Sail
It only works a few times before you have to capsize the boat in a soap lagoon again.
It only works a few times before you have to capsize the boat in a soap lagoon again.
A billowing sail sometimes looks like the first stage of blowing a bubble. Cueball is clearly surprised when a bubble is actually formed by the filled sail.
Readers infer from the title text that the water is also part of this fantastical scenario. If the boat was overturned (capsized) in a soap lagoon, a film would form between the mast and the boom (horizontal bar that adjusts the sail). The film would become like the sail in the comic, filling with air and forming bubbles until the film is used up.