the inner shell has insufficient water drainage; the bottom of the inner shell perhaps need to be redesigned with perforation, but with an air gap between the bottom of the inner shell and raft, while still providing sufficient structural support
As to better describe its functional purpose; a floating vegetable garden that can be used to produce edible crops, as well as cultivating a source of PLA bio-plastic for 3D printer filament for producing more of itself - inspired by the original concepts of the RepRap movement.
water reservoir needs better aeration; perhaps warranting a redesign of inner shell to be circular as to allow for air gap between inner and outer shell, as well as rotation about z-axis, allowing for better water movement and aeration