Cross bow X Rugby ball Launcher

The project is to design something similar to a "Jugs machine" in purpose, ( [login to view URL] ) but without a motor. My idea is to use the theory behind a crossbow to provide enough kinetic energy to launch the ball - using some kind of winch geared system to pull the bow back and a trigger to release the ball when ready by the user. In essence the project will be to produce a fully detailed Product Design Specification on Solidwork 2015 & Validate the chosen design with calculations to prove it will fundamentally operate according to the Product Design Spec