Alka Seltzer Powered Bathtub Boat





Introduction: Alka Seltzer Powered Bathtub Boat

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

My daughter had a school assignment to bring a boat that could cross a fish tank under its own power. It was legal for dads to help. Some chose rubber band power. I decided on bubbles from Alka Seltzer mixing with water.

I used a piece of styrofoam about 1/2 inch thick (See the right portion of the graphic.) and a plastic canister from a roll of 35 mm film. Not shown is a piece of clear plastic tube for a fish tank air pump about 3/16 inch in diameter on the outside or less.

Cut out the styrofoam to receive, but still support the film canister. The hole at the rear of the boat is for the clear plastic tube. Shape the styrofoam to resemble a boat hull.

Step 1: Inside the Film Canister

Make wire support to hold an Alka Seltzer tablet up from the bottom of the film canister near the top of the canister.

The left portion of the graphic shows a cutaway view of the inside of the canister with the wire support in place. The right portion of the graphic shows the wire support.

Step 2: Just Add Water and an Alka Seltzer

Fill the film canister about half full with water. Rest an Alka Seltzer tablet on top of the wire support.

At the right half of the graphic you see the film canister cap with clear plastic tube inserted through a hole drilled in the cap. The tube should fit snugly in the cap. The tube should also be a bit longer than shown here.

Without allowing the water to come into contact with the Alka Seltzer tablet yet, place the cap firmly onto the canister.

Step 3: Use the Boat

Insert the capped film canister into the opening for it in the boat's hull while holding the hull vertical. When ready to use, turn the hull horizontal and place it into water. The water inside the canister will come into contact with the Alka Seltzer and begin making bubbles. The bubbles will travel through the tube and move the boat forward until the Alka Seltzer is fully dissolved.

I would like to say my daughter won the challenge at her school. She was too young and small to insert the Alka Seltzer reliably after arriving at school. So, she had to walk about three blocks to school and the water in the canister came into contact with the tablet before she arrived. But, it worked well when we tested it at home. She is an adult now. But, she wrote me a nice thank you on tablet paper, which note I still treasure.



    • Make it Move Contest

      Make it Move Contest
    • Oil Contest

      Oil Contest
    • Woodworking Contest

      Woodworking Contest

    We have a be nice policy.
    Please be positive and constructive.




    Oh, please re-create this with photos.

    Preferably embarrassing ones of your daughter carrying it to school. You have a parental duty to make her cringe in public.

    9 replies

    She was probably about six or seven years old at the time. She is now 36 and lives 2,100 miles away. I think I already embarrass my kids by just being. Thanks, though.

    Haha. Still, you should add photos, maybe a video to give an idea of the speed.

    At present I do not have the materials to make one of these, nor do I have the original I described making. I am also not equipped to do and post video. I would say the little boat moves about the speed of an ant migrating across the top of a table, assuming the ant does not stop and knows where it is going.

    I'm glad you posted w/o photos, Phil. Photos are nice but the idea is what matters most. I look forward to experimenting with this when I next see my grandson and it never would have occurred to me w/o your photo-less post!

    Thanks. A friend made one of these for the preschool class she teaches. She made the Styrofoam boat much larger than it needed to be. Her boat worked, but the water resistance increases when the Styrofoam is larger than necessary. It will not be very fast, but it amuses small children as it put-puts under its own power. Let me know how your grandson likes it.

    dude honestly leave people alone all 3 of mine dont have fotos get a like you nerd look at that big note that says BE NICE

    Firstly, you're replying to a comment I made two years ago.

    Secondly, I am being nice.  That was called constructive criticism.  Look it up.

    Thirdly, it is site policy that projects should have original photographs, which you would know if you paid attention.

    Fourthly, what "3 or yours don't have photos"?  You only have one project published,  which has photos (of a sort), and it has only had one view since the middle of February.  Two if you count me checking it.

    Fifthly, to tell somebody off for breaking the "be nice" policy by insulting them is called hypocrisy.  Look it up.

    Bad grammar, lies and an insult.  Way to go with gaining respect, dude.

    and a scan of the thank-you note, too

    I tried a couple of methods to scan or photograph the note. It is in pencil and very faint on the paper. I could not get anything legible to show.

    As soon as the water makes contact with the Alka Seltzer tablet, the tablet begins to fizz and also to use itself up.  I needed a way to enclose the tablet inside the film canister with the water, but without the water and the tablet making contact.  I made a wire shelf to hold the tablet above the water until the boat is turned from vertical to horizontal.  Then the water and the tablet come together.  The tablet begins to produce bubbles, which flow through the tube and propel the boat forward.  I hope this helps.

    can you explain it better i dont get not bein mean just dont understand

    I had only 2 of the ingredients.So I used a bottle with a piece of tubing stuck in a hole in the cap.Then I filled it half full of water and dropped a broken tablet in.I then stuck it in the bathtub and it went across the tub twice.Then I tried baking soda and vinegar.It went across the tub like a bullet,spraying a visible jet stream of vinegar.Thanks for the inspiration.

    2 replies

    Thanks for the report. I am glad it worked for you. The vinegar and baking soda is a good idea.

    Yeah.The baking soda and vinegar produces more CO2 than than alka-seltzer tablets but it runs out faster.