Design a small low power electric generator

I need a small electric generator designed. Requirements: -10 watts min, 20W max. -in an envelope of 60mm diameter and 30mm height or less. this includes the stator. the armator will be static. the stator will spin (being spun by water stream hitting fins). -brushless -7 to12VDC output (likely through a three phase rectifier) -Spin speed Deliverables: -sketch of the calculations -a list of all of the components that will need to be built, purchased or found off third party devices. -source(s) of where to components. Location: USA and Canada (or order from China) -Actual armature length for above requirements in accordance with components chosen -Actual armature width for above requirements in accordance with components chosen -instructions of how to assemble (if required). -explanation of limitations with the requirements (if I have pushed it beyond the laws of physics ;)