Just brainstorming but I was wondering if anyone was (for example) Drag Racing or Speed Boating, maybe even the opposite of striving for hight; Deep Water Depth Challenge.
How would someone shoot a 'rocket' straight down into the water and have it 'breath' and not go out? How would you know just how far it got? What would you construct it out of, and for that matter; how to recover it (depth performance vs buoyancy, etc).
Hmmm.
berk