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.