Treasure Island

This is my floating "Treasure Island" for the #MakeItFloat Challenge. It is designed to allow burying a treasure (coins) inside !

Video : https://youtu.be/ma-QDHCmzo8

Experiments:
My first design was a simple hemisphere (like a bowl) and coins attached at the bottom (I wanted it to be as simple as possible). It was a total fail and I learned two things for floating/ partially submersible objects :
- the air must be captured inside the object and should have no way to get out under pressure (the hemisphere was not stable and when the air began to get out it returned and sank instantaneously)
- All the added weight (coins) shall be placed on the vertical axis where the gravitiy center is located for best stability.
My final design is stable and doesn't sink ;-)

Technical specifications :
Designed with OpenSCAD (http://www.openscad.org/)
Filament used for printing : PLA 1.75mm (yellow, black and green)
Printer : Prusa I3 Hephestos
Coin size : all currency wil