Project 1, Concept 3: The Sinking Sub
James DR Raskob

The Sinking Sub is a toy for the tub. The toy would be weighted and balanced such that with the weight attached it sinks, but when the weight is removed it floats. The weight is clipped to the model, and can be released by squeezing two tabs which release the hooks. The toy gives some understanding of bouancy. It is quite simple and would be easy to make, but is a sufficiently different idea for a bath toy that it ought to sell fairly well.
The toy will have to be made out of non-corroding materials, probably plastic or plastic-coated metal for the weight. The toy would be too big to fit into the child's mouth, and so would not really present any safety hazards.