grab both ends and rub the print side back and forth against a corner a few times until it takes on a bit of a curve. The

Next, there are two dashed lines that indicate where to fold. You can fold them with a ruler, corner or pliers. Bend them toward the pattern side. Now cut all 22 of the short, solid lines from the edge to the fold. This creates flaps to make strong connections with the deck on the bottom and the roof on top. You can take off the pattern and the tape now.

Attaching the cabin wall to the deck neatly is a bit tricky, so we'll break it into several steps. Put the deck and wall together so that one set of flaps bends underneath the deck. It's hard to describe--look at the pictures. Since it is symmetrical, it doesn't matter which bunch of flaps attaches to the deck.

Notice that there are 12 flanges on the top and the bottom of the wall. If you have 6 flaps on each side you're exactly at the middle of the wall. That middle point has to be right at the front. Tape the middle two flaps (tape is purple in the illustration). Make sure they are right at the front and pushed tight against the deck. Then tape the two flaps right at the end. Flip the assembly over and make sure the wall is tight against the deck so you can't see parts of the flaps from the top. If there is a gap, re-tape before proceeding.

Back on the bottom, hot-glue the flaps down that haven't been taped, then un-tape the rest of the flaps and glue those down too. Finally, apply a heavy bead of hot glue over all the flaps and also the space in between the paper clip and the flaps. This makes the assembly strong and resists the tendency of the hull to crush the it.

Attaching the roof is a similar operation. The key to success is making sure that the edge of every one of the twelve wall flaps lines up with the edge of the roof. Once again, temporarily tape the middle and the end flaps first, then glue. Make sure the non-print side is facing out. You could staple this instead of gluing since the roof doesn't take much stress. If you use glue, go easy. Too much glue will make the boat top heavy, which will result in listing (tilting). You can counter this by gluing paper clips or coins to the bottom of the boat hull.

Attaching the smokestack, too, can make the boat top heavy. The smokestack is optional. If you decide to put it on, cut it out and bend it around a corner just as you did to the wall. Cut the slot on one end where indicated, remove the pattern and push through the slot from the outside in (it looks better hidden). Notice that it has a slant. Usually a ship's smokestack slants back, so the seam would go in front. Put the smokestack where you want it on the roof. Cut a hole or just cut two slits in the roof, depending on whether you are really going to get smoke out of it.

8th grade student Brittany B. made a rudder with a paper clip and a little piece of milk carton stuck together with hot glue. Here is a short (5 second) video of it. Unless you have a fast internet connection you should right click and "save target as" and remember where you saved it. Boat with a rudder.

I got a wonderful tip about making a rudder for the boat from young Australians Elana (12) and Alex (10) who made putt putt boats with their granddad Les. Click here to see the PDF of the drawing of their ingenious rudder system (if for some reason your PDF reading program is not working, click here).

Step (experimental)

Create nozzles at the ends of the straws.

Sometimes it seems that by restricting the opening of the end of the straws, it forces the water coming out to speed up. This in turn causes the boat to move faster in reaction. The engine might go faster with a constriction, just as rockets constrict exhaust gases to go faster. The problem is, with the boat engines it works sometimes, while other times it doesn't work at all. Fortunately, it's easy to remove the constrictions if it doesn't work.

If you saved the 4 short pieces of straw, use those. If not, cut 4 pieces of straw 1" long. Slice all the pieces lengthwise with scissors. Fit one inside another (like the old-fashioned telescopes). Roll them firmly between thumb and forefinger to make them as thin as possible, and insert them into the end of one of the straws on the engine. Push them in until they are flush with engine straw. Repeat with the other two pieces and the other engine straw. If it works, you can even slice up another short piece of straw and narrow the jet even more. If they don't work, just pinch the main straw in front of them and squeeze them out. Or, hook them out with a paper clip straightened except for a hook on the end.

I got a wonderful tip about making a rudder for the boat from young Australians Elana (12) and Alex (10) who made putt putt boats with their grandad Les. Click here to see the PDF of the drawing of their ingenious rudder system (if for some reason your PDF reading program is not working, click here).

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Putt putt engine design notes

I'd like to know how this project goes for you. I'm happy to answer questions about it. Feedback from you is an important way for me to know what works and what needs clarification.
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