Making a Pop-Pop Boat Out of Used Tins

Philip the II's Spanish Armada...
Teddy Roosevelt's Great White Fleet...
Admiral Halsey's Third Fleet...
All pale in comparison to Toy Making Dad's Fish Tin Flotilla.

When I was I little, my buddy Jack had a toy boat that he told me used to actually propel itself around the bathtub or pond using just a candle for power. It was made of tin and had two narrow tubes that ran down the hull and extended just a bit past the stern. It was missing the magic part that made it go so his boat was relegated to being a landing craft for our Airfix soldiers as they staged amphibious assaults on our rec-room carpet. Still, the idea that a toy boat could move with just a candle really stuck with me.

Flash forward thirty something years later, right to the moment that I was sure I had found absolutely everything on the internet there was to find. Suddenly I thought about Jack's boat. A quick search for "candle powered toy boat" opened my eyes to the world of "pop-pop" boats and closed that little loop from my childhood.

In short, it really does work with just a candle and a little water. It is one of those toys that relies on a bit of simple science but at this point, since most of us are so removed from all things mechanical or steam related it seems magic. In short:

• A small amount of water is in a shallow metal "boiler" (a tube or flat-ish pan with a flexible top or bottom.)
• A flame heats it.
• The water heats up rapidly and flashes to steam.
• The steam escapes from two tubes that lead from the boiler out the back of the boat and into the water.
• A vacuum then forms in the boiler and sucks fresh water back in through those same tubes.
• As soon as the water hits the inside of the boiler, it turns back into steam and the process starts over. 

And for us visual learners...

(Click to enlarge)

Simple, huh? One other thing... it happens crazy fast. Multiple times a second fast. When you use the flat boiler type a rapid putt-putt or pop-pop noise starts and it really adds to the fun.

I found instructions on how to make a really simple flat pan type of boiler here - http://www.sciencetoymaker.org/boat/index.htm and I won't pretend that I could describe the process any better that you will find there. My only advice is follow the instructions exactly and don't rush through it. Take your time and make nice clean folds.

I decided to use copper tubing instead of the drinking straws though because I wanted the toy to last 6 or 700 years. On this one I used tubes that have an outside diameter of  3/16". Bend the tubes to the correct angle before you epoxy everything into place. It makes things much easier and you'll be less likely to damage the boiler. I also used the legendary JB Weld two part epoxy to seal everything up. The stuff really is amazing.

I wanted to use a metal hull but since I lack soldering skills, I didn't trust myself to follow any of the hull patterns that are out there. So, I turned to one of my great little joys in life... Smoked Herring!

Okay, I could go on for hours about how wonderful smoked herring is (and honestly I have on numerous occasions) but there is a time and a place for everything. Basically it is wonderful stuff and some brands come in these deeper rounded cans. (This one is from Germany and I purchased it at Trader Joe's.) The rounded edges make it less likely to run into a wall and stop moving. After you let the cat finish cleaning out the tin, you can run it through the dishwasher to get it super clean.

I drilled two 3/16" holes out the back of the can and used some more JB Weld to hold the boiler assembly in place. Unfortunately, I didn't take any pictures before I took it for its maiden voyage so it looks a bit sooty here. The coins were all at the back to help push the stern lower in the water and to keep the tubes submerged.

And here is the first boat in action:




Another kind of flash boiler you can make is with a simple coil of copper wire.
It works on exactly the same principle as the other style boiler but requires no solder or epoxy to create and is just one continuous piece of tube. So, this makes it super easy to make and long lasting. You really could knock one of these out in just a few minutes. The only drawback... a very muted or non-existent pop-pop noise as it motors around.

For my hull, I strayed from the wonderful world of smoked herring and took a stroll down the international aisle and found this delightfully shaped and quite colorful tin of Japanese sardines in sweet soy sauce. (The fish are actually from Thailand... the can from Japan. Yes. I read labels... and yes I only purchased it because it looked cool. And YES, I actually ate it. Not bad, but clearly not smoked herring.)


Since this is a smaller boat, I went with 1/8" outside diameter tubing. I drilled a 1/2 diameter hole in a piece of scrap wood and put a 1/2" dowel in it. I then took a length of the copper tubing and tightly wrapped it around the dowel five times making sure that the last loop ended with the tube heading in the same direction as I started. I also made sure that the long pieces away from the coil were going to be long enough that when bent to their final shape a candle could sit under the boiler and the tubes would still be long enough to extend past the end of the hull.

Have a long enough lead before your first bend for the boiler	Keep the tube tight as you wrap it.

I bent the leads to the boiler so that the boiler would stand up about 1 1/2" once it was installed. I also bent them out slightly. Then with the hull flipped upside down, I marked and drilled 1/8" holes making sure that the tubes would extend past the end of the hull. I flipped it back upright and used JB Weld to hold it in place and make the holes in the hull watertight.

Putting the holes through the bottom guarantees that the tubes will be submerged. I didn't get the weight quite right on this so the boat was a bit too bit stern heavy when she went out for her sea trials. I just left an unlit tea light candle at the front to counteract that. I also used a cut down small candle because while it doesn't burn as long as the tea lights do, the flame is clearly larger.

Here you go:



As fun as the obvious use of fish tins has been, I'm working up for the next boat to actually look like a boat. Preferably something that looks like a tug or steam boat. I now see these larger sardine cans that have the perfect shape I'm looking for and the cans themselves are not printed on; it is just a paper label. They are deeper and slightly longer than the herring tins with a more pointed bow and stern shape. And... with this brand I've noticed that the sardines are actually listed as being herring! YEAH!

Oh, and if you aren't a fan of canned fish. No worries. I'm sure you can find someone or something around the house to give you a hand making sure the fish doesn't go to waste. I sure did.